Faculty of Science, Sydney School of Veterinary Science
Abstract
This thesis examines the epidemiology of staphylococci in the Australian veterinary setting, focussing on methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP). A nationwide surveillance study collected 1080 clinical staphylococci from veterinary diagnostic laboratories. Carriage samples were also prospectively collected from veterinary personnel, canine hospital admissions and veterinary-owned pets. Whole genome sequencing and bioinformatics were used in all studies. Inferences generated from genomic data were verified using phenotypic tests. MRSA was detected in Australian companion animals at low rates but was not detected amongst dairy cattle. MRSA carriage was found in prospectively screened veterinary personnel at a higher rate than reported for the general public, but carriage was not echoed in canine patients or veterinary-owned pets. Internationally established and novel MRSP lineages were found in Australian animals, indicating that MRSP has arisen both endogenously and from countries outside Australia. Antimicrobial resistance profiles varied significantly amongst MRSP lineages and geographic clustering of MRSP lineages was evident. Staphylococcus felis was found to possess previously unrecognised virulence factors including coagulation of feline plasma, suggesting it is a potential pathogen of cats. Qac genes, associated with increased biocide tolerance in MRSA, were detected in MRSP for the first time. The globally dominant ST71 MRSP clone was significantly more likely to carry qac genes than other MRSP clones. The presence of qac genes did not affect MRSP tolerance to veterinary biocides but protein contamination significantly increased biocide tolerance, a finding which has important infection control implications. This thesis is the first to characterise antimicrobial resistance in veterinary staphylococci nationally and paves the way for interesting future studies
