student profile: Miss Kate Worthing


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Thesis work

Thesis title: Veterinary drugs and superbugs: antimicrobial resistance in Staphylococcus from animals in Australia

Supervisors: Jacqueline NORRIS

Thesis abstract:

Background: Antimicrobial resistance is a growing problem in human and animal health care. Methicillin resistance in bacteria correlates highly with multidrug-resistance, leaving clinicians with few options when treating these infections. Several methicillin-resistant Staphylococcus species have been detected in animals including methicillin-resistant S. aureus (MRSA), a major pathogen in human medicine, and methicillin-resistant S. pseudintermedius (MRSP), which is important in companion animal medicine. While it is known that methicillin-resistant Staphylococcus exists in human hospitals in Australia, the prevalence of MRSA and MRSP in the Australian veterinary setting is unknown.
Aim: To characterise staphylococcal infections in animals in Australia, with a focus on resistant infections.
Methods: Clinical Staphylococcus isolates submitted to the 22 Australian veterinary diagnostic laboratories during 2013 were collected. Epidemiological data including animal species, sample site and clinical syndrome were recorded along with phenotypic microbiological data. The species of each bacterial isolate was determined using phenotypic and molecular tests. Antimicrobial resistance profiles were determined by disc diffusion and minimum inhibitory concentration. Resistant isolates were further characterised using whole genome sequencing to allow determination of their clonal type and the presence of various virulence and resistance factors. Data was analysed using multivariable logistic regression.                                                                                                                             
Results and discussion: A total of 1200 Staphylococcus isolates were collected from a range of animal species. Methicillin resistance was found in 73/737 (10%) canine isolates, 8/74 (11%) feline isolates and 10/67 (15%) equine isolates. Of the 217 bovine isolates, only one (0.5%) was methicillin-resistant. Over half the methicillin-resistant S. pseudintermedius isolates (37/69) were extensively drug resistant, meaning they were resistant to all but one antimicrobial class. Such extensive drug resistance was uncommon in MRSA isolates. Genome sequencing determined that 7 of the 14 MRSA isolates were from the CC22 clone, which is a major cause of healthcare-associated infections in humans. ST71, a common clone of MRSP in Europe, was also the most common clone in Australia. Sixteen MRSP and 2 MRSA isolates housed qac genes, which encode for resistance to a range of biocides such as quaternary ammonium compounds (QACs). QACs are common disinfectants used in human and veterinary hospitals, so the presence of QAC resistance may enable bacteria to survive routine hospital disinfection procedures. Isolates from the ST71 clones were significantly more likely than other clones to carry qac genes (p<0.05) and this may explain why they are the predominant MRSP clone in Australia and overseas.
Conclusions: The prevalence of methicillin-resistance in Australian veterinary Staphylococcus isolates is 10%. MRSPdemonstrates a more extensive level of antimicrobial resistance than MRSA. Sequence typing suggests that common clones of MRSA can be transferred between humans and animals. The presence of resistance to common disinfectants may explain why some strains of MRSA and MRSP are more prevalent than others.

Selected grants

2017

  • Vets and their pets: unravelling the transmission cycle of methicillin-resistant Staphylococcus species in small animal practice; Worthing K, Norris J; Australian Companion Animal Health Foundation/Research Support.

2016

  • Phenotypic expression of biocide tolerance in clinical veterinary Staphylococcus isolates: are our disinfectants working?; Norris J, Worthing K; Australian Companion Animal Health Foundation/Research Support.

2015

  • Determining risk factors for development of a resistant post-operative infection with methicillin or multiresistant Staphyloccus.; Norris J, Worthing K; Australian Companion Animal Health Foundation/Research Support.

Selected publications

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Journals

  • Saputra, S., Jordan, D., Worthing, K., Norris, J., Wong, H., Abraham, R., Trott, D., Abraham, S. (2017). Antimicrobial resistance in coagulase-positive staphylocci isolated from companion animals in Australia: A one year study. PloS One, 12(4), e0176379. [More Information]
  • Worthing, K., Coombs, G., Pang, S., Abraham, S., Saputra, S., Trott, D., Jordan, D., Wong, H., Abraham, R., Norris, J. (2016). Isolation of mecC MRSA in Australia. Journal of Antimicrobial Chemotherapy, 71(8), 2348-2349. [More Information]
  • Worthing, K., Wigney, D., Dhand, N., Fawcett (Quain), A., McDonagh, P., Malik, R., Norris, J. (2012). Risk factors for feline infectious peritonitis in Australian cats. Journal of Feline Medicine and Surgery, 14(6), 405-412. [More Information]

2017

  • Saputra, S., Jordan, D., Worthing, K., Norris, J., Wong, H., Abraham, R., Trott, D., Abraham, S. (2017). Antimicrobial resistance in coagulase-positive staphylocci isolated from companion animals in Australia: A one year study. PloS One, 12(4), e0176379. [More Information]

2016

  • Worthing, K., Coombs, G., Pang, S., Abraham, S., Saputra, S., Trott, D., Jordan, D., Wong, H., Abraham, R., Norris, J. (2016). Isolation of mecC MRSA in Australia. Journal of Antimicrobial Chemotherapy, 71(8), 2348-2349. [More Information]

2012

  • Worthing, K., Wigney, D., Dhand, N., Fawcett (Quain), A., McDonagh, P., Malik, R., Norris, J. (2012). Risk factors for feline infectious peritonitis in Australian cats. Journal of Feline Medicine and Surgery, 14(6), 405-412. [More Information]

Note: This profile is for a student at the University of Sydney. Views presented here are not necessarily those of the University.