Multidrug resistance among Acinetobacter baumannii isolates from Iran: changes in antimicrobial susceptibility patterns and genotypic profile.

Background And Aim: Widespread multidrug-resistant Acinetobacter baumannii (MDR-AB) strains have limited therapeutic options for treating intensive care unit (ICU) patients with MDR-AB infection in Iran. We aimed to evaluate MDR-AB diversity and antimicrobial susceptibility in Tehran (Iran) to address the need for feasible and effective control approaches against severe MDR-AB infections.

Methods: We used amplified fragment length polymorphism (AFLP) and minimum inhibitory concentration (MIC) determinations to compare genotypic diversity and susceptibility patterns of 100 MDR-AB isolates from ICU patients in two medical centers in Tehran (Iran), from 2006 to 2011.

Results: Within 5 years, drastic genotypic changes occurred among MDR-AB isolates, and resistance to antimicrobials increased 0-30%. In 2011, 6-100% of isolates were resistant to every agent tested. All isolates remained susceptible to either minocycline or tobramycin, however, MIC50 concentrations against these agents increased. Novel international clone (IC) variants (not IC I-III types) comprised 36% MDR-AB isolates in 2011.

Conclusions: The MDR-AB population in Tehran is rapidly changing toward growing resistance to various antimicrobials, including colistin and tigecycline. Although increasing resistance to last-resort antimicrobials is alarming, simultaneous susceptibility of all MDR-AB isolates to some conventional antibiotics highlights the merits of investigating their synergistic activity against extended-spectrum and pandrug resistant A. baumannii. Integrating the novel Iranian MDR-AB IC variants into epidemiologic clonal and susceptibility profile databases can help global efforts toward the control of MDR-AB pandemic.