Production of carbapenemases in imipenem-resistant gram-negative rods

Objective To study the production of carbapenemases in carbapenem-resistant gram- negative rods.Methods Antimicrobial susceptibility testing was performed by agar dilution method.Carbapenemases were screened by Modified Hodge Test and EDTA-disk synergy test.The encoding genes of MBLs and oxacillinase were amplified and analyzed by PCR and DNA sequencing.Results Two of the 75 Pseudomonas aeruginosa isolates and 10 Pseudomonas spp.strains were found to produce VIM-2.All the 6 isolates of carbapenem-resistant Acinetobacter spp.were positive for OXA-23.All the 8 strains of Citrobacter freundii produced a new subtype of IMP.Conclusion The production of carbapenemases is among the main mechanisms of imipenem resistance in Citrobacter freundii and Acinetobacter spp.,while in Pseudomonas aeruginosa it is not the main mechanism.