Characterisation of Staphylococcus spp from South Australian wallabies

Author: Michelle Min Shiew Chen

Chen, Michelle Min Shiew, 2017 Characterisation of Staphylococcus spp from South Australian wallabies, Flinders University, School of Biological Sciences

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Abstract

Staphylococcus aureus and coagulase-negative staphylococci are major problems in the hospital environment and are also significant contributors to community-acquired infections in humans and animals. Previous research investigating the prevalence of methicillin-resistant staphylococci has focussed almost exclusively on methicillin-resistant S. aureus and/or S. pseudintermedius in humans, livestock and companion animals. This is the first study to bring animal health data together with an investigation on the presence, diversity and antibiotic susceptibility of staphylococcal species recovered from apparently healthy captive and free-ranging animals. Baseline staphylococcal species diversity data is seldom explored with a large portion of studies focussed on the detection and characterisation of S. aureus, S. epidermidis and S. pseudintermedius from humans and companion animals. Here, we report the presence of 14 staphylococcal species from both captive and free-ranging wallaby populations using standard microbiological culturing and molecular identification methods. Staphylococcal species diversity was greater in captive wallaby populations compared to their free-ranging counterparts. Across the wallabies sampled, common staphylococcal species recovered included S. delphini, S. succinus, S. xylosus and S. warneri. Single isolates of S. carnosus, S. cohnii and S. hominis were also identified. In tandem with investigating baseline staphylococcal species diversity, antibiotic resistance data is crucial for future surveillance studies. A significant proportion of staphylococcal isolates were found to be resistant to first generation penicillins however resistance against other antimicrobial classes was common. Interestingly, multidrug resistant staphylococci were recovered exclusively from free-ranging wallabies and S. aureus appears to be a benign member of the wallaby nasal microbiome with minimal demonstrable ability to resist antibiotic challenges. The staphylococcal cassette chromosome SCCmec, which harbours the methicillin-resistance gene element, is integral in the characterisation of methicillin-resistant staphylococcal isolates. Typing of this element revealed the presence of both hospital and community acquired elements in addition to novel subtypes. This represents the first report of methicillin-resistant staphylococci in wallabies in Australia and findings suggest SCCmec carriage is unrelated to captivity status. Epidemiological studies have shown global dissemination of successful clones of methicillin-resistant and -sensitive S. aureus among a diverse host range. The clonal relationships of seven S. aureus isolates were investigated via an interrogation of their genomes by DNA microarray profiling and compared against international typing databases. The majority of the clonal complexes identified were primarily associated either with avian hosts or sporadic human and veterinary cases confined to Western Europe. South Australian wallabies neither harbour unique host-specific S. aureus clonal complexes, nor did they carry typical “Australian” clones. This thesis comprises a body of work aimed at furthering our understanding of the wallaby nasal microbiome with respect to staphylococci carriage and is the first study of its kind to be performed in Australia.

Keywords: Macropod, Beta-lactamase, methicillin resistance, blaZ, mecA, Staphylococcus
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: Prof Melissa Brown