Decrease of Virulence by in a Model.

Social bacterial interactions are considered essential in numerous infectious diseases, particularly in wounds. Foot ulcers are a common complication in diabetic patients and these ulcers become frequently infected. This infection is usually polymicrobial promoting cell-to-cell communications. is the most prevalent pathogen isolated. Its association with , commensal Gram-positive cocci, is frequently described. The aim of this study was to assess the impact of co-infection on virulence of both and strains in a model. To study the host response, qRT-PCRs targeting host defense genes were performed. We observed that strains harbored a very low (LT50: 5.7 days ± 0.4) or an absence of virulence (LT50: 6.9 days ± 0.5). In contrast, strains (LT50: 2.9 days ± 0.4) were significantly more virulent than all ( < 0.001). When and strains were associated, significantly reduced the virulence of the strain in nematodes (LT50 between 4.4 and 5.2 days; < 0.001). To evaluate the impact of these strains on host response, transcriptomic analysis showed that the ingestion of led to a strong induction of defense genes (, and ) while did not. No statistical difference of host response genes expression was observed when were infected with either alone or with + . Moreover, two well-characterized virulence factors ( and ) present in were down-regulated when were co-infected with . This study showed that decreased the virulence of without modifying directly the host defense response. Factor(s) produced by this bacterium modulating the staphylococci virulence must be investigated.