الفهرس 
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Abstract
Persisters or metabolically dormant bacterial cells are much less sensitive to antibiotic and do not grow in their presence. Different explanations for this phenomena are widely circulated in the literature and in the heart of it is the role of toxin and antitoxin (TA) systems. Where, the more labile antitoxins are readily degraded under stress conditions, allowing the toxins to exert their effect and force some cells to be dormant. The diversity of toxin and antitoxin system(s) in persisters derived from Staphylococcus aureus subsp. aureus Rosenbach (ATCC® 43300-MINI-PACK™) was the major objective of this study. MRSA-derived persisters were isolated under vancomycin stress. Classically they were characterized by persister’s assay, catalase test, Baird-Parker assay and mannitol fermentation. Molecular characterization included: plasmid DNA profiles, protein banding patterns and toxin-antitoxin operons, comparing persisters to the parent strain ATCC43300 and its closely related stain ATCC6538 (FDA 209). Biochemically, persisters were similar to the ATCC43300 and ATCC6538 strains apart from the catalase reaction that was very weak in persisters. No significant differences were seen in the plasmid profile but distinctive differences were observable in the protein banding patterns and the toxin-antitoxin PCR products’ profiles. Seven toxin-antitoxin operons namely, HipAB, RelEB, HigAB, MazFE, MqsRA, CcdAB, HicAB were detected in the standard MRSA strain (ATCC43300) and its laboratory derived persister. This is to detect 7 toxin-antitoxin systems in the laboratory derived persisters from the MRSA stain ATCC43300. These systems appear to be the reason for remission of infection and further complicate the discovery of the real mechanism for persister’s emergence.