Infection and Immunity最新文献

The vaginal tract is a complex environment that changes throughout various life stages. Recent advances have improved our understanding of the vaginal microbiota and the influence of host factors on microbial colonization. The vaginal niche is characterized by unique qualities such as high abundances of glycogen and mucin, low pH, active cellular immunity, and fluctuations in hormone signaling that support a complex microbiota. While traditionally thought to be dominated by Lactobacillus species, emerging research highlights a more diverse microbiota, including both commensal and potentially pathogenic microbes. Given the interconnectedness of the microbial and host factors in this environment, minor shifts can lead to significant downstream effects on health. This review takes an ecosystems approach to explore the multifaceted relationship between the vaginal mucosa, the microbiota, and influences of environmental factors on shaping the two. We discuss the contribution of hormone signaling in shaping microbial communities, concepts of vaginal community stability and dysbiosis, and the emerging understanding of microbial metabolism and cross-feeding dynamics within the vaginal tract. Additionally, we will examine the interactions between microbes and immune cells in the vaginal mucosa, including mechanisms by which the immune system modulates the local environment. By considering the feedback loops between the host and the resident microbiota, we propose key knowledge gaps and suggest interdisciplinary avenues for future research aimed at improving our understanding of vaginal health and disease. Understanding these complex interactions is important for advancing vaginal healthcare across all individuals.

While Candida albicans is a common, commensal yeast colonizing 50%-60% of humans, it has the potential to expand in the gastrointestinal tract and enter the blood stream resulting in invasive candidiasis. Invasive candidiasis carries a mortality approaching 50%, especially in the most vulnerable, immunocompromised population. Antibacterial use causes an increase in C. albicans gastrointestinal colonization, indicating that the colonic microbiota plays a major role in preventing an uncontrolled expansion, a phenomenon known as colonization resistance. Antibacterials, medications, diet, and co-morbid conditions can all alter the microbiome, creating an altered environment known as dysbiosis. Our understanding of the microbiome continues to advance, and there is increasing evidence that the interactions that the microbiome has on the host are vital in maintaining colonization resistance to pathogens including C. albicans. This review will focus on colonization resistance to C. albicans within the gastrointestinal tract. The scope includes the benefits and consequences of C. albicans colonization, interkingdom interactions of the microbiome on C. albicans, microbiome-host interactions and how these modulate C. albicans colonization, and the impact of medications and diet on colonization resistance.

Streptococcus canis is an important opportunistic pathogen of cats, dogs, and cows, which can cause a range of infections, ranging from skin and soft tissue infections to septicemia and endocarditis. As a zoonotic agent, S. canis has also recently been implicated in serious human infections, following trauma or immunosuppression. In this work, we describe a novel protease of S. canis, termed IdeC (Immunoglobulin G degrading enzyme of S. canis), which may be involved in bacterial immune evasion. The cleaving ability of IdeC against IgG from various species was assessed; this revealed that IdeC successfully cleaved canine, feline, and human IgG. We also confirmed that IdeC is a cysteine protease, similar to IdeS of Streptococcus pyogenes. Investigation of the cleavage site in IgG sequences showed that it is highly conserved across IgGs from all species tested. From this analysis, it was determined that IdeC cleavage occurs between the CH2 and hinge regions of IgG. Interestingly, feline IgG was consistently cleaved with the highest efficiency, with human and canine IgG displaying less efficient cleavage. High-resolution crystal structures of two IdeC constructs provided insights into the catalytic machinery and substrate recognition. Modeling of the full-length IdeC:IgG complexes for human, canine, and feline cases explains the mechanism of action of the protease and reveals the molecular basis for the observed cleavage preference for feline IgG. Understanding and managing S. canis as a pathogen is important in both veterinary and human medicine, as this bacterium underscores the need for awareness of zoonotic transmission.

Microbes rarely exist alone; instead, they live in dynamic multi-species communities with a range of metabolic capacities. To establish within a polymicrobial community, an organism must compete with the other members of the community for space and nutrients. In addition, microbes form complex metabolic interdependencies in polymicrobial environments, and these nutrient exchanges are central to overall community function. Interactions between microbial community members dictate key processes, including nutrient cycling, tolerance to disturbances, and disease progression, and these interactions are known to depend on the environment in which they are measured. Therefore, understanding these ecological interactions is fundamental to our understanding of community composition, function, and impacts on disease. In this mini-review, we will describe the mechanisms microbes use to exchange nutrients in host-associated environments, with a focus on the oral and respiratory tracts. We will particularly emphasize the environmental factors that influence community composition and how interactions between organisms, ranging from cooperation to competition, impact nutrient bioavailability and overall community function during infection.

Yersinia pestis is a gram-negative bacterium and the causative agent of bubonic, septicemic, and pneumonic plague. Y. pestis is most commonly transmitted to humans by infected fleas that deposit the bacteria into the dermis at the bite site, leading to bubonic plague. The bacteria ultimately access the bloodstream, and after deposition in the lung, can be transmitted person-to-person through infectious respiratory droplets, resulting in primary pneumonic plague, a highly lethal and rapidly progressing pneumonia. Pathogenesis is mediated by a suite of chromosomally encoded and plasmid-borne virulence factors, and infection is maintained by temperature-dependent coordinated modifications in gene expression that facilitate bacterial survival in both the flea and mammalian hosts. BipA (BPI-inducible protein A) is a highly conserved translational GTPase that is a Y. pestis virulence factor. BipA modulates protein expression under stress conditions, and its deletion renders Y. pestis more sensitive to killing by neutrophils and attenuates bacterial growth in a murine infection model of pneumonic plague. In the work described here, we show that BipA also regulates specific Y. pestis proteins at flea/environmental temperatures. We show that BipA is responsible for the induction of a recently described type 6 secretion system (T6SS), as well as the transcriptional regulator RovC. We also show that BipA regulates the production of the known Y. pestis bacteriocin pesticin, and that bacteria lacking BipA have a defect in competition not solely attributable to the T6SS or pesticin. Our results show that in addition to its role in the mammalian host, regulation of specific proteins by BipA also likely contributes to bacterial survival during the flea/environmental phase, where Y. pestis must compete with other species of bacteria within a particular niche.

Akkermansia muciniphila is a specialized mucin-degrading bacterium that plays a pivotal role in gut health and disease. This review examines the dualistic nature of A. muciniphila mucin degradation, exploring its potential benefits and risks. As a mucin specialist, A. muciniphila uses glycosyl hydrolases and mucinases to degrade mucins, producing metabolites like short-chain fatty acids (SCFAs), branched-chain fatty acids (BCFAs), succinate, and other compounds. These metabolites benefit host health and cross-feed other commensal microbes, such as butyrate producers. A. muciniphila levels are inversely correlated with several disease states, such as obesity, diabetes, and inflammatory states, and administration of A. muciniphila has been found by several groups to restore and maintain gut homeostasis. However, under certain conditions, such as low dietary fiber or conditions with an altered gut microbiota, excessive mucin degradation by A. muciniphila can compromise the mucus barrier, increasing susceptibility to inflammation, infection, and pathogenic overgrowth. Elevated A. muciniphila levels have been associated with various diseases and medications, including graft versus host disease (GVHD) and irradiation, and shown to exacerbate infections by enteric pathogens. The context-dependent effects of A. muciniphila and mucin degradation underscore the need for a nuanced understanding of its interactions with the host and microbial community. This review aims to provide a balanced perspective on the implications of gut microbial mucus degradation, highlighting that it can be good, and it can be bad depending on the context.

The prevailing dogma is that enterotoxigenic Escherichia coli (ETEC) use plasmid-borne colonization factors (CFs) to adhere to the intestinal epithelium, where the organisms proliferate and produce their diarrhea-causing virulence factors, the heat-stable (ST) and/or heat-labile (LT) enterotoxins. However, vaccines that target major CF antigens fail to induce complete protective immunity, indicating that ETEC may also use other antigens to colonize the small intestines. We previously demonstrated that ST intoxication limits magnesium bioavailability in the intestinal lumen, but the role of magnesium in ETEC pathogenesis has not been rigorously evaluated. Here, we demonstrate that addition of magnesium at concentrations found in the intestinal mucosa promotes biofilm formation in ETEC H10407 and other clinical isolates, especially in the presence of lactate. ETEC H10407 biofilms fail to express high levels of colonization factor antigen I(CFA/I) fimbriae, but ETEC H10407 biofilms remain significantly better than planktonic counterparts at adhering to intestinal epithelial cells. Furthermore, ETEC H10407 biofilms are more acid-resistant than their planktonic counterparts, indicating that biofilms may promote survival through gastric acidity. Finally, using intragastric infection of neonatal mice, ETEC H10407 biofilms are significantly more virulent than their planktonic counterparts. Scanning electron micrographs of biofilm-infected mice show ETEC H10407 adheres to small intestinal villi. Thus, ETEC may respond to changes in environmental conditions to alter adherence mechanisms. Therefore, identification of biofilm antigens should be prioritized in ETEC vaccine development.

Coxiella burnetii is a gram-negative, obligate intracellular pathogen that causes Q fever in humans. In vivo research on C. burnetii is limited due to the classification of the Nine Mile phase I (NMI) strain as a select agent that requires biosafety level 3 containment. The isogenic Nine Mile phase II (NMII) strain can be cultured safely at biosafety level 2 and has been shown to infect immunocompromised mice, which suggests this strain could be used to investigate virulence phenotypes in vivo. This study developed a bioluminescent imaging (BLI) model using NMII to non-invasively monitor C. burnetii infections in mice. Here, we show that BLI enables tracking of bacteria in an animal host, identification of bacterial virulence differences, and investigation of host determinants of immunity. Using BLI, we show that NMII resides primarily in visceral adipose tissue following intraperitoneal infection of mice. Intracellular replication of C. burnetii in adipocytes was confirmed using cultured cells ex vivo. These data indicate that adipose tissue can serve as a niche for C. burnetii replication. This study underscores the utility of BLI in advancing C. burnetii research and highlights the need for further exploration into the role of adipocytes in the disease Q fever and bacterial persistence in vivo.