Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Biological Sciences

First Advisor

Dr. Lesley Cotter

Second Advisor

Dr. Brigid Lucey


Mupirocin is a topical antibiotic used in hospital infection control practices to control transmission of staphylococci, in particular MRSA, which has become a major problem in Irish hospitals and has a significant impact on patient morbidity and mortality. Overreliance on mupirocin to eradicate MRSA carriage and to prevent infection has led to mupirocin resistance among staphylococcal species. Two distinct types of resistance have developed within strains: low'-level mupirocin resistance (LMR) and high-level mupirocin resistance (HMR).

The aim of this study was to assess the prevalence and types of mupirocin resistance in a large population of clinical staphylococcal isolates including Methicillin Resistant Staphylococcus aureus (MSSA), Methicillin Resistant Staphylococcus aureus (MRSA) and Coagulase Negative Staphylococci (CoNS). CLSI guidelines for mupirocin susceptibility have not yet been established, so the most recently-described criteria were used to interpret zone sizes. Based on these criteria a total of 26 isolates (3% of MRSA, 1% of MSSA, and 22% of CoNS as a proportion of the entire population of strains) were designated HMR, which is interpreted as the more clinically-significant fonn of mupirocin resistance. Mupirocin E-tests were used to confirm disc diffusion results, and confirmatory genotypic analysis using PCR was performed to confirm that the HMR isolates possess the mupA gene which confers HMR. All three methods demonstrated complete correlation and no discrepancies were observed. This study revealed that the incidence of mupirocin resistance, both HMR and LMR, was much greater in the CoNS isolates than the MSSA isolates (32% versus 2%). Previous studies suggest that CoNS may be a reservoir for mupiroein resistance transfer to MRSA; therefore these strains could serve as a potential reservoir for the spread of resistance to MSSA isolates and thereby further increase the mupiroein resistance rates in this clinically-significant pathogen.

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