title: Modification of the susceptibility of gram-negative rods producing ESβLS to β-lactams by the efflux phenomenon.
abstract: The production of β-lactamases is the most important mechanism of Gram-negative rod resistance to β-lactams. Resistance to ceftazidime and cefepime in clinical isolates of Enterobacteriaceae (especially ESβL-positive E. coli and K. pneumoniae) and P. aeruginosa is life-threatening. However, all strains of the above mentioned species possess chromosomally encoded RND efflux pump systems in addition to β-lactamase production. The main goal of this study was to assess the role of efflux pump systems in cefepime and/or ceftazidime resistant phenotypes of ESβL-positive clinical strains of Enterobacteriaceae and P. aeruginosa. The influence of the efflux pump inhibitor PAβN on the minimum inhibitory concentration (MIC) values of tested cephalosporins was species-dependent. Generally, a significant reduction (at least four-fold) of β-lactam MICs was observed in the presence of PAβN only in the case of P. aeruginosa clinical isolates as well as the ESβL-producing transformant PAO1161 ΔampC. The usage of this agent resulted in the restoration of susceptibility to cefepime and/or ceftazidime in the majority of the P. aeruginosa ESβL-positive strains with low and moderate resistance to the above cephalosporins. Moreover, an outer membrane permeabilizing effect in the presence of PAβN was identified. Strain-dependent β-lactamase leakage upon PAβN or β-lactam treatment was demonstrated. The most important observation was the restoration of susceptibility of P. aeruginosa WUM226 to cefepime (MIC decrease from 32 to 4 mg/L) and ceftazidime (MIC decrease from 128 to 4 mg/L) in the presence of PAβN, which occurred despite an almost complete lack of β-lactamase leakage from bacterial cells. In conclusion, these data indicate that RND efflux pumps can modify the susceptibility to β-lactams in Gram-negative rods producing ESβLs. However, this phenomenon occurs only in P. aeruginosa strains and was not observed among E. coli and K. pneumoniae strains, representing the Enterobacteriaceae family.
authors: Department of Pharmaceutical Microbiology, Medical University of Warsaw, Warsaw, Poland.
authors: Agnieszka E
authors: AE
authors: Laudy
authors: Department of Pharmaceutical Microbiology, Medical University of Warsaw, Warsaw, Poland.
authors: Paula
authors: P
authors: Osińska
authors: Department of Pharmaceutical Microbiology, Medical University of Warsaw, Warsaw, Poland.
authors: Alicja
authors: A
authors: Namysłowska
authors: Department of Pharmaceutical Microbiology, Medical University of Warsaw, Warsaw, Poland.
authors: Olga
authors: O
authors: Zając
authors: Department of Pharmaceutical Microbiology, Medical University of Warsaw, Warsaw, Poland; Department of Antibiotics and Microbiology, National Medicines Institute, Warsaw, Poland.
authors: Stefan
authors: S
authors: Tyski
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D001618:beta-Lactamases