Antibiotic susceptibility patterns in CTX-M-15-producing Enterobacteraceae isolated from healthy Afghan refugees in Iran

Extended-spectrum β-lactamases (ESBL), including the most wide spread CTX-M-15 enzyme, are major antibiotic resistant mechanisms of Enterobacteriaceae. Emergence of this plasmid-mediated enzyme poses a global threat particularly in Asian countries struggling with war. In this study, we investigated CTX-M-15 in clinical isolates of Enterobacteriaceae from healthy Afghan refugees in Iran and analyzed the association between CTX-M-15 and pattern of antibiotic resistance as well as the location of this gene among the isolates. No correlation was found between clonal groups and antimicrobial resistance patterns of the Enterobacteriaceae species. The frequency of cephalosporin resistance was significantly higher among CTX-M-15-producing isolates compared with other ESBL-producing isolates (P<0.05) with 70 and 30 resistant isolates, respectively; however the association between CTX-M-15 and quinolone resistance was not significant as 4 isolates were quinolone resistant in both CTX-M-15-positive and other ESBL-producing group of isolates. All 20 tetracycline resistant isolates were CTX-M-15-positive (P<0.05) and resistance to aminoglycosides among CTX-M-15-positive isolates were considerably higher (n=22) than other ESBL-producing isolates (n=7) (P<0.05). Resistance to meropenem, imipenem, aztreonam, piperacillin and ampicillin was not significantly associated with CTX-M-15-production. Plasmid analysis revealed that the CTX-M-15 gene is located on a large plasmid ranged between 90 and 100 kb. This is amongst the premier report describing the association between CTX-M-15-production and different antibiotic resistance patterns in Enterobacteriaceae isolates collected from healthy individuals. The significant association between cephalosporin, aminoglycoside and tetracycline resistance and CTX-M-15-production emphasizes a need for introducing new antibiotic choices for the treatment of infections caused by Enterobacteriaceae. Key words: Extended-spectrum β-lactamases (ESBL), CTX-M-15, Enterobacteriaceae, antibiotic resistance, plasmid.