Staphylococcus aureus Alters Growth Activity, Autolysis, and Antibiotic Tolerance in a Human Host-Adapted Pseudomonas aeruginosa Lineage

Abstract

Interactions among members of polymicrobial infections or between pathogens and the commensal flora may determine disease outcomes. Pseudomonas aeruginosa and Staphylococcus aureus are important opportunistic human pathogens and are both part of the polymicrobial infection communities in human hosts. In this study, we analyzed the in vitro interaction between S. aureus and a collection of P. aeruginosa isolates representing different evolutionary steps of a dominant lineage, DK2, that have evolved through decades of growth in chronically infected patients. While the early adapted P. aeruginosa DK2 strains outcompeted S. aureus during coculture on agar plates, we found that later P. aeruginosa DK2 strains showed a commensal-like interaction, where S. aureus was not inhibited by P. aeruginosa and the growth activity of P. aeruginosa was enhanced in the presence of S. aureus. This effect is mediated by one or more extracellular S. aureus proteins greater than 10 kDa, which also suppressed P. aeruginosa autolysis and prevented killing by clinically relevant antibiotics through promoting small-colony variant (SCV) formation. The commensal interaction was abolished with S. aureus strains mutated in the agr quorum sensing system or in the SarA transcriptional virulence regulator, as well as with strains lacking the proteolytic subunit, ClpP, of the Clp protease. Our results show that during evolution of a dominant cystic fibrosis lineage of P. aeruginosa, a commensal interaction potential with S. aureus has developed. M ost microbial species are embedded within mixed-species communities where mutualistic, antagonistic, and neutral interactions within the community control behaviors and activities of the individual species. In relation to microbial infections, it is becoming clear that interactions between bacterial pathogens and other microbial species present at the infection site (either coinfecting pathogens or commensal bacteria) can result in altered pathogen behaviors such as enhanced virulence (1, 2), biofilm formation (3), and antibiotic tolerance (4), which may influence disease progression and clinical outcome of the infection. Despite advances in elucidating the molecular details underlying microbial interactive processes, the extent to which evolutionary processes remodel interspecies interactions during the course of infection and therapy is currently not understood. Thus, studies of interaction patterns between species and the evolution within polymicrobial infections are a critical first step toward developing novel interference strategies against such infections.Chronic cystic fibrosis (CF) airway infections caused by the bacterium Pseudomonas aeruginosa offer optimal opportunities to study evolutionary dynamics within a natural environment because of systematic routine sampling of the ecosystem over extended time periods (years) and because of the well-characterized ecological properties of the system (5). We have recently determined the genetic basis of adaptation in a highly successful P. aeruginosa ...

Bacterial competition and quorum‐sensing signalling shape the eco‐evolutionary outcomes of model in vitro phage therapy

“…For example, S. maltophilia has been observed to influence P. aeruginosa biofilm architecture and protein synthesis (Ryan et al. 2008), while P. aeruginosa has been shown to have negative effects on S. aureus due to upregulation of antistaphylococcal substances such as pyocyanin and phenazine (Michelsen et al., 2014). Even though S. aureus has not been shown to have direct negative effects on P. aeruginosa , the S. aureus presence has been shown to favour the increase in the frequency of QS‐deficient mutants (Harrison et al., 2008).…”

“…Even though S. aureus has not been shown to have direct negative effects on P. aeruginosa , the S. aureus presence has been shown to favour the increase in the frequency of QS‐deficient mutants (Harrison et al., 2008). In line with this study, it has been found that a QS‐positive PAO1 strain interacts more negatively with S. aureus compared to a QS‐negative lasR strain (Michelsen et al., 2014). Recent evidence suggests that reduced antagonism between S. aureus on P. aeruginosa lasR mutants could be due to metabolic divergence (Frydenlund Michelsen et al., 2015).…”

Iron Depletion Enhances Production of Antimicrobials by Pseudomonas aeruginosa

“…This report additionally found that agtR, a response regulator involved in metabolite sensing and uptake, was required for this activity, suggesting metabolite sensing as a possible means for bacterial cross talk. An additional report indicated that S. aureus secretes one or more proteins to manipulate the growth characteristics of P. aeruginosa (53). It is therefore likely that iron-regulated AQ production is not the sole driver of interactions between these two bacterial species.…”

Interactions between Pseudomonas aeruginosa and Staphylococcus aureus during co-cultivations and polymicrobial infections

“…Co-culture with S. aureus similarly promotes selection of P. aeruginosa SCVs, resulting in increased survival and antimicrobial tolerance of P. aeruginosa isolates in the CF lung (Michelsen et al 2014). This interaction is dependent upon the Agr quorum sensing system, which regulates the expression of multiple virulence factors in S. aureus (Novick 2003).…”

“…Analysis of the DK-2 lineage of P. aeruginosa , isolated from multiple CF patients between 1973 and 2008 (Yang et al 2011), showed that this strain's ability to inhibit S. aureus growth was reduced as it adapted to the CF lung environment (Michelsen et al 2014). A separate analysis of 24 P. aeruginosa isolates from 8 distinct CF patients at multiple stages of chronic lung infection showed a similar reduction in the ability of P. aeruginosa to inhibit S. aureus growth (Baldan et al 2014).…”