A rare case of infective endocarditis caused by Kodamaea ohmeri

INTRODUCTION

Infective endocarditis (IE) is a severe inflammatory and proliferative disease of the endocardium that affects mainly the heart valves.^[1] It is predominantly caused by bacteria, with fungal endocarditis being a rare but often more severe and difficult-to-treat form of the disease. The timely identification and treatment of the causative pathogen are crucial for patient outcomes. The diagnosis of IE is based on microbiological confirmation and echocardiographic findings, as described in the modified duke criteria.^[2]

Fungal etiology is uncommon and associated with high mortality, especially if not treated early.^[3] Candida and Aspergillus are the most common fungal species causing IE, usually associated with bulky vegetation. Kodamaea, particularly Kodamaea ohmeri, is an uncommon yeast-like fungal pathogen rarely implicated in human infections. Kodamaea species are opportunistic pathogens, typically affecting individuals with compromised immune systems or those with significant underlying comorbidities. Its presence in blood cultures, especially in cases of IE, is exceedingly rare. K. ohmeri infections usually occur due to predisposing factors such as an immunocompromised state, use of endovascular devices, or previous reconstructive cardiac surgery.^[4] The first case of K. ohmeri fungemia was reported in 1998 in a 48-year-old diabetic female with multiple complications, who ultimately succumbed despite treatment with high-dose amphotericin B.^[5] Here, we present a rare case report of K. ohmeri detected in the blood culture of a patient diagnosed with IE.

CASE REPORT

A 36-year-old woman from Balaghat, Madhya Pradesh, had a history of rheumatic heart disease. She underwent mitral valve repair in February 2023 with a TTK Chitra heart valve prosthesis implantation. She also had stage 5 chronic kidney disease and was on maintenance hemodialysis. The patient presented to the nephrology outpatient department with a 7-day history of fever, burning during urination, and abdominal pain.

On admission, her general condition was poor, with a temperature of 103.2° F, a pulse of 123/min, and an oxygen saturation of 98%. Her contrast enhanced computed tomography (CECT) thorax showed minimal right- and left-sided pleural effusion with consolidation of lung parenchyma. Consolidation was observed in the anterior segment of the right upper lobe. An ophthalmic examination revealed Roth’s spots and multiple hemorrhages in both eyes. On 2D echo, cardiomegaly was noted, and the left atrium and left ventricle were enlarged. Left ventricular (LV) ejection fraction was 20% with global LV hypokinesia. The mitral prosthesis was in situ with severe LV dysfunction. CECT abdomen showed a splenic abscess and splenic infarct with hepatomegaly. Kidney and liver functions were also deranged. Due to the persistent fever and the presence of Roth spots in both eyes, the case was provisionally diagnosed as end-stage renal disease with IE.

Her blood investigations revealed hemoglobin of 5.6 g/dL, white blood cell (WBC) count of 8.40 × 10³ cells/mL, platelet count of 193 × 103/μL, red blood cell counts of 2.29 × 10⁶/μL, and hematocrit-16.9%. Deranged international normalized ratio and coagulation profile raised C-reactive protein-106.9 mg/L and procalcitonin 10.44 ng/mL.

Three sets of automated blood cultures, each approximately 8–9 mL in volume, were collected 30 min apart from the forearm, fistula, and femoral sites and sent to the clinical microbiology laboratory for culture and sensitivity. Empirically ,the patient was started on the antibiotic injection piperacillin-tazobactam (2.225g)and vancomycin (750mg) stat once and 500 mg post hemodialysis every session.

Out of three sets of blood cultures, two bottles – one from the forearm and one from the fistula – flagged positive after 48 h of incubation in an automated blood culture system (BacT/ALERT Microbial Detection System, BioMèrieux SA, France). Direct Gram’s stain smears from positive blood culture bottles revealed the presence of budding yeast-like cells [Figure 1]. The treating clinician was immediately informed of the Gram stain report. The samples were inoculated on Blood agar, MacConkey agar, and Sabouraud’s dextrose agar (SDA). The next day, blood agar and SDA showed growth of white, opaque, dry, and circular colonies [Figure 2], confirmed as Gram-positive budding yeast cells on a colony Gram stain [Figure 3]. On Candida chrome agar, it appeared as pink colonies [Figure 4]. The isolates were identified as K. ohmeri on the VITEK 2 compact system (BioMérieux Pvt. Ltd.) using the VITEK 2 Y.S.T. card on the 14^th day of hospitalization, and antifungal susceptibility testing was performed using the AST YS06 card.

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Figure 1:

Gram stain from a positive blood culture bottle showing gram-positive budding yeast-like cells.

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Figure 2:

Growth of white, opaque, dry, and circular colonies on Sabouraud’s dextrose agar.

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Figure 3:

Gram stain of growth on Sabouraud’s dextrose agar: Gram-positive budding yeast like cells.

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Figure 4:

Purple to pink colored colonies on Candida chrome agar.

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Both isolates were susceptible to voriconazole (minimum inhibitory concentrations [MIC] <0.12 μg/mL), amphotericin B (MIC <0.25 μg/mL), fluconazole (MIC 2 mcg/mL), and micafungin (0.25 mcg/mL). The patient was put on injection liposomal-amphotericin B (25 mg in 100 mL D5% OD for 7 days) and fluconazole (200 mg OD for 7 days).

The patient suddenly experienced hemodynamic compromise, marked by a gradual decrease in oxygen saturation that progressed to respiratory failure. Despite attempts at resuscitation, the patient could not be saved.

DISCUSSION

Fungal IE remains a rare but highly lethal condition, with Candida and Aspergillus species accounting for most cases. However, K. ohmeri, a yeast-like fungus, has emerged as an opportunistic pathogen, particularly in immunocompromised individuals or patients with invasive medical devices. This case described here is significant for the involvement of K. ohmeri in IE, an exceedingly rare condition for this pathogen.

K. (Pichia) ohmeri is a relatively uncommon yeast species found in various environmental sources, including seawater, fruits, and pools. It exhibits characteristics such as the ability to form pseudohyphae and blastoconidia. Its anamorphic state was previously identified as Candida guilliermondii var. membranaefaciens, although this classification has yet to be widely accepted in recent literature.^[6] The genus Kodamaea comprises five species, namely, Kodamaea anthrophila, Kodamaea kakaduensis, Kodamaea laetipori, Kodamaea nitidulidarum, and K. ohmeri. Among these, K. ohmeri is the only species known to infect humans. Although initially considered a contaminant when isolated from clinical specimens, such as pleural fluid, as early as 1984, subsequent reports have increasingly recognized it as a potential pathogen capable of causing human infections.^[7]

K. ohmeri has been implicated in various clinical presentations, including fungemia, peritonitis, and endocarditis.^[7] Infections caused by K. ohmeri primarily occur in immunocompromised patients, although they can also occur in immunocompetent individuals. Factors such as the presence of indwelling catheters, central venous catheters (CVC), malignancy, previous chemotherapy, parenteral nutrition, recent surgery, and recent antibiotic use are highly prevalent in patients with K. ohmeri fungemia, indicating that these factors are essential risk contributors.^[7] A review by Zhou et al.^[6] highlights that the majority of K. ohmeri infections occur in immunocompromised individuals or those with invasive devices, particularly CVCs. Similar to our case, Sundaram et al.^[3] reported K. ohmeri tricuspid valve endocarditis in a neonate with a structurally normal heart associated with an indwelling catheter. These findings align with the patient’s clinical profile, which includes a prosthetic mitral valve and end-stage chronic kidney disease on maintenance hemodialysis, both of which are potential risk factors for fungal invasion. The presence of prosthetic cardiac and vascular access devices, along with prior exposure to broad-spectrum antibiotics that disrupt the gut microbiota, may have contributed to an environment conducive to fungal overgrowth.

The isolation of K. ohmeri from both peripheral and fistula-site blood cultures suggests that the catheter or vascular access site may act as the source of infection. Hence, in patients with CVCs, the skin puncture site may provide an entry point for fungi, most commonly in conditions of compromised skin integrity or suboptimal catheter care.

Accurate identification of K. ohmeri in clinical settings is challenging due to its phenotypic similarities with other yeast species, such as Candida parapsilosis and Candida tropicalis. The primary approach to identifying most yeasts includes evaluating their carbohydrate assimilation and fermentation capacity and observing their macroscopic and microscopic traits post-growth on specialized media. However, distinguishing K. ohmeri from other yeast species such as C. parapsilosis, Candida haemulonii, and C. tropicalis can be challenging when using conventional identification techniques alone.^[8] Advanced diagnostic methods such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) and the VITEK-2 system, as used in our case, have improved accuracy but remain limited in accessibility in some healthcare settings. In this instance, MALDI-TOF was utilized due to the confusion of Gram stain morphology with Candida species. Nevertheless, the accessibility of advanced identification systems could pose a limitation. Similar challenges were reported by Lee et al.^[9] who highlighted the difficulty of distinguishing Kodamaea from other yeasts using standard methods.

The treatment of K. ohmeri infections is complicated by the lack of established clinical susceptibility breakpoints and variability in antifungal resistance profiles. There are no published clinical susceptibility thresholds for K. ohmeri by the European Committee on Antimicrobial Susceptibility Testing or Clinical and Laboratory Standards Institute.

Amphotericin B is considered the first-line therapy based on clinical guidelines from the European Society for Clinical Microbiology and Infectious Diseases and the European Confederation of Medical Mycology. However, resistance to fluconazole and echinocandins has been observed in some strains of K. ohmeri, complicating treatment choices. For instance, Al-Sweih et al.^[10] reported a case where K. ohmeri demonstrated higher MIC for fluconazole, suggesting that alternative antifungals may be required. In our case, despite susceptibility to both fluconazole and amphotericin B, the patient’s condition rapidly deteriorated, highlighting the aggressive nature of fungal IE and the potential for treatment failure even when susceptibility testing indicates effectiveness.

Management of Kodamaea ohmeri endocarditis, as with other fungal infections, involves both antifungal therapy and, when feasible, removal of infected prosthetic devices or material.

CONCLUSIONS

This case report highlights a rare instance of Kodamaea detected in the blood culture of a patient diagnosed with IE. Diagnosing K. ohmeri remains challenging due to its similarity to other yeast species, and accurate identification often requires advanced methods. Further research into its epidemiology, virulence factors, and treatment options will be crucial to managing infections caused by this emerging pathogen.