Simple screening tests for detection of carbapenemases in clinical isolates of nonfermentative Gram-negative bacteria.

Background & objectives: The production of carbapenemases is an important mechanism responsible for the carbapenem resistance. A simple and inexpensive testing method for screening of carbapenemase producers is essential. A prospective study was undertaken to detect metallo-β-lactamases (MBLs) and AmpC β-lactamases in nonfermentative Gram negative bacteria and to evaluate the various methods for detection of carbapenemases and MBLs. Methods: A total of 100 Acinetobacter spp. (78 A. baumannii and 22 A. lwoffi i) and 140 Pseudomonas spp. (103 P. aeruginosa and 37 other Pseudomonas spp.) were screened for meropenem resistance by Kirby- Bauer disc diffusion method. Modifi ed Hodge test, EDTA disk synergy (EDS) test and AmpC disk test were used for the detection of carbapenemases, MBLs and AmpC β-lactamases, respectively. Results: Forty six (59.0%) A. baumannii, 7 (31.8%) A. lwoffi i, 32 (31.1%) P. aeruginosa and 7 (18.9%) Pseudomonas spp. were resistant to meropenem. Among the 32 meropenem resistant P. aeruginosa, 15 (46.9%) were AmpC β-lactamase producers, 16 (50.0%) MBL producers by EDS test, but only 9 (28.1%) found positive for carbapenemases by modifi ed Hodge test. Among the 46 meropenem resistant A. baumannii, 31 (67.4%) were AmpC β-lactamase producers, 3 (6.5%) MBL producers, but only 1 (14.3%) was positive for carbapenemases by modifi ed Hodge test. One P. aeruginosa was positive for carbapenemase by modifi ed Hodge test, but was negative for MBL and AmpC β-lactamase. Interpretation & conclusions: MBL production is an important mechanism of carbapenem resistance among Pseudomonas species but not among Acinetobacter species. EDS is more sensitive for detection of MBLs than modifi ed Hodge test. Both EDTA-meropenem and EDTA-ceftazidime combination must be used to detect all the MBL producers. Carbapenemases other than MBL may also be responsible for carbapenem resistance. AmpC β-lactamase is also a contributory factor for carbapenem resistance among the isolates in the hospital.

Risk factors analysis in hospital-acquired pneumonia caused by nonfermentative bacteria / 中国感染与化疗杂志

Objective To analyze the risk factors of hospital acquired pneumonia (HAP) caused by nonfermentative bacteria in ICU.Methods Using binary logistic regression analysis,we reviewed the related risk factors of hospital acquired pneumonia caused by nonfermentative bacteria from January,2002 to May,2006 in ICU of our hospital.Results Univariate regression ana- lysis identified 22 variables associated with HAP,including age,diabetes mellitus,malignant tumor,chronic obstructive pul- monary disease (COPD),smoking,Glasgow Coma Scale (GCS) score,Acute Physiology and Chronic Healthy EvaluationⅡ(APACHEⅡ) score.Multivariate regression analysis confirmed 6 high risk factors:aspiration,COPD,use of antacids,seda- tive agents,mechanical ventilation and tracheal intubation or tracheostomy.Conclusions Aspiration,COPD,use of antacids, sedative agents,mechanical ventilation,tracheal intubation or tracheostomy are high risk factors associated with HAP.

Antimicrobial Resistance of Nonfermentative Bacteria in Lower Respiratory Tract Infection / 中华医院感染学杂志

OBJECTIVE To investigate the epidemic situation of nonfermentative bacteria in lower respiratory tract infection and guide rational use of antimicrobials.METHODS API system was applied for bacterial identification.K-B disk diffuse method was used in susceptibility testing.WHONET 5.3 software was used for data analysis.Pseudomonas aeruginosa,Acinetobacter baumannii and Stenotrophomonas maltophilia isolates were included in this study.RESULTS Less than 20% of P.aeruginosa isolates were resistant to amikacin,imipenem or cefoperazone/sulbactam.For A.baumannii,the most active compounds tested were imipenem and cefoperazone/sulbactam with resistance rates of 4.8% and 7.3%,respectively.26.6% And 27.4% of A.baumannii isolates were resistant to piperacillin/tazobactam and ticarcillin/clavulanic acid.The resistance rate of S.maltophilia to cefoperazone/sulbactam,ticarcillin/clavulanic acid and piperacillin/tazobactam was 0,2.7% and 10.8%,respectively.CONCLUSIONS The isolation rate of nonfermenters is increasing in the lower respiratory tract infection,and the ways to improve the cure rate are to avert nosocomial infection and choose antimicrobials properly.