The Acinetobacter baumannii-calcoaceticus complex: virulence and antimicrobial resistance

Abstract

Objective: To gather information regarding the Acinetobacter baumannii – calcoaceticus complex, including its characteristics, virulence, and antimicrobial resistance. To characterize genes associated with these factors and discuss the increasing bacterial resistance to antimicrobial agents. Literature review: Acinetobacter is among the most frequent pathogens associated with Healthcare-Associated Infections (HAIs), presenting a high prevalence of multidrug-resistant (MDR) isolates. A. baumannii was one of the bacterial species most frequently identified during the COVID-19 pandemic. Virulence factors contribute to bacterial survival in abiotic environments, favoring its persistence in hospital settings. Resistant isolates producing beta-lactamases have been reported worldwide. Aminoglycosides became a therapeutic alternative; however, resistance to these drugs rendered them ineffective in 50–87% of isolates. Tetracyclines were considered effective, although resistance rates varied considerably, remaining below 20% in Europe and exceeding 70% in African countries. Polymyxins B and E have been reintroduced into clinical practice; nevertheless, continuous use of these drugs has increased the number of resistant isolates. Consequently, combination antimicrobial therapy has been extensively investigated, although inconsistencies among studies hinder the establishment of standardized therapeutic protocols. Final considerations: The high capacity of Acinetobacter to persist in hospital environments, combined with the elevated incidence of MDR isolates and the difficulty in establishing effective treatment protocols, highlights the critical need for the development of new therapeutic strategies.