From the wound to the bench: exoproteome interplay between wound-colonizing <i>Staphylococcus aureus</i> strains and co-existing bacteria

Wound-colonizing microorganisms can form complex and dynamic polymicrobial communities where pathogens and commensals may co-exist, cooperate or compete with each other. The present study was aimed at identifying possible interactions between different bacteria isolated from the same chronic wound of a patient with the genetic blistering disease epidermolysis bullosa (EB). Specifically, this involved two different isolates of the human pathogen <i>Staphylococcus aureus</i>, and isolates of <i>Bacillus thuringiensis</i> and <i>Klebsiella oxytoca</i>. Particular focus was attributed to interactions of <i>S. aureus</i> with the two other species, because of the high staphylococcal prevalence among chronic wounds. Intriguingly, upon co-cultivation, none of the wound isolates inhibited each other's growth. Since the extracellular proteome of bacterial pathogens is a reservoir of virulence factors, the exoproteomes of the staphylococcal isolates in monoculture and co-culture with <i>B. thuringiensis</i> and <i>K. oxytoca</i> were characterized by Mass Spectrometry to explore the inherent relationships between these co-exisiting bacteria. This revealed a massive reduction in the number of staphylococcal exoproteins upon co-culturing with <i>K. oxytoca</i> or <i>B. thuringiensis</i>. Interestingly, this decrease was particularly evident for extracellular proteins with a predicted cytoplasmic localization, which were recently implicated in staphylococcal virulence and epidemiology. Furthermore, our exoproteome analysis uncovered potential cooperativity between the two different <i>S. aureus</i> isolates. Altogether, the observed exoproteome variations upon co-culturing are indicative of unprecedented adaptive mechanisms that set limits to the production of secreted staphylococcal virulence factors.