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

In the last few years, fluoroquinolone treatment failure has been steadily increased in Salmonella spp. infection. Both chromosomal and plasmid-mediated quinolone-resistance mechanisms have been reported. The aim of study was to identify the prevalence of these mechanisms in a total of 81 Salmonella spp. isolates of poultry origin. Antibiotic sensivity discs determined the antimicrobial susceptibility to nalidixic acid, enrofloxacin, norfloxacin and ciprofloxacin. Ninety five percent of the isolates showed nalidixic acid resistance while39.5%, 56.8 % and 26 % of the isolates were resistant to ciprofloxacin, norfloxacin and enrofloxacin respectively. By PCR techniques qnrA, qnrB, qnrS and qepA genes were detected in 13.5%, 11.1%, 14.8 % and 7.4% of the isolates respectively, while aac(6)-Ib-crgene was absent. DNA sequencing of gyrA gene showed substitutions in the amino acid Serine 83and Aspartate 87 while parC gene showed substitutions in the amino acid Serine 57, Serine 80 and Isoleucine 153. Mutations in the quinolones resistance determination region (gyrA and parC genes) were critical for fluoroquinolone resistance while the plasmid-mediated quinolone resistance (PMQR) did not seem to play a major role. It is clear that overuse without awareness to antibiotics in cases of bacterial infection leads to strong threats for both animal and human health due to production of a new generation of bacteria have the strength and resistance to stop the effectiveness of antibiotics and is considered the first step to the spread of epidemics and killer diseases to whether animal and human

Issued also as CD