First case of a human Candida berthetii systemic infection in a preterm infant: a case report

TL;DR

A preterm infant died from a rare Candida berthetii infection, highlighting the need for better diagnostic tools for uncommon yeast pathogens.

Contribution

This is the first reported case of a systemic human infection caused by Candida berthetii in a preterm infant.

Findings

Candida berthetii was identified through ribosomal DNA sequencing in a preterm infant with persistent candidemia.

Antifungal susceptibility testing showed high resistance to fluconazole and anidulafungin but lower resistance to amphotericin B.

The infant's death was attributed to severe underlying conditions and delayed effective antifungal treatment.

Abstract

We report the first case of invasive human infection caused by Candida berthetii in a preterm infant.

A premature neonate who required prolonged hospitalization, intensive care support, multiple surgical interventions, and broad-spectrum antibiotics developed persistent candidemia due to C. berthetii. Species identification was confirmed through sequencing of the internal transcribed spacer region of ribosomal DNA. Antifungal susceptibility testing, performed using the the European Committee on Antimicrobial Susceptibility Testing (EUCAST) microbroth dilution method, revealed high minimal inhibitory concentrations (MICs) to fluconazole and anidulafungin but low MICs for amphotericin B. Despite switching to liposomal amphotericin B, the infant progressed to multiple organ dysfunction and died. The poor clinical outcome was attributed to both the severity of underlying conditions associated with candidemia and the delay in starting adequate antifungal therapy.

This case broadens the current understanding of rare yeast pathogens and highlights the critical need for improved diagnostic tools to accurately detect and identify uncommon Candida species. Clinicians should remain vigilant to the emergence of rare yeast pathogens causing fungemia, especially among immunosuppressed hosts undergoing invasive medical procedures and prolonged exposure to broad-spectrum antimicrobials.

Tables

TABLE 1. In vitro antifungal susceptibility of eight Candida berthetii clinical isolates

Isolate	Sampling site	Sampling date	MIC (µg/mL) of:
			Fluconazole	Voriconazole	Anidulafungin	Amphotericin B
2078/2021	Peritoneal fluid	05/04/2021	64	2	1	0.25
2079/2021	Blood	05/06/2021	64	2	1	0.25
2080/2021	Blood	05/06/2021	64	2	1	0.25
2120/2021	Blood	05/06/2021	64	1	1	0.25
2121/2021	Blood	05/25/2011	64	1	1	0.25
2122/2021	Proximal catheter tip	05/06/2021	64	1	1	0.25
2123/2021	Distal catheter tip	05/27/2021	64	1	1	0.25
2124/2021	Blood	05/31/2021	32	0.5	1	0.25

Full text

INTRODUCTION

Invasive fungal infections in neonates, particularly in premature infants with complex medical conditions, pose significant challenges in both diagnosis and treatment (1, 2). Rare and emerging Candida species have been increasingly associated with these infections, but there remains a lack of detailed documentation regarding their clinical impact and antifungal susceptibility (3, 4). Candida berthetii (Boidin, Pignal, Mermiér & Arpin), first described in 1963 from an isolate found in gum arabic from a forest tree, was later identified in the ambrosia beetle Xyleborus volvulus (5, 6). Notably, this species has not been documented in wildlife animals or humans, highlighting challenges in understanding its ecological niche and its potential role in human infections. This study describes the first case of human systemic infection caused by C. berthetii in a premature neonate, who developed a persistent bloodstream infection despite antifungal therapy.

CASE PRESENTATION

A preterm male neonate, the first of a twin pregnancy, was transferred to the neonatal intensive care unit (NICU) of a tertiary care center with 6 days of life for the surgical management of hypoplastic left heart syndrome (HLHS). The infant was born at 28 weeks via an emergency cesarean section due to preterm labor triggered by congenital heart disease, with a birth weight of 1,610 g and Apgar scores of 7 and 6 at 1 and 5 min, respectively. Intrauterine diagnosis of HLHS was established by fetal echocardiography.

During the first 7 days of NICU admission, the infant remained intubated and received empirical broad-spectrum antibiotics to treat a putative clinical event of sepsis with all cultures negative. Extubation was possible at 12 days of life, followed by support with non-invasive positive pressure ventilation. Total parenteral nutrition (TPN) and enteral feeding were initiated, targeting adequate weight gain for surgical intervention.

On day 16 of life, the patient developed low cardiac output syndrome secondary to imbalance between pulmonary and systemic blood flow (Qp:Qs), which was complicated by necrotizing enterocolitis (NEC). Management of NEC included bowel rest, broad-spectrum antibiotics, and reintubation. Two days later, pneumoperitoneum was diagnosed, and a percutaneous abdominal drain was placed at the bedside. At that time, antimicrobial therapy included meropenem (40 mg/kg/day), daptomycin (6 mg/kg/day), and fluconazole (12 mg/kg/day). The antifungal was added to the empirical antimicrobial regimen for NEC due to the presence of risk factors for Candida infection and was maintained for 37 days.

Surgical correction of HLHS was postponed due to the clinical instability of the neonate. At 25 days of life, the patient underwent ductal stent placement and bilateral pulmonary artery banding to optimize systemic perfusion. Postoperatively, the patient developed acute kidney injury (KDIGO stage 2), significant fluid overload (>20% above baseline), and was managed with diuretics, albumin, and mannitol. Due to low body weight and contraindications, renal replacement therapy was not pursued. The patient gradually improved.

Due to clinical instability, intestinal perforation caused by NEC was initially managed conservatively with peritoneal drainage. Following clinical improvement, corrective surgery was performed at 39 days of life (exploratory laparotomy, lysis of adhesions, jejunostomy at 40 cm distal to the ligament of Treitz, multiple enterectomies, and primary jejunal anastomosis). At 47 days, he underwent a balloon atrial septostomy (Raskind procedure) for restrictive atrial septal defect.

The patient continued under intensive care, and at 3 months of age, the infant developed signs and laboratory findings suggestive of bloodstream infection, including hypothermia, hypotension, and thrombocytopenia (67,000/mm^3^, reference value:150,000–450,000/mm^3^), and elevated C-reactive protein (CRP) (13.23 mg/dL, reference value: <0.3 mg/dL). Blood cultures were obtained via central venous catheter and processed using BD BACTEC (Becton Dickinson, NJ, USA) for automatic detection. Preliminary identification of the blood stream pathogen was obtained by MALDI-TOF-MS (VITEK MS V.3.2, BioMérieux, Marcy l'Etoile, France) which reported Candida spp. with low confidence level to species identification. Fluconazole therapy was initiated immediately. However, despite 30 days of antifungal treatment and intensive care support, the infant remained clinically unstable. Along this period, a total of eight cultures of different clinical samples (blood, catheter tips, and peritoneal fluid) were all positive for Candida spp.

Considering the lack of accurate identification of the yeast pathogens and the persistent clinical instability of the infant, all isolates were sent to Laboratório Especial de Micologia (LEMI)-Federal University of Sao Paulo, a reference laboratory for fungal identification and antifungal susceptibility in Brazil. Species identification of all isolates was performed by sequencing the ITS1–5.8S-ITS2 rDNA region (7, 8). Sequences were aligned and compared with the reference sequences in the NCBI database using BLASTn (http://ncbi.nlm.nih.gov). Sequences with a percentage of identity and sequence coverage of ≥98% and an E-value of <10^−5^ were considered (8).

Antifungal susceptibility testing was performed according to the EUCAST E.Def 7.4 method (9) against the following antifungal agents: fluconazole, voriconazole, anidulafungin, and amphotericin B (AMB) (Sigma-Aldrich, St. Louis, MO, USA). Minimal inhibitory concentration (MIC) readings were performed spectrophotometrically after 24 h of incubation, at 35 ± 2°C, using a 50% inhibition threshold for azoles and echinocandins, and 100% inhibition for AMB.

The ITS-sequencing results identified all isolates as C. berthetii, a species not previously associated with human infection. Eight isolates from blood, peritoneal fluid, and catheter tips were recovered at distinct time points throughout the course of infection, and all of them were identified as C. berthetti. All isolates displayed elevated MICs to fluconazole (>64 µg/mL), voriconazole (1–2 µg/mL), and anidulafungin (1 µg/mL), with low MIC to AMB (MIC = 0.25 µg/mL) (Table 1). Antifungal therapy was switched to liposomal amphotericin B. Nevertheless, the patient’s condition continued to deteriorate, progressing to multiple organ dysfunction and dying 5 days later despite therapy with AMB along this period.

Due to the rarity of C. berthetti isolation in BSIs, environmental surveillance was performed by the local hospital infection control team, but no single culture was positive across all samples collected from hospital surfaces, intravenous solutions, and medicines. C. berthetii was only identified in the clinical samples.

DISCUSSION

This report represents the first documented instance of C. berthetii causing invasive infection in a human being in the setting of immunosuppression and long-term exposure to intensive care support. Previously, this species had been scarcely cultured from a few environmental samples collected from Acacia gum and an insect called Xyleborus volvulus (5, 6).

In the present case, systemic infection was confirmed by the accurate identification of the pathogen across eight cultures collected at different time points from multiple clinical specimens, including four blood samples. Identification was achieved via sequencing of the ITS region of rDNA, which provided high-resolution species-level assignment. Based on this method, all isolates were unequivocally identified as C. berthetii, exhibiting 100% sequence identity and coverage compared with the reference strain C. berthetii CBS 6113. As expected, MALDI-TOF MS commercial database failed to identify this pathogen, highlighting the need for updates to available libraries for the detection of rare yeast species, such as C. berthetii (10).

High MICs for fluconazole and anidulafungin were obtained using standardized broth microdilution method according to EUCAST protocol. Rare yeast pathogens, such as Candida berthetii, often express elevated MICs for at least one class of antifungal agents (4, 11). Infections caused by these rare pathogens are particularly challenging to manage due to the limited clinical data available in the literature and the lack of susceptibility breakpoints to interpret antifungal susceptibility tests (11, 12). The persistence of candidemia despite antifungal treatment is consistent with in vitro data, suggesting low susceptibility of C. berthetii to the antifungal used. These findings underscore the critical need for precise species identification and comprehensive antifungal susceptibility testing, particularly in the context of refractory infections caused by rare and emerging yeast pathogens.

Preterm neonates are uniquely predisposed to invasive infections caused by a large spectrum of pathogens, including rare yeasts (13). The immunological immaturity and low weight at birth of preterm infants, prolonged hospitalization and intensive care support, exposure to broad-spectrum antibiotics and multiple invasive medical procedures are all conditions that increase the risk of preterm neonates to acquire infections by emerging yeast pathogens (2, 14–18). All these risk conditions were present in our present case of systemic infection due to C. berthetii.

The poor prognosis observed in the present infant case was likely attributable to the severity of the underlying comorbidities associated with candidemia, the inherent immunological immaturity of preterm neonates, and delays in both the accurate pathogen identification and the initiation of appropriate antifungal therapy. This case broadens the current understanding of rare yeast pathogens and also underscores the critical need for improved diagnostic tools to accurately detect uncommon Candida species. Early recognition and tailored treatment are essential, particularly in immunocompromised patients undergoing invasive medical procedures and exposed to broad-spectrum antibiotics. Clinicians should remain vigilant to the emergence of rare yeast pathogens causing fungemia, particularly in immunocompromised patients undergoing multiple invasive medical procedures and receiving prolonged broad-spectrum antibiotics (13, 14). Further investigation is warranted to elucidate the eco-epidemiology, virulence factors, and mechanisms of antifungal resistance of C. berthetii.