First report of colistin resistance among carbapenem-resistant isolates recovered from hospitalized patients in Egypt.

is an opportunistic pathogen that poses an increasing threat in the health-care community. Colistin is one of the promising options for treatment of multidrug-resistant . The current study investigated the emergence of colistin resistance among carbapenem-resistant strains of in Egypt. It involved identification of clinically recovered . isolates using the VITEK-2 system, and screening of their antimicrobial susceptibilities using broth microdilution techniques. Characterizations of carbapenemase and 16S rRNA methyltransferase genes were performed using PCR. Colistin-resistance determinants were characterized by sequencing. Carbapenem-resistant isolates ( = 40) showed resistance to amoxicillin-clavulanic acid, cefotaxime, gentamicin and amikacin. Most isolates revealed resistance to ciprofloxacin (95%;  = 38) and co-trimoxazole (92.5%;  = 37). Resistance to tobramycin and doxycycline was 80% ( = 32) and 62.5% ( = 25), respectively. Only two isolates demonstrated colistin resistance. Carbapenemase activity was tested by modified Hodge test and 78% of isolates were positive. All isolates carried -like genes whereas - was detected in 80% ( = 32) of isolates. Among 16S rRNA methylase genes, was detected in 22.5% ( = 9) of the isolates. Analyses of , , and genetic sequences suggest that colistin resistance could be attributed to mutations in genes. Alarmingly, colistin resistance was associated with high levels of resistance to other antimicrobials. The current findings represent a serious health-care problem capable of restraining future therapeutic options.