Introduction: While some aspects of the host–pathogen interface are common to all infection sites, localized environments can have unique factors specific to the body site. Chronic infections are often polymicrobial in nature, with great variation in microbial communities between patients. Additionally, nutrient compositions vary at infection sites across the body. Our research demonstrates that the antibiotic susceptibilities of pathogens can dramatically shift depending on nutritional composition and the presence of other microorganisms.
Methods: Antimicrobial susceptibility testing (AST) was performed for Enterococcus faecalis in Cation-Adjusted Mueller–Hinton Broth (CAMHB), both for the organism alone and the organism grown in a polymicrobial community containing three other common wound pathogens (Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii). We then performed the same AST in an anaerobic chamber to create an environment without oxygen. Further AST was then performed in media mimicking different body sites (Lubbock Chronic Wound Media (LCWM) and Synthetic Cystic Fibrosis Media 2 (SCFM2)).
Results: Our results demonstrate that Enterococcus faecalis grown in a polymicrobial community in CAMHB displayed increased susceptibility to gentamicin. We believe this is due to heme cross-feeding allowing more gentamicin to enter the cell via altered proton motive force. However, performing the same AST in anaerobic conditions reversed this phenotype. When gentamicin AST was performed in media more representative of different body sites (LCWM and SCFM2), the AST results differed from the CAMHB results. In SCFM2, E. faecalis no longer demonstrated increased susceptibility in the community. However, in LCWM, E. faecalis displayed increased susceptibility to gentamicin regardless of community presence.
Conclusions: Overall, our results demonstrate that environmental conditions play a role in determining an individual bacterium’s antibiotic susceptibility. By accounting for the infection environment when determining susceptibilities, we can prescribe more effective treatments and improve patient outcomes.
