Molecular epidemiologic characterization of infection outbreaks caused by carbapenemresistant Acinetobacter baumannii

Abstract:

ObjectiveTo investigate the epidemiologic characteristics and drug resistance mechanism of carbapenemresistant Acinetobacter baumannii (CRAB) isolated from a hospital, so as to guide prevention and control of  healthcareassociated infection(HAI).MethodsA total of 32 CRAB strains  isolated clinically from January 2010 to May 2012 were performed  genotyping by randomly amplified polymorphic DNA fingerprinting, and epidemiological analysis was conducted; carbapenemase were screened by modified Hodge test and EDTAdisk synergy test. The effect of efflux pump inhibitor carbonyl cyanide mchlorophenyl hydrazone （CCCP）on minimum inhibitory concentration of meropenem  was detected, efflux pump positive strains were screened.Results32 CRAB strains displayed 9 kinds of genotypes,  type A, H, I,B, E, and other types were 10,7,4,3,3,and 1-2 isolates respectively. From March to May,2012, 11 CRAB strains were isolated,  type H,I,and A were 7,3, and 1 isolates respectively. 21  (65.63%) CRAB strains expressed oxacillinase (OXA23), and were positive in  modified Hodge test (including 11 strains isolated in MarchMay,2012); Except 1 isolate was detected New DelhiMetallo1(NDM1), all other strains were negative for metallolactamase test; the presence of CCCP slightly changed the  MIC of meropenem to CRAB,all were negative for phenotype of efflux pump. CRAB strains were mainly isolated from patients in intensive care unit(13 isolates)  and neurology department(7 isolates).ConclusionThe outbreak of HAI of the clone with identical genotype occurred in this ICU between March and May,2012. Carbapenemresistance mechanism of A. baumannii can be attributed to the expression of OXA23, and meropenemresistance is not related to the efflux pump, CRAB strain expressing NDM1 has been detected in this hospital.