MOLECULAR DETERMINANTS OF ACQUIRED COLISTIN RESISTANCE AMONG CLINICAL ISOLATES OF KLEBSIELLA PNEUMONIAE

Background and Aim:Colistin is among the few antimicrobial agents that retain activity against problematic Gram negative bacilli (GNB) and often considered as the last-line defense against infections caused by these superbugs. Recently, increased use of colistin has resulted in development of resistance to this last hope antibiotic. The most common mechanism of bacterial resistance includes covalent modification of LPS through incorporation of positively charged groups which neutralize the negative charges of LPS and reduce binding affinity of colistin to its target. LPS modifications are mediated by genetic alterations in the PmrA-PmrB or PhoP-PhoQ two component regulatory systems or their regulators (MgrB). Recently a plasmid mediated resistance mechanism (mcr genes) has been identified among GNBMethods:We explored the underlying mechanisms of colistin resistance among 20 colistin resistant clinical isolates of Klebsiella pneumoniae. The presence of mcr-1, mcr-2, mcr-3, and mcr-4 genes were examined by PCR and nucleotide sequences of pmrA, pmrB, phoP, phoQ, and mgrB genes were determine. The expression levels of LPS modifying enzymes PmrK and PmrC was evaluated by RT-qPCR method.Results:All col-R isolates lacked mcr genes or any genetic alterations in the pmrA, phoP, and phoQ genes and substitutions identified in the pmrB were not found to be involved in resistance conferring .Inactivation of MgrB due to nonsense mutations and insertion of IS elements was found in 15 isolates (75%) which was associated with overproduction of LPS modifying enzymes.Conclusion:MgrB alterations was found to be the main mechanism of colistin resistance among the studied K. pneumoniae isolates.

Keywords:

colistin , Klebsiella pneumoniae , MgrB , PmrAB , PhoPQ