Detection of plasmid-borne mcr genes conferring colistin resistance in MDR and XDR Gram-negative bacterial isolates from an Egyptian hospital

Background: Infections with multi-drug resistant (MDR) Gram-negative bacteria represent a serious public health risk, especially with the emergence of colistin resistance. Colistin resistance is mainly mediated by chromosomal mutations; however, there are reports of transferable plasmid-mediated colistin resistance genes, namely mcr, which have been universally documented. Thus, our study aimed to examine the incidence of mobile colistin resistance genes (mcr-1 and mcr-2) among MDR and extensively drug-resistant (XDR) Gram-negative bacteria. Methods Two hundred and forty-two Gram-negative clinical bacterial isolates were obtained in our study. Using standard microbiological methods, the bacteria were isolated and identified. Colistin resistance was phenotypically detected utilizing the broth microdilution technique. The colistin-resistant isolates were examined for their antimicrobial susceptibility profile using the Kirby-Bauer disk diffusion method. We used PCR to identify the mcr-1 and mcr-2 genes. Results Our data revealed that up to 18 (7.8%) isolates were colistin-resistant, including 11 Klebsiella spp. isolates, six Pseudomonas spp. isolates and only one Escherichia coli isolate. The PCR results revealed that mcr-1 was found in two isolates (11.1%), including one isolate of Klebsiella spp. (colistin MIC=32 µg/ml) and one isolate of Escherichia coli (colistin MIC=4 µg/ml). None of the colistin-resistant isolates carried mcr-2. Conclusions Based on our data, a relatively low incidence of colistin resistance was observed among clinical isolates. However, the detection of mcr-1 in two isolates of different species is concerning because of the possibility of spreading to susceptible strains. Public Health authorities should implement colistin resistance monitoring programs and infection control strategies in healthcare settings.