Biology subjects

Bastien, S.

Publications and source records attributed to Bastien, S..

6 recordsLinked to original sources

bioRxiv2022

Staphylococcus aureus virulence factor expression matters: input from targeted proteomics shows Panton-Valentine leucocidin impact on mortality

In the case of commensal bacteria such as Staphylococcus aureus, the transition from commensalism to invasion and disease as well as disease severity in the course of an infection remain poorly predictable on the sole basis of virulence gene content. To determine whether variations in the levels of expression of the numerous S. aureus virulence factors could affect disease occurrence and/or severity, we developed a targeted proteomic approach that monitored 149 peptide surrogates targeting 44 proteins. Semi-quantification was achieved by normalization on the signal of ribosomal proteins. We then evaluated this approach on a series of S.aureus strains from 136 patients presenting a severe community-acquired pneumonia, all admitted to an intensive care unit. After adjusting to the Charlson Comorbidity Index score the multivariate analysis of severity parameters found that HlgB, Nuc, and Tsst-1 were positively associated while BlaI and HlgC were negatively associated with leucopenia. BlaZ and HlgB were positively associated with hemoptysis and HlgC was negatively associated with hemoptysis. Regarding mortality, both the multivariate (1.28; 95%CI[1.02;1.60]) and survival (1.15; 95%CI[1.016;1.302]) analyses showed that only PVL was associated with death in a dose-dependent manner. Beyond highlighting the decisive role of PVL in community-acquired pneumonia severity, this study brings the proof of concept that "expression matters" and proposes a method that can be routinely implemented in laboratories, for any Staphylococcal disease, and which could be developed for other commensal bacteria. One Sentence SummaryA highly multiplexed semi-quantitative mass spectrometry method was developed for 44 Staphylococcus aureus virulence factors; applied to a 136-strain collection from severe community-acquired pneumonia patients, it showed that Panton-Valentine leucocidin was the only factor to impact mortality in a dose-dependent manner.

microbiology↗

bioRxiv2022

All Staphylococcus aureus bacteraemia strains have the potential to cause infective endocarditis: results of GWAS and experimental animal studies

Abstract and KeywordsO_ST_ABSAimsC_ST_ABSInfective endocarditis (IE) complicates 10-20% of Staphylococcus aureus bacteraemia (SAB). We aimed to determine whether IE strains of S. aureus are genotypically different or behave differently in experimental endocarditis models as compared to non-IE SAB strains. Methods and ResultsWe conducted a genome wide association study (GWAS) of 924 S. aureus genomes from IE (274) and non-IE (650) SAB patients, and tested a subset of strains in two experimental animal models of IE, one studying the early step of bacterial adhesion to inflamed mice valves, the second evaluating the local and systemic developmental process of IE on mechanically damaged rabbit valves. The genetic profile of S. aureus IE and non-IE SAB strains did not differ when considering single nucleotide polymorphisms, coding sequences and k-mers analyses in GWASs. In the inflammation-induced IE model in mice no difference was observed between IE and non-IE SAB strains both in adhesion to the cardiac valves and in the propensity to cause IE; in the mechanical IE-induced rabbit model, there was no difference between IE and non-IE SAB strains regarding vegetation size and CFU. ConclusionS. aureus isolates from SAB patients with and without IE were indistinguishable, by GWAS and by two in vivo models of IE. Thus, S. aureus strain variation is not the primary determinant of IE. Pending the possible identification of host factors predisposing to IE, all strains of S. aureus must be considered in patients as capable of causing this common, lethal infection once they have accessed the bloodstream. Translational PerspectiveStaphylococcus aureus endocarditis (IE) is a deadly complication of S. aureus bacteraemia (SAB). Beyond well-identified host related IE risk factors, whether bacterial features may influence the occurrence of IE in the course of bacteraemia remain elusive. We analysed the genomes of 924 S. aureus strains from IE and non-IE SAB and compared some in two in vivo IE models. We demonstrated that the propensity of S. aureus to cause IE in the course of bacteraemia does not depend on the intrinsic genetic or virulence factors of S. aureus. These findings are of importance for the management of S. aureus bacteraemia.

microbiology↗

bioRxiv2020

Trophic cooperation promotes bacterial survival of Staphylococcus aureus and Pseudomonas aeruginosa

In the context of infection, Pseudomonas aeruginosa and Staphylococcus aureus are frequently co-isolated, particularly in cystic fibrosis (CF) patients. Within lungs, the two pathogens exhibit a range of competitive and coexisting interactions. In the present study, we explored the impact of S. aureus on the physiology of P. aeruginosa in the context of coexistence. Transcriptomic analyses showed that S. aureus significantly and specifically affects the expression of numerous genes involved in P. aeruginosa carbon and amino acid metabolism. In particular, 65% of the strains presented considerable overexpression of the genes involved in the acetoin catabolic (aco) pathway. We demonstrated that acetoin is (i) produced by clinical S. aureus strains, (ii) detected in sputa from CF patients, and (iii) involved in P. aeruginosas aco system induction. Furthermore, acetoin is catabolized by P. aeruginosa, a metabolic process that improves the survival of both pathogens by providing a new carbon source for P. aeruginosa and avoiding the toxic accumulation of acetoin on S. aureus. Due to its beneficial effects on both bacteria, acetoin catabolism could testify to the establishment of trophic cooperation between S. aureus and P. aeruginosa in the CF lung environment, thus promoting their persistence.

microbiology↗

bioRxiv2019

NorK, a novel norfloxacin efflux pump in Staphylococcus aureus

A novel efflux pump similar to Nor efflux pumps and designated as NorK was identified in Staphylococcus aureus. It contributes to norfloxacin resistance and presents a high level of expression in different strains. Its expression is not regulated by MgrA, unlike other genes of the nor gene family, suggesting that NorK could be important in the absence of expression of other nor genes.

microbiology↗

bioRxiv2019

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

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.

microbiology↗

bioRxiv2019

Necrotizing Soft-Tissue Infections-Staphylococcus aureus -but not Streptococcus pyogenes- isolates display high rate of internalization and cytotoxicity toward human myoblasts

Necrotizing Soft Tissue Infections (NSTIs), often reaching the deep fascia and muscle, are mainly caused by group A Streptococcus (GAS) and to a lesser extent by Staphylococcus aureus (SA). Conversely SA is a leading etiologic agent of pyomyositis suggesting that SA could have a specific tropism for the muscle. To assess the pathogenicity of these two bacterial species for muscles cells in comparison to keratinocytes, adhesion and invasion of NSTI-GAS and NSTI-SA were assessed on these cells. Bloodstream infections (BSI) SA isolates and non-invasive coagulase negative Staphylococci (CNS) isolates were used as controls. SA isolates from NSTI and from BSI exhibited stronger internalization into human keratinocytes and myoblasts than CNS or NSTI-GAS. While the median level of SA internalization culminated at 2% in human keratinocytes, it reached over 30% in human myoblasts due to a higher percentage of infected myoblasts (>11%) as compared to keratinocytes (<3%) assessed by transmission electron microscopy. Higher cytotoxicity for myoblasts of NSTI-SA as compared to BSI-SA, was attributed to higher levels of psm and RNAIII transcripts in NSTI group as compared to hematogenous group. However, the two groups were not discriminated at the genomic level. The cellular basis of high internalization rate in myoblasts was attributed to higher expression of 5{beta}1 integrin in myoblasts as compared to keratinocytes. Major contribution of FnbpAB-integrin 5{beta}1 pathway to internalization was confirmed by isogenic mutants. Our findings suggest the contribution of NSTI-SA severity by its unique propensity to invade and kill myoblasts, a property not shared by NSTI-GAS. ImportanceNecrotizing Soft Tissue Infection (NSTI) is a severe infection caused mainly by group A Streptococcus (GAS) and occasionally by S. aureus (SA); the latter being more often associated with pyomyositis. NSTIs frequently involve the deep fascia and may provoke muscle necrosis. The goal of this study was to determine the tropism and pathogenicity of these two bacterial species for muscle cells. The results revealed a high tropism of SA for myoblasts and myotubes followed by cytotoxicity as opposed to GAS that did not invade these cells. This study uncover a novel mechanism of SA contribution to NSTI with a direct muscle involvement, while in GAS NSTI this is likely indirect, for instance, secondary to vascular occlusion.

molecular biology↗