Characterization of imipenem non-susceptible Pseudomonas aeruginosa isolates from patients without carbapenem treatment

Abstract

Objectives To investigate characterization of imipenem resistance among imipenem non susceptible Pseudomonas aeruginosa isolated from patients who treated without imipenem and explore risk factors of imipenem resistance. Methods From April, 2006 to March, 2008, a total of 37 non-susceptible to imipenem without imipenem therapy isolates were collected from affiliated 3201st Hospital of Medical College of Xi′an Jiaotong University.The minimum inhibition concentration (MIC) to 11 antimicrobial agents were determined by the broth dilution method.We also tested imipenem MIC combined with efflux pump inhibitor PAβN.PCR was performed to check for the presence of carbapenem-hydrolylzing MBL genes and oprD gene.The expression level of oprD2 and ampC were evaluated by qRT-PCR.Molecular typing was performed using PFGE. Results There is significant difference (t=-2.9004,P<0.01) of the average number days of therapy between with two or more antibiotics in the 16 patients (20.0±9.5) d and that with only one antibiotic in the other 21 patients (12.6±4.4) d before imipenem-non-susceptible strains were isolated.In all 37 strains, 32 strains showed resistance to more than three antibiotics.The MBL gene (IMP-9) was only found in one strain, but its phenotype is negative.oprD2 gene from the 29 strains were found forward inserted by ISpa1328.Thirty-five isolated were considered to have no oprD expression.The patterns of the total DNA of 37 strains appeared six PFGE types.The 26 strains belonged to C2 PFGE type.In the presence of PAβN, all 37 strains increased sensitivity to meropenem. Conclusion Fluoroquinolones and cephalosporins treatment could play an important role in imipenem non-susceptible production in the research isolates.（Chin J Lab Med,2012,35:716-721） Key words: Pseudomonas aeruginosa; Imipenem; Drug resistance，bacterial