ABSTRACT
BACKGROUND: The existing modified carbapenem inactivation methods (mCIMs) recommended by the CLSI for detecting carbapenemase production have not been applicable for Acinetobacter baumannii. We evaluated the influence of matrices used in mCIMs and CIMTris on the stability of the disks for detecting carbapenemase producers and suggested optimal mCIM conditions for detecting carbapenemase-producing A. baumannii. METHODS: Seventy-three A. baumannii isolates characterized for antimicrobial susceptibility and carbapenemase encoding genes were tested for carbapenemase production using mCIM and CIMTris. The influence of the matrices (Tryptic soy broth [TSB] and Tris-HCl) used in these methods on the stability of the meropenem (MEM) disk was also evaluated. The mCIM conditions were adjusted to enhance screening sensitivity and specificity for detecting carbapenemase-producing A. baumannii. RESULTS: The matrices had an impact on the stability of the MEM disk after the incubation period (two or four hrs). TSB nutrient broth is an appropriate matrix for mCIM compared with Tris-HCl pH 7.6, which leads to the loss of MEM activity in CIMTris. The sensitivity and the specificity of the optimal mCIM were both 100%. CONCLUSIONS: We established optimal mCIM conditions for simple, accurate, and reproducible detection of carbapenemase-producing A. baumannii.
Subject(s)
Acinetobacter baumannii , Acinetobacter , Hydrogen-Ion Concentration , Mass Screening , Methods , Sensitivity and SpecificityABSTRACT
Objective To evaluate the reliability of the inhibitor enhanced carbapenem inactivation method (ieCIM) in the detection and preliminary classification of carbapenemase in gram-negative rods.Methods The carbapenem inactivation method (CIM) was modified by adding tazobactam or ethylene diamine tetraacetic acid disodium salt as carbapenemase inhibitors into the reaction system.A total of 198 isolates of Enterobacteriaceae and 35 strains of nonfermenters were collected,and their preliminary classification of carbapenemase was performed by the ieCIM.Meanwhile,their carbapenemase genes were detected by polymerase chain reaction (PCR),and the results were compared with that of the ieCIM.Results Among 198 strains of Enterobacteriaceae,101 were positive for carbapenemase genes,while 99 were detected by the CIM.Among the other 97 strains with negative carbapenemase gene,the results of the ieCIM were also negative.Among 35 strains of nonfermenters,25 were positive for carbapenemase genes,while 24 were detected by the CIM.Among the other 10 strains with negative carbapenemase gene,the results of the CIM were also negative.Using the ieCIM,97.7％ (85/87) of strains producing class A carbapenemase and 88.0％ (22/25) of strains producing class B carbapenemase were detected.Twelve strains producing class D carbapenemase and 2 strains producing both class A and class B carbapenemase were detected by the ieCIM.The total detection sensitivity and specificity of the ieCIM were 96％ and 100％,respectively.Conclusion The ieCIM has the consistent results with the detection method of carbapenemase genes,which may be used to detect and classify carbapenemase in clinical microbiology laboratories.
ABSTRACT
Objective To evaluate the utility of carbapenem inactivation method (CIM) in detecting carbapenemase-producing Acinetobacter baumannii.Methods A total of 121 strains of A. baumannii were identified and subjected to antimicrobial susceptibility testing by VITEK compact. Carbapenem inactivation method (CIM) was applied to detect the carbapenemase in the A. baumannii strains. The OXA-23 type carbapenemase-encoding genes were analyzed by common PCR method.Results Six-eight of the 121 strains showed resistance to imipenem and meropenem. PCR showed that 65 of the 68 strains carried OXA-23 gene. CIM was positive in 66 of the 68 strains. And 52 of the 121A. baumannii strains were susceptible to imipenem and meropenem. PCR showed that OXA-23 gene was negative in 49 of the 52 strains. CIM was negative in the 52 strains of non-carbapenemase-producing A. baumannii. Only one strain was resistant to imipenem but susceptible to meropenem. CIM was negative but QXA-23 was positive for this strain. The sensitivity and the specificity of CIM was 94.2% and 98.1% respectively in detecting carbapenemase-producing A. baumannii.Conclusions The results of CIM were consistent with the results obtained by PCR to detect the encoding gene of OXA-23. CIM is inexpensive, easier to operate and interpret than PCR method. CIM is applicable to detect OXA-23 type carbapenemase rapidly inA. baumannii.
ABSTRACT
BACKGROUND: We evaluated the carbapenem inactivation method (CIM) compared with the modified Hodge test (MHT) for the detection of carbapenemase-producing Gram-negative bacilli. METHODS: A total of 61 isolates of carbapenemase-producing Enterobacteriaceae (CPE: 14 KPC, 7 GES-5, 8 NDM-1, 9 VIM-2, 9 IMP-1, and 14 OXA-48-like), 34 isolates of metallo-β-lactamase (MBL)-producing Pseudomonas spp. (14 VIM-2 and 20 IMP-6), and 70 carbapenem-nonsusceptible carbapenemase-negative isolates were included. The CIM and MHT were performed for all of the isolates. To perform the CIM, a meropenem disk was incubated with a suspension of the isolate to be tested and then on Mueller-Hinton agar with the Escherichia coli ATCC 29522 strains. The absence of an inhibition zone indicates presence of a carbapenemase. The presence of a clearing zone indicates lack of a carbapenemase. RESULTS: The total sensitivity and specificity of CIM (96% sensitivity and 100% specificity) in carbapenem-nonsusceptible Enterobacteriaceae and Pseudomonas spp. were better than those of the MHT (77% sensitivity and 94% specificity). The interpretation of CIM results was easy, with no or 20 mm inhibition zones indicating negative carbapenemase activity. CONCLUSION: The CIM had excellent sensitivity and specificity for detection of CPE and MBL-producing Pseudomonas spp., and a positive result was easily determined, unlike the MHT.