Robinsoniella peoriensis bacteremia in a patient with colorectal cancer: a case report and literature review

Abstract

Background

Robinsoniella peoriensis, an anaerobic, Gram-positive bacillus within the phylum Firmicutes and family Lachnospiraceae, is a putative commensal anaerobe of the human gut and an infrequent cause of opportunistic infection, including severe bloodstream infections (BSI). We report a case of BSI due to R. peoriensis and analyze its pertinent clinical and microbiological characteristics.

Case presentation

The patient was a 71-year-old male who developed BSI secondary to anastomotic leakage following laparoscopic radical resection for rectal adenocarcinoma. Anaerobic blood cultures obtained on postoperative day 4 signaled positive after 96 h of incubation. The isolate was identified as R. peoriensis by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Whole-genome sequencing revealed a notably diverse array of antimicrobial resistance genes, as well as two virulence-associated genes (tufA and groEL). Etest-based antimicrobial susceptibility testing demonstrated susceptibility to vancomycin, piperacillin-tazobactam, meropenem, and imipenem; intermediate resistant to clindamycin; and resistant to penicillin. The infection was effectively controlled after clinicians promptly initiated empirical therapy with meropenem monotherapy, and the patient eventually recovered and was discharged.

Conclusion

This case highlights that R. peoriensis infection can be associated with disruption of the intestinal mucosal barrier, as may occur following surgery for malignancy. A marked discordance between the genotypic resistance profile and phenotypic susceptibility was observed, emphasizing the critical role of standardized in vitro susceptibility testing to guide therapy. Carbapenems (e.g., meropenem) represent an effective therapeutic option for such infections. Due to the rarity of Robinsoniella peoriensis infections, our literature review identified only 22 previously documented cases, we aim to provide insights to aid in the diagnosis and treatment of infections caused by this rare pathogen.

Background

Robinsoniella peoriensis (R. peoriensis) is an anaerobic, Gram-positive bacillus with an ovoid to rod-shaped morphology, belonging to the phylum Firmicutes and the family Lachnospiraceae [1]. It was first isolated from a swine manure storage pit in 2003 [2] and subsequently recovered from the feces of premature neonates [3], suggesting its potential role as a commensal bacterium in the human gut microbiota [4]. Reported infections caused by R. peoriensis include bloodstream infections, osteomyelitis, skin and soft tissue infections, and pyometra. Patients are at risk of mortality if effective treatment is not administered promptly. Among the 22 reported cases of R. peoriensis infection included in this review, the in-hospital mortality rate was 27% (6/22). This article describes a case of R. peoriensis bacteremia, analyzing the clinical features, laboratory findings, and management. Combined with a review of the relevant literature, we aim to provide insights to aid in the diagnosis and treatment of infections caused by this rare pathogen.

Case presentation

A 71-year-old male presented with a 5-month history of altered bowel habits and a 1-month history of hematochezia without an obvious cause. He underwent colonoscopy at our hospital, which revealed multiple colonic polyps (treated with endoscopic mucosal resection [EMR] plus argon plasma coagulation [APC] and hemoclip placement), multiple rectal polyps, and a rectal proliferative lesion. He was admitted for further treatment. The patient, an urban resident, denied any travel or contact with animals during the previous year. Subsequent pathological examination confirmed rectal adenocarcinoma, staged as cT4aN0M0. His past medical history included Parkinson’s disease and chronic obstructive pulmonary disease (COPD), for which he was on long-term oral pramipexole and carbidopa-levodopa. On admission, physical examination showed stable vital signs (temperature 36.7 °C, heart rate 70 beats/min, respiratory rate 18 breaths/min, blood pressure 110/80 mmHg). On admission, the patient was alert and oriented. He appeared lean on physical examination (BMI: 18.6 kg/m²). The abdomen was flat and soft with no tenderness OR rebound tenderness. Digital rectal examination did not reveal a definite mass, but the examination glove was stained with dark red blood, indicating a positive finding. Admission laboratory tests showed: white blood cell (WBC) count 7.89 × 10^9/L, neutrophils 62.5%, hemoglobin 155 g/L, platelet count 205 × 10^12/L. Liver and renal function tests were within normal limits. Tumor markers were elevated: carcinoembryonic antigen (CEA): 19.10 ng/mL, carbohydrate antigen 19 − 9 (CA 19 − 9): 21.7 U/mL, CA-125: 10.2 U/mL, CA 15 − 3: 12.3 U/mL, CA 72 − 4: 0.96 U/mL, and CA 242: 9.73 U/mL.

Day 2 of hospitalization, the patient underwent laparoscopic total mesorectal excision, pericolonic lymph node dissection, and sigmoidorectal anastomosis. Perioperative antimicrobial prophylaxis was administered as a single intravenous dose of cefradine (1 g) immediately preoperatively.

On postoperative day 1, the patient reported no significant abdominal pain or distension. Serosanguinous fluid was drained via the upper (30 mL) and lower (30 mL) abdominal drains. However, laboratory findings were consistent with an inflammatory response: high-sensitivity C-reactive protein (hs-CRP) 19.88 mg/L, WBC count 10.39 × 10⁹/L, neutrophil percentage 82.7%. Empirical intravenous antimicrobial therapy was initiated with cloxacillin (3 g twice daily) combined with sulbactam (1.5 g twice daily) in response to these inflammatory markers.

On postoperative day 3, the patient developed fever (peak temperature 39℃) accompanied by lower abdominal pain and watery diarrhea. Turbid, thin fluid was collected from the upper (70 mL) and lower (10 mL) abdominal drains. Blood cultures were obtained immediately. Abdominal computed tomography (CT) demonstrated postoperative changes in the rectum, a small amount of free air in the abdomen and abdominal wall, and no significant lymphadenopathy in the para-aortic, mesenteric root, or pelvic regions. Emergency colonoscopy revealed a linear ulcerative lesion adjacent to the anastomosis with a central micro-perforation, which was closed using three hemoclips. Concurrent laboratory tests showed exacerbated inflammatory responses. In view of clinical deterioration, confirmed anastomotic leakage, and suspected intra-abdominal infection, antimicrobial therapy was escalated to meropenem (0.5 g intravenously every 8 h) for broader coverage of enteric Gram-negative bacilli and anaerobes.

On postoperative day 8, blood cultures returned positive for Robinsoniella peoriensis. The patient remained afebrile with only mild lower abdominal tenderness, and drainage volume reduced to 5 mL from each drain (thin fluid). The meropenem regimen was therefore continued without modification.

On postoperative day 10, the patient’s temperature normalized completely, and drainage volume further decreased to 1 mL from both drains. Laboratory markers improved significantly. Meropenem was discontinued on postoperative day 11, completing an 8-day course of therapy. Subsequently, the patient achieved uneventful recovery and was discharged in stable condition on postoperative day 14 for outpatient follow-up.

On the third postoperative day, the anaerobic bottle from a set of blood cultures (aerobic and anaerobic) signaled positive in the bioMérieux BacT/Alert blood culture system, with a time-to-positivity of 96 h. The bottle was immediately subcultured. Gram staining of the direct smear revealed ovoid to short rod-shaped Gram-positive bacilli without obvious spore formation (Fig. 1A). Concurrently, the broth was subcultured onto solid media. After 24 h of incubation, no bacterial growth was observed on plates incubated aerobically. However, small, smooth, non-hemolytic, grayish-white colonies were present on the blood agar plate incubated under anaerobic conditions (Fig. 1B). The isolate was identified as Robinsoniella peoriensis (confidence level of 99.9, bioMérieux VITEK MS 3.1 library version 3.2.0) using the matrix-assisted laser desorption ionization-time of flight mass spectrometry MALDI-TOF MS system. The corresponding mass spectrum is shown in Fig. 2. A single colony from the plate was subjected to another Gram stain, which revealed ovoid, subterminal spores within some bacilli upon microscopic examination (Fig. 1C).

Fig. 1.

Microscopic morphology and colonial characteristics of R. peoriensis. (A) Gram stain of the direct smear from the original positive anaerobic blood culture bottle (×100 oil immersion). (B) Colonial morphology on anaerobic blood agar after 24 h of incubation. (C) Gram stain of a colony subculture from the blood agar plate (×100 oil immersion); the arrow indicates a spore-forming bacillus. Scale bars represent 10 μm

Fig. 2.

MALDI-TOF mass spectrum of a purified R. peoriensis colony

Genomic DNA was extracted from the isolate using a commercial DNA extraction kit and transported under refrigerated conditions to Shanghai Lingen Biotechnology Co., Ltd. for sequencing. Sequencing libraries were prepared with the NEXT Ultra DNA Library Prep Kit and sequenced on the DNBSEQ-T7 platform (MGI Tech) using paired-end 150 bp chemistry. Raw reads were quality-filtered using fastp v 0.20.1 and assembled with SPA des v 3.15.0 using default parameters. Assembly quality was assessed using QUAST v 5.0.2. Gene prediction was performed using GeneMarkS v 4.1.7. Functional annotation was conducted against the NCBI Virulence Factor Database (VFDB) and Comprehensive Antibiotic Resistance Database (CARD). The 16 S rRNA gene sequence of the isolate showed 99.44% identity (100% query coverage) with the Robinsoniella peoriensis reference strain PPC44 (NCBI GenBank AF445283.2), confirming the species identification. And this strain harbored an exceptionally rich and diverse repertoire of ARGs (Table 1). The most prominent findings included vancomycin resistance-related genes vanR, vanS, vanH, vanD and vanX; various genes mediating multidrug efflux (e.g., macB, msbA, and optrA); and other clinically significant resistance genes, including mecA. Virulence factor analysis of the whole-genome sequence was conducted using the Virulence Factor Database (VFDB). Two genes of interest, tufA (encoding elongation factor Tu) and groEL (encoding heat shock protein 60/GroEL), were identified in the R. peoriensis isolate. It should be noted, however, that these genes are highly conserved housekeeping genes present in a wide range of bacterial species, including both pathogenic and commensal organisms [5, 6]. TufA plays an essential role in bacterial protein synthesis, while groEL functions as a molecular chaperone involved in protein folding under stress conditions. Although these genes may indirectly contribute to bacterial fitness and survival within the host environment, their presence alone does not confer specific pathogenic potential, and they are not considered canonical virulence factors. The assembled genome sequence has been submitted to the GenBank database under the accession number JBTOPR010000000.

Table 1.

Prediction of putative antibiotic resistance genes in Robinsoniella peoriensis based on whole-genome sequencing

Category	Gene name	Predicted resistance mechanism
Glycopeptide resistance	vanR, vanS, vanH, vanX, vanD	Cell wall precursor modification (Target alteration)
Efflux pump-mediated multidrug resistance	macB, msbA, bcrA, patB, efrA, mdtC, cdeA, tetA (58), tet (38), tet (35), mef (B), optrA, vgaD	Antibiotic efflux
Other classical resistance gene families	mecA, blaR1, sul4, catV, aph (3’)-IVa, aadK, vatF, cfrE	Target replacement, Enzyme-mediated inactivation, Ribosomal methylation

Given the absence of established species-specific susceptibility breakpoints for Robinsoniella peoriensis, the laboratory determined the minimum inhibitory concentrations (MICs) of key antibiotics using the Etest method under anaerobic conditions (see Table 2). The results were interpreted according to the breakpoints for anaerobic bacteria provided in the CLSI M100 guidelines.

Table 2.

Comparison of antimicrobial susceptibility testing results and key genotypic profiles for Robinsoniella peoriensis

Antibiotic	MIC	Interpretation (S/I/R)	Predicted genotype(s) (from Table 1)	Phenotype-genotype concordance analysis
TZP	3.0	S	Predicted to harbor blaR1	The resistance gene(s) may encode a β-lactamase that remains susceptible to inhibition by β-lactamase inhibitors.
MEM	0.38	S	No carbapenemase genes predicted	Susceptible phenotype is consistent with the absence of corresponding resistance genes.
IPM	0.125	S	No carbapenemase genes predicted	Susceptible phenotype is consistent with the absence of corresponding resistance genes.
CLI	4.0	I	Predicted to harbor multiple efflux pump genes (e.g., macB, msbA, vgaD)	The “intermediate” phenotype may be associated with low-level expression or incomplete regulation of efflux pump genes.
VA	0.125	S	Predicted to harborclusters of regulatory and structural gene elements (e.g., vanR, vanS) associated with vancomycin resistance operons	The susceptible phenotype is highly discordant with the prediction of abundant resistance gene clusters, suggesting potential gene silencing or tight transcriptional regulation.
P	8.0	R	Predicted to harbor mecA, blaR1	Phenotypic resistance to penicillin correlates with the detection of mecA (encoding low-affinity PBP2a) and blaR1 (encoding β-lactamase regulatory protein).

TZP: piperacillin-tazobactam, MEM: meropenem, IPM: imipenem, CLI: clindamycin, VA: vancomycin, P: Penicillin

Methods of literature review

A literature search was conducted using the subject term “Robinsoniella peoriensis” in the Wanfang Database and China National Knowledge Infrastructure (CNKI), and the same term in the PubMed database. The search timeframe covered from their inception to November 30, 2025. Inclusion criteria: Case reports and review articles that explicitly documented human infections caused by Robinsoniella peoriensis were included. The articles were required to contain information on patient demographics, medical history, clinical manifestations, microbiological identification and susceptibility testing, treatment regimens, and outcomes. Exclusion criteria: Studies were excluded if they did not clearly establish an association between the infection and R. peoriensis, reported only microbiological identification without relevant clinical patient information, or were only available in abstract form with no access to the full text.

Discussion and conclusion

A total of 19 publications reporting human infections associated with Robinsoniella peoriensis were identified. These publications encompassed 22 individual patient cases, distributed across 11 countries including China, the United States, France, Germany, and South Korea. Including the present case, a total of 23 cases were included in the final analysis, with their data summarized in Table 3 [7–25].

Table 3.

Analysis of characteristics for the current case and all reviewed cases of Robinsoniella peoriensis Infection

Case number	Year reported	Sex	Age (years)	Country	Underlying condition(s)	Diagnosis	Related surgery	Pre-existing medication	Antimicrobial therapy	Surgical intervention	Outcome
1 [7]	2009	Female	79	SWE	Not reported	Deep foot infection	None	Not reported	Not reported	Debridement	Improved
2 [8]	2010	Male	50	ESP	Hepatitis B-related cirrhosis; acute alcoholic hepatitis; grade II esophageal varices	Spontaneous muscular hematoma	None	CLI, CIP	MNZ, CIP	Aspiration	Died
3 [9]	2010	Male	42	CHN	Chronic hepatitis B; secondary cirrhosis	Post-pancreatectomy with worsening jaundice	Pancreatectomy	None	MNZ	None	Died
4 [10]	2011	Female	61	USA	Not reported	Diverticulitis	Laparoscopic sigmoidectomy	MXF, CLI	VA, TZP	Drainage	Improved
5 [10]	2011	Female	68	USA	None	Open pelvic and femoral fractures	Fracture surgery	None	Broad-spectrum antibiotic	Debridement	Improved
6 [10]	2011	Male	45	USA	None	Fracture	Open reduction and internal fixation (ORIF) of fracture	LZD	CLI, LZD	Debridement, Removal of fixation hardware	Improved
7 [10]	2011	Female	79	USA	Diabetes mellitus; hypertension; hypercholesterolemia	Myocardial infarction	Coronary artery bypass grafting	None	TZP, LEV, MNZ	None	Died
8 [11]	2012	Female	45	FRA	Chronic urinary tract infections	Progressive scoliosis	Scoliosis correction surgery	AMC	RFP, CLI	Debridement, Removal of bone graft	Improved
9 [12]	2012	Male	76	KOR	Middle cerebral artery infarction	Aspiration pneumonia	None	TZP, LEV	VA, MEM, SXT	None	Died
10 [13]	2016	Female	74	DEU	Not reported	Displaced femoral neck fracture	Left hip cementless total hip arthroplasty; two subsequent revisions	SAM	SAM, RFP	Removal of prosthesis, Insertion of gentamicin-clindamycin spacer	Improved
11 [14]	2017	Female	67	USA	Hypertension; chronic kidney disease	Subperiosteal abscess	Open reduction and internal fixation (ORIF) of right femur; two subsequent revisions	VA, SAM	ETP	Debridement, Removal of fixation hardware	Improved
12 [15]	2017	Male	70	BEL	Transverse aortic pseudoaneurysm	Transverse aortic mycotic pseudoaneurysm	None	CAZ, VA	CRO, MNZ, CLI	Graft excision, Debridement, evacuation of pseudoaneurysm thrombus	Improved
13 [16]	2017	Male	63	KOR	Diabetes mellitus; small-cell lung cancer	Aspiration pneumonia	None	TZP	IPM	None	Died
14 [17]	2019	Male	58	DEU	Not reported	Open ankle fracture	Open reduction and internal fixation (ORIF) of fracture; two subsequent revisions	LEV, DAP, TZP	MNZ	Debridement, Removal of prosthetic material	Improved
15 [18]	2020	Female	79	FRA	Chronic kidney disease	Acute heart failure; infective endocarditis	None	Fluoroquinolone	AMX, DOX	None	Improved
16 [19]	2021	Male	3	TUR	None	Open tibial fracture	Open reduction and internal fixation (ORIF)	None	SAM, AK	Debridement	Improved
17 [20]	2022	Male	73	CHN	Diabetes mellitus; hypertension	Prostate cancer	Laparoscopic radical prostatectomy	Not reported	Not reported	Not reported	Improved
18 [21]	2022	Male	14	CAN	None	Open comminuted fracture	Open reduction and internal fixation (ORIF) of midfoot and forefoot fractures; partial left foot amputation	CFZ	TZP, MNZ	Debridement	Improved
19 [22]	2022	Female	47	CAN	Jejunal adenocarcinoma; endometrial cancer	Pyometra	Total hysterectomy with bilateral salpingo-oophorectomy	CRO, MNZ	TZP, DOX	Drainage	Improved
20 [23]	2023	Female	84	JPN	Peritoneal carcinoma; uterine cancer	Small bowel obstruction	Total hysterectomy with bilateral adnexectomy	TZP	MEM, VA	None	Improved
21 [24]	2024	Male	65	USA	Diabetes mellitus; hypertension; stroke	Open fracture	Fracture surgery	DOX	MNZ	Debridement	Improved
22 [25]	2025	Male	60	USA	End-stage renal disease	Empyema	None	CRO, AZM, SAM	MEM, MNZ	Drainage	Died
23	Our case	Male	71	CHN	Parkinson’s disease; chronic obstructive pulmonary disease (COPD)	Colorectal cancer	Laparoscopic total mesorectal excision with sigmoidorectal anastomosis	CLO, SUL	MEM	None	Improved

SWE: Sweden, ESP: Spain, CHN: China, USA: UnitedStates, FRA: France, KOR: SouthKorea, DEU: Germany, BEL: Belgium, TUR: Turkey, CAN: Canada, JPN: Japan.CIP: Ciprofloxacin, MXF: Moxifloxacin, LEV: Levofloxacin, MNZ: Metronidazole, VA: Vancomycin, TZP: Piperacillin-tazobactam, LZD: Linezolid, AMC: Amoxicillin-clavulanate, RFP: Rifampin, MEM: Meropenem, ETP: Ertapenem, SXT: Trimethoprim-sulfamethoxazole, SAM: Ampicillin-sulbactam, CAZ: Ceftazidime, CRO: Ceftriaxone, DAP: Daptomycin, CFZ: Cefazolin, AK: Amikacin, DOX: Doxycycline, AMX: Amoxicillin, AZM: Azithromycin, CLO: Cloxacillin, SUL: Sulbactam, CLI: Clindamycin

Biological Characteristics Robinsoniella peoriensis is a Gram-positive bacillus with a short rod-shaped to ovoid morphology, typically occurring singly or in pairs. Ovoid spores, often located terminally or subterminally, can be observed a morphological feature characteristic of many bacteria within the order Clostridiales. The bacterium is an obligate anaerobe, requiring an oxygen-free environment for growth. After 48 h of incubation on anaerobic blood agar, it forms circular, grayish-white colonies approximately 1–3 mm in diameter with smooth edges and a translucent to opaque appearance, and exhibits no hemolysis. R. peoriensis is considered a commensal anaerobe within the gut microbiota of animals and humans. It is an opportunistic pathogen capable of causing infection when host immunity is compromised or when physical barriers are breached, such as following surgery or trauma.

Epidemiological Characteristics The spectrum of Robinsoniella peoriensis-associated infections among the 22 patients was as follows: bone and joint infections (n = 9, 41%), BSIs (n = 8, 36.5%), skin and soft tissue infections (n = 2, 9%), intra-abdominal infection (n = 1, 4.5%), thoracic infection (n = 1, 4.5%), and vascular graft infection (n = 1, 4.5%). Of the eight patients with BSI, one had a concurrent pyometra and another had concurrent infective endocarditis. The relevant case reports of R. peoriensis infection were reviewed to analyze and summarize patient demographics (sex, age), underlying conditions, clinical manifestations, and outcomes. Among the 22 patients, 12 were male (54.5%) and 10 were female (45.5%). The mean age was 59 years, with a range from 3 to 84 years. Underlying medical conditions were documented in 14 patients (64%), absent in 4 patients (18%), and not reported in the remaining 4 patients (18%). Among the 14 patients with reported comorbidities, 9 had one or more conditions associated with potential immunosuppression: solid malignancies (n = 5), diabetes mellitus (n = 4), chronic hepatitis (n = 2), and end-stage renal disease (n = 1). Regarding clinical presentation, among the 22 patients, 4 (18%) presented with both fever and localized infection; 8 (36.5%) presented with fever alone, of whom 2 developed sepsis; 9 (41%) presented with localized infection only; and 1 patient (4.5%) presented solely with hypotension and tachycardia.

Among the nine patients with bone and joint infections, which constituted the largest proportion of infection types, five (55.5%) involved open fractures. Three patients (33.3%) underwent revision surgery, and four (44.4%) had implanted orthopedic hardware. All patients in this group underwent at least one debridement procedure after the initial fracture surgery.

BSIs represented the second most common type of infection (n = 8). Among these, five patients had an underlying solid malignancy, and four of them were receiving chemotherapy. Fever was present in 87.5% of the patients with BSI. Only one patient with a positive blood culture for R. peoriensis was reported to be afebrile. The time-to-positivity (TTP) of blood cultures was reported in five cases, with values of 20 h, 1 day, 3 days, 3.07 days, and 5 days. Following antibiotic treatment, blood culture clearance was achieved in five patients (62.5%). Follow-up blood cultures were not performed for the remaining three patients due to various unspecified reasons.

Laboratory Identification and Antimicrobial Susceptibility The identification methods employed for the 22 Robinsoniella peoriensis isolates were categorized into three primary types: biochemical identification systems (e.g., API 20 A, VITEK 2), MALDI-TOF MS, and 16 S ribosomal RNA (rRNA) gene sequencing (Table 4). 16 S rRNA gene sequencing was utilized in 20 cases (91%). Among these, it provided the definitive identification in 6 cases, served as confirmatory testing following MS-based identification in another 6 cases, and was used as a supplementary method when other techniques failed in the remaining 8 cases. MALDI-TOF MS was attempted in 12 cases (54.5%). Successful identification of R. peoriensis was achieved in 7 cases, albeit with a low-confidence score in one instance. Of the 5 unsuccessful attempts, one resulted in misidentification as a Lactobacillus species, while the other four yielded no identification. Biochemical identification systems predominantly misidentified R. peoriensis as various species within the genus Clostridium.

Table 4.

Identification Details for the Current Case and All Reviewed Cases of Robinsoniella peoriensis Infection

Identification method	Identification
	1 [7]	2 [8]	3 [9]	4 [10]	5 [10]	6 [10]	7 [10]	8 [11]	9 [12]	10 [13]	11 [14]	12 [15]	13 [16]	14 [17]	15 [18]	16 [19]	17 [20]	18 [21]	19 [22]	20 [23]	21 [24]	22 [25]	Our case
16 S rRNA	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	-	A	A	-	A
MS	-	-	-	-	-	-	-	N	-	-	N	N	-	A	A	A	A	A	A	A	-	A	A
Biochemical identification	-	M	M	-	-	-	-	-	M	N	-	-	M	-	-	-	-	-	-	-	-	-	-

A: Accurate identification, N: Not identified, M: Misidentificatio

Due to its exceptionally low clinical isolation rate, standardized antimicrobial susceptibility testing (AST) methods and interpretive breakpoints specific to Robinsoniella peoriensis have not been established. In the available literature, the Etest method is predominantly employed for AST, with results interpreted by referencing guidelines from either the Clinical and Laboratory Standards Institute (CLSI) or the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Among the 22 cases, antimicrobial susceptibility results for R. peoriensis were reported in only 15. Of these, the testing methodology was not specified in one case, while the remaining 14 explicitly utilized the Etest method. The aggregated results are presented in Table 5. Analysis of the 15 susceptibility profiles revealed a high resistance rate to penicillin among β-lactam antibiotics, approximately 92.3% (12/13). Resistance to levofloxacin was 100% (2/2). The bacterium also demonstrated considerable resistance to clindamycin, with about 73.3% (11/15) of strains reported as resistant or exhibiting intermediate resistance. In contrast, high in vitro activity was observed against β-lactamase inhibitor combinations, carbapenems, metronidazole, and vancomycin.

Table 5.

Summary of antimicrobial susceptibility testing results for the current isolate and those from the literature

Reference	Testing method	MIC	Interpretive criteria	P	TZP	ETP	IPM	MEM	CLI	MNZ	VA	RFP	MXF	TE	FOX	AMC	SAM	AMP	GEN	LEV
2 [8]	E-Test	/	CLSI	(S)	(S)	-	(S)	-	(S)	(S)	-	-	-	-	S	S	-	-	-	-
3 [9]	E-Test	µg/ml	CLSI	-	6(S)	-	1(S)	-	4(I)	0.064(S)	-	-	-	-	8(S)	0.5(S)	-	-	-	-
4 [10]	E-Test	g/ml	Not reported	6–8(R)	8–16(S)	0.75-1.0(S)	-	-	8–12(R)	0.094-0.5(S)	-	-	-	-	-	-	-	-	-	-
5 [10]	E-Test	g/ml	Not reported	6–8(R)	8–16(S)	0.75-1.0(S)	-	-	8–12(R)	0.094-0.5(S)	-	-	-	-	-	-	-	-	-	-
7 [10]	E-Test	g/ml	Not reported	6–8(R)	8–16(S)	0.75-1.0(S)	-	-	8–12(R)	0.094-0.5(S)	-	-	-	-	-	-	-	-	-	-
8 [11]	E-Test	/	CLSI	(R)	-	-	(S)	-	(S)	(S)	(S)	(S)	-	-	-	S	-	-	-	-
10 [13]	E-Test	µg/ml	EUCAST	6(R)	0.03(S)	-	0.094(S)	-	4–6(R)	0.12(S)	0.38(S)	-	1.5	-	-	-	0.25(S)	0.12(S)	0.75(S)	-
11 [14]	E-Test	µg/ml	CLSI	8(R)	8(S)	-	-	0.5(S)	4(I)	0.5(S)	-	-	-	-	-	-	1(S)	-	-	-
12 [15]	E-Test	mg/L	Not reported	-	-	-	-	0.125(S)	2(S)	0.125(S)	-	-	-	-	-	0.5(S)	-	-	-	-
14 [17]	E-Test	µg/ml	EUCAST	8(R)	0.5(S)	0.5(S)	0.5(S)	0.5(S)	2(S)	0.25(S)	1(S)	-	-	-	-	0.5(S)	0.5(S)	0.5(S)	-	32(R)
15 [18]	E-Test	µg/ml	EUCAST	4(R)			0.125 (S)	0.38 (S)	≥ 256 (R)				6			0.38 (S)		0.38 (S)		32(R)
17 [20]	E-Test	µg/ml	EUCAST	4(R)	8(S)	0.5(S)	0.125(S)	0.5(S)	> 512(R)	≤ 0.5(S)	0.125(S)	-	-	-	-	-	-	-	-	-
19 [22]	E-Test	µg/ml	CLSI	8(R)	16(S)	-	-	1(S)	4(I)	0.25(S)	-	-	-	-	16(S)	-	-	-	-	-
20 [23]	E-Test	µg/ml	CLSI	≥ 2(R)	≤ 4(S)	-	-	0.5(S)	4(I)	-	-	-	-	≤ 0.25(S)	-	-	≤ 4(S)	-	-	-
21 [24]	Not reported	/	Not reported	(R)	(S)	(S)	-	-	(R)	(S)	-	-	-	-	-	-	-	-	-	-
Our case	E-Test	µg/ml	CLSI	8(R)	3(S)	-	0.125(S)	0.38 (S)	4(I)	-	0.125(S)	-	-	-	-	-	-	-	-	-

“-”, not tested. Not all isolates were tested against all antimicrobial agents. P: Penicillin, TZP: Piperacillin-tazobactam, ETP: Ertapenem, IPM: Imipenem, MEM: Meropenem, CLI: Clindamycin, MNZ: Metronidazole, VA: Vancomycin, RFP: Rifampin, MXF: Moxifloxacin, TE: Tetracycline, FOX: Cefoxitin, AMC: Amoxicillin-clavulanate, SAM: Ampicillin-sulbactam, AMP: Ampicillin, GEN: Gentamicin, LEV: Levofloxacin

Treatment and Prognosis Current treatment strategies for Robinsoniella peoriensis infections are not supported by robust clinical trial data. Guidance is primarily derived from empirical regimens documented in case reports and general therapeutic principles for anaerobic infections. Analysis of the therapeutic courses in the 22 patients revealed that management primarily encompassed three key components: administration of effective antimicrobial agents, necessary surgical intervention, and active management of underlying conditions. Surgical intervention was employed in all 14 patients whose infections were not solely bloodstream infections.

Regarding antimicrobial selection, penicillin-based agents and clindamycin are generally not considered first-line options due to the high prevalence of resistance and frequent intermediate susceptibility to these drugs, respectively. Based on the reviewed cases, metronidazole—used either as monotherapy or in combination—was the most frequently reported agent, accounting for approximately 36.4% of treatment regimens. This was followed by β-lactam/β-lactamase inhibitor combinations and carbapenems. Fluoroquinolones were infrequently reported in the reviewed literature, with susceptibility data available for only two cases [17, 18]. Isolates from both cases exhibited resistance to levofloxacin. Although data remain limited, the available evidence suggests that fluoroquinolones may have limited activity against R. peoriensis and should not be regarded as first-line empirical therapy for infections suspected to be caused by this organism. If fluoroquinolones are considered for use, treatment decisions should be guided by antimicrobial susceptibility testing. Other agents such as vancomycin, doxycycline, and rifampin were also utilized in some cases.

Regarding patient outcomes, clinical improvement was observed in 16 of the 22 patients (73%), corresponding to an in-hospital mortality rate of 27% (6/22). Among the six deceased patients, three had negative follow-up culture results prior to death, effectively ruling out uncontrolled infection as the direct cause of mortality.

This study reports the isolation of Robinsoniella peoriensis from the blood culture of a patient with colorectal cancer. Treatment with meropenem resulted in a favorable outcome. Follow-up blood cultures were not performed prior to discharge, because the patient showed a favorable clinical response to antimicrobial therapy and achieved definitive source control following endoscopic closure of the anastomotic leak. This practice aligns with existing evidence indicating that repeat blood cultures are not routinely necessary in patients with Gram-negative bacteremia who demonstrate clinical improvement and effective source control [26, 27]. Outpatient follow-up after discharge revealed no clinical or laboratory evidence of active infection, further supporting the rationality of this management strategy.

Since its initial isolation and report from a swine manure storage pit in 2003, Robinsoniella peoriensis (R. peoriensis) has subsequently been recovered from diverse sources including wood turtle feces, feces of premature neonates, and rectal swabs from ICU patients [3, 28, 29]. It is therefore regarded as a commensal anaerobic bacterium inhabiting the intestinal tracts of various animals, particularly swine, as well as humans. Facilitated by the widespread adoption of molecular diagnostic techniques, an increasing number of cases documenting its role as an opportunistic human pathogen have been reported. By analyzing a case of postoperative R. peoriensis bloodstream infection complicating colorectal cancer surgery and conducting a systematic review of the literature (encompassing 22 cases), this study provides a comprehensive elucidation of the clinical features, diagnostic challenges, treatment strategies, and prognostic outcomes associated with this organism. Our analysis indicates that infections caused by this bacterium are not incidental but are closely linked to specific disruptions of the host microenvironment. This finding offers new insights for clinical understanding and practice.

Published case reports suggest that Robinsoniella peoriensis infections may be acquired via environmental exposure or endogenous translocation. Environmental acquisition is supported by cases associated with farm-related injury [21], and open wounds exposed to soil [10, 17]. In contrast, cases such as that reported by Lim et al., describing an urban patient with no identifiable environmental exposure, support an endogenous origin [16]. This dichotomy highlights a key pathogenic feature: in the absence of an exogenous source, mechanical disruption of the intestinal mucosal barrier plays a predominant role [30]. The present case illustrates this mechanism. Following radical resection for rectal cancer, the patient developed an anastomotic leak that compromised intestinal barrier integrity, enabling bacterial translocation into the bloodstream. This mechanism is corroborated by our literature review, in which most cases with an identifiable source had underlying intestinal barrier compromise (e.g., abdominal surgery, gastrointestinal malignancy, or bowel obstruction). This observation suggests a potential divergence in pathogenic mechanisms between R. peoriensis and traditional enteric pathogens such as Bacteroides fragilis. B. fragilis harbors multiple virulence determinants (e.g., polysaccharide capsule, enterotoxin) that enable invasive disease even in hosts with relatively intact mucosal barriers [30–32]. By contrast, excluding cases with clear environmental exposure, clinically evident R. peoriensis infection occurs predominantly in the setting of severe intestinal mucosal barrier compromise. However, given the paucity of direct comparative data on intrinsic virulence, it remains unclear whether this divergence reflects bacterial factors alone or a complex interplay with host susceptibility and clinical context. Further research is needed to elucidate the virulence mechanisms of R. peoriensis and the conditions driving its transition from commensal to pathogen. It is worth noting that in clinical practice, patient at high risk for intestinal barrier disruption, including those with malignancy-related erosion, complex gastrointestinal surgery, or severe mucositis following chemotherapy or radiotherapy—bloodstream infection caused by low-virulence gut commensals should be included in the differential diagnosis when signs of sepsis are present.

Current laboratory identification of Robinsoniella peoriensis remains challenging, a fact that directly contributes to the underestimation of its true prevalence.16 S ribosomal RNA (rRNA) gene sequencing serves as the current gold standard for definitive identification of R. peoriensis. It plays an indispensable role, particularly in confirming isolates for which MALDI-TOF MS yields no identification or provides inconclusive results. Ongoing advancements in mass spectrometry technology and updates to microbial spectral libraries have improved the success rate of anaerobic bacteria identification by MALDI-TOF MS [33]. Nevertheless, the accuracy of such identifications should still be verified in conjunction with clinical context and the isolate’s phenotypic characteristics. In our literature review, the three cases (20%) where MS identification failed were primarily attributable to the absence of a reference spectrum for this organism in earlier versions of the spectral databases.

To further enhance the detection rate of Robinsoniella peoriensis, we advocate for establishing a proactive clinical-microbiological collaborative diagnostic pathway. The first crucial step lies in predictive alerting by clinicians. Routine bacterial culture protocols in most clinical microbiology laboratories are optimized for common, rapidly growing aerobic pathogens, with standard incubation lasting 2–3 days. However, this conventional approach may fail to recover fastidious organisms requiring specialized conditions or strict anaerobes unable to grow aerobically. Additionally, some microorganisms grow intrinsically slowly and need prolonged incubation to form detectable colonies. Thus, when clinicians strongly suspect infections caused by fastidious or anaerobic pathogens, proactive communication with the microbiology laboratory is essential. This allows timely implementation of targeted diagnostic strategies, reducing the risk of false-negative results and diagnostic delays. Secondly, the microbiology laboratory should implement a targeted workflow. Step 1: Direct smear microscopy to observe Gram-positive, ovoid to short rod-shaped bacilli. Step 2: Culture confirmation under strict anaerobic conditions, noting its characteristically slow growth. Step 3: Molecular diagnosis. If the morphology and growth characteristics are suggestive and MALDI-TOF MS fails to provide a definitive identification, 16 S rRNA gene sequencing should be prioritized for species-level identification to prevent diagnostic delays associated with reliance on conventional phenotypic methods [34].

The susceptibility data from this case and the literature review indicate that R. peoriensis exhibits very high resistance rates to penicillin G and clindamycin (approximately 92% and 73%, respectively), yet retains high susceptibility to β-lactam/β-lactamase inhibitor combinations (e.g., piperacillin-tazobactam, amoxicillin-clavulanate) and carbapenems (e.g., meropenem, imipenem). This suggests that broad-spectrum β-lactam/β-lactamase inhibitor combinations or carbapenems can be prioritized for the treatment of R. peoriensis, as their antimicrobial spectrum provides activity against both R. peoriensis and common aerobic pathogens. De-escalation of therapy can be considered once reliable susceptibility results are available. Vancomycin serves as an effective alternative for patients with β-lactam allergies. Although R. peoriensis is frequently susceptible to metronidazole in vitro, its clinical efficacy in vivo requires further investigation. Metronidazole was included in the treatment regimen of all three reported fatal cases of R. peoriensis infection. However, owing to the small sample size and presence of confounding factors (e.g., disease severity and comorbidities), definitive conclusions regarding the clinical efficacy of metronidazole cannot be drawn. Consequently, for high-risk patients—such as the postoperative oncology patient with an enteric fistula described here, or those with suspected hospital-onset bloodstream infections of gastrointestinal origin—the initial empirical regimen should be selected to cover the likely pathogens.

Whole-genome sequencing of the R. peoriensis isolate revealed that the strain carries a rich and diverse array of resistance genes, but no virulence factors typical of enteric pathogens—such as genes encoding toxins, adhesins, or capsule biosynthesis—were detected. The absence of specific virulence factors suggests that R. peoriensis is more appropriately classified as an opportunistic pathogen. In this context, the patient’s bacteremia was likely driven by host factors, including loss of mucosal barrier integrity and an immunosuppressed state. Regarding the resistance genes identified, classical vancomycin resistance systems (such as the vanA or vanB-type gene clusters) require the synergistic action of a set of core genes to confer a resistant phenotype [35]. A complete vanA-type gene cluster comprises at least five core genes—vanR, vanS, vanH, vanA, and vanX [36, 37]—and the integrity of these five genes is essential for the expression of high‑level vancomycin resistance [38]. Although the present study detected the regulatory genes vanR and vanS, as well as vanH and vanX, the absence of the key ligase gene vanA may have directly led to the failure of the resistance system, because VanA is responsible for synthesizing D‑alanyl‑D‑lactate (D‑Ala‑D‑Lac), the crucial step in replacing the drug target [36]. This may be the key reason for the marked discrepancy between the genotypic resistance profile and phenotypic susceptibility.

The prognosis of Robinsoniella peoriensis infection is closely associated with several factors, including the patient’s underlying conditions, the type of infection, and the efficacy of the administered treatment. In the present case, despite the patient’s diagnosis of rectal cancer, prompt empirical initiation of meropenem—an agent whose in vitro susceptibility was later confirmed—combined with surgical intervention and supportive care, led to effective infection control and subsequent discharge. However, the aggregate literature reveals an overall mortality rate as high as 27%, underscoring the need for a cautious assessment of the life-threatening potential of this infection. A deeper analysis of the fatal cases indicates that death directly attributable to refractory septic shock was uncommon. Most patient deaths resulted from the decompensation of irreversible underlying conditions, such as end-stage malignancy or multi-organ failure. This delineates a dual nature of the prognosis in R. peoriensis infection. On one hand, the infection itself is typically treatable given the organism’s susceptibility to several antibiotics. On the other hand, these infections often act as sentinels signaling that the host is in a state of profound immunosuppression or physiological derangement.

This report has several limitations. First, concomitant intra-abdominal culture was not performed, and bacteremia was detected in only one anaerobic blood culture bottle. Although this raises the possibility of contamination, we regard this as a genuine infection because: (1) a confirmed anatomical defect (anastomotic leak) served as a portal of entry; (2) the patient presented with systemic inflammatory response syndrome; (3) clinical improvement was rapid after appropriate antibiotic therapy; (4) R. peoriensis, a fastidious gut anaerobe, is an extremely unlikely skin contaminant. Thus, even a single positive blood culture for this organism should be considered clinically significant in the appropriate setting. Second, echocardiography was not performed to rule out infective endocarditis. While subclinical endocarditis cannot be entirely excluded, the risk was deemed low given the absence of suggestive clinical features (e.g., new murmur, peripheral stigmata, or embolic events). We recommend that echocardiography be considered in future cases of bacteremia to improve diagnostic confidence and clinical management.

Robinsoniella peoriensis is an important, albeit rare, opportunistic pathogen. Its ability to cause bloodstream infection is intimately linked to mechanical or functional disruption of the intestinal barrier. Successful management hinges on clinicians’ ability to recognize high-risk patients, maintain effective communication with the microbiology laboratory, and select appropriate initial antibiotic therapy informed by current susceptibility data. Future efforts should focus on establishing standardized antimicrobial susceptibility testing methods and breakpoints for this organism, employing genomic techniques to elucidate the evolutionary mechanisms underlying its transition from commensal to pathogen, and conducting prospective studies in high-risk populations, such as hematopoietic stem cell transplant recipients and patients with advanced gastrointestinal malignancies. By enhancing clinical awareness and refining diagnostic and therapeutic strategies, we can better confront this subtle yet significant clinical challenge.

Abbreviations

BSI

Bloodstream infection

MALDI-TOF

MS Matrix-assisted laser desorption ionization-time of flight mass spectrometry

CT

Computed tomography

MIC

Minimum Inhibitory Concentration

WBC

White blood cell

AST

Antimicrobial susceptibility testing

Author contributions

The manuscript has been reviewed and approved by all the authors and is not under consideration for publication elsewhere. All the authors contributed to this work. Y. L. and F.L. collected clinical data and wrote the initial draft of the manuscript. Y. L., N. X., W.Z. and Y.Z. conducted a literature review. J. L. and W. F. Z. supervised and edited the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported by the Yangpu District Gaoling Medical Discipline Group Construction Plan (Summit Disciplines, No. 25YPGL311) and the project of the Dual Committees of Yangpu District (YPM 202309, YPM 202508).

Data availability

The datasets generated and/or analysed during the current study are available in the DDBJ/ENA/GenBank repository, under the accession number JBTOPR010000000 (BioProject: PRJNA1403197; BioSample: SAMN54621269).

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report.

Competing interests

The authors declare no competing interests.