Genetic and Phenotypic Characteristics of Five Staphylococcus aureus Strains Isolated from Yakutian Cattle

To date, the problem of mastitis in cattle remains relevant for both the industrial sector and scientific research. Despite numerous active investigations, the causes of this disease have not been fully established. It is postulated that several factors may be involved, such as bacterial pathogens, animal husbandry practices, and weather and climatic conditions. In this study, we selected cows from farms in Yakutia to investigate microbial isolates present in the milk of cows affected by mastitis and treated with antibiotics. Five identified Staphylococcus aureus isolates were investigated using whole-genome sequencing (Illumina sequencing and nanopore sequencing), followed by analysis of virulence factors in the genomes and cultural properties of the isolates. The profile of S. aureus virulence genes (exotoxins, cytotoxins, superantigen-like proteins, adhesins) was identified via WGS. Hemolysin gene (hla) was detected in all isolates. An investigation of the cultural properties of the isolates, specifically through hemolysis of rabbit erythrocytes and Western blot analysis of the culture liquid of S. aureus, revealed different expression levels of alpha-hemolysin among the strains. One isolate (17-21) exhibited the highest secretion level of about 320 ± 37 ng, both in the hemolysis test and immunoblotting assay. An investigation of the isolates’ antibiotic resistance showed that all isolates exhibited multidrug resistance, as confirmed by the presence of antibiotic resistance genes in these isolates. One isolate (7-7) exhibited the broadest range of phenotypic resistance and was resistant to all tested antibiotics (except clindamycin). Phylogenetic analysis suggested that the evolution of these isolates occurred independently in their respective ecological niches, although their transfer from cattle to humans, and vice versa, is possible. Isolates 7-7, 18-22, 33-40, and 35-42 are most typical to Yakutian cattle, while isolate 17-21 might have been introduced from a different region. To the best of our knowledge, this is the first in-depth study into a range of S. aureus isolates associated with mastitis infection in Yakutian cattle.