Phenotypic Detection of Metallo-β-Lactamase in Imipenem-Resistant Pseudomonas aeruginosa

• Published in: TheScientificWorld 2012, Vol.2012 (2012), p.1-7
• Main Authors: Khosravi, Yalda, Loke, Mun Fai, Chua, Eng Guan, Tay, Sun Tee, Vadivelu, Jamuna
• Format: Article
• Language: English
• Subjects: Acinetobacter; Anti-Bacterial Agents - pharmacology; Antibiotics; Antimicrobial agents; beta-Lactamases - genetics; beta-Lactamases - isolation & purification; Carbapenems; Chelating agents; Drug Resistance, Bacterial - genetics; False Positive Reactions; Genotyping Techniques; Humans; Imipenem; Imipenem - pharmacology; Laboratories; Metallo-β-lactamase; Metallography; Methods; Microbial Sensitivity Tests; Phenotype; Pseudomonas; Pseudomonas aeruginosa; Pseudomonas aeruginosa - drug effects; Pseudomonas aeruginosa - enzymology; Sensitivity; Sensitivity and Specificity
• ISSN: 2356-6140; 1537-744X; 1537-744X
• DOI: 10.1100/2012/654939

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.