Subinhibitory Cefotaxime and Levofloxacin Concentrations Contribute to Selection of Pseudomonas aeruginosa in Coculture with Staphylococcus aureus.

Bacterial species in the polymicrobial community evolve interspecific interaction relationships to adapt to the survival stresses imposed by neighbors or environmental cues. Pseudomonas aeruginosa and Staphylococcus aureus are two common bacterial pathogens frequently coisolated from patients with burns and respiratory disease. Whether the application of commonly used antibiotics influences the interaction dynamics of the two species still remains largely unexplored. By performing a series of on-plate competition assays and RNA sequencing-based transcriptional profiling, we showed that the presence of the cephalosporin antibiotic cefotaxime or the quinolone antibiotic levofloxacin at subinhibitory concentration contributes to selecting P. aeruginosa from the coculture with S. aureus by modulating the quorum-sensing (QS) system of P. aeruginosa. Specifically, a subinhibitory concentration of cefotaxime promotes the growth suppression of S. aureus by P. aeruginosa in coculture. This process may be related to the increased production of the antistaphylococcal molecule pyocyanin and the expression of lasR, which is the central regulatory gene of the P. aeruginosa QS hierarchy. On the other hand, subinhibitory concentrations of levofloxacin decrease the competitive advantage of P. aeruginosa over S. aureus by inhibiting the growth and the las QS system of P. aeruginosa. However, pqs signaling of P. aeruginosa can be activated instead to overcome S. aureus. Therefore, this study contributes to understanding the interaction dynamics of P. aeruginosa and S. aureus during antibiotic treatment and provides an important basis for studying the pathogenesis of polymicrobial infections. IMPORTANCE Increasing evidence has demonstrated the polymicrobial characteristics of most chronic infections, and the frequent communications among bacterial pathogens result in many difficulties for clinical therapy. Exploring bacterial interspecific interaction during antibiotic treatment is an emerging endeavor that may facilitate the understanding of polymicrobial infections and the optimization of clinical therapies. Here, we investigated the interaction of cocultured P. aeruginosa and S. aureus with the intervention of commonly used antibiotics in clinic. We found that the application of subinhibitory concentrations of cefotaxime and levofloxacin can select P. aeruginosa in coculture with S. aureus by modulating P. aeruginosa QS regulation to enhance the production of antistaphylococcal metabolites in different ways. This study emphasizes the role of the QS system in the interaction of P. aeruginosa with other bacterial species and provides an explanation for the persistence and enrichment of P. aeruginosa in patients after antibiotic treatment and a reference for further clinical therapy.