ACINETOBACTER BAUMANNII RESISTANT TO LAST-LINE ANTIBIOTICS: AN EMERGING THREAT IN THE WESTERN BALKANS

Abstract

Acinetobacter baumannii is considered one of the greatest threats to public health on a global scale. This Gram-negative pathogen causes severe infections, mostly of nosocomial origin, with a high mortality rate. In recent years, the rapid increase in the emergence and spread of antibiotic resistance in A. baumannii has significantly limited the effective therapeutic options against infections caused by this bacterium. The last-line antibiotics used in the treatment of multidrug-resistant (MDR) A. baumannii are carbapenems, tigecycline and polymyxins. However, resistance to these antibiotics is steadily increasing, especially to carbapenems, leading to an extensively drug-resistant (XDR) and even pandrug-resistant (PDR) phenotype of A. baumannii. In 2021, the European Centre for Disease Prevention and Control (ECDC) reported that resistance of Acinetobacter spp. to carbapenems reached 50% or more, mostly in Southern and Eastern European countries. Although the Western Balkans is a part of this region, detailed studies on the epidemiology and antibiotic resistance of A. baumannii are mainly limited to Serbia and Croatia. In most cases, carbapenem resistance in A. baumannii is due to the production of carbapenemases, in particular b-lactamases belonging to the class D known as oxacillinases. The studies from the Western Balkan countries revealed that besides the intrinsic blaOXA-51-like gene, the most prevalent acquired oxacillinase gene was the blaOXA- 24-like followed by the blaOXA-23-like, while the blaOXA-58-like and metallo- b-lactamase blaNDM-1 genes were less common. Although significantly lower compared to carbapenem-resistant, the number of A. baumannii isolates resistant to tigecycline and colistin is on a continual rise in the Western Balkans. As worldwide, the main mechanism conferring tigecycline resistance to A. baumannii from the Western Balkans was overexpression of efflux pumps. Also, the majority of reported alternations leading to colistin resistance in A. baumannii were found in the pmrCAB operon, which is responsible for the modification of the colistin target, LPS.