Researches On The Resistance Of Pseudomonas Aeruginosa To Aminoglycosides And Carbenpenems And Their Correlated Resistant Genes

Objective: To investigate the prevalence, resistance and genotype in clinical isolates of Pseudomonas aeruginosa producing aminoglycoside-modifying enzyme (AME) and metallo-beta-lactamase (MBLs) or with loss of OprD₂, in order to probe into the genetic resistant mechanisms of the two kinds of antibiotics.Methods: A total of 160 strains of pseudomonas aeruginosa were isolated from clinical specimens in West China Hospital of SiChuan University from April 2003 to Feb. 2004. The MICs of 14 antimicrobial agents against the strains were detected by 2-fold agar dilution method. The AME, MBLs and OprD₂ encoding genes were amplified by PCR. The nucleotide sequences of AME and MBLs encoding genes were detected by automatic sequencer, and determined the enzyme-encoding gene type by Blastx searching.Results: The rate of pseudomonas aeruginosa carrying AME was 20.6%. In 33 AME -producing strains, the percentage of AAC (3) - IK AAC (6' ) -IK AAC (6' ) -I , ANT (3" ) -IlandAAC (3) -I was 48.5*^ 45.8 % ^ 36.4% ., 9.1 % and 9.1 %, respectively, among which 22 strains carried two or more AME(66.7%). aac (3) -Ilandaac (6' ) -IIaccounts for the majority of AME gene type. About 72.7% AME-producing strains were multidrug resistant. For all AME-carrying strains, the resistant rates to beta-lactams and quinolone were: cefoperazone66.7% ^ ciprofloxacin 57.8 % > cefotaxime45.5 % ^ cefoperazone/sulbactam39.4 % piperacillin/tazobactam27.3 % > cefepimel8.2 % , panipeneml5.1 % ^ meropenem 12.1 % and imipenem9.1 %. The rate of loss of OprD2 in 16 strains of imipenem-resistant pseudomonas aeruginosa was 62.5 % . No MBLs was detected in pseudomonas aeruginosa. The cross-resistant rate to meropenem and panipenem in 10 strains with loss of OprD2was 92.9%and 100%, respectively. The resistant rate in these 10 strains to cefoperazone> cefotaxime> cefoperazone/sulbactanu ciprofloxacin and four aminoglycosides was above 70%, and to cefepime> piperacillin/tazobactam and amikacin was below 40%.Conclusions: Aminoglycoside-modifying enzyme was common in clinical isolates of pseudomonas aeruginosa in our hospital, and the rate of AME-producing strains carrying more than one type of AME was high. AAC (3) -IlandAAC (6' ) - II was the main AME types, and aac (3) -Hand aac (6' ) -II was the main genotypes. The majority of AME-producing strains were multidrug resistant. Piperacillin/tazobactam , cefepime and carbepenems was a good choice for nosocomial infections caused by AME-producing pseudomonas aeruginosa. Loss of OprD2 was one of the main carbepenems resistant mechanisms of pseudomona aeruginosa.