Analysis on drug-resistance and molecular epidemiology of Acinetobacter baumannii isolated from the clinical samples in two Chinese hospitals

In the present study, the drug-resistance genes encodingβ-lactamases, aminoglycoside modifying enzymes, DNA topoisomerases and integron as well as their molecular epidemiology were investigated by means of analyzing the drug-resistance and molecular epidemiology of Acinebacter bau mannii isolated from the clinical samples in two hospitals in Qiangzhou and Huzhou city of Jiangsu and Zhejiang province from July 2000 to March 2005. The minimal inhibitory concentrations (MICs) of these 307 isolates were detected by automatic microbiological system, and 35 strains against 5-fluoro-quinolones were performed by agar dilution assay. Meanwhile, the resistant genes in 80 isolates were amplified by PCR with identification by DNA sequencer. It was found that most of the 307 isolates of A . baumannii were resistant to multiple antibiotics tested, in which the resistance rates of the isolates against piperacillin, piperacillin/tazobactam, amoxacillin/clavulanic acid, cefotaxime, ceftazidime, cefepime, gentamicin, amikacin, ciprofloxacin, chloramphenicol and sulfamethoxazole/trimethoprim were all above 35% , but those of imipenem and meropenem were quite low, ranged only 2.6% and 3.3%. In addition, it was also demonstrated that the positive rates of TEM and SHVβ-lactamase genes accounted for 93.8% and 22.5% respectively, and those of the aminoglycoside-modifying enzyme genes including aacC1, aacC2, aacC3, aacC4, aacC4A, aphA6, ant(2')-I and ant(3') I were 58.8%, 8.8%, 7.5%, 28.8%, 45.0%, 2.5%, 28.8% and 65.0% respectively. The mutations in the quinolone-resistant determining region (QRDR) of gyrA and parC genes indicated that substitution in Ser-83 residue of GyrA protein was most frequently occurred among strains with MIC for ciprofloxacin of more than 4μg/ml, whereas a double mutation at Ser-83 residue of gyrA and Ser-80 of parC was found in strains with MIC of ciprofloxacin of more than 8μg/ml. As to the positive rates of class 1 integron (Int I -1) and qacE△1-sul-1, it was found to be 60.0% and 77.5% respectively, and the rates of resistant genes of strains isolated in these two hospitals varied considerably. The results obtained in the present study indicate the presence of the multiple resistant genes in strains of A. baumannii , and great measures should be taken to control the spread of the resistant strains carrying the resistant genes.

Surveillance on the multi-drug resistance and the β-lactamase resistance genes in Pseudomonas aeruginosa

In the present study,27 multi-drug resistant strains of Pseudomonas aeruginosa were isolated from clinical specimens in our hospital from Jan 2005 to Nov 2005,in which the resistant genes encodingβ-lactamase including TEM,SHV,OXA,PER,VEB,GES,CARB,IMP,VIM,SPM,GIM,DHA and OprD2 were tested by PCR amplification and sequenced by DNA sequencer.It was found that the detection rates of bla_(VEB),bla_(GES) and bla_(CARB) genes in these 27 isolates of P.aeruginosa were 11.1%, 11.1% and 48.1%,respectively,but almost the oprD2 gene was lacked(92.6%).In addition,the resistant genes encoding TEM,SHV,OXA,PER,IMP,VIM,SPM,GIM and DHAβ-lactamase were all not found.It was also demonstrated that the sequence of bla_(VEB) gene appeared to be identical to that of the bla_(VEB-1)(AY536743),while the bla_(CES) and bla_(CARB) genes shared 99% identity with bla_(GES-1) (AY219651)and bla_(CARB-3)(S46063) genes.From these observations,it is evident that P.aeruginosa carrying the bla_(VES),bla_(GES) and bla_(CARB) resistant genes isolated in our hospital confers the resistance toβ- lactams,and the loss of the oprD2 gene may be the important cause to develop resistance to imipenem in P.aeruginosa.

Correlation of the antiseptic resistance in Acinetobacter baumannii and the antiseptic resistance gene qacEΔ1 located in classⅠintegron

In the past decade, uses of antiseptics and disinfectants in hospitals and other health care centers are rather common, but the chance to develop resistance to antiseptics and disinfectants is also increased. Acinetobacter baumannii is one of the opportunistic bacteria involving in the nosocomial infection . In the present study, the correlation of the antiseptic resistance in A . baumannii and the antiseptic resistance gene qacEΔ1 was investigated by means of determination of MICs. Meanwhile, the MICs of glutaraldehyde, chlorhexidine, benzalkonium bromide, iodophor and trichloroisocyanurate to 80 clinical isolates of A. baumannii were detected by tube dilution assay and the resistance genes intI1 and qacEΔ1 in these isolates were amplified by PCR and verified by DNA sequencer. It was found that the MIC50 for these 5 antiseptics tested were 32, 8, 8, 4 and 1μg/ml respectively, and the detection rates of intI1 and qacEΔ1 gene were 60.0% and 77.6% respectively. In addition, 55% of the 80 isolates simultaneously possessed both intll and qacEΔ1 gene, and the percentage of antiseptic resistance of A . baumannii carring both genes to benzalkonium bromide were higher than that without these two genes, however, there was no significant difference between intll and qacEΔ1 gene. The result in bactericidal efficiency assay indicated that chlorhexidine could still produce rapid and strong bactericidal effect at concentration of 1 MIC after 10 min exposure. These results suggest that the antiseptic resistance of A . baumannii to various antiseptics is correlated with the presence of the antiseptic resistance genes qacEΔ1 in bacteria, thus warning that the increase of the antiseptic resistance should not be ignored and the relative high concentration or prolonged application time is required to achieve a sufficient bactericidal effect.

Study of Klebsiella pneumoniae producing extendedspectrum β-lactamases against aminoglycosides

Klebsiella pneumoniae(K.pneumoniae)is one of the main gram-negative bacilli in clini- cal practice.Nosocomial infections caused by K.pneumoniae producing extended-spectrumβ-lactama- ses(ESBLs)are very difficult to treat.This paper investigated the resistant characteristics of K.pneu- moniae producing ESBLs and their aminoglycoside-modifying enzyme gene expressions including N- acetyhransferases and O-adenyhransfemses.Bacteria identification and ESBLs confirmatory tests were performed by Phoenix^(TM)-100 system.And minimum inhibitory concentrations(MICs)of gentamicin, amikacin,kanamycin,tobramycin,netilmicin and neomycin in 53 K.pneumoniae isolates were de- tected by agar dilution.In addition,six aminoglycoside-modifying enzyme genes were amplified by polymerase chain reaction(PCR)and verified by DNA sequencer.It was found that imipenem and meropenem against 120 K.pneumoniae isolates produced powerful antimicrobial activities.The resis- tant rates of gentamicin and amikacin were 55.0% and 46.7%,respectively.Except neomycin, MIC_(50)and MIC_(90)of gentamicin,amikacin,kanamycin,tobramycin and netilmicin in 53 K.pneumoni- ae were all>128μg/ml,and the resistant rates were 83.0%,52.3%,75.5%,81.1% and 69.8%,respectively.However,neomycin was only 39.6%.In addition,five modifying enzyme genes,including aac(3)-Ⅰ,aac(3)-Ⅱ,aac(6')-Ⅰb,ant(3″)-Ⅰ,ant(2″)-Ⅰgenes,were found in 53 isoahes except aac(6')-Ⅱ,and their positive rates were 11.3%,67.9%,47.2%, 1.9% and 39.6%,respectively.It was also confirmed by nucleotide sequence analysis that the above resistant genes shared nearly 100% identities with GenBank published genes.The results obtained in the present study indicated that K.pneumoniae producing ESBLs strains are rapidly spreading in our hospital,and their resistance to aminoglycosides may be associated with aminoglycoside-modifying enz- yme gene expressions.