Genomic Comparative Study of Bovine Mastitis Escherichia coli

Abstract

Escherichia coli, one of the main causative agents of bovine mastitis, is responsible for significant losses on dairy farms. In order to better understand the pathogenicity of E. coli mastitis, an accurate characterization of E. coli strains isolated from mastitis cases is required. By using phylogenetic analyses and whole genome comparison of 5 currently available mastitis E. coli genome sequences, we searched for genotypic traits specific for mastitis isolates. Our data confirm that there is a bias in the distribution of mastitis isolates in the different phylogenetic groups of the E. coli species, with the majority of strains belonging to phylogenetic groups A and B1. An interesting feature is that clustering of strains based on their accessory genome is very similar to that obtained using the core genome. This finding illustrates the fact that phenotypic properties of strains from different phylogroups are likely to be different. As a consequence, it is possible that different strategies could be used by mastitis isolates of different phylogroups to trigger mastitis. Our results indicate that mastitis E. coli isolates analyzed in this study carry very few of the virulence genes described in other pathogenic E. coli strains. A more detailed analysis of the presence/absence of genes involved in LPS synthesis, iron acquisition and type 6 secretion systems did not uncover specific properties of mastitis isolates. Altogether, these results indicate that mastitis E. coli isolates are rather characterized by a lack of bona fide currently described virulence genes.

<b>Etiological and molecular profile of pathogens causing clinical mastitis, and antimicrobial use in dairy herds</b>

“…Phylogenetic groups A and B1 were chiefly associated with commensal strains of E. coli in dairy cows (HOUSER et al, 2008;SON;VAN KESSEL;KARNS, 2009), which may explain the highest prevalence of this groups among isolates recovered from bovine IMI in our and other studies (KEMPF et al, 2016). Results found in our study also suggest that the most of isolates are commensals, having the gastro-intestinal tract of dairy cows as the main source of infection.…”

“…Some phylogroups identified in our study were not described (phylogroup C) or had low frequency in other studies describing their relationship with IMI in dairy cows (phylogroup E; KEMPF et al, 2016). Because many phylogenetic studies are based on the initial rapid determination scheme purposed by Clermont et al (2000), which only allows to distinguish isolates among four phylogenetic groups (A, B1, B2, and D), the frequency of phylogroup C and E may have been underestimated in previous studies.…”

“…Mastitis-associated strains were found across five (A, B1, B2, D and E) out seven E. coli sensu strictu groups (KEMPF et al, 2016). However, to the best of our knowledge, this is the first study reporting E. coli of phylogroup C as the cause of CM.…”

“…Only few reports described the use of the improved quadruplex PCR method (KEMPF et al, 2016), which allows the identification of seven phylogenetic groups (A, B1, B2, C, D, E and F; belonging to phylogroups C, E and F are scarce in the indexed literature (KEMPF et al, 2016). In addition, to our knowledge, studies describing the phylogeny of E. coli isolates in bovine CM has not been evaluated in Brazil.…”

Genetic relationship between Escherichia coli strains isolated from dairy mastitis and from the stable fly Stomoxys calcitrans

“…The circulation of common genetic patterns provides evidence of the circulation of specific lineages between herds which possibly occurred due to the low level of milking hy- giene at the farms visited as verified by Kempf et al (2016). Careless milking practices were often observed, without routine cleaning of the teats and hand washing by the farm workers, practices that favor the spread of bacteria as reported by De Vliegher et al (2012).…”