Colistin-Resistant Klebsiella pneumoniae: Prevalence of Integrons and Synergistic Out Turn for Colistin-Meropenem

Klebsiella pneumoniae has the potential to disseminate at speed among the hospital environment, hence included as a major nosocomial pathogen cause of severe infections. This work mainly focused on finding out the prevalence of different classed of integrons in colistin-resistant Klebsiella pneumoniae and to analyze the efficacy of colistin-meropenem in combination.
For this cross-sectional study, random non-biased sampling technique was followed and non-repetitive, Klebsiella pneumoniae clinical isolates were collected (Jan 2015 - Jan 2016) from 2 diagnostic centers located at Chennai and Trichy in Tamil Nadu, India. Isolates were identified as Klebsiella pneumoniae using the VITEK identification system. All the 24 isolates collected were studied for resistance using disk diffusion and minimal inhibitory concentration (MIC). Integrons (class 1, 2, 3) and mcr-1/2 genes were screened for all the isolates. Synergism for colistin-meropenem was tested using checkerboard, time-kill, and modified time-kill analysis.
Klebsiella pneumoniae isolates (n = 24) that were resistant to colistin were studied, and MIC50, as well as MIC90 values for colistin, were 64 µg/mL and 16 µg/mL, respectively. Whereas the gene mcr-1/2 was absent in all the isolates tested. Our results revealed the prevalence of class 1 integron among 10/24 isolates (41.6%) and its integron gene cassette in 60% of the isolates with a pattern of variable regions ranging between 700 bp to 2000 bp. The combination of colistin-meropenem implies that by the checkerboard method 86% (21/24) of the isolates, by time-kill analysis 76% (16/21), and by modified time-kill analysis 94% (15/16) of the colistin-resistant isolates showed synergism.
This study reveals that the prevalence of integrons might have an impact in spreading colistin resistant Klebsiella pneumoniae among hospital environment, which is a major threat for clinicians. The combination of colistin with meropenem had bactericidal effect against colistin- resistant Klebsiella pneumoniae.