Background: Several incidences worldwide have marked the emergence of colistin and carbapenem resistance in K. pneumoniae and increased morbidity and mortality associated with their infections. A retrospective observational study was conducted to study the prevalence and molecular events contributing colistin resistance among K. pneumoniae isolates at a tertiary hospital, New Delhi, India.Methods and materials: Clinical samples were screened for susceptibility towards antibiotics. Colistin resistant K. pneumoniae isolates were analyzed by MLST to understand the clonal relation. The mechanism underlying colistin resistance was determined by sequence analysis of two component regulatory system genes. The phenotypic effect of amino acid substitutions were predicted using a combination of SIFT, PROVEAN and PolyPhen-2 based analysis. Gene expression of pmrC and pmrK was analyzed by qRT-PCR.Results: Of the 335 Klebsiella spp. isolated, 11 (3.2%) were found colistin resistant. K. pneumoniae isolates belong to Clonal complex-11 with serotypes (ST): 14, 16, 43, 54, 147 and 395, four isolates had three novel ST profiles. High MIC-values were noted for colistin (>128 g/ml), amoxyclav (>256 g/ml), imipenum (>256 g/ml), gentamycin (>256 g/ml), ciprofloxacin (>256 g/ml), Cotrimaxazole (>32 g/ml), rifampicin (>128 g/ml) and tetracycline (>128 g/ml). Sequence analysis revealed non-synonymous deleterious mutations in phoP (T151A), phoQ (del87-90, del263-264, L30Q and A351D), pmrA (Q140L and G53S), pmrB (D150 V, T157P, L237R, G250C, A252G, R256G, R315P and Q331H) and mgrB (C28G and IS element) genes. mgrB gene in three strains were found to be disrupted by insertion sequences encoding glycosyl transferase-IS1-like and IS5/IS1182 family-like transposase genes and found to be with associated with high MIC. All isolates were negative for mcr-gene, while blaNDM-1, blaOXA-48 and blaCTX-M gene were positive in MRK-8, 5 and 9 isolate, respectively. All colistin resistant K. pneumoniae isolates showed an elevation in transcription level of pmrK and pmrC genes under colistin treated and untreated conditions.
Conclusion:All the colistin and carbapenem resistant K. pneumoniae isolates were distinct with no clonal relatedness and presents emergence of discrete resistance mechanisms.