Health risk posed by direct ingestion of yeasts from polluted river water.

River water is an essential human resource that may be contaminated with hazardous microorganisms. However, the risk of yeast infection through river water exposure is unclear because it is highly dependant on individual susceptibility and has therefore not been well-studied, to date. To evaluate this undefined risk, we analysed the fungal communities in less polluted (LP) and highly polluted (HP) river water, as determined using principal coordinate analysis of pollution indicators. We enumerated culturable yeasts using a thermally selective isolation procedure (37 °C) and thus promoted the growth of potentially opportunistic species. Yeast species identified as clinically relevant were then tested for antifungal resistance. In addition, we propose a quantitative microbial risk assessment (QMRA) framework to quantitatively assess the potential risk of yeast infection. Our results indicated that pollution levels significantly altered fungal communities (p = 0.007) and that genera representing opportunistic and pathogenic members were significantly more abundant in HP waters (p = 0.038). Additionally, the yeast species Candida glabrata and Clavispora lusitaniae positively correlated with other pollution indicators, demonstrating the species' indicator potential. Our QMRA results further indicate that higher risk of infection is associated with increased water pollution levels (considering both physicochemical and bacterial indicators). Furthermore, yeast species with higher pathogenic potential present an increased risk of infection despite lower observed concentrations in the river water. Interestingly, the bloom of Meyerozyma guilliermondii during the wet season suggests that other environmental factors, such as dissolved oxygen levels and water turbulence, might affect growth characteristics of yeasts in river water, which consequently affects the distribution of annual infection risks. The presence of antifungal resistant yeasts, observed in this study, could further contribute to variation in risk distribution. Research on the ecophysiology of yeasts in these environments is therefore necessary to ameliorate the uncertainty and sensitivity of the proposed QMRA model. In addition to the vital knowledge on opportunistic and pathogenic yeast occurrence in river water and their observed association with pollution, this study provides valuable methods and insights to initiate future QMRAs of yeast infections.

Physiological characterisation of Corynebacterium uterequi associated with pregnancy complications in mares.

Increasing cases of equine infertility and early embryonic loss in the Western Cape, South Africa, were documented in recent years. These appeared to be associated with Corynebacterium uterequi isolated from the uteri of infected mares. The purpose of this study was, therefore, to investigate the physiology and potential pathogenicity of this bacterium. Histopathological analyses were conducted on five mares suffering from reproductive complications, and from which Corynebacterium strains were detected on culture of uterine swabs. The histopathology revealed that the mares suffered from various forms of endometritis, suggesting a potential role of Corynebacterium strains in the disease. An isolate from one of the biopsies, and 11 other tentatively identified C. uterequi isolates from the urogenital tracts of other mares, which all had a history of pregnancy complications, were subsequently identified using molecular techniques and characterised based on environmental stress tolerance, enzyme profiles, antibiotic susceptibility and ability to form biofilms. It was found that representatives of C. uterequi possessed several virulence-associated characteristics, including trypsin and urease activity, as well as the ability to form weakly adherent monoculture biofilms. Several isolates displayed resistance to trimethoprim-sulfamethoxazole. In conclusion, this study provided some insight into the general physiology and pathogenic potential of C. uterequi, and points to the possible role of C. uterequi in the onset of equine pregnancy complications. Moreover, the ability to form biofilms suggests the potential for chronic infection, which was observed in 60% of the mares. Further research, however, is needed to implicate C. uterequi as an equine pathogen.