Phenotypic and genotypic characterization of carbapenem-resistant Acinetobacter baumannii isolates from Egypt

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Abstract Background Antibiotic use is largely under-regulated in Egypt leading to the emergence of resistant isolates. Carbapenems are last resort agents to treatAcinetobacter baumanniiinfections resistant to other classes of antibiotics. However, carbapenem-resistant isolates are emerging at an alarming rate. This study aimed at phenotypically and molecularly characterizing seventy four carbapenem-unsusceptibleA. baumanniiisolates from Egypt to detect the different enzymes responsible for carbapenem resistance. Methods Carbapenemase production was assessed by a number of phenotypic methods: modified Hodge test (MHT), carbapenem inactivation method (CIM), combined disc test (CDT), CarbAcineto NP test and boronic acid disc test. Polymerase chain reaction (PCR) was used to screen the isolates for the presence of some genes responsible for resistance to carbapenems, as well as some insertion sequences. Results PCR amplification of class D carbapenemases revealed the prevalence ofblaOXA-51andblaOXA-23in 100% of the isolates and ofblaOXA-58in only one isolate (1.4%).blaVIMandblaNDM-1belonging to class B metallo-β-lactamases were present in 100 and 12.1% of the isolates, respectively. The prevalence of ISAba1, ISAba2and ISAba3was 100, 2.7 and 4.1%, respectively. None of the tested isolates carriedblaOXA-40,blaIMP,blaSIM,blaSPM,blaGIMor the class AblaKPC. Taking PCR as the gold standard method for the detection of different carbapenemases, the sensitivities of the MHT, CIM, CDT, CarbAcineto NP test and boronic acid disc/imipenem or meropenem test for this particular collection of isolates were 78.4, 68.9, 79.7, 95.9, and 56.8% or 70.3%, respectively. Conclusions The widespread detection of carbapenem-resistantA. baumannii(CR-AB) has become a real threat to the efficacy of treatment regimens. Among the studied cohort of CR-AB clinical isolates,blaOXA-51,blaOXA-23andblaVIMwere the most prevalent, followed byblaNDM-1andblaOXA-58. The genotypic detection of carbapenemases among CR-AB clinical isolates using PCR was most conclusive, followed closely by the phenotypic testing using CarbAcineto NP test.

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