ABSTRACT
Detection of metallo-beta-lactamases [MBLs] and extended spectrum-beta-lactamases [ESBLs] among Gram negative bacilli [GNB] is crucial for the optimal treatment of patients and to control spread of resistance. However, NCCLS documents do not contain a method for detection of MBL producing isolates. Lack of sufficient reports from Egypt indicated the need for this study to determine the proportion of MBL producers among GNB isolated from clinical multi-drug resistant [MDR] pathogens. We also attempted to assess the efficiency of several phenotypic tests for the rapid and convenient detection of MBLs among Pseudomonas and Acinetobacter spp. The efficiency of testing ceftazidime [CAZ] resistant versus imipenem [IMP] resistant pathogens was also compared. A total of 70 CAZ intermediate/resistant GNB were identified and tested for antibiotic sensitivity by Vitek 2 Automated System [bioMérieux]. Screening for ESBLs was performed by Oxoid combined test [CD02] and confirmed by Vitek 2. The phenotypic detection of MBL production among Pseudomonas and Acinetobacter isolates was performed by modified Hodge test, EDTA-disk synergy test [EDST], IMP-EDTA combined disk test [CDT] and E-test MBL strips. Negative control strain [P. aeruginosa ATCC 27853] was included in the tests. Of the 70 GNB pathogens, 25[35.7%] were ESBL producers mainly Escherichia coli [E. coli] and Klebsiella pneumoniae [K. pneumoniae], while 8[11.4%] P. aeruginosa isolates were IMP resistant. Their MIC was 16ug/ml as confirmed by E-test. None of the Acinetobacters showed resistance to IMP. Isolates were considered as MBL producers when three of the phenotypic tests were positive. Both DST and CDT [7/8] were superior to Hodge and E-tests [4/8] for detection of MBL production. One IMP resistant isolate was negative by all tests suggesting non-MBL production. None of the IMP resistant isolates was an ESBL producer. In conclusion the majority of our IMP resistant P. aeruginosa isolates seemed to be MBL producers. Genetic confirmation and analysis of MBL producers is mandatory for positive isolates screened by phenotypic tests. Among the latter DST and CDT proved to be more rapid and convenient tests for their detection in the clinical laboratory. Testing IMP resistant rather than CAZ resistant isolates could reduce screening work for MBL detection. Colistin may be recommended for treatment of serious infections caused by MDR MBL positive P. aeruginosa