Thesis (Ph.D.) - Cairo University - Faculty of Medicine - Department of Microbiology and Immunology

Background: Staphylococcus aureus is a common cause of many healthcare-associated and community-acquired infections. Methicillin resistance in S. aureus has become prevalent worldwide. Moreover biofilm-formation makes it more difficult to eradicate bacteria by antibiotics. mazEF toxin antitoxin system consists of a stable toxin called mazF which acts as an endoribonuclease and a labile antitoxin called mazE which opposes the toxin action. mazEF genes are located on S. aureus chromosome and can be used as an alternative target in treatment of infections. Objectives: The aim of the present work was to detect mazEF expression in MRSA isolates compared to MSSA isolates as well as determining mazEF system expression in relation to biofilm-formation. Methods: One hundred non-duplicate S. aureus isolates were collected from patients admitted to Kasr Al-Aini University Hospitals and categorized into 50 MRSA and 50 MSSA. All isolates were tested for antimicrobial susceptibility using disk diffusion method and biofilm-formation using tissue culture plate method. Finally, mazEF expression was detected by real time PCR and correlated to both methicillin susceptibility and biofilm-formation. Results: MRSA isolates were shown to be more resistant to antimicrobial agents tested than MSSA isolates. Linezolid and gentamycin showed the best sensitivity results with both MRSA and MSSA. 88% of MRSA and 96% of MSSA isolates were sensitive to linezolid while 76% of MRSA and 84% of MSSA isolates were sensitive to gentamycin. Biofilm-formation was statistically significantly higher in MRSA isolates than MSSA isolates (p value = 0.037). Expression of mazEF was statistically significantly higher in MRSA isolates compared to MSSA isolates (p value < 0.001), but no statistically significant correlation was detected between mazEF expression and biofilm-formation

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