Molecular genotyping reveals multiple carbapenemase genes and unique bla_OXA-51-like (oxaAb) alleles among clinically isolated Acinetobacter baumannii from a Philippine tertiary hospital

Background: Acinetobacter baumannii continued to be an important Gram-negative pathogen of concern in the clinical context. The resistance of this pathogen to carbapenems due to the production of carbapenemases is considered a global threat. Despite the efforts to track carbapenemase synthesis among A. baumannii in the Philippines, local data on its molecular features are very scarce. This study aims to characterize A. baumannii clinical isolates from a Philippine tertiary hospital through genotyping of the pathogen's carbapenemase genes.

Methods: Antibiotic susceptibility profiling, phenotypic testing of carbapenemase production, and polymerase chain reaction assays to detect the different classes of carbapenemase genes (class A bla_KPC, class B bla_NDM, bla_IMP, bla_VIM, and class D bla_OXA-23-like, bla_{OXA-24/40-like}, bla_OXA-48-like, bla_OXA-51-like, ISAba1-bla_OXA-51-like, bla_OXA-58-like) were performed in all collected A. baumannii, both carbapenem resistant and susceptible (n = 52).

Results: Results showed that the majority of the carbapenem-resistant strains phenotypically produced carbapenemases (up to 84% in carbapenem inactivation methods) and possessed the ISAba1-bla_OXA-51-like gene complex (80%). Meanwhile, both carbapenem-resistant and carbapenem-susceptible isolates possessed multi-class carbapenemase genes including bla_NDM (1.9%), bla_VIM (3.9%), bla_{OXA-24/40-like} (5.8%), bla_OXA-58-like (5.8%), bla_KPC (11.5%), and bla_OXA-23-like (94.2%), which coexist with each other in some strains (17.3%). In terms of the intrinsic bla_OXA-51-like (oxaAb) genes, 23 unique alleles were reported (bla_OXA-1058 to bla_OXA-1080), the majority of which are closely related to bla_OXA-66. Isolates possessing these alleles showed varying carbapenem resistance profiles.

Conclusions: In summary, this study highlighted the importance of molecular genotyping in the characterization of A. baumannii by revealing the carbapenemase profiles of the pathogen (which may not be captured accurately in phenotypic tests), in identifying potent carriers of transferrable carbapenemase genes (which may not be expressed straightforwardly in antimicrobial susceptibility testing), and in monitoring unique pathogen epidemiology in the local clinical setting.