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Objective: Acinetobacter baumannii is an opportunistic pathogen associated healthcare infections with high mortality in intensive care units all over the globe. Over-expression of efflux pumps has been reported as contributing factor in escalating drug resistance and renders the treatment ineffective. This study aimed to investigate the mechanism responsible for escalating resistance of carbapenem resistant A. baumannii (CRAB) retrieved from clinical isolates. Methodology: A total of 64 CRAB isolates were enrolled in the present study from two tertiary care hospitals situated in North India from 2013 to 2016. Disk diffusion and agar dilution based MIC methods were used to determine the antimicrobial susceptibility pattern. Screening of Class-D and Class-B beta-lactamases was executed for all isolates using PCR. Relative gene expression of four RND, one MATE efflux pumps and outer membrane proteins' genes were determined using RT-qPCR. Results: All the isolates showed presence of efflux transporter and porin genes by PCR amplification method. Relative gene expressions for adeG, adeY and abeM were significantly found over-expressing (>2 fold) in all the 64 isolates followed by adeJ and adeB genes, which showed over-expression in 72% and 44% isolates respectively. Porin gene carO reported under-expression/downregulation (<0.5 fold) in 66% (42/64) isolates suggesting the resistant phenotypic nature of the isolates. The prevalence of adeB and oprD were absent in 92% and 93% respectively. High prevalence of OXA-23 (96.8%) observed amongst CRAB isolates followed by NDM-1 (29.7%) and OXA-58 (4.6%). Conclusion: This study indicated the significant role of RND efflux transporters and carbapenemases in conferring carbapenem resistance to A. baumannii. [ABSTRACT FROM AUTHOR]

With the advent of antibiotics, bacterial infections were supposed to be a thing of past. However, this instead led to the selection and evolution of bacteria with mechanisms to counter the action of antibiotics. Antibiotic efflux is one of the major mechanisms, whereby bacteria pump out the antibiotics from their cellular interior to the external environment using special transporter proteins called efflux pumps. Inhibiting these pumps seems to be an attractive strategy at a time when novel antibiotic supplies are dwindling. Molecules capable of inhibiting these pumps, known as efflux pump inhibitors (EPIs), have been viewed as potential therapeutic agents that can rejuvenate the activity of antibiotics that are no longer effective against bacterial pathogens. EPIs follow some general mechanisms of efflux inhibition and are derived from various natural as well as synthetic sources. This review focuses on EPIs and identifies the challenges that have kept these futuristic therapeutics away from the commercial realm so far., Competing Interests: None

The present study deals with membrane-bound efflux pumps, MexAB-OprM and MexXY and their respective regulatory genes mexR, nalC, nalD and mexZ in multidrug resistant (MDR) Pseudomonas aeruginosa. Following antibiotic sensitivity testing and detection of various beta-lactamases, hyperexpression of efflux pump genes, mexB and mexY in the isolates was investigated using semi-quantitative and real-time reverse transcription-PCR. Amplicons from regulatory genes were sequenced and subjected to mutational and phylogenetic analysis. Twenty-nine clinical isolates of P. aeruginosa were obtained from a total of 144 MDR gram-negative bacteria collected from Kerala State, South India. All strains were found to be resistant to ampicillin and nalidixic acid with 13.8, 44.8 and 31% testing positive for extended-spectrum beta-lactamases, metallo-beta-lactamases and AmpC producers respectively. Increased mexB and mexY transcription was detected respectively in 10.3 and 20.7% of the isolates in comparison with P. aeruginosa reference strain, PAO (MTCC). Co-expression of MexY was also observed in MexB overproducers. Various synonymous/and non-synonymous mutations in regulatory gene sequences of efflux pump operons were detected. In the strain designate Pa16, mexR was found to harbour four novel point mutations with one transversion and three transitions which included a substitution of an ochre codon with that for serine. The gene also displayed a novel mutation involving insertion of a cysteine at the 444th base position, followed by an opal codon. The genetic divergence and homogeneity of the concatenated (mexR, nalC and nalD) regulatory gene sequences of mexAB-oprM operon was apparent in the phylogram generated with similar sequences retrieved from public database.