Characterization of quinolone resistant genes and control of qnrB transfer by Potentox in clinical isolates

Objective The objective of the present study was to analyze the presence of qnr genes among different clinical isolates and, subsequently, antibacterial activity of drugs was tested against all of the clinical isolates. Next, we examined the effect of different concentrations of ethylenediaminetetraacetic acid (EDTA) and half of minimum inhibitory concentration (MIC) of drugs on conjugation. Methods Analysis of the presence of qnr genes ( qnrA , qnrB and qnrS ) was done using previously reported primers by polymerase chain reaction. The antibacterial activity of all drugs was determined by MIC and antimicrobial susceptibility (AST) according to the Clinical and Laboratory Standards Institute guidelines (CLSI, 2009). Conjugation was carried out according to the broth mating method. Results The qnrA gene was detected in Acinetobacter baumannii and Citrobacter braakii , whereas qnrB gene was found in Escherichia coli , A. baumannii , C. braakii , Pseudomonas aeruginosa and Klebsiella pneumoniae . However, qnrS was not detected in any of the clinical isolates. The results revealed that Potentox has potential antimicrobial activity against all of the clinical isolates compared to other drugs. Conjugal transfer of qnrB gene from donor to recipient was inhibited at 10 mM EDTA. Similarly, when various drugs at half of MIC were evaluated on conjugation, interestingly, only Potentox could inhibit conjugal transfer of qnrB gene, whereas rest of the drugs failed to inhibit conjugation. Conclusion Potentox has enhanced in vitro antibacterial activity compared to other drugs against quinolone resistant clinical isolates. 10 mM EDTA effectively prevents the conjugal transfer of qnrB gene from donor to recipient. When the same concentration of EDTA was used as a solvent for Potentox, it has again inhibited the conjugal transfer of qnrB gene from donor to recipient. Therefore, inhibition of conjugation can be a novel antimicrobial approach to combat spreading of antibiotic resistance which can be achieved only with Potentox the novel antibiotic adjuvant entity (US patent - US8178501B2).