Sleeper agents: asymptomatic Acinetobacter colonization and underlying mechanisms

Acinetobacter baumannii and other Acinetobacter species are a growing public health concern because they commonly cause healthcare-associated infections. Acinetobacter spp. are often multi-drug resistant, leading to significant morbidity and mortality. Therefore, understanding the reservoirs for Acinetobacter spp. in healthcare settings is particularly important to infection control. Acinetobacter spp. are known to asymptomatically colonize the human gut, skin, and respiratory flora, and recent work has found the prevalence of Acinetobacter colonization is high in patients in healthcare environments, such as hospitals and long-term care facilities. Patients colonized by A. baumannii are at increased risk of developing clinical infections, including by the same strains. Additionally, multiple studies report transmission of A. baumannii strains to other patients in the same healthcare setting. Recent mechanistic studies on A. baumannii gut colonization have found that the microbiota, host immunity, and diet contribute to colonization resistance in animal models. Here, we review the epidemiologic evidence for asymptomatic colonization as a clinically important reservoir for A. baumannii and examine the nascent study of the molecular mechanisms of Acinetobacter colonization. We discuss future prospects for understanding Acinetobacter colonization that may help develop strategies to support colonization resistance and prevent infections.