Staphylococcus aureus is a clinically important pathogen that causes a wide range of human infections, from minor skin infections to severe tissue infection and sepsis. S. aureus has a high level of antibiotic resistance and is a common cause of infections in hospitals and the community. The rising prevalence of community-acquired methicillin-resistant S. aureus (CA-MRSA), combined with the important severity of S. aureus infections in general, has resulted in the frequent use of anti-staphylococcal antibiotics, leading to increasing resistance rates. Antibiotic-resistant S. aureus continues to be a major health concern, necessitating the development of novel therapeutic strategies. S. aureus uses a wide range of virulence factors, such as toxins, to develop an infection in the host. Recently, anti-virulence treatments that directly or indirectly neutralize S. aureus toxins have showed promise. In this review, we provide an update on toxin pathogenic characteristics, as well as anti-toxin therapeutical strategies.

Staphylococcus sp. is the most common bacterial genus in infections related to diabetic foot ulcers (DFUs). The emergence of multidrug-resistant bacteria places a serious burden on public health systems. Phage therapy is an alternative treatment to antibiotics, overcoming the issue of antibiotic resistance. In this study, six phages (SAVM01 to SAVM06) were isolated from effluents and were used against a panel of staphylococcal clinical samples isolated from DFUs. A genomic analysis revealed that the phages belonged to the Herelleviridae family, with sequences similar to those of the Kayvirus genus. No lysogeny-associated genes, known virulence or drug resistance genes were identified in the phage genomes. The phages displayed a strong lytic and antibiofilm activity against DFU clinical isolates, as well as against opportunistic pathogenic coagulase-negative staphylococci. The results presented here suggest that these phages could be effective biocontrol agents against staphylococcal clinical isolates from DFUs.

Staphylococcus pettenkoferi is a coagulase-negative Staphylococcus identified in 2002 that has been implicated in human diseases as an opportunistic pathogenic bacterium. Its multiresistant character is becoming a major health problem, yet the pathogenicity of S. pettenkoferi is poorly characterized. In this study, the pathogenicity of a S. pettenkoferi clinical isolate from diabetic foot osteomyelitis was compared with a Staphylococcus aureus strain in various in vitro and in vivo experiments. Growth kinetics were compared against S. aureus, and bacteria survival was assessed in the RAW 264.7 murine macrophage cell line, the THP-1 human leukemia monocytic cell line, and the HaCaT human keratinocyte cell line. Ex vivo analysis was performed in whole blood survival assays and in vivo assays via the infection model of zebrafish embryos. Moreover, whole-genome analysis was performed. Our results show that S. pettenkoferi was able to survive in human blood, human keratinocytes, murine macrophages, and human macrophages. S. pettenkoferi demonstrated its virulence by causing substantial embryo mortality in the zebrafish model. Genomic analysis revealed virulence factors such as biofilm-encoding genes (e.g., icaABCD; rsbUVW) and regulator-encoding genes (e.g., agr, mgrA, sarA, saeS) well characterized in S. aureus. This study thus advances the knowledge of this under-investigated pathogen and validates the zebrafish infection model for this bacterium.

Staphylococcus pettenkoferi is a recently described coagulase-negative Staphylococcus identified in human diseases, especially in infections of foot ulcers in patients living with diabetes mellitus. To date, its pathogenicity remains underexplored. In this study, whole-genome analysis was performed on a collection of 29 S. pettenkoferi clinical strains isolated from bloodstream and diabetic foot infections with regard to their phylogenetic relationships and comprehensive analysis of their resistome and virulome. Their virulence was explored by their ability to form biofilm, their growth kinetics and in an in vivo zebrafish embryo infection model. Our results identified two distinct clades (I and II) and two subclades (I-a and I-b) with notable genomic differences. All strains had a slow bacterial growth. Three profiles of biofilm formation were noted, with 89.7% of isolates able to produce biofilm and harbouring a high content of biofilm-encoding genes. Two virulence profiles were also observed in the zebrafish model irrespective of the strains’ origin or biofilm profile. Therefore, this study brings new insights in S. pettenkoferi pathogenicity.

Staphylococcus aureus possesses a large arsenal of immune-modulating factors, enabling it to bypass the immune system’s response. Here, we demonstrate that the acid phosphatase SapS is secreted during macrophage infection and promotes its intracellular survival in this type of immune cell. In animal models, the SA564 sapS mutant demonstrated a significantly lower bacterial burden in liver and renal tissues of mice at four days post infection in comparison to the wild type, along with lower pathogenicity in a zebrafish infection model. The SA564 sapS mutant elicits a lower inflammatory response in mice than the wild-type strain, while S. aureus cells harbouring a functional sapS induce a chemokine response that favours the recruitment of neutrophils to the infection site. Our in vitro and quantitative transcript analysis show that SapS has an effect on S. aureus capacity to adapt to oxidative stress during growth. SapS is also involved in S. aureus biofilm formation. Thus, this study shows for the first time that SapS plays a significant role during infection, most likely through inhibiting a variety of the host’s defence mechanisms.

Caractérisation des souches de Staphylocoques isolées des ulcères des pieds diabétiques: Les ulcères du pied diabétique (UPD) représentent un problème de santé publique important en raison de leur association fréquente avec des infections récurrentes causées par des bactéries multirésistantes, le plus souvent des espèces du genre Staphylococcus. Dans les UPD, la transition de la colonisation à l'invasion est difficile, ce qui entraîne une utilisation inappropriée d'antibiotiques, un traitement retardé et une prévalence accrue d'infections particulièrement dues à S. aureus résistant à la méticilline (SARM), qui peuvent causer une morbidité grave, y compris des amputations. Cependant, le rôle des staphylocoques à coagulase négative (CoNS) dans ces infections est souvent négligé. Récemment, S. pettenkoferi, un CoNS, a été de plus en plus associée à l'ostéomyélite du pied diabétique, indiquant son implication potentielle dans la physiopathologie de ces infections et dans l’aggravation des résultats de traitement. Pour répondre à ces défis, cette thèse de doctorat a été divisée en deux grandes parties.La première partie visait à caractériser la pathogénicité de S. pettenkoferi en examinant sa survie intracellulaire, sa morphologie, sa virulence, sa formation précoce de biofilm et l'expression de ses facteurs de virulence. Les résultats ont révélé que S. pettenkoferi, à croissance lente, était très virulente in vivo, capable de former des biofilms et de persister dans les cellules. De plus, les souches étudiées de S. pettenkoferi isolées du sang humain et des UPD ont été divisées en deux clades distincts et ont présenté des différences génomiques importantes.La deuxième partie de ce travail visait à étudier un prophage connu sous le nom de ROSA-like, qui avait été précédemment découvert dans des souches de S. aureus isolés des plaies non infectées. Les études ont montré que la présence de ROSA-like dans S. aureus l'empêchait de se répliquer dans les ostéoblastes. Cependant, ces données ont été collectées à l'aide d'un milieu conventionnel. Pour étudier l'impact d'un environnement stressant sur le comportement bactérien et le rôle de ROSA-like dans l'adaptation à de telles conditions, nous avons utilisé un milieu qui imitait les conditions de la plaie chronique, mettant l'accent sur l'environnement microbiologique et cellulaire de ces plaies. Le prophage jouait un rôle dans la capacité de S. aureus à s'adapter à de telles conditions et augmentait la virulence de cette bactérie in vivo, ainsi que sa formation précoce de biofilm et sa survie intracellulaire. Enfin, ce travail s’est concentré sur l'étude d’un gène codant pour une protéine de liaison à l'ADN simple brin (SSB-P) unique au prophage ROSA-like et surexprimé par rapport aux autres gènes de prophage. Les résultats ont montré que SSB-P pouvait réduire la virulence de S. aureus et diminuer la survie intra macrophagique et la cytotoxicité de S. aureus. Ceci suggère que cette nouvelle molécule prometteuse pourrait être une cible thérapeutique pour lutter contre les infections causées par les staphylocoques.