Characterisation of clinical isolates of 'Staphylococcus aureus' collected from the UK and Malta

Gould, Simon William James (2006) Characterisation of clinical isolates of 'Staphylococcus aureus' collected from the UK and Malta. (PhD thesis), Kingston University, .


'Staphylococcus aureus' ('S. aureus') and especially methicillin-resistant 'S. aureus' (MRSA) have become a major problem in hospital acquired infections worldwide. These organisms may be resistant to multiple numbers and classes of antibiotics making their treatment complicated and challenging. As well as being resistant to antibiotics, 'S. aureus' produces numerous pathogenicity factors including toxins and extra-cellular enzymes. Previous investigations into the relationship between antibiotic resistance and toxin production in both MRSA and methicillin sensitive 'S. aureus' (MSSA) strains have found small or no differences in toxin production. However, no investigation has examined the production of pathogenic enzymes and their relationship to antibiotic resistance. A study panel of 680 isolates of 'S. aureus' was collected from the UK and Malta. This investigation addressed several critical phenotypic characteristics of this clinically important pathogen. The isolates were tested against several significant antibiotics, analysed for selected pathogenic factors, analysed by Pulse Field Gel Electrophoresis (pFGE) to determine molecular epidemiological distribution and subjected to novel differentiation methods. The isolates were tested against a range of fourteen antibiotics. Additionally, the production of three enzymes, DNase, lipase and proteinase, and one toxin, haemolysin was determined for each isolate. The level of antibiotic resistance between the isolate groups for both countries was found to be similar. However, some significant differences were seen in resistance levels to certain antibiotics. No differences in the production of pathogenic factors could be detected between the isolates of MRSA and MSSA from both countries. The isolates were also divided into a strain types via Smaldigestion, with DNA fragments separated by PFGE. Three UK-recognised epidemic MRSA strain profile types were identified and, interestingly, these types were also observed in the Maltese strain panel. Novel chromogenic substrates for detecting lipase activity were tested against the 'S. aureus' strains. Results suggest these substrates would have limited applicability as a diagnostic tool for differentiation between MRSA and MSSA. However, these compounds may have an application as a research tool for the study of 'S. aureus'. A further study examined the effect of antimicrobials on the growth of phenotypically resistant organisms. This pilot study of fourteen isolates, showed significant differences in the fmal cell population and significant decreases in the production of some pathogenic enzymes. The results of this experiment warrant further investigation.

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