Phenotypic and Genotypic Investigation of Yeast Species Associated with Bovine Subclinical Mastitis with a Special Reference to their Virulence Characteristics

Abstract

This study aimed to investigate yeast species associated with subclinical bovine mastitis in dairy farms. It is based on isolation using Sabouraud dextrose agar (SDA) followed by identification of isolates using HiCrome Candida agar and ITS-PCR-RFLP. Out of 405 milk samples, 31.6% were positive for yeast isolation on SDA. Based on HiCrome Candida agar and ITS-PCR assay, isolates were classified into 90 pure isolates and 38 mixed cultures. Only pure isolates were subjected to species identification and virulence evaluation. By HiCrome Candida agar media, the most frequently isolated species were C. krusei, C. tropicalis, and C. albicans (13.3% for each) while C. guilliermondii was the least isolated Candida species (1.5%). ITS-PCR-RFLP identified 67 isolates which included non-albicans Candida (NAC) species and Trichosporon assahii. Neither C. albicans nor C. galabrata were identified. Twenty-three isolates could not be identified by ITS-PCR-RFLP. Difference between the results of HiCrome Candida agar and ITS-PCR-RFLP methods was obvious. Considering slime production, 83.6% were slime producers while 16.4% were not. All strains of C. krusei, and C. tropicalis were slime producers. Regarding biofilm production, 80.6% of isolates had the ability to form biofilm ranged from strong (6%), moderate (14.9%) to weak (59.7%) while only 19.4% were non-biofilm producers. In vitro antifungal susceptibility of isolates displayed different susceptibility and resistance patterns. Conclusively, yeast mastitis in dairy cows demonstrates a growing problem. The diagnosis must rely on accurate laboratory diagnostic tests. The significance of NAC and other yeast genera specifically genus Trichosporon and their role in the etiology of mycotic mastitis should be emphasized.