Acinetobacter baumannii: much more than a human pathogen

Acinetobacter baumannii is a major human nosocomial pathogen. Due to this, a significant amount of knowledge has been gained about human clinical isolates over a substantial period of time. More recently, studies have begun to pay attention to non-human isolates of A. baumannii. In reviewing these studies, we highlight some major trends. First, A. baumannii has been found in a variety of sources/hosts: from diverse types of animals, to food products, to plants and even aquatic environments. Second, considering the molecular epidemiology of A. baumannii, two scenarios are possible. One implies transmission between human and non-human populations, and this has been described in several international clones (ICs): IC1, IC2, IC5, IC7, and IC8. In the other scenario, human populations are well differentiated from non-human populations, and there is no exchange between them. Third, in terms of antibiotic resistance in the non-human populations, these populations tend to have fewer antibiotic resistance genes, mostly intrinsic in nature. However, when non-clinical bacterial populations come into closer contact with humans, the antibiotic resistance profiles of the non-human bacterial population become more similar to those of clinical populations. Also, there are some instances of non-human isolates showing extensive drug resistance phenotypes. By far, the least studied aspect is the virulence potential of A. baumannii from non-human sources. A small number of studies suggest that some non-human isolates can be as virulent as the human isolates. Finally, we discuss gaps in knowledge and future research avenues when considering non-human populations of A. baumannii and their relationship with human populations.