Escherichia coli modulates extraintestinal spread of Staphylococcus aureus

Staphylococcus aureus FadB is a dehydrogenase that mediates cholate resistance and survival under human colonic conditions

Staphylococcus aureus is a common colonizer of the human gut and in doing so it must be able to resist the actions of the host's innate defences. Bile salts are a class of molecules that possess potent antibacterial activity that control growth. Bacteria that colonize and survive in that niche must be able to resist the action of bile salts, but the mechanisms by which S. aureus does so are poorly understood. Here we show that FadB is a bile-induced oxidoreductase which mediates bile salt resistance and when heterologously expressed in Escherichia coli renders them resistant. Deletion of fadB attenuated survival of S. aureus in a model of the human distal colon.

The antibacterial activity and mechanism of imidazole chloride ionic liquids on Staphylococcus aureus

Ionic liquids (ILs) have garnered increasing attention in the biomedical field due to their unique properties. Although significant research has been conducted in recent years, there is still a lack of understanding of the potential applications of ILs in the biomedical field and the underlying principles. To identify the antibacterial activity and mechanism of ILs on bacteria, we evaluated the antimicrobial potency of imidazole chloride ILs (C_nMIMCl) on Staphylococcus aureus (S. aureus). The toxicity of ILs was positively correlated to the length of the imidazolidinyl side chain. We selected C₁₂MIMCl to study the mechanism of S. aureus. Through the simultaneous change in the internal and external parts of S. aureus, C₁₂MIMCl caused the death of the bacteria. The production of large amounts of reactive oxygen species (ROS) within the internal parts stimulated oxidative stress, inhibited bacterial metabolism, and led to bacterial death. The external cell membrane could be destroyed, causing the cytoplasm to flow out and the whole cell to be fragmented. The antibacterial effect of C₁₂MIMCl on skin abscesses was further verified in vivo in mice.

Staphylococcus aureus MnhF mediates cholate efflux and facilitates survival under human colonic conditions

Resistance to the innate defenses of the intestine is crucial for the survival and carriage of Staphylococcus aureus, a common colonizer of the human gut. Bile salts produced by the liver and secreted into the intestines are one such group of molecules with potent antimicrobial activity. The mechanisms by which S. aureus is able to resist such defenses in order to colonize and survive in the human gut are unknown. Here we show that mnhF confers resistance to bile salts, which can be abrogated by efflux pump inhibitors. MnhF mediates the efflux of radiolabeled cholic acid both in S. aureus and when heterologously expressed in Escherichia coli, rendering them resistant. Deletion of mnhF attenuated the survival of S. aureus in an anaerobic three-stage continuous-culture model of the human colon (gut model), which represents different anatomical areas of the large intestine.

Direct translocation of staphylococci from the skin surface to deep organs

BACKGROUND

Staphylococcus aureus can invade the bloodstream and cause bacteremic infections, but this organism frequently produces serious deep infections without bacteremia or an identifiable portal of entry.

METHODS

We used experimental cutaneous S. aureus infections in mice to determine if the bacteria could reach deep organs without travel through the bloodstream.

RESULTS

After skin surface application the bacteria rapidly distributed to lymph nodes, spleen, kidneys and other organs. In these animals, blood cultures were negative, dissemination was more efficient after surface application than injection near dermal blood vessels, and kidney bacterial localization sites were unlike those of bacteremic infections. Whereas normal mice eventually cleared bacteria from the deep sites, those with prolonged immunosuppression became moribund from these infections; they also had negative blood cultures and kidney localization not consistent with hematogenous dissemination. Bacteria were also found in the intervening abdominal wall outside the spleen and kidney sites, suggesting direct movement of the organisms from the skin surface through connecting tissues.

CONCLUSIONS

Although capable of hematogenous dissemination, S. aureus can also spread from skin to deep organs by a non-bacteremic process. In this case the bacteria appear to migrate directly from the skin surface to the deep organs below.

The influence of Staphylococcus aureus on gut microbial ecology in an in vitro continuous culture human colonic model system

An anaerobic three-stage continuous culture model of the human colon (gut model), which represent different anatomical areas of the large intestine, was used to study the effect of S. aureus infection of the gut on the resident faecal microbiota. Studies on the development of the microbiota in the three vessels were performed and bacteria identified by culture independent fluorescence in situ hybridization (FISH). Furtheremore, short chain fatty acids (SCFA), as principal end products of gut bacterial metabolism, were measured along with a quantitative assessment of the predominant microbiota. During steady state conditions, numbers of S. aureus cells stabilised until they were washed out, but populations of indigenous bacteria were transiently altered; thus S. aureus was able to compromise colonisation resistance by the colonic microbiota. Furthermore, the concentration of butyric acid in the vessel representing the proximal colon was significantly decreased by infection. Thus infection by S. aureus appears to be able to alter the overall structure of the human colonic microbiota and the microbial metabolic profiles. This work provides an initial in vitro model to analyse interactions with pathogens.