Role of plasmid carrying bla(NDM) in mediating antibiotic resistance among Acinetobacter baumannii clinical isolates from Egypt

We investigated antibiotic resistance levels among bla(NDM)-positive (n = 9) and -negative (n = 65) A. baumannii clinical isolates collected in 2010 and 2015 from Alexandria Main University Hospital, Egypt using disc diffusion and minimum inhibitory concentration (MIC) determination. Plasmids from bla(NDM)-positive isolates were transformed into a carbapenem-susceptible A. baumannii (CS-AB) isolate to assess the role of plasmid transfer in mediating carbapenem resistance. Imipenem, meropenem, and ertapenem MIC90 values against bla(NDM)-positive isolates were 128, > 256, and 256 µg/mL, respectively. Plasmid isolation and polymerase chain reaction revealed that bla(NDM) was plasmid mediated. The plasmids were electroporated into the cells of a CS-AB isolate at an efficiency of 1.3 × 10(–8) to 2.6 × 10(–7), transforming them to bla(NDM)-positive carbapenem-resistant cells with an imipenem MIC increase of 256-fold. In addition to carbapenem resistance, the bla(NDM)-positive isolates also exhibited higher levels of cephalosporins, tetracycline, aminoglycosides, fluoroquinolones, and colistin resistance than the bla(NDM)-negative isolates. Acquisition of bla(NDM)-carrying plasmids dramatically increased imipenem resistance among A. baumannii isolates. Intriguingly, bla(NDM)-positive isolates also showed a high degree of resistance to antibiotics of different classes. The potential co-existence of different resistance determinants on A. baumannii plasmids and their possible transfer owing to the natural competence of the pathogen are especially alarming. More effective infection control and antibiotic stewardship programs are needed to curb the spread and treat such infections in both hospital and community settings. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-020-2157-y) contains supplementary material, which is available to authorized users.