Imipenem Induced Transcriptional Modulation of Multidrug Efflux Pumps and Porin Genes in Carbapenem Resistant Escherichia coli Isolates of Animal Origin

The emergence of a multidrug resistance phenotype is most likely outcome of co-existing multiple mechanisms. The underlying molecular mechanism of carbapenem resistance is poorly understood in bacterial isolates of animal origin. The present study investigates the resistance mechanism for reduced susceptibility to carbapenem in E. coli.

The study includes 12 multidrug resistant E. coli isolates showing decreased susceptibility to imipenem. Carbapenemase production was evaluated by the mCarba-NP test. The presence of the carbapenem resistance gene was confirmed by multiplex PCR. Efflux pump activity was accessed by broth microdilution method with or without selective efflux pump inhibitor. We analyzed differential expression of the outer membrane porin genes (ompF, ompC) and efflux pump genes (acrA, acrB) by quantitative realtime PCR analysis.

We observed increased expression of acrA and acrB genes in all the E. coli isolates under imipenem stress. A positive correlation (p<0.001) was evident between imipenem MIC and acrA and acrB over-expression in these isolates. A significant decrease in ompF and ompC expression was observed in these isolates under imipenem stress. The change in MIC was not correlated with the corresponding OmpC and OmpF gene expression. The results suggest the importance of efflux pump and porins proteins in the emergence of multidrug resistance besides carbapenemase production.