Multidrug-resistant Corynebacterium striatum-induced severe pneumonia complicated with multiple organ failure: a diagnostic breakthrough guided by phagocytosis and therapeutic strategy

Abstract

Background

Corynebacterium striatum (C. striatum), a Gram-positive opportunistic pathogen, is increasingly linked to healthcare-associated pneumonia (HAP) in immunocompromised patients, but its nonspecific manifestations and multidrug resistance cause diagnostic delays. This case adds to literature by highlighting neutrophil phagocytosis in sputum smears as a pivotal clue for distinguishing C. striatum infection from contamination, especially in mixed infections.

Case summary

A 56-year-old female with uncontrolled diabetes, hypertension, and post-cerebral hemorrhage sequelae developed severe pneumonia, complicated by septic shock, CRRT-requiring acute kidney injury, and gastrointestinal bleeding. Initial therapy for Klebsiella pneumoniae and Pseudomonas aeruginosa failed. Sputum smear showed neutrophils phagocytosing Gram-positive rods; culture confirmed multidrug-resistant C. striatum. Therapy with ceftazidime-avibactam, vancomycin, and caspofungin improved outcomes.

Conclusion

Microscopic detection of phagocytosis aids early C. striatum identification; dynamic etiological monitoring and individualized combination therapy are critical for refractory HAP in immunocompromised patients.

Introduction

C. Striatum is a commensal bacterium of the skin and mucous membranes, but in recent years, it has emerged as an important etiologic agent of healthcare-associated infections (HAIs). This is particularly true for patients with prolonged hospitalization, invasive procedures (e.g., mechanical ventilation), or immunocompromised states [1]. Two key challenges complicate the clinical management of C. striatum infections: its intrinsic resistance to β-lactam antibiotics and its frequent co-infection with other multidrug-resistant (MDR) pathogens [2]. Severe pneumonia caused by C. striatum is often overlooked due to its nonspecific clinical presentation [3], leading to delayed targeted therapy and an increased risk of multiple organ failure (MOF) [4]. Notably, the detection of pathogens phagocytosed by neutrophils in smear specimens has been validated as a valuable diagnostic clue for distinguishing pathogenic bacteria from contaminants [5]. However, published cases of C. striatum pneumonia mostly rely on culture diagnosis and report only anecdotal observations of phagocytosis; no quantitative studies of phagocytosis-guided diagnosis exist.

We report a case of MDR C. striatum-induced severe pneumonia complicated by MOF, highlighting the diagnostic value of neutrophil phagocytosis.

Case presentation

A 56-year-old female with a medical history of hypertension, poorly controlled type 2 diabetes mellitus, post-cerebral hemorrhage surgery, and left ocular vascular embolism was admitted to our hospital with complaints of “cough, expectoration, and dyspnea for over 2 months, with worsening symptoms over the past 10 days”.

Clinical history and initial presentation

Two months prior to the current admission, the patient developed fever (peak temperature 38.6℃), cough, and hypoxemia (peripheral oxygen saturation, SpO₂ 88%) during a hospitalization. She required endotracheal intubation and non-invasive ventilator support. Sputum culture at that time yielded MDR Klebsiella pneumoniae, so empiric anti-infection therapy with piperacillin-tazobactam was initiated. Due to persistent elevation of inflammatory markers, amikacin was added to the regimen. A tracheotomy was performed later because the patient remained comatose and unable to expectorate spontaneously. Subsequent clinical deterioration—including the development of septic shock, acute kidney injury (requiring CRRT), thrombocytopenia (platelet count, PLT 22 × 10⁹/L), and hypoalbuminemia—prompted escalation of therapy to meropenem combined with ceftazidime-avibactam. Chest computed tomography (CT) showed extensive bilateral ground-glass opacities and patchy consolidations involving the upper and lower lobes, consistent with severe infectious infiltrates (Fig. 1).

Fig. 1.

Chest X-ray(left) and CT(right) scan of the patient

Disease progression

On April 14, the patient suffered a sudden cardiac arrest. After successful resuscitation, she was transferred to our hospital. On admission, recurrent high fever (Fig. 2) and markedly elevated inflammatory markers (procalcitonin, PCT 11.86 ng/mL; C-reactive protein, CRP 175.1 mg/L) were noted. Sputum culture on April 30 identified Pseudomonas aeruginosa and Klebsiella pneumoniae. The therapeutic regimen was adjusted to ceftazidime-avibactam (2.5 g every 8 h) combined with voriconazole, but no satisfactory clinical response was observed, The patient’s body temperature remained fluctuating between 38.5℃ and 38.9℃.

Fig. 2.

Patient’s medication cycle and body temperature change

Sample collection and processing

Endotracheal sputum samples were collected and transported to the laboratory within 30 min for immediate processing. Gram staining was performed and examined under ×1000 oil immersion magnification. For culture, specimens were inoculated onto 5% sheep blood agar and incubated at 35 ℃ with 5% CO₂ for 24 h. Bacterial identification was carried out using MALDI-TOF MS (Bruker) with a log score ≥ 2.0 as the confirmatory criterion. Antimicrobial susceptibility testing was performed using the broth microdilution method according to EUCAST 2024 breakpoints. Multidrug resistance was defined as non-susceptibility to ≥ 3 antimicrobial categories relevant for the treatment of Corynebacterium infections. The phagocytic index was calculated as the percentage of neutrophils containing phagocytosed Gram-positive rods among 200 neutrophils observed in 5–8 high-power fields, with a threshold of > 50% adopted based on previous literature.

Targeted therapy and clinical outcome

Sputum smear showed phagocytic index 68% (Fig. 3A). Pure culture of C. striatum was grown on blood agar (Fig. 3B). AST results are listed in Table 1.The triple antimicrobial regimen was rationally designed to cover the complex infectious condition: ceftazidime-avibactam was used to target multidrug-resistant Gram-negative pathogens, vancomycin was administered against the susceptible multidrug-resistant Corynebacterium striatum isolate, and caspofungin was continued due to the high risk of fungal infection associated with prolonged broad-spectrum antibiotic exposure, immunosuppression, and critical illness. Given the patient’s dependence on continuous renal replacement therapy, vancomycin trough concentrations and renal function were closely monitored to minimize the risk of nephrotoxicity. Concurrently, the patient developed gastrointestinal bleeding (manifested as bloody stools, with hemoglobin), which was managed with acid suppression therapy, hemostatic agents, blood transfusion, and consultation with the gastroenterology team. Three days after the treatment adjustment, the patient’s temperature decreased, and key inflammatory markers (PCT, CRP, white blood cell count, WBC) showed a significant downward trend (Fig. 4). The pathogenesis and diagnostic–therapeutic workflow are illustrated in Fig. 5.

Fig. 3.

Microscopic examination and culture of sputum. Left: Sputum smear (10 × 100 magnification) showing abundant neutrophils phagocytosing Gram-positive rods (phagocytic index > 50%); Corynebacterium striatum appears as Gram-positive, slender, slightly curved bacilli with club-shaped swellings at one or both ends; Right: On 5% sheep blood agar, after 24 h of incubation at 35℃ in 5% CO₂, colonies of C.striatum are small (1–2 mm in diameter), circular, convex, smooth, semi-translucent to grayish-white, and non-hemolytic. They are firm in texture and difficult to emulsify

Table 1.

Antimicrobial susceptibility test results of Corynebacterium striatum (MIC Method)

Antimicrobial agent	MIC result (μg/mL)	Susceptibility
Penicillin	>4	Resistant (R)
Gentamicin	8	Intermediate (I)
Erythromycin	>4	Resistant (R)
Ciprofloxacin	>4	Resistant (R)
Rifampicin	≤0.5	Susceptible (S)
Vancomycin	≤1	Susceptible (S)
Linezolid	≤0.5	Susceptible (S)
Clindamycin	>2	Resistant (R)
Trimethoprim-Sulfamethoxazole (TMP-SMX)	≤1/19	Susceptible (S)
Tetracycline	>8	Resistant (R)

Fig. 4.

Trends of inflammatory markers (PCT, CRP, WBC) before and after targeted therapy for multidrug-resistant Corynebacterium striatum infection

Fig. 5.

Pathogenesis and diagnostic–therapeutic workflow

Discussion

Most reported C. striatum pneumonia cases face substantial diagnostic delays due to contamination skepticism, nonspecific symptoms, and coinfection. Phagocytosis has been mentioned anecdotally but not quantitatively studied. This case confirms that a phagocytic index > 50% can rapidly identify pathogenic C. striatum in severe pneumonia with MOF. This case offers three key clinical and microbiological insights into the diagnosis and management of C. striatum infections:

Diagnostic challenge and the pivotal role of phagocytosis detection

A major barrier to diagnosing C. striatum infection is its frequent misclassification as a contaminant—especially in cases of co-infection with other pathogens (e.g., Klebsiella pneumoniae, Pseudomonas aeruginosa) as seen here [6]. In this case, the detection of Gram-positive rods phagocytosed by neutrophils in the sputum smear provided a critical diagnostic breakthrough, clearly distinguishing C. striatum as a pathogenic agent rather than a contaminant [7]. This finding underscores the importance of integrating microscopic smear observations with culture results to achieve an accurate etiological diagnosis, particularly in patients with refractory infections who fail initial empiric therapy.

Multidrug resistance and the rationale for combination therapy

C. striatum exhibits high resistance to β-lactam antibiotics, primarily due to its production of β-lactamase [8]. This resistance explains why the patient failed initial therapy with piperacillin-tazobactam and meropenem. Antimicrobial susceptibility testing confirmed the isolate’s sensitivity to vancomycin and linezolid—consistent with findings from previous studies [9]. The patient’s favorable response to the combination of ceftazidime-avibactam, vancomycin, and caspofungin highlights the efficacy of broad-spectrum combination therapy that covers both Gram-negative pathogens and MDR Gram-positive pathogens in cases of mixed infections. Importantly, this case reinforces that individualized therapy, guided by antimicrobial susceptibility testing, is crucial for improving outcomes in patients with MDR C. striatum infections [10].Phagocytosis observation is rapid, low-cost, and highly specific. Combination antimicrobial therapy was used for mixed MDR infection. Nephrotoxicity was carefully monitored in the setting of CRRT.

Risk factors and the value of multidisciplinary management

The patient’s risk factors for C. striatum infection were well-defined: immunocompromise, prolonged mechanical ventilation, and prior exposure to broad-spectrum antibiotics [11]. The development of MOF—including septic shock, acute kidney injury, and gastrointestinal bleeding—required a multidisciplinary approach involving teams from critical care medicine, infectious diseases, nephrology, and gastroenterology [12]. Interventions such as CRRT, blood transfusion, and supportive care played key roles in stabilizing the patient’s condition while the targeted anti-infection therapy took effect [13]. This underscores that comprehensive management of complications, alongside pathogen-specific treatment, is essential for optimizing outcomes in complex cases of C. striatum infection [14].

Conclusion

Corynebacterium striatum (C. striatum) should be considered a potential pathogenic agent in immunocompromised patients with refractory severe pneumonia—especially those who fail initial therapy targeting common Gram-negative pathogens [15]. The detection of phagocytosed Gram-positive rods in sputum smear is a simple yet valuable diagnostic tool for distinguishing C. striatum infection from contamination. To improve outcomes, clinicians should prioritize dynamic etiological monitoring, timely antimicrobial susceptibility testing, and individualized combination therapy [16]. This single-case observation requires large-scale prospective validation and does not replace conventional diagnostic methods. Individualized combination therapy and multidisciplinary supportive care improve clinical outcomes in critically ill patients.

Abbreviations

HAP

Healthcare-Associated Pneumonia

HAIs

Healthcare-Associated Infections

MDR

Multidrug-Resistant

MOF

Multiple Organ Failure

CRRT

Continuous Renal Replacement Therapy

SpO₂

Peripheral Oxygen Saturation

PLT

Platelet Count

PCT

Procalcitonin

CRP

C-Reactive Protein

CT

Computed Tomography

WBC

White Blood Cell Count

Hb

Hemoglobin

TMP-SMX

Trimethoprim-Sulfamethoxazole

EUCAST

European Committee on Antimicrobial Susceptibility Testing

CLSI

Clinical and Laboratory Standards Institute

ASHP

American Society of Health-System Pharmacists

Author contributions

Ruofan Wang, Xiaosong Xu, Zhilong Zheng, Ruiying Li: Participated in the collection of clinical data, collation of laboratory data, literature search, and drafting of the initial manuscript; Xiangsheng Cai: Designed the research protocol, guided data analysis and manuscript writing, reviewed and revised the initial draft, and is responsible for the research results. All authors have read and approved the final version of the manuscript and agree to its submission for publication.

Funding

This study was funded by the Fund of Guangzhou Municipal Health Commission (20241A010099, 20242A011033) and the Fund of Guangdong Provincial Administration of Traditional Chinese Medicine (20241242).

Data availability

The clinical data, laboratory test results, and related materials involved in this study have been properly archived. Requests for access to the raw data or related materials of this study can be made to the corresponding author. The use of data must comply with relevant ethical norms and data confidentiality requirements.

Declarations

Ethical approval and consent to participate

This study has been approved by the Ethics Committee of The First Affiliated Hospital of Guangdong Pharmaceutical University. Given the patient’s critical condition and comatose state, she was unable to provide the informed consent form independently. Written informed consent has been obtained from the patient’s immediate family members for participation in the study and the collection and analysis of relevant data. All research procedures comply with the ethical principles of the Helsinki Declaration.

Consent for publication

The patient’s family members have provided written consent for the publication of this case report and related clinical data (including imaging pictures, laboratory test data, and treatment records), and have signed the informed consent form for publication, agreeing to the use of relevant materials for academic exchange and publication.

Competing interests

The authors declare no competing interests.