Microbiology-Sgm最新文献

Nutritional immunity, a key component of the vertebrate innate immune response, involves the modulation of zinc availability to limit the growth of pathogens. Pseudomonas aeruginosa counteracts host-imposed zinc starvation through metabolic adaptations, including reprogramming of gene expression and activating efficient metal uptake systems. To unravel how zinc shortage contributes to the complexity of bacterial adaptation to the host environment, it is critical to use model systems that mimic fundamental features of P. aeruginosa-related diseases in humans. Among available animal models, Galleria mellonella has recently emerged as a promising alternative to mammalian hosts. This study aims to evaluate whether G. mellonella can recapitulate the zinc-related nutritional immunity responses observed in mammalian infections. Our results show that, upon P. aeruginosa infection, the larvae upregulate several zinc transporters, suggesting an active redistribution of the metal in response to the pathogen. Additionally, P. aeruginosa colonizing the larvae induces Zn uptake regulator-controlled genes, consistent with bacterial adaptation to zinc starvation. Disruption of bacterial zinc uptake capability significantly reduces P. aeruginosa virulence, underscoring the importance of zinc acquisition in pathogenesis also within this model host. As a proof of concept, we also demonstrate that this in vivo model can serve as a viable preliminary screening tool to unveil novel players involved in P. aeruginosa response to zinc starvation, offering valuable insights into the host-pathogen battle for micronutrients.

Salmonella Typhimurium is a major Salmonella serovar that is found globally. It is responsible for outbreaks of self-limiting gastroenteritis that are broadly linked to the industrialization of food production. S. Typhimurium is a pathogen with a broad host range and remarkable metabolic versatility. The ∼5 Mb genome includes the pSLT virulence plasmid and has a characteristic prophage repertoire. The major virulence determinants are encoded by a variety of pathogenicity islands. Emerging multidrug-resistant lineages of epidemics of S. Typhimurium are currently causing bloodstream infections in sub-Saharan Africa. The versatility and adaptability of S. Typhimurium pose an important public health challenge.

Sphingoid bases, including sphingosine, are important components of the antimicrobial barrier at epithelial surfaces where they can cause growth inhibition and killing of susceptible bacteria. Pseudomonas aeruginosa is a common opportunistic pathogen that is less susceptible to sphingosine than many Gram-negative bacteria. Here, we determined that the deletion of the sphBCD operon reduced growth in the presence of sphingosine. Using deletion mutants, complementation and growth assays in P. aeruginosa PAO1, we determined that the sphC and sphB genes, encoding a periplasmic oxidase and periplasmic cytochrome c, respectively, were important for growth on sphingosine, while sphD was dispensable under these conditions. Deletion of sphBCD in P. aeruginosa PA14, Pseudomonas protegens Pf-5 and Pseudomonas fluorescens Pf01 also showed reduced growth in the presence of sphingosine. The P. aeruginosa sphBC genes were also important for growth in the presence of two other sphingoid bases, phytosphingosine and sphinganine. In WT P. aeruginosa, sphingosine is metabolized to an unknown non-inhibitory product, as sphingosine concentrations drop in the culture. However, in the absence of sphBC, sphingosine accumulates, pointing to SphC and SphB as having a role in sphingosine metabolism. Finally, the metabolism of sphingosine by WT P. aeruginosa protected susceptible cells from full growth inhibition by sphingosine, pointing to a role for sphingosine metabolism as a public good. This work shows that the metabolism of sphingosine by P. aeruginosa presents a novel pathway by which bacteria can alter host-derived sphingolipids, but it remains an open question whether SphB and SphC act directly on sphingosine.

Antimicrobial resistance (AMR) is a major threat to global public health that continues to grow owing to selective pressure caused by the use and overuse of antimicrobial drugs. Resistance spread by plasmids is of special concern, as they can mediate a wide distribution of AMR genes, including those encoding extended-spectrum β-lactamases (ESBLs). The CTX-M family of ESBLs has rapidly spread worldwide, playing a large role in the declining effectiveness of third-generation cephalosporins. This rapid spread across the planet is puzzling given that plasmids carrying AMR genes have been hypothesized to incur a fitness cost to their hosts in the absence of antibiotics. Here, we focus on a WT plasmid that carries the bla _{CTX-M 55} ESBL gene. We examine its conjugation rates and use head-to-head competitions to assay its associated fitness costs in both laboratory and wild Escherichia coli strains. We found that the wild strains exhibit intermediate conjugation levels, falling between two high-conjugation and two low-conjugation laboratory strains, the latter being older and more ancestral. We also show that the plasmid increases the fitness of both WT and lab strains when grown in lysogeny broth and Davis-Mingioli media without antibiotics, which might stem from metabolic benefits conferred on the host, or from interactions between the host and the rifampicin-resistant mutation we used as a selective marker. Laboratory strains displayed higher conjugation frequencies compared to WT strains. The exception was a low-passage K-12 strain, suggesting that prolonged laboratory cultivation may have compromised bacterial defences against plasmids. Despite low transfer rates among WT E. coli, the plasmid carried low fitness cost in minimal medium but conferred improved fitness in enriched medium, indicating a complex interplay between plasmids, host genetics and environmental conditions. Our findings reveal an intricate relationship between plasmid carriage and bacterial fitness. Moreover, they show that resistance plasmids can confer adaptive advantages to their hosts beyond AMR. Altogether, these results highlight that a closer study of plasmid dynamics is critical for developing a secure understanding of how they evolve and affect bacterial adaptability that is necessary for combating resistance spread.

Most Gram-negative bacteria synthesize a plethora of cell surface polysaccharides that play key roles in immune evasion, cell envelope structural integrity and host-pathogen interactions. In the predominant polysaccharide Wzx/Wzy-dependent pathway, synthesis is divided between the cytoplasmic and periplasmic faces of the membrane. Initially, an oligosaccharide composed of 3-8 sugars is synthesized on a membrane-embedded lipid carrier, undecaprenyl pyrophosphate, within the cytoplasmic face of the membrane. This lipid-linked oligosaccharide is then translocated to the periplasmic face by the Wzx flippase, where it is polymerized into a repeat-unit polysaccharide. Structural alterations to the O-antigen repeating oligosaccharide significantly reduce polysaccharide yield and lead to cell death or morphological abnormalities. These effects are attributed to the substrate recognition function of the Wzx flippase, which we postulated to act as a gatekeeper to ensure that only complete substrates are translocated to the periplasmic face. Here, we labelled Salmonella enterica serovar Typhimurium group B1 with [¹⁴C] d-galactose. Our results showed that strains unable to synthesize the full O-antigen repeat unit accumulate significantly higher levels of Und-P-linked material (~10-fold). Importantly, this sequestration is alleviated by membrane disruption which opens the lipid-linked oligosaccharide at the cytosolic face to periplasmic ligation to support accumulation occurs at the cytosolic face of the membrane.

Human skin is our primary physical barrier and largest immune organ, and it also hosts a protective microbiota. Staphylococci are prominent members of the skin microbiota, including the ubiquitous coagulase-negative staphylococci (CoNS). The coagulase-positive Staphylococcus aureus is found as part of the microbiota, but it poses clinical concern due to its potential pathogenicity and antibiotic resistance. Recently, a CoNS, Staphylococcus lugdunensis, has been shown to inhibit S. aureus growth via the production of a novel antibiotic, lugdunin. In this study, we use human skin models to understand the spatial relationships between the CoNS Staphylococcus epidermidis and S. lugdunensis with S. aureus during colonization of human skin. We investigated the attachment patterns of the bacteria, both individually and in competition. Surprisingly, we found that attachment did not always correlate with colonization ability. S. lugdunensis exhibited significantly reduced attachment to human skin stratum corneum but was an efficient longer-term colonizer. S. lugdunensis had a distinct attachment pattern on human corneocytes, with no significant overlap, or competitive exclusion, with the other strains. S. lugdunensis is a potential probiotic strain, with a proven ability to suppress S. aureus. Before this potential can be realized, however, further research is needed to understand how this strain adheres and interacts with other bacteria in the human skin microenvironment.

Microbiome-animal host symbioses are ubiquitous in nature. Animal-associated microbiomes can play a crucial role in host physiology, health and resilience to environmental stressors. As climate change drives rising global temperatures and increases the frequency of thermal extremes, microbiomes are emerging as a new frontier in buffering vulnerable animals against temperature fluctuations. In this primer, we briefly introduce key concepts of microbiome-host symbiosis and microbial responses to temperature shifts. We then summarize the current evidence and understanding of how microbes can buffer the thermal stress faced by their hosts. We identify key challenges for future research. Finally, we emphasize the potential of harnessing microbiomes to improve conservation strategies in a rapidly changing climate, offering a concise overview of this evolving field.

Inorganic polyphosphates (polyPs) are energy-storing biopolymers synthesized by all three domains of life. PolyP accumulation has been well studied with respect to its role in stress response, but its role in dental disease has received less attention. Dental decay can be promoted by changes in pH as well as the chemical activity of ions such as phosphate in oral fluids at the enamel interface. Previous work has shown that the drawdown of phosphate from biofilm fluids can alter the saturation state of oral fluids to thermodynamically favour mineral dissolution. The members of the Lactobacillaceae are known to accumulate polyP and play a role in early-stage and late-stage dental caries. In this study, we examined the effects of potential metabolic inhibitors on polyP accumulation in Lacticaseibacillus rhamnosus. We observed that two inhibitors of the enzyme responsible for polyP synthesis, gallein and fluoride, inhibited polyP accumulation in a balanced medium. However, fluoride and gallein treatments amended with either glucose or lactate were found to enhance polyP accumulation. These results illustrate the potential complexity of polyP metabolism in the oral environment.

Candida glabrata is a fungal microbe associated with multiple vertebrate microbiomes and their terrestrial environments. In humans, the species has emerged as an opportunistic pathogen that now ranks as the second-leading cause of candidiasis in Europe and North America (Beardsley et al. Med Mycol 2024, 62). People at highest risk of infection include the elderly, immunocompromised individuals and/or long-term residents of hospital and assisted-living facilities. C. glabrata is intrinsically drug-resistant, metabolically versatile and able to avoid detection by the immune system. Analyses of its 12.3 Mb genome indicate a stable pangenome Marcet-Houben et al. (BMC Biol 2022, 20) and phylogenetic affinity with Saccharomyces cerevisiae. Recent phylogenetic analyses suggest reclassifying C. glabrata as Nakaseomyces glabratus Lakashima and Sugita (Med Mycol J 2022, 63: 119-132).