Status of qnr and aac(6')-lb-cr Genes in Quinolone-Resistant Non-Fermenters
Abstract
Non-fermenters are aerobic non-spore forming Gram-negative bacilli that either incapable of catabolized carbohydrates as a source of energy or degrade them via oxidative rather than fermentative metabolic pathways. In the group of non-fermenters Pseudomonas aeruginosa is eminent pathogen followed by Acinetobacter baumanni. Both of these organisms are reported for their intrinsic resistance against antibiotics and their ability to acquire gens that encode resistance. Resistant against quinolones like ciprofloxacin is common against Gram’s negative non-fermenters. For most of the mechanism of resistant in both of these organisms against quinolone, is the production of aminoglycoside modifying enzymes, mutations in topoisomerases, up-regulation of efflux pumps and presence of plasmid mediated qnr genes. In this study, during the study period total 94 non-fermenters were isolated from 378 numbers of different clinical specimens. Out of 94; 21 isolates were found resistant against quinolone antibiotics like ciprofloxacin-5 µg, levofloxacin-5 µg , norfloxacin-10 µg, which were subjected for PCR studies to detect resistant genes, only five (23.81%) isolates were found to be associated with aac(6’)-lb-cr and two (9.52%) were found positive for carrying qnrD gense as additional with aac(6’)-lb-cr genes. Organisms that processed qnrD and aac(6’)-lb-cr gens were, Pseudomona aeruginosa, Acinetobacter baumanni , Alcaligenes faecalis , Acinetobacter calcoaceticus, and Pseudomonas sp.
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Introduction
Because of wide spread use of antibiotics now a day’s resistance is a global problem. Resistant bacterial infection is always typical because of the high antibiotic selection pressure and concentration of susceptible patients. Problem has started to reach into the community setting as exemplified by the recent emergence of community-acquired quinolones resistant non-fermenters in many parts of the world. 1
Families of broad-spectrum synthetic antibacterial drug that drive from quinoline compounds are called quinolones. It is a class of antibiotics that acts by interrupting the replication of DNA molecules in bacteria. The action involves inhibition of the bacteria’s gyrase so that positively super coiled DNA cannot be relaxed for DNA transcription and replication [Hawkey PM. (2003). Mechanisms of quinolone action and microbial response. J antimicrobe chemother, 51 (Suppl 1):29-35]. These quinolones are like Norfloxacin, Ciprofloxacin, Levofloxacin etc.
By definition group of aerobic non-spore forming Gram’s negative bacilli that either incapable of catabolized carbohydrates as source of energy or degrade them via oxidative rather than fermentative metabolic pathways are called non-fermenters. 3
Conclusion
Clinical isolates of non-fermenters, along with others are constantly exposed to hospital environments where they have gained resistance to most antibiotics by various mechanisms. In this study it was found that isolated non-fermenters process aac(6’)-lb-cr and qnrD type gens that mostly encoded by plasmid DNA. These non-fermenters could pose a serious health hazardous if given a chance to infect the community.