Colistin resistance and heteroresistance in Klebsiella pneumoniae & Escherichia coli clinical isolates from intensive care units.

Objective: Colistin resistance poses a serious clinical problem. This study aims to investigate the presence of plasmid-mediated resistance and heteroresistance among Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) clinical isolates at intensive care units of Main Alexandria University Hospital.

Methods: Seventy colistin-resistant and 30 colistin-susceptible K. pneumoniae and E. coli isolates constituted the material of the study. The rapid polymyxin NP (Nordmann Poirel) test was performed. Heteroresistance in colistin-susceptible isolates was investigated by population analysis profile. mcr-1 and mcr-2 genes were amplified by polymerase chain reaction (PCR).

Results: The rapid polymyxin NP test showed 100% concordance with the results of BMD (broth microdilution method). Heteroresistance to colistin was detected in 23.3% of colistin-susceptible K. pneumoniae isolates. All colistin-resistant isolates were negative for mcr-1 and mcr-2 genes.

Conclusions: The rapid polymyxin NP test is a reliable screening tool for colistin resistance, but not for heteroresistance. Other colistin resistance mechanisms should be investigated.