Abstract

Different metallo-β-lactamases (MBL) have been increasingly recognized among imipenem (IMP)-resistant Pseudomonas aeruginosa (P. aeruginosa) isolates. The existence of MBL IMP-susceptible isolates has been lately reported bearing the risk of unnoticed spread in hospitals. Early detection of MBL-producing organisms is critical to stop their uncontrolled spread and to allow for the prompt use of appropriate antibiotic. The current study aimed to determine MBL frequency among IMP-resistant and susceptible P. aeruginosa isolates by phenotypic and molecular testing in a medical hospital setting in Cairo. A total of 50 P. aeruginosa isolates from Theodor Bilharz Research Institute (TBRI) hospital were identified and examined for the phenotypic expression of MBL by Imipenem-EDTA com-bined disk test (CDT) and the MBL E test. MBL coding genes, bla_VIM-2 and bla_IMP-1, were detected by PCR. Of all P. aeruginosaisolates, 41 (82%) were MBL producers by phenotypic methods while PCR assay detected VIM-2 type of MBL gene in 35 (70%) and all test isolates were negative for IMP-1 gene. Based on data from the combined use of the three methods, 32 (64%) were confirmed to be MBL producers. MBLs were detected in 64% (23/36) IMP-resistant, 58.3% (7/12) IMP-sensitive and 100% (2/2) IMP-intermediate isolates by both phenotypic tests and gene amplification of bla_VIM-2. All MBL carrying IMP-sensitive isolates had zone diameter between 16 to 20 mm by the Kirby-Bauer disk diffusion method. This study reports the occurrence of VIM-2 in IMP-susceptible P. aeruginosa isolates which may repre-sent a risk for therapeutic failure. We propose that isolates having an IMP zone diameter ≤20mm should be screened for the presence of MBL. The CDT is an alternative phenotypic assay to detect MBL production in our population in circumstances where PCR is not a feasible option. The high prevalence of isolates possessing MBL activity in the present study represents an emerging threat of complete resistance to carbapenemes among P. aeruginosa in Egypt.

Key words: Pseudomonas aeruginosa, imipenem-resistance, metallo-β-lactamase (MBL) detection, VIM, imipenem (IMP).