OBJECTIVETo investigate the mechanism of carbapenems resistance in Acinetobacter baumannii.

METHODSWHONET-5 software was used to analyze the trend of carbapenem resistance in Acinetobacter baumannii collected from 1999 to 2001 at Peking Union Medical College Hospital. Analytical isoelectric focusing was used to measure the pI of the beta-lactamase. Conjugation experiment was used to study the transfer of carbapenem resistance and plasmid DNA was extracted and purified with Qiagen Plasmid Mini Kit. The homology of the isolates was determined by pulsed field gel electrophoresis (PFGE). Integrase genes and blaIMP-, blaVIM-, blaOXA- genes for resistant isolates were amplified and sequenced.

RESULTSImipenem resistance in A. baumannii was ranged from 1.8%-8.5%, but only 9 resistant isolates were viable. They were co-resistant to other carbapenems, ceftazidime, aztreonam, and gentamicin, and four isolates were resistant to ciprofloxacin. Impipenem resistance could not be transferred to susceptible strains. No plasmid was extracted. Each isolate produced TEM-1, AmpC, and two enzymes (pI 6.7, 6.0), which can not be inhibited by cloxacillin and clavulanic acid. Each isolate had class I intergase gene. Nine isolates were all negative for PCR of blaIMP- and blaVIM- genes, but positive for blaOXA-23 specific PCR. Sequencing found 100% homology with blaOXA-23. PFGE found 3 clones (A type: 5 isolates; B type: 3 isolates; C type: 1 isolate). Control isolates (imipenem-susceptible, but ceftazidime, ciprofloxacin, and gentamicin resistant) were also A clone.

CONCLUSIONSProduction of OXA-23 carbapenemase in A. baumannii was one of the main mechanisms of carbapenems resistance at our hospital. It brings concern that imipenem-resistant clone has evoluted from nosocomial multiple-resistant strains.

Acinetobacter baumannii ; drug effects ; genetics ; Bacterial Proteins ; metabolism ; Carbapenems ; pharmacology ; Ceftazidime ; pharmacology ; Cephalosporin Resistance ; Drug Resistance, Microbial ; Drug Resistance, Multiple, Bacterial ; Electrophoresis, Gel, Pulsed-Field ; Humans ; Microbial Sensitivity Tests ; Sequence Analysis, DNA ; beta-Lactamases ; metabolism

Although extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-EC) has emerged as a significant community-acquired pathogen, there is little epidemiological information regarding community-onset bacteremia due to ESBL-EC. A retrospective observational study from 2006 through 2011 was performed to evaluate the epidemiology of community-onset bacteremia caused by ESBL-EC. In a six-year period, the proportion of ESBL-EC responsible for causing community-onset bacteremia had increased significantly, from 3.6% in 2006 to 14.3%, in 2011. Of the 97 clinically evaluable cases with ESBL-EC bacteremia, 32 (33.0%) were further classified as healthcare-associated infections. The most common site of infection was urinary tract infection (n=35, 36.1%), followed by biliary tract infections (n=29, 29.9%). Of the 103 ESBL-EC isolates, 43 (41.7%) produced CTX-M-14 and 36 (35.0%) produced CTX-M-15. In the multilocus sequence typing (MLST) analysis of 76 isolates with CTX-M-14 or -15 type ESBLs, the most prevalent sequence type (ST) was ST131 (n=15, 19.7%), followed by ST405 (n=12, 15.8%) and ST648 (n=8, 10.5%). No significant differences in clinical features were found in the ST131 group versus the other group. These findings suggest that epidemic ESBL-EC clones such as CTX-M-14 or -15 type ESBLs and ST131 have disseminated in community-onset infections, even in bloodstream infections, which are the most serious type of infection.
Aging ; Bacteremia/drug therapy/*epidemiology ; Biliary Tract Diseases/epidemiology/microbiology ; Cephalosporin Resistance/genetics ; Cephalosporins/therapeutic use ; Community-Acquired Infections/*epidemiology/microbiology ; Escherichia coli/isolation & purification/metabolism ; Escherichia coli Infections/drug therapy/*epidemiology ; Female ; Humans ; Male ; Microbial Sensitivity Tests ; Molecular Epidemiology ; Multilocus Sequence Typing ; Prevalence ; Retrospective Studies ; Urinary Tract Infections/epidemiology/microbiology ; beta-Lactamases/*metabolism