Antibiotic-resistant Acinetobacter calcoaceticus-baumannii complex in the environment: a narrative review

Acinetobacter calcoaceticus-baumannii complex comprises of both environmental and pathogenic bacterial species. Pathogenic species are responsible for nosocomial infections, which are increasingly difficult to treat due to growing resistance to antibiotics. In addition to nosocomial settings, ACB complex has also been found in other environmental niches, including animals, food, soil, and water, where human activity has contributed to the development of antibiotic resistance. For instance, improper disposal of solid waste and release of wastewater effluent carrying antibiotic-resistant pathogens have introduced antibiotic resistance genes into the natural environment. Additionally, soil and water environments near agricultural operations are hotspots for ACB complex strains and antibiotic resistance. Antibiotic resistant ACB complex are also transmitted through food production system. While antibiotic resistance level in strains from healthy animals is low, it can be highly prevalent on meat. Meat and produce fertilized by manure from antibiotic-treated animals are a pathway for transmission of ACB complex back to human and clinical environments, reflecting the interconnectedness of humans, animals, and the environment. This review has revealed research gaps, particularly on non-Acinetobacter baumannii ACB complex species in the environment. Understanding the "One Health" dimension of these important nosocomial pathogens is critical for informing policies on antibiotic use, agriculture, and waste management to reduce and prevent the emergence of antibiotic resistant strains.