Screening for Metallo- ß-Lactamase Production by Pseudomonas Aeruginosa Isolated from Clinical Specimens

Background: Pseudomonas aerugonisa is an important nosocomial pathogen. P. aeruginosa posses several virulence factors including resistance genes which encode expression of many mechanisms of resistance. One of these mechanisms is the production of metallo-ß-lactamase (MBL) which tenders the isolates resistant to carbapenems. Patients and Methods: This work was performed to study the prevalence of MBL production among clinical isolates of P. aeruginosa, to study the clinical characteristics of the patients infected with MBL producing strains and to evaluate rapid and cost beneficial techniques for detection of MBL production in P. aeruginosa isolates. Results and Conclusion: Fifty ceftazidime resistant P. aeruginosa isolates were selected from different units. We evaluated the performance of 2 tests: the double disk synergy method containing CuCl2, FeCl2, EDTA and thiol compounds and IPM-EDTA disk method in comparison to E-test for detection of MBL as the gold standard. Results showed a high prevalence of MBL production (62%). Infection with MBL producing strains was highest among neonates with blood stream and lower respiratory tract infections (p = 0.007). Sepsis and respiratory tract infections presented the most significant infections (p = 0.007). No statistical correlation was found between underlying disease, the use of indwelling devices or the intake of a particular type of antibiotic and the production of MBL enzyme. The use of CAZ resistant strains (rather than IPM resistant strains) was more valuable in detection of MBL production since it gave lower rates of false negative results. The IPM-EDTA disk method results were more sensitive than those of the double disk method (87 and 77.4% respectively). In addition, the former was found to be more simple, rapid, specific and cost-beneficial method than the latter.