# Pseudomonas aeruginosa differentially influences antibiotic-resistant Staphylococcus aureus emergence and expansion in hyperglycemic environments

## TL;DR

In diabetic infections, Pseudomonas aeruginosa affects how Staphylococcus aureus becomes resistant to antibiotics, but this effect is less clear in real infections.

## Contribution

The study reveals that P. aeruginosa inhibits Rif-r S. aureus emergence in vitro under hyperglycemic conditions but not in diabetic mice during co-infection.

## Key findings

- P. aeruginosa exoproducts inhibit Rif-r S. aureus emergence in vitro under glucose-replete conditions.
- Diabetic mice show similar Rif-r S. aureus burdens during mono- and co-infection with P. aeruginosa.
- The diabetic infection microenvironment supports Rif-r S. aureus emergence despite P. aeruginosa's influence.

## Abstract

Individuals with poorly controlled diabetes mellitus often develop multispecies skin and soft tissue infections, with Staphylococcus aureus and Pseudomonas aeruginosa among the most prevalent bacteria isolated from infection sites worldwide. Diabetic infections are recalcitrant to conventional antibiotic regimens and may be a reservoir for emergent antibiotic-resistant bacterial strains. Supporting this, we have previously shown that rifampicin treatment elicits the emergence and expansion of rifampicin-resistant (Rif-r) S. aureus only in diabetic mice, potentially due to greater bacterial outgrowth increasing the frequency of resistance-conferring mutations. However, whether S. aureus exhibits altered resistance outcomes during multispecies diabetic infections is unclear. During co-infection with P. aeruginosa under normoglycemic conditions, S. aureus exhibits reduced growth and altered susceptibility to several antibiotics. In contrast, we previously observed that glucose availability allows S. aureus to largely overcome P. aeruginosa-mediated growth inhibition. Here, we explored S. aureus resistance outcomes under hyperglycemic conditions in the context of co-infection with P. aeruginosa during antibiotic challenge. We found that P. aeruginosa exoproducts regulated by the Pseudomonas quinolone signal quorum sensing system inhibit the emergence but not the expansion of Rif-r S. aureus in vitro under glucose-replete conditions. In contrast, we recovered equivalent Rif-r S. aureus burdens from diabetic mice during mono- and co-infection with P. aeruginosa. These results demonstrate that the diabetic infection microenvironment is conducive to emergent Rif-r S. aureus despite external pressures elicited by P. aeruginosa.

Poorly controlled diabetes mellitus confers an increased susceptibility to bacterial infections, with Staphylococcus aureus and Pseudomonas aeruginosa frequently isolated from diabetic skin wounds. S. aureus readily develops antibiotic resistance during diabetic mono-infection under antibiotic pressure, but whether this occurs during diabetic co-infection is unclear. Under normoglycemic conditions, secreted P. aeruginosa factors alter S. aureus tolerance to several antibiotics. Here, we show that these P. aeruginosa exoproducts further inhibit the emergence of antibiotic-resistant S. aureus regardless of glucose availability in vitro, but this does not occur during subcutaneous co-infection in diabetic mice. These results provide initial insights regarding conditions that may inhibit S. aureus resistance development in hyperglycemic environments but underscore the influence of the host infection microenvironment in shaping resistance outcomes.