Phenotypic detection of metallo-β-lactamase in imipenem-resistant Pseudomonas aeruginosa.
Carbapenems are the primary choice of treatment for severe Pseudomonas aeruginosa infection. However, the emergence of carbapenem resistance due to the production of metallo-β-lactamases (MBLs) is of global concern. In this study, 90 imipenem- (IPM- or IP-) resistant P. aeruginosa (IRPA) isolates, including 32 previously tested positive and genotyped for MBL genes by PCR, were subjected to double-disk synergy test (DDST), combined disk test (CDT), and imipenem/imipenem-inhibitor (IP/IPI) E-test to evaluate their MBLs detection capability. All three methods were shown to have a sensitivity of 100%. However, DDST was the most specific of the three (96.6%), followed by IP/IPI E-test interpreted based on the single criteria of IP/IPI ≥8 as positive (62.1%), and CDT was the least specific (43.1%). Based on the data from this evaluation, we propose that only IRPA with IP MIC >16 μg/mL and IP/IPI ≥8 by IP/IPI E-test should be taken as positive for MBL activity. With the new dual interpretation criteria, the MBL IP/IPI E-test was shown to achieve 100% sensitivity as well as specificity for the IRPA in this study. Therefore, the IP/IPI E-test is a viable alternative phenotypic assay to detect MBL production in IRPA in our population in circumstances where PCR detection is not a feasible option.
Department of Medical Microbiology, University of Malaya, 50603 Kuala Lumpur, Malaysia.
Yalda
Y
Khosravi
Mun Fai
MF
Loke
Eng Guan
EG
Chua
Sun Tee
ST
Tay
Jamuna
J
Vadivelu
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005189:False Positive Reactions; D060005:Genotyping Techniques; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000201:enzymology*; D012680:Sensitivity and Specificity; D001618:beta-Lactamases / Q000235:genetics* / Q000302:isolation & purification*
D000900:Anti-Bacterial Agents; D015378:Imipenem; C533914:metallo-beta-lactamase (VIM-13), Pseudomonas aeruginosa; D001618:beta-Lactamases