Global Epidemiology and Mechanisms of Resistance of Acinetobacter baumannii-calcoaceticus Complex

Acinetobacter baumannii-calcoaceticus complex (ABC) became an important group of organisms causing human infections worldwide. A small number of clones are responsible for the increased number of infections and resistance to numerous antimicrobial agents. We describe the current epidemiology and resistance mechanisms in ABC. Acinetobacter baumannii-calcoaceticus complex is the most commonly identified species in the genus Acinetobacter and it accounts for a large percentage of nosocomial infections, including bacteremia, pneumonia, and infections of the skin and urinary tract. A few key clones of A. baumannii-calcoaceticus are currently responsible for the dissemination of these organisms worldwide. Unfortunately, multidrug resistance is a common trait among these clones due to their unrivalled adaptive nature. A. baumannii-calcoaceticus isolates can accumulate resistance traits by a plethora of mechanisms, including horizontal gene transfer, natural transformation, acquisition of mutations, and mobilization of genetic elements that modulate expression of intrinsic and acquired genes.