CONICET | Buscador de Institutos y Recursos Humanos

Staphylococcus aureus and Pseudomonas aeruginosa are bacterial species that provoke infections in patients with chronic deasses, after surgery or long-term catheter usage. Bacteria can form communities and co-infections and lead to worse patient prognosis. In general terms the interaction between these species is thought to be antagonist but in-vivo studies suggest it is a far more complex. Mutations were described in both species during individual infections, but no study analyzed the effect during co-infections. Our hypothesis is that there are mutations in S. aureus that can modify the interaction with P. aeruginosa. To detect new genes involved in S. aureus-P. aeruginosa interaction we use the Nebraska Library that comprises an ordered collection of S. aureus mutant clones with a transposon (Tn) interrupting non-essential genes and P. aeruginosa PAO1 with a fluorescent protein under a constitutive promotor. We performed a 2000 clones from the Nebraska Library screening to detect modifications in P. aeruginosa PAO1 growth when was co-culture with the wild type S. aureus USA300 strain or the mutant clones. Our results showed S. aureus clones that presented an altered interaction with P. aeruginosa were mutated in genes of involved in envelope biosynthesis, iron and energy metabolisms, adhesion and biofilm formation and hypothetical proteins. Among them, we studied the survival of S. aureus lrgA and upp mutant strains, both genes related with envelope biosynthesis and its modifications. We showed 5 times decrease in survival of lrgA strain in co-cultures of 24 hours when P. aeruginosa was present in comparison with the USA300 under aerobic conditions but interestingly a 2-times increase of survival under low oxygen conditions. Survival of upp also showed differences depending on oxygen availability, while under aerobic conditions survival was 10 times lower in comparison with the wild type strain at microaerobiosis the survival was similar between both strains. A bioinformatic analysis of upp gene was conserved among different S. aureus strains and a phylogenetic analysis using MEGA software showed a clustering similar to that observed for the rRNA gene. On the contrary, for lrgA analysis we observed that while 16S coding gene from S. aureus form a cluster with other human commensal Staphylococci species (such as S. capiatis and S. epidermidis), LrgA sequence form a cluster with other pathogenic Stphylococci like S. feli (produces infections in cats), S. intermedius and S. pseudointermedius (cause infection in dogs) and S. delphini (causes infections in horses among other animals), suggesting a role in virulence. We will focus on these gene in future in-vitro and in-vivo interaction experiments.