Comparative molecular analysis of ovine and bovine Streptococcus uberis isolates

Streptococcus uberis causes clinical and subclinical mastitis in cattle and sheep, but it is unknown whether the composition of Strep. uberis populations differs between host species. To address this, we characterized a collection of bovine and ovine Strep. uberis isolates with shared geographical and temporal origins by means of an expanded multilocus sequence typing scheme. Among 14 ovine and 35 bovine isolates, 35 allelic profiles were detected. Each allelic profile was associated with a single host species and all but one were new to the multilocus sequence typing database. The median number of new alleles per isolate was higher for ovine isolates than for bovine isolates. None of the ovine isolates belonged to the global clonal complexes 5 or 143, which are commonly associated with bovine mastitis and which have a wide geographical distribution. Ovine isolates also differed from bovine isolates in carriage of plasminogen activator genes, with significantly higher prevalence of pauB in ovine isolates. Isolates that were negative for yqiL, one of the targets of multilocus sequence typing, were found among ovine and bovine isolates and were not associated with a specific sequence type or global clonal complex. One bovine isolate carried a gapC allele that was probably acquired through lateral gene transfer, most likely from Streptococcus salivarius. We conclude that ovine isolates are distinct from bovine isolates of Strep. uberis, and that recombination between isolates from different host species or bacterial species could contribute to changes in virulence gene profiles with relevance for vaccine development.