Bahare Salehi1,2, Zohreh Ghalavand3, Abbas Yadegar4, Gita Eslami2. 1. Infectious Diseases and Tropical Medicine Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 2. Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3. Department of Microbiology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. zghalavand@sbmu.ac.ir. 4. Foodborne and Waterborne Diseases Research Center, Research Institute for Gastroenterology and Liver Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran. a.yadegar@sbmu.ac.ir.
Abstract
BACKGROUND: This study was aimed to characterize the genetic diversity and expression of three putative resistance-nodulation-cell division (RND)-type efflux systems and their contribution to multidrug efflux in clinical isolates of Acinetobacter baumannii. METHODS: Antimicrobial susceptibility testing of 95 A. baumannii isolates was determined by Kirby-Bauer disk diffusion for 18 antibiotics and minimum inhibitory concentration (MIC) of colistin was determined by the broth microdilution method. Moreover, the MIC of five classes of antibiotics was assessed using E-test strips in the presence and absence of phenylalanine-arginine beta-naphthylamide (PAβN). Regulatory genes of the RND efflux pumps (adeRS, adeL, adeN and baeSR) were subjected to sequencing. The relative expression of adeB, adeG and adeJ genes was determined by quantitative real-time PCR (qRT-PCR). RESULTS: Overall, the majority of isolates (94%) were extensively drug-resistant (XDR). In the phenotypic assay, efflux pump activity was observed in 40% of the isolates against multiple antibiotics mainly tigecycline. However, we found no efflux activity against imipenem. Several amino acid substitutions were detected in the products of regulatory genes; except in AdeN. Of note, G186V mutation in AdeS was found to be associated with overexpression of its efflux pump. No insertion sequences were detected. CONCLUSIONS: Our findings outlined the role of RND efflux pumps in resistance of A. baumannii to multiple antibiotics particularly tigecycline, and pointed out the importance of a variety of single mutations in the corresponding regulatory systems. Further studies are required to decipher the precise role of RND efflux pumps in multidrug-resistant clinical isolates of A. baumannii.
BACKGROUND: This study was aimed to characterize the genetic diversity and expression of three putative resistance-nodulation-cell division (RND)-type efflux systems and their contribution to multidrug efflux in clinical isolates of Acinetobacter baumannii. METHODS: Antimicrobial susceptibility testing of 95 A. baumannii isolates was determined by Kirby-Bauer disk diffusion for 18 antibiotics and minimum inhibitory concentration (MIC) of colistin was determined by the broth microdilution method. Moreover, the MIC of five classes of antibiotics was assessed using E-test strips in the presence and absence of phenylalanine-arginine beta-naphthylamide (PAβN). Regulatory genes of the RND efflux pumps (adeRS, adeL, adeN and baeSR) were subjected to sequencing. The relative expression of adeB, adeG and adeJ genes was determined by quantitative real-time PCR (qRT-PCR). RESULTS: Overall, the majority of isolates (94%) were extensively drug-resistant (XDR). In the phenotypic assay, efflux pump activity was observed in 40% of the isolates against multiple antibiotics mainly tigecycline. However, we found no efflux activity against imipenem. Several amino acid substitutions were detected in the products of regulatory genes; except in AdeN. Of note, G186V mutation in AdeS was found to be associated with overexpression of its efflux pump. No insertion sequences were detected. CONCLUSIONS: Our findings outlined the role of RND efflux pumps in resistance of A. baumannii to multiple antibiotics particularly tigecycline, and pointed out the importance of a variety of single mutations in the corresponding regulatory systems. Further studies are required to decipher the precise role of RND efflux pumps in multidrug-resistant clinical isolates of A. baumannii.
Authors: Michael Hornsey; Matthew J Ellington; Michel Doumith; Claire P Thomas; Nicola C Gordon; David W Wareham; John Quinn; Karen Lolans; David M Livermore; Neil Woodford Journal: J Antimicrob Chemother Date: 2010-06-16 Impact factor: 5.790
Authors: Vincent Trebosc; Sarah Gartenmann; Kevin Royet; Pablo Manfredi; Marcus Tötzl; Birgit Schellhorn; Michel Pieren; Marcel Tigges; Sergio Lociuro; Peter C Sennhenn; Marc Gitzinger; Dirk Bumann; Christian Kemmer Journal: Antimicrob Agents Chemother Date: 2016-11-21 Impact factor: 5.191