Investigation of plasmid-mediated quinolone resistance among extended-spectrum β-lactamase isolates of E. coli and K. pneumoniae.

Escherichia coli and Klebsiella pneumoniae are important members of the Enterobacteriaceae family, involved in many infections. The increased resistance rate towards β-lactams and fluoroquinolones -which are the main therapeutic options- limits their treatment options. This study aimed to assess the local resistance patterns against different antimicrobials and to determine the extended-spectrum β-lactamase (ESBLs) producers. The study revealed that 36% of clinical isolates were ESBL producers, showing high resistance rates towards β-lactams and non-β-lactams, especially sulphamethoxazole-trimethoprim and fluoroquinolones. However, they were susceptible to chloramphenicol and doxycycline (33% and 20%; respectively). Also, the investigation aimed to screen the plasmid profile of quinolone-resistant ESBLs-producers and to detect the plasmid-mediated quinolone resistance genes including qnrA, qnrS, qnrB, qnrC, qnrD, and qnrVC. Moreover, the conjugative plasmid among the quinolone-resistant isolates was elucidated. The results showed that extracted plasmids of sizes ranging from ≈0.9 to 21.23 Kb, divided into 7 plasmid patterns were detected. A plasmid of approximately 21.23 Kb was found in all isolates and the QnrS gene was the most predominant gene. Moreover, the frequency of transconjugation within the same genus was higher than that recorded between different genera; where 68% of E. coli isolates transferred the resistance genes compared to Klebsiella isolates (36.6%). Plasmid profiles of transconjugants demonstrated great similarity, where 21.23 Kb plasmid was detected in all transconjugants. Since these transconjugants were quinolone-resistant ESBL producers, it has been suggested that quinolone resistance determinants might be carried on that plasmid.