Different phenotypic and molecular mechanisms associated with multidrug resistance in Gram-negative clinical isolates from Egypt

OBJECTIVES: We set out to investigate the prevalence, different mechanisms, and clonal relatedness of multidrug resistance (MDR) among third-generation cephalosporin-resistant Gram-negative clinical isolates from Egypt. MATERIALS AND METHODS: A total of 118 third-generation cephalosporin-resistant Gram-negative clinical isolates were included in this study. Their antimicrobial susceptibility pattern was determined using Kirby–Bauer disk diffusion method. Efflux pump-mediated resistance was tested by the efflux-pump inhibitor-based microplate assay using chlorpromazine. Detection of different aminoglycoside-, β-lactam-, and quinolone-resistance genes was done using polymerase chain reaction. The genetic diversity of MDR isolates was investigated using random amplification of polymorphic DNA. RESULTS: Most of the tested isolates exhibited MDR phenotypes (84.75%). The occurrence of efflux pump-mediated resistance in the different MDR species tested was 40%–66%. Acinetobacter baumannii isolates showed resistance to most of the tested antibiotics, including imipenem. The bla(OXA-)(23-like) gene was detected in 69% of the MDR A. baumannii isolates. The MDR phenotype was detected in 65% of Pseudomonas aeruginosa isolates, of which only 23% exhibited efflux pump-mediated resistance. On the contrary, efflux-mediated resistance to piperacillin and gentamicin was recorded in 47.5% of piperacillin-resistant and 25% of gentamicin-resistant MDR Enterobacteriaceae. Moreover, the plasmid-mediated quinolone-resistance genes (aac(6′)-Ib-cr, qnrB, and qnrS) were detected in 57.6% and 83.33% of quinolone-resistant MDR Escherichia coli and Klebsiella pneumoniae isolates, respectively. The β-lactamase-resistance gene bla(SHV-31) was detected for the first time in one MDR K. pneumoniae isolate from an endotracheal tube specimen in Egypt, accompanied by bla(TEM-1), bla(CTX-M-15), bla(CTX-M-14), aac(6′)-Ib-cr, qnrS, and multidrug efflux-mediated resistance. CONCLUSION: MDR phenotypes are predominant among third-generation cephalosporin-resistant Gram-negative bacteria in Egypt and mediated by different mechanisms, with an increased role of efflux pumps in Enterobacteriaceae.