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

The opportunistic pathogen P. aeruginosa causes severe infections which are extremely difficult to eradicate due to the its ability to produce several types of cell-associated and extracellular virulence factors and its ability to acquire resistance against several classes of antibiotics. The alternative to antibiotic-mediated bacteria killing or growth inhibition is the attenuation of bacterial virulence such that the organism fails to establish successful infection and, in consequence, is cleared by the host immune response. Antipathogenic drugs target key regulatory bacterial systems (Quorum sensing systems) that govern the expression of virulence factors. Quantitative estimation of six virulence factors of P. aeruginosa was performed where 100 isolates collected from clinical and environmental sources were screened parallel to P. aeruginosa reference strain (ATCC 9027) for elastolytic activity, biofilm formation, rhamnolipids, heat-stable and heat-labile haemolysins and pyocyanin production. It was observed that these virulence factors were detected in both clinical and environmental strains of P. aeruginosa. Studying the effects of sub-inhibitory concentrations of 15 antimicrobial agents and herbal extracts on production of virulence factors of P.aeruginosa strain E24 and ATCC9027 revealed that the sub-MIC (1/75) of all tested antimicrobials caused inhibition of virulence factors production of the environmental strain (E24), while it caused induction of virulence factors production of the standard strain ATCC 9027.

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