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Title: The role of antibacterial agents on the pathogenicity of Staphylococcus aureus
Author: Doss, Sally
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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Staphylococcus aureus is a pathogenic bacterium which has an impressive armoury of extracellular toxic factors. In recent years, S. aureus has developed resistance to the new 4-quinolone antibacterials. Since this resistance is a result of a chromosomal mutation, it was proposed that the resistant bacteria might be less pathogenic. This thesis has studied this postulate. Ciprofloxacin sensitive and resistant strains of S.aureus were compared to establish any differences in their respective production of virulence factors both in vitro and in vivo. Since S.aureus produces a large number of virulence factors, four were studied in detail; coagulase, Protein A, alpha and delta toxin. The in vitro production of the four factors by ciprofloxacin sensitive and resistant strains was investigated in the presence and absence of 1/4 and 1/2 Minimum Inhibitory Concentrations (MIC) levels of six antibiotics: ciprofloxacin, enoxacin, methicillin, gentamicin, chloramphenicol and tetracycline. The production of soluble and bound coagulase was measured by a chromogenic substrate assay. The production of bound and soluble Protein A, alpha toxin and delta toxin were measured by ELISAs. In the absence of the antibiotics, the production of the four virulence factors was similar in the sensitive and resistant strains. The acquisition of ciprofloxacin resistance did not affect the production of these factors. Conversely, the presence of 1/4 and 1/2 MIC levels of gentamicin, chloramphenicol and tetracycline reduced the production of both bound and soluble coagulase, and bound and soluble Protein A, in both sensitive and resistant strains. In the presence of 1/2 MIC levels of ciprofloxacin, enoxacin, gentamicin, chloramphenicol and tetracylcine, the production of alpha and delta toxins was reduced and in some cases completely inhibited. The presence of 1/4 MIC levels of the antibiotics had a reduced effect on the inhibition of the toxins. The presence of 1/4 and 1/2 MIC levels of methicillin both increased the production of the toxins, though the increase was less significant in the presence of 1/4 MIC levels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available