In a recent study published in Tropical Medicine and Infectious Disease, a team of researchers from Brazil presented a fatal case of a patient developing Saccharomyces cerevisiae infection and succumbing to septic shock after contracting and recovering from a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Study: SARS-CoV-2 Post-Infection and Sepsis by Saccharomyces cerevisiae: A Fatal Case Report—Give attention to Fungal Susceptibility and Potential Virulence Attributes. Image Credit: Kateryna Kon/Shutterstock

Background

While the mortality rates related to the coronavirus disease 2019 (COVID-19) were extremely high worldwide, many patients hospitalized or admitted to intensive care units also faced the extra complication of bacterial and fungal co-infections. Moreover, the immune dysregulation brought on by COVID-19 exacerbated the danger of opportunistic bacterial and fungal infections.

Various studies have reported co-infections with yeasts reminiscent of Candida species, S. cerevisiae, and Cryptococcus neoformans, molds reminiscent of Aspergillus, Rhizopus, and Mucor, and dimorphic fungi reminiscent of Paracoccidioides species and Histoplasma capsulatum in severe COVID-19 patients.

A recent increase in Saccharomyces infections has been observed amongst critically sick patients, which is considered linked to the probiotic dietary supplements given to ease diarrhea brought on by antibiotics. Given the increasing risk of Saccharomyces infections amongst immunocompromised and critically sick patients, its virulence needs further investigation.

In regards to the study

In the current study, the researchers reported a case study of a 75-year-old woman with other health complications who was scheduled for a left foot amputation after being admitted for an arterial ulcer and whose condition rapidly declined after being symptomatically treated for a SARS-CoV-2 infection. Although the patient died as a consequence of septic shock 4 days after hospitalization, blood samples were collected and cultured, and yeast-like organisms were detected.

The yeast-like organisms, identified to be S. cerevisiae were used to guage whether the biofilm-forming and planktonic cells were liable to standard antifungal medications, whether fungal virulence was related to the production of siderophores, hemolysins, and hydrolytic enzymes, whether these cells could grow in various nutrient sources, and whether or not they could infect the Tenebrio molitor larvae or mealworm larvae in vivo.

Results

The case report indicated that the patient had a history of smoking, systemic arterial hypertension, and stroke with aphasia. Positive SARS-CoV-2 polymerase chain response (PCR) tests 30 and 10 days before hospital admission indicated COVID-19, which was treated at home symptomatically.

Nevertheless, the patient’s condition worsened rapidly with metabolic acidosis, bradycardia, hypotension, leukocytosis, high levels of C-reactive protein, and disorientation. She was treated with intravenous antimicrobials and monitored for atrial fibrillation. 4 days after hospitalization, the patient succumbed to septic shock, and blood cultures of samples taken six hours before her death revealed yeast-like organisms that were later identified as S. cerevisiae.

The identification of the yeast was based on metabolic, enzymatic, and carbohydrate assimilation profiles based on a yeast card, in addition to the amplification of ITS1-5.8S-ITS2 gene sequences, which were matched to those of Saccharomyces within the GenBank database.

Five antifungals — amphotericin B, caspofungin, fluconazole, 5-flucytosine, and voriconazole — were tested against the strain, and for all five, the strain displayed low minimal inhibitory concentrations, indicating that it was susceptible. Nevertheless, the fungal strain was in a position to produce biofilms and virulence aspects, including extracellular bioactive molecules reminiscent of aspartic peptidase, catalase, esterase, hemolysin, phospholipase, phytase, and siderophore.

While the antifungals were effective against planktonic cells, they weren’t in a position to suppress mature biofilms by way of viability and biomass parameters. Experiments with Tenebrio molitor also showed that the isolated S. cerevisiae strain caused the death of the larvae, and the mortality rate increased based on fungal inoculum and the suppression of the larval immunity using corticosteroids.

The authors also discussed one other report of a COVID-19 patient developing S. cerevisiae infection after being prescribed Saccharomyces supplements to alleviate diarrhea brought on by the antibiotics. While treatment with fluconazole was successful against the fungal infection, the patient succumbed to pulmonary infection and other COVID-19 secondary complications.

The outcomes indicated that classical antifungals are effective in treating S. cerevisiae infections, except fluconazole, which has various susceptibility profiles. Moreover, the reduced effectivity of the antifungals against biofilms presents a further challenge in treating opportunistic fungal infections in critically sick patients.

Conclusions

The case study indicated that the patient succumbed to septic shock after contracting an S. cerevisiae infection post-SARS-CoV-2 infection. The isolated Saccharomyces cerevisiae strain was seen to be liable to classical antifungals within the planktonic cell state but not as biofilms.

Moreover, the production of extracellular bioactive molecules indicated virulence. Given the usage of S. cerevisiae as dietary supplements during antibiotic treatment, the authors imagine that S. cerevisiae needs to be recognized as an opportunistic pathogen.