Abstract:
Staphylococcus aureus is one of the most common etiological agents of contagious
bovine mastitis worldwide. The purpose of this study was to genetically characterize
a collection of S. aureus isolates (bovine = 146, human = 12) recovered from cases
of bovine mastitis and nasal swabs of close human contacts in the dairy environment.
Isolates were screened for a combination of clinically significant antimicrobial and
virulence gene markers whilst the molecular epidemiology of these isolates and possible
inter-species host transmission was investigated using a combination of genotyping
techniques. None of the isolates under evaluation tested positive for methicillin or
vancomycin resistance encoding genes. Twenty seven percent of the bovine S. aureus
isolates tested positive for one or more of the pyrogenic toxin superantigen (PTSAg)
genes with the sec and sell genes predominating. Comparatively, 83% of the human
S. aureus isolates tested positive for one or more PTSAg genes with a greater variety
of genes being detected. Genomic DNA macrorestriction followed by pulsed-field gel
electrophoresis (PFGE) of the bovine isolates generated 58 electrophoretic patterns including: ST8 (CC8), ST97 (CC97), ST351 (CC705), ST352 (CC97), ST508 (CC45),
ST2992 (CC97) and a novel sequence type, ST3538 (CC97). Based on PFGE analysis,
greater genetic diversity was observed among the human S. aureus isolates. Bovine
and human isolates from three sampling sites clustered together and were genotypically
indistinguishable. Two of the isolates, ST97 and ST352 belong to the common bovine
lineage CC97, and their isolation from close human contacts suggests zoonotic transfer.
In the context of this study, the third isolate, ST8 (CC8), is believed to be a human clone which has transferred to a dairy cow and has subsequently caused mastitis. The
detection of indistinguishable S. aureus isolates from bovine and human hosts at three
of the sampling sites is suggestive of bacterial transmission and supports the need for
vigilant monitoring of staphylococcal populations at the human-animal interface.
which grouped into 10 pulsotypes at an 80% similarity level. The majority of the bovine
isolates, 93.2% (136/146), clustered into four major pulsotypes. Seven sequence types
(ST) were identified among the representative bovine S. aureus isolates genotyped,
