High Prevalence of ST502 Carrying an OXA-24 Carbapenemase gene in Carbapenem-Nonsusceptible Acinetobacter baumannii-calcoaceticus Isolates in Romania

Background: Acinetobacter baumannii can cause difficult-to-treat infections because it can acquire extensive antimicrobial resistance mechanisms. We aim to describe the antimicrobial resistance pattern and the genetic basis of carbapenem-nonsusceptible A. baumannii isolates in a University Hospital in Romania, a country where multidrug-resistant A. baumannii is widespread.Methods: We collected 104 consecutive meropenem-nonsusceptible A. baumannii isolates from 104 patients (36% female, mean age [SD] of 63 [16] years) between May 2015 and August 2017 from a large tertiary center in Romania. Whole-genome sequencing of representative isolates from amplified fragment length polymorphism clusters was used to determine clonality and resistance patterns.Results: All isolates were resistant to piperacillin/tazobactam, ceftazidime, and ciprofloxacin; 88.5% to gentamicin; and 90.4% to trimethoprim/sulfamethoxazole. In contrast, 79.8% and 99.0% were susceptible to tobramycin and colistin, respectively. The only isolate resistant to colistin had an minimum inhibitory concentration (MIC) of >= 16 mg/L. The bla(OXA-24) gene was detected in 79.1% and bla(OXA-23) in 20.9% of the isolates. In one isolate, bla(OXA-23) was copresent with bla(OXA-24). ST502 (Oxford scheme) was the most prevalent sequence type and was exclusively associated with bla(OXA-24).Conclusions: ST502 associated with bla(OXA-24) was frequently observed in the region where carbapenem-nonsusceptible A. baumannii was found to be endemic. In these isolates, tobramycin and colistin might be the remaining therapeutic options. Due to differences in gentamicin and tobramycin resistance in these isolates, surveillance data should not group gentamicin, tobramycin, and amikacin together as aminoglycosides.

Automated summary

In this study, we collected 104 meropenem-nonsusceptible A. baumannii isolates from a University Hospital in Romania. We found that these isolates exhibited a high level of resistance to multiple antimicrobial agents, indicating the presence of extensive antimicrobial resistance mechanisms. Whole-genome sequencing revealed the prevalence of the bla(OXA-24) gene and the association of ST502 sequence type with bla(OXA-24) in these isolates. Tobramycin and colistin were identified as potential therapeutic options.