Relationship between antimicrobial resistance and aminoglycoside-modifying enzyme gene expressions in Acinetobacter baumannii

Background Acinetobacter baumannii is one of the main gramnegative bacilli in clinical practice Nosocomial infections caused by multidrug resistance Acinetobacter baumannii is very difficult to treat This study was designed to investigate the antimicrobial resistance characteristics and four resistant gene expressions of aminoglycosidemodifying enzymes including Nacetyltransferases and Ophosphotransferases in Acinetobacter baumannii Methods Bacterial identification and antimicrobial susceptibility test were performed by PhoenixTM system in 247 strains of Acinetobacter baumannii Minimal inhibitory concentrations (MICs) of seven aminoglycosides including gentamicin, amikacin, kanamycin, tobramycin, netilmicin, neomycin and streptomycin in 15 strains of multidrug resistant Acinetobacter baumannii were detected by agar dilution Four aminoglycosidemodifying enzyme genes were amplified by polymerase chain reaction (PCR) and verified by DNA sequencerResults The resistance rates of 247 strains of Acinetobacter baumannii against cefotaxime, levofloxacin, piperacillin, aztreonam, tetracycline, ciprofloxacin and chloramphenicol were more than 50% Imipenem and meropenem showed high antibacterial activities with resistance rates of 32% and 41% MIC50 and MIC90 of gentamicin, amikacin, streptomycin and kanamycin in 15 strains of multidrug resistant Acinetobacter baumanii were all more than 1024 mg/L, and the resistance rates were 100%, 100%, 100% and 933%, respectively But their resistance rates to tobramycin, netilmicin and neomycin were 867%, 933% and 467%, respectively Three modifying enzyme genes, including aacC1, aacC2 and aacA4 genes, were found in 15 strains, but aphA6 had not been detected Their positive rates were 933%, 200% and 200%, respectively These three genes existed simultaneously in No19 strain Nucleotide sequences of aacC1, aacC2 and aacA4 genes shared 100%, 979% and 997% identities with GenBank genes (AY307113, S68058 and AY307114)Conclusion Multidrug resistant Acinetobacter baumannii strains are rapidly spreading in our hospital, and their resistance to aminoglycosides may be associated with aminoglycosidemodifying enzyme gene expressions

Inhibitory effects of reserpine and carbonyl cyanide m-chloro-phenylhydrazone on fluoroquinolone resistance of Acinetobacter baumannii

Mechanisms of bacterial resistance to fluoro-quinolones may be grouped intothree principal categories: gene mutations of DNA topoisomerase Ⅱ (GyrA or GyrB), DNA topoisomeraseⅣ ( ParC or ParE), decrease of outer membrane permeation and upregulation of multi-drug effluxpump (active efflux system). Efflux pumps are transport proteins removing toxic substrates(including virtually all classes of clinically relevant antibiotics) from cells to the externalenvironment. These proteins exist in both Gram positive bacteria and Gram negative bacteria as wellas in fungi and mammalian (tumour) cells. It has been reported that alkaloid reserpine and carbonylcyanide m-chlorophenylhydrazone (CCCP) can inhibit NorA multi-drug efflux. In order to explore theuniversality of drug efflux in microorganisms, 85 strains of Acinetobacter baumannii (A. baumannii)were tested using reserpine and CCCP. The quinolone-resistant-determining region (QRDR) of gyrA andparC genes in 35 isolates of A. baumannii were amplified by polymerase chain reaction (PCR) andsequenced by DNA sequencer. The correlation between resistant mutation regularity and bacterial drugefflux were analysed.