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URL: https://dx.doi.org/DOI:10.17504/protocols.io.zhrf356

Authors: Lis Rocha

Summary: Many efforts have been made to understand the pathogenesis of bovine mastitis to reduce losses and promote animal welfare. Staphylococcus aureus may cause bovine clinical mastitis, but it is mainly associated with subclinical infection, which is usually persistent and can easily reoccur. Here, we conducted a comparative genomic analysis between four strains of S. aureus causing subclinical infection (Sau170, 302, 1269, 1364), previously sequenced by our group, and two well-characterized strains causing clinical mastitis (N305 and RF122) to find differences that could be linked to mastitis outcome. A total of 146 virulence-associated genes were compared and no appreciable differences were found between the bacteria. However, several nonsynonymous single nucleotide polymorphisms (SNPs) were identified in genes present in the subclinical strains when compared to RF122, especially in genes encoding host immune evasion and surface proteins. The comparison of orthologous genes using OrthoMCL identified a membrane transporter in the genomes of the bacteria belonging to the subclinical group, but this finding was not confirmed by polymerase chain reaction (PCR) on a collection of field isolates of S. aureus associated with clinical or subclinical mastits. The secreted and surface proteins predicted by different in silico tools were compared through multidimensional scaling analysis, revealing a high degree of similarity among the six strains. However, differences were seen in the nucleotide sequences of a gene that codes for a hypothetical protein (cl3309) and a lipoprotein (cl3700). These findings were also analyzed by PCR on DNA extracted from field isolates of S. aureus. The lipoprotein, but not the hypothetical protein, was able to separate the clinical isolates from the subclinical ones. These results show that sequence variation among bovine S. aureus, and not only the presence/absence of virulence factors, is an important aspect to consider when comparing isolates causing different mastitis outcomes

Affiliations: Universidade Federal de Viçosa

Version: 2

Publication Date: 2019

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