Insects May Aid Spread of Fluconazole-Resistant Candida auris

A study on the South African brown locust (Locustana pardalina) suggests that insects may play a role in the spread of the pathogenic yeast Candida auris (C auris). The researchers isolated three strains of C auris from the locusts, one of which showed resistance to fluconazole, a common antifungal treatment. Based on phenotypic analysis and genome sequencing, the strain was found to thrive in conditions such as 50°C temperatures and high salinity (15% NaCl), but remained susceptible to certain disinfectants and antifungals. The strain belongs to Clade III, a subtype found in South Africa. This discovery provides insights into the potential environmental reservoirs for C auris and highlights the role of insects in the spread and evolution of this pathogen.

The study adds to ongoing research that speculates C auris may be transmitted from various environmental sources—such as avian species, marine environments, and now insects—to humans. The findings emphasize the need for further investigation into the environmental reservoirs and transmission pathways of C auris, particularly in light of its growing resistance to antifungal drugs. In an email interview, Carlien Pohl-Albertyn, PhD, a professor of microbial biochemical and food biotechnology and holder of the NRF SARChI Chair in pathogenic yeasts at the University of the Free State, South Africa, elaborated on the study’s implications.

Environmental Spread of C auris and Potential Public Health Risks

The discovery of fluconazole-resistant C auris in insects raises concerns about potential environmental contamination. Pohl explained, "The implication is that strains with lower susceptibility to a common antifungal is circulating in the environment. We do not yet know if this is due to clinical strains contaminating the environment or not, but given the remote location of the sampling site, it is more likely that the C auris in the locusts were obtained from the environment."

The study aims to better understand the natural hosts of C auris, a pathogen that has been increasingly identified in clinical settings due to its resistance to common antifungal treatments. Insects, such as locusts, could play a role in spreading C auris, as they serve as food sources for animals—including birds and, in certain regions, humans. Pohl noted, “Of course, the fact that locusts and other insects are a food source for animals, such as birds, as well as people in many countries, could lead to eventual distribution of the yeast to people.” This raises concerns about the potential for wider distribution and transmission of C auris, highlighting the urgent need for effective measures to prevent further spread.

Fluconazole resistance is already known to be a characteristic of C auris, so the presence of resistant strains in environmental samples is not unexpected. Pohl said, "Fluconazole resistance is a common characteristic of C auris (and indeed for many emerging pathogenic yeasts) and it is thus not surprising that this is also seen in environmental isolates." Although, the study brings to light the challenges of treating infections caused by resistant pathogens and stresses the need for new antifungal drug development.

A key finding of the study is the ability of the C auris isolates to survive under extreme conditions, such as high temperatures and salinity, which may suggest that C auris evolved in stressful environments. Pohl explained, “It may imply that C auris evolved in stressful environments with high temperature and salt concentrations. However, resistance to one type of stress may also evolve when an organism is exposed to a completely different type of stress (cross-resistance).”

For example, heat resistance may indirectly increase fluconazole resistance, while salt tolerance could also enhance the organism’s ability to withstand desiccation. Pohl pointed out, "The significance is that cross-resistance to various stresses as well as combinatorial stresses may allow C auris to survive in a variety of habitats."

Insects and the Evolution and Transmission of Emerging Pathogens

The study also delves into the broader implications of insects in the evolution and transmission of emerging infectious diseases. Pohl observed, "Insects are the most successful group of animals on Earth, and it is speculated that the interaction between yeasts and insects is an ancient one, dating to before the evolution of flowering plants." Many insects rely on yeasts for essential nutrients, which makes them potential hosts for these microbes.

The role of insects in transmitting C auris highlights a broader concern about how human activity and ecological disturbances can expose us to new pathogens. Pohl explained, "This may be another example of how human activity leading to ecological disturbances could expose us to new microbes in the environment." While many microbes may not become pathogens, the mechanisms that enable them to survive in their natural environments might also allow them to adapt to human hosts. By understanding these mechanisms, researchers may be better equipped to address the broader challenge of emerging infectious diseases.

In conclusion, Pohl’s research on C auris and its interaction with insects emphasizes the evolution of pathogens and transmission. The study highlights the risks of fluconazole-resistant strains and calls for further efforts to understand how these pathogens evolve and spread. Moreover, it stresses the need for more research into antifungal treatments and strategies to prevent the distribution of these pathogens.

Reference

Ogundeji A, Bello-Akinosho M, Swart V, et al. South African brown locusts, Locustana pardalina, hosts fluconazole resistant Candidozyma (Candida) auris (Clade III). bioRxiv. Published January 22, 2025. doi:10.1101/2025.01.22.634428.