Four cases of bacteremia caused by Enterocloster clostridioformis

Sir,

Enterocloster is a new genus of anaerobic bacteria composed by Gram-positive fusiform rods that currently includes seven species of which E. clostridioformis is the type species. E. clostridioformis was first identified by Ankersmit in 1906 as Bacterium clostridiiforme from a bovine intestinal tract [1]. After several changes, Haas and Blanchard proposed the reclassification of the Clostridium clostridioforme as E. clostridioformis [2]. To the best of our knowledge, only two cases of bacteremia due to E. clostridioformis have been published [3, 4]. In this report, we present four cases of bloodstream infection due to E. clostridioformis isolated in pure culture, providing full clinical data and information on the isolation of this pathogen from blood samples.

Case 1

A 75-year-old woman with a clinical history of diabetes mellitus, without other risk factors was admitted to the Emergency Department of our hospital after an episode of hyperglycemia with decreased consciousness. Blood analysis showed increased glucose [700 mg/dL (75-115 mg/dL)], C-reactive protein [271 mg/L, (0-5 mg/dL)] and white blood cell count [26.11 x 10³/mm³ (3.5-10.5 x 10³/mm³)]. The patient developed a systemic inflammatory response syndrome with respiratory insufficiency; empirical therapy with levofloxacin (500 mg/12 h) was started.

Case 2

A 58-year-old woman with ovarian cancer was admitted to the Surgery Department for surgical treatment due to an intestinal dehiscence after a recent surgery. Subsequently, the patient developed fever (38° C) and low blood pressure. Physical examination revealed tachycardia (100 bpm). Blood analysis showed increased levels of C-reactive protein (11 mg/dL). Empirical treatment with meropenem (1g/8 h) was started.

Case 3

A 93-year-old man with a clinical history of diabetes mellitus was admitted to the Emergency Department due to abdominal pain and fever. Physical examination revealed fever (38.5° C), tachycardia (128 bpm) and tachypnea (30 bpm). Blood analysis demonstrated increased levels of glucose (308 mg/dL), urea (169 mg/dL), creatinine (1.89 mg/dL), white blood cell count (14.83 x 10³/mm³) and C-reactive protein (293.2 mg/dL). An abdominal CT scan showed compatible signs of peritonitis due to intestinal perforation secondary to colon cancer. Empirical treatment with meropenem (1g/8 h) was started. The patient died as a consequence of septic shock.

Case 4

A 82-year-old woman was admitted to the Medicine Department due to fever for a week. The patient had a clinical history of breast cancer since 2023. Blood analysis showed increased levels of C-reactive protein (78.2 mg/dL). Empirical treatment with meropenem (1 g/8 h) was started.

Isolation and identification

In all cases, two sets of blood cultures were obtained and sent to the microbiological laboratory, where samples were incubated in the BACTEC^™ FX 40 (Becton, Dickinson and Company^®, Franklin Lakes, NJ) blood culture system. After 48 h, the two anaerobic bottles in the sets were positive for all patients. The samples were subcultured on aerobic and anaerobic blood agar (BD Columbia Agar with 5% Sheep Blood, Becton Dickinson and Company^®, Franklin Lakes, NJ). All media were incubated at 35-37 °C. The anaerobic atmosphere was generated with the AnaeroGen^™ Compact anaerobic system (Oxoid Ltd., Wide Road, Basingstoke, England). Gram staining of the blood cultures revealed Gram-positive bacilli. After 24h of incubation, colonies of these microorganisms were observed in pure culture on anaerobic blood agar alone. MALDI-TOF MS (Bruker Biotyper^®, Billerica, MA) identified the strains as C. clostridioforme (the first three cases) and E. clostridioformis (the last one) (log scores >2.0 in all cases, Table 1). The gradient diffusion strip method (Etest^®, bioMérieux) was used for antimicrobial susceptibility testing based on EUCAST criteria [5]. MIC values and interpretation are shown in Table 2.

Table 1.

Clinical and microbiologic characteristics of patients with Enterocloster clostridioformis bacteremia.

Author (year) [reference]	Age (years)/sex	Underlying conditions and/or risk factors	Probable source of infection	Clinical features	Diagnosis	Treatment	Outcome
Ogah K (2012) [3]	6/Female	Liver abscesses Portal vein thrombosis	Abdominal	Fever, lethargy, weight loss	16S rRNA gene sequencing	Cefuroxime metronidazole meropenem	Successful
Kitagawa H (2024) [4] *	47/Female	NR	Genital	Fever, genital bleeding, lower abdominal pain	MALDI-TOF MS	Cefmetazole Amoxicillin-clavulanate	Successful
Cobo F (2024) [PR]	75/Female	Diabetes mellitus	Pulmonary	Hyperglycemia with decreased consciousness	MALDI-TOF MS	Levofloxacin	Successful
Cobo F (2024) [PR]	58/Female	Ovarian cancer	Abdominal	Fever, abdominal pain	MALDI-TOF MS	Meropenem	Successful
Cobo F (2024) [PR]	93/Male	Diabetes mellitus Colon cancer	Intestinal	Fever, abdominal pain	MALDI-TOF MS	Meropenem	Died
Cobo F (2024) [PR]	82/Female	Breast cancer	Unknown	Fever	MALDI-TOF MS	Meropenem	Successful

^*In this case, Dialister micraerophilus and Eggerthella lenta were also isolated from blood.

PR: present report NR: not reported.

Table 2.

MIC values and interpretation of 4 patients with Enterocloster clostridioformis bacteremia.

Case	Antibiotic, MIC value and interpretation
	Benzylpenicillin	Piperacillin/tazobactam	Meropenem	Clindamycin	Metronidazole
1	0.047 (S)	0,032 (S)	0,016 (S)	0.19 (S)	0,25 (S)
2	<0.016 (S)	0.19 (S)	0.064 (S)	1 (S)	0.5 (S)
3	0.5 (S)	0.38 (S)	0.75 (S)	16 (R)	0.032 (S)
4	0.016 (S)	0.094 (S)	0.25 (S)	0.032 (S)	0.023 (S)

E. clostridioformis has been rarely isolated in human samples, but it has demonstrated to be a cause of invasive infections, such as osteomyelitis, empyema, paravertebral abscess and meningitis and bacteremia [3,4,6–8]. The main factors that can contribute to spread the bacteria from the bowel to the blood are the presence of immunossupressive factors and the permeability of the mucous barrier. Analyzing the available data, the presence of any type of cancer and/or diabetes mellitus could be considered the main risk factors for developing bacteremia due to E. clostridioformis, although other factors such as previous surgery are also associated. Patients with diabetes mellitus are at high risk of infections due to anaerobes because they may have poor blood flow, which in turn reduces the body’s ability to fight infections and heal wounds. In this series, most cases were produced in women (5 from 6 cases), and the mean age was 60 years. Most patients had a successful outcome, but from our patients, one of them died as a consequence of this infection due to a septic shock. The scientific literature did not show special level of resistance of the isolates analyzed. A study showed 43% of resistance to penicillin G, 9% to clindamycin, and 5% to moxifloxacin in 21 isolates of C. clostridioforme [9]. A few case reports demonstrated resistance to penicillin in isolated strains [3]. Our isolates were susceptible to the antibiotics tested, except for one strain that was resistant to clindamycin. Regarding identification, almost all recently published isolates were identified by using MALDI-TOF MS, so this technique has proven to be an adequate method for identifying this bacterium, providing high confidence of identification at species level.

In conclusion, this manuscript aims to contribute information on the possible clinical significance of this rare pathogen isolated from blood cultures. E. clostridioformis has been rarely implicated in serious human infections to date. As with other anaerobes, the presence of any type of cancer and/or diabetes mellitus, among other factors, may be considered risk factors contributing to the development of this infection. Finally, although limited data on antimicrobial susceptibility in this bacterium exist, resistance to penicillin has been demonstrated in some isolates.

Funding

None to declare.

Conflict of interest

Authors declare no conflict of interest.