Coexistence with Pseudomonas aeruginosa alters Staphylococcus aureus transcriptome, antibiotic resistance and internalization into epithelial cells

Abstract

Cystic fibrosis (CF) is the most common life-threatening genetic disease among Caucasians. CF patients suffer from chronic lung infections due to the presence of thick mucus, caused by cftr gene dysfunction. The two most commonly found bacteria in the mucus of CF patients are Staphylococcus aureus and Pseudomonas aeruginosa. It is well known that early-infecting P. aeruginosa strains produce anti-staphylococcal compounds and inhibit S. aureus growth. More recently, it has been shown that late-infecting P. aeruginosa strains develop commensal-like/coexistence interaction with S. aureus. The aim of this study was to decipher the impact of P. aeruginosa strains on S. aureus. RNA sequencing analysis showed 77 genes were specifically dysregulated in the context of competition and 140 genes in the context of coexistence in the presence of P. aeruginosa. In coexistence, genes encoding virulence factors and proteins involved in carbohydrates, lipids, nucleotides and amino acids metabolism were downregulated. On the contrary, several transporter family encoding genes were upregulated. In particular, several antibiotic pumps belonging to the Nor family were upregulated: tet38, norA and norC, leading to an increase in antibiotic resistance of S. aureus when exposed to tetracycline and ciprofloxacin and an enhanced internalization rate within epithelial pulmonary cells. This study shows that coexistence with P. aeruginosa affects the S. aureus transcriptome and virulence.

Trophic cooperation promotes bacterial survival ofStaphylococcus aureusandPseudomonas aeruginosa

“…This trophic specialization commonly leads to the slower growth of chronic isolates and thus less competitive 4 behavior regarding shared resources (16). Several independent studies observed this state of coexistence between S. aureus and P. aeruginosa isolated from chronic infections (10,15,17,18). Briaud et al recently demonstrated that this interaction pattern appears to be more frequent than expected.…”

“…As schematized in Figure S1A, interaction state was determined for each pair by growth inhibition tests on Tryptic Soy Agar (TSA) and in liquid cultures (18). As previously described, coexistence was characterized by: (i) the absence of inhibition halo on agar tests, and (ii) similar growth in mono and co-cultures for 8 hours (18).…”

“…Genome sequencing and annotation of PA2596 and PA2600 strains were performed as previously described (18). In order to compare CDS from PA2596 and PA2600, PAO1 strain (NC_002745.2) was used as a reference.…”

“…In these conditions, coexisting bacteria demonstrated increased tolerance to antibiotics: to tobramycin and tetracycline for S. aureus and to gentamicin for P. aeruginosa. This appeared to be related to the induction of small colony variants (15,17,18,20). However, the effects of coexistence on general bacterial physiology, and not only virulence-associated traits, have not yet been explored.…”

“…Briaud et al recently demonstrated that this interaction pattern appears to be more frequent than expected. Indeed, among the quarter of CF patients co-infected by both pathogens, 65% were infected by a coexisting S. aureus-P. aeruginosa pair (18,19). Recent studies have shown that coexistence between P. aeruginosa and S. aureus could promote their persistence throughout the establishment of cooperative interaction.…”