Investigation of metallo-beta-lactamase producing pseudomonas aeruginosa and acinetobacter baumannii isolates by imipenem-edta/meropenem-edta disk method and modified hodge test

Metallo-beta-lactamase (MBL) hydrolyzes all betalactam group antibiotics, including carbapenems, except for aztreonam. In order to prevent the spread of antibiotic resistance and to guide the treatment, carbapenem resistance types should be determined. The aim of this study is to investigate MBL production by using two different phenotypic methods in increasing imipenem and meropenem resistant Pseudomonas aeruginosa and Acinetobacter baumannii clinical isolates. Combined disk diffusion (CDT) test and Modified Hodge test (MHT) were performed to detect MBL of 51 A.baumannii and 40 P.aeruginosa clinical strains with resistant to carbapenem.The CDT:0.5 McFarland bacteria suspension was plated into the Muller Hinton Agar.The two imipenem disks (10μg) were placed on the medium surface with a minimum of 22 mm between them, 10 μl of EDTA was added onto one of the imipenem disks. The same method was applied for meropenem/EDTA.The results were considered to be positive if zone diameters of imipenem and meropenem disks were less than 7 mm from the zone diameters of EDTA disks.MHT: E.coli ATCC 25922 standard strain was spread on Müller Hinton Agar medium,10 μg of meropenem was placed in the center of the plate.Isolates were plated from the imipenem disk to the periphery. The deterioration of sensitivity zone clover leaf accepted as positive. In this study, 5 (12.5%) of 40 strains of P.aeruginosa were positive by MHT,and 21 (52.5%) were positive by imipenem/EDTA disk test and 23 (57.5%) by meropenem/EDTA disk test.43(84.3%) of 54 A.baumannii strains were detected by MHT, 35 (68.6%) were by imipenem/EDTA disk test and 46 (90.2%) were positive by meropenem/EDTA disk test. In our study,we found that MBL rates obtained with CDT and MHT were consistent with the studies performed in our country and abroad. In conclusion,antibiotic susceptibility profiles should be determined in order to prevent the rapidly growing resistance problem against antibiotics and MBL should be screened by different methods to prevent resistance spread. Antibiotics should be prescribed in according to antibiotic susceptibility test results for the treatment of A.baumannii and P.aeruginosa infections. Key Words: Pseudomonas aeruginosa, Acinetobacter baumannii, Metallo beta-lactamase