Appl Environ Microbiol. 2021 Jul 7:AEM0074721. doi: 10.1128/AEM.00747-21. Online ahead of print.
We here sought to test the resistance of human pathogens to unaltered environmental free-living amoebae. Amoebae are ubiquitous eukaryotic microorganisms and important predators of bacteria. Environmental amoebae have also been proposed to serve both as potential reservoir and training ground for human pathogens. However, studies addressing their relationship with human pathogens often rely on a few domesticated amoebae selected to feed on rich medium, thereby possibly overestimating the resistance of pathogens to these predatory phagocytes. From an open-air composting site, we recovered over a hundred diverse amoebae able to feed on Acinetobacter baumannii and Klebsiella pneumoniae. In a standardized and quantitative assay for predation, the isolated amoebae showed a broad predation spectrum, killing clinical isolates of A. baumannii, K. pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. Interestingly, A. baumannii, previously reported to resist predation by laboratory strains of Acanthamoeba, is efficiently consumed by closely related environmental amoebae. The isolated amoebae are capable of feeding on highly virulent carbapenem-resistant or methicillin-resistant clinical isolates. In conclusion, the natural environment is a rich source of amoebae with broad-spectrum bactericidal activities, including against antibiotic resistant isolates. Importance Free-living amoebae have been proposed to play in important role in hosting and disseminating various human pathogens. The resistance of human pathogens to predation by amoebae is often derived from in vitro experiments using model amoebae. We here sought to isolate environmental amoebae and test their predation on diverse human pathogens, with results that challenge conclusions based on model amoebae. We found that the natural environment is a rich source of diverse amoebae with broad-spectrum predatory activities against human pathogens, including highly virulent and antibiotic resistant clinical isolates.