Disruption of intestinal oxygen balance in acute colitis alters the gut microbiome.

The juxtaposition of well-oxygenated intestinal colonic tissue with an anerobic luminal environment supports a fundamentally important relationship that is altered in the setting of intestinal injury, a process likely to be relevant to diseases such as inflammatory bowel disease. Herein, using two-color phosphorometry to non-invasively quantify both intestinal tissue and luminal oxygenation in real time, we show that intestinal injury induced by DSS colitis reduces intestinal tissue oxygenation in a spatially defined manner and increases the flux of oxygen from the tissue into the gut lumen. By characterizing the composition of the microbiome in both DSS colitis-affected gut and in a bioreactor containing a stable human fecal community exposed to microaerobic conditions, we provide evidence that the increased flux of oxygen into the gut lumen augments glycan degrading bacterial taxa rich in glycoside hydrolases which are known to inhabit gut mucosal surface. Continued disruption of the intestinal mucus barrier through such a mechanism may play a role in the perpetuation of the intestinal inflammatory process.

Preservation of conjugated primary bile acids by oxygenation of the small intestinal microbiota in vitro.

Bile acids play a critical role in the emulsification of dietary lipids, a critical step in the primary function of the small intestine, which is the digestion and absorption of food. Primary bile acids delivered into the small intestine are conjugated to enhance functionality, in part, by increasing aqueous solubility and preventing passive diffusion of bile acids out of the gut lumen. Bile acid function can be disrupted by the gut microbiota via the deconjugation of primary bile acids by bile salt hydrolases (BSHs), leading to their conversion into secondary bile acids through the expression of bacterial bile acid-inducible genes, a process often observed in malabsorption due to small intestinal bacterial overgrowth. By modeling the small intestinal microbiota in vitro using human small intestinal ileostomy effluent as the inocula, we show here that the infusion of physiologically relevant levels of oxygen, normally found in the proximal small intestine, reduced deconjugation of primary bile acids, in part, through the expansion of bacterial taxa known to have a low abundance of BSHs. Further recapitulating the small intestinal bile acid composition of the small intestine, limited conversion of primary into secondary bile acids was observed. Remarkably, these effects were preserved among four separate communities, each inoculated with a different small intestinal microbiota, despite a high degree of taxonomic variability under both anoxic and aerobic conditions. In total, these results provide evidence for a previously unrecognized role that the oxygenated environment of the small intestine plays in the maintenance of normal digestive physiology. IMPORTANCE: Conjugated primary bile acids are produced by the liver and exist at high concentrations in the proximal small intestine, where they are critical for proper digestion. Deconjugation of these bile acids with subsequent transformation via dehydroxylation into secondary bile acids is regulated by the colonic gut microbiota and reduces their digestive function. Using an in vitro platform modeling the small intestinal microbiota, we analyzed the ability of this community to transform primary bile acids and studied the effect of physiological levels of oxygen normally found in the proximal small intestine (5%) on this metabolic process. We found that oxygenation of the small intestinal microbiota inhibited the deconjugation of primary bile acids in vitro. These findings suggest that luminal oxygen levels normally found in the small intestine may maintain the optimal role of bile acids in the digestive process by regulating bile acid conversion by the gut microbiota.

Dietary carbohydrates regulate intestinal colonization and dissemination of Klebsiella pneumoniae.

Bacterial translocation from the gut microbiota is a source of sepsis in susceptible patients. Previous work suggests that overgrowth of gut pathobionts, including Klebsiella pneumoniae, increases the risk of disseminated infection. Our data from a human dietary intervention study found that, in the absence of fiber, K. pneumoniae bloomed during microbiota recovery from antibiotic treatment. We thus hypothesized that dietary nutrients directly support or suppress colonization of this gut pathobiont in the microbiota. Consistent with our study in humans, complex carbohydrates in dietary fiber suppressed the colonization of K. pneumoniae and allowed for recovery of competing commensals in mouse models. In contrast, through ex vivo and in vivo modeling, we identified simple carbohydrates as a limiting resource for K. pneumoniae in the gut. As proof of principle, supplementation with lactulose, a nonabsorbed simple carbohydrate and an FDA-approved therapy, increased colonization of K. pneumoniae. Disruption of the intestinal epithelium led to dissemination of K. pneumoniae into the bloodstream and liver, which was prevented by dietary fiber. Our results show that dietary simple and complex carbohydrates were critical not only in the regulation of pathobiont colonization but also disseminated infection, suggesting that targeted dietary interventions may offer a preventative strategy in high-risk patients.

Enterobacteriaceae Growth Promotion by Intestinal Acylcarnitines, a Biomarker of Dysbiosis in Inflammatory Bowel Disease.

BACKGROUND & AIMS: Altered plasma acylcarnitine levels are well-known biomarkers for a variety of mitochondrial fatty acid oxidation disorders and can be used as an alternative energy source for the intestinal epithelium when short-chain fatty acids are low. These membrane-permeable fatty acid intermediates are excreted into the gut lumen via bile and are increased in the feces of patients with inflammatory bowel disease (IBD). METHODS: Herein, based on studies in human subjects, animal models, and bacterial cultures, we show a strong positive correlation between fecal carnitine and acylcarnitines and the abundance of Enterobacteriaceae in IBD where they can be consumed by bacteria both in vitro and in vivo. RESULTS: Carnitine metabolism promotes the growth of Escherichia coli via anaerobic respiration dependent on the cai operon, and acetylcarnitine dietary supplementation increases fecal carnitine levels with enhanced intestinal colonization of the enteric pathogen Citrobacter rodentium. CONCLUSIONS: In total, these results indicate that the increased luminal concentrations of carnitine and acylcarnitines in patients with IBD may promote the expansion of pathobionts belonging to the Enterobacteriaceae family, thereby contributing to disease pathogenesis.

Social connectedness, functional capacity, and longevity: A focus on positive relations with others.

RATIONALE: A large literature links social connectedness to health, but there is growing recognition of considerable nuance in the ways social connectedness is defined, assessed, and associated with health. OBJECTIVE: This study centers on positive relations with others - a measure derived from philosophical notions of the components of a "good life" - and the extent to which it predicts functional limitations and mortality using data from the national, longitudinal Mid-Life in the United States (MIDUS) study. We also assess whether these associations are independent of two common measures of social connectedness: social integration and social support. METHODS: Data on social connectedness came from the first wave of MIDUS (1994-1996), self-reported functional limitations were from the first (MIDUS 1) and third (MIDUS 3; 2013-2014) waves, and mortality data through 2022 were obtained from the National Death Index. RESULTS: Linear regression analyses showed that higher scores on positive relations with others predicted significantly less increase in functional limitations over time, and logistic regression models showed reduced probability of onset of functional limitations between MIDUS 1 and MIDUS 3 in those scoring higher on positive relations with others. Mortality was also significantly lower in those with higher scores on positive relations with others. All models adjusted for demographic and health characteristics, and all associations were robust to the inclusion of social integration and social support in the models. CONCLUSIONS: These results show that positive relations with others, a component of a well-lived life that describes sustained investment in social relationships that are mutual and trusting, is associated with two key health outcomes in aging adults: functional limitations and longevity. That these associations are independent of social integration and social support suggests a unique role for this formulation of social connectedness in the health of aging adults.

Changes in fecal lipidome after treatment with ivacaftor without changes in microbiome or bile acids.

BACKGROUND: Alterations in gastrointestinal health are prominent manifestations of cystic fibrosis (CF) and can independently impact pulmonary function. Ivacaftor has been associated with robust improvements in pulmonary function and weight gain, but less is known about the impact of ivacaftor on the fecal microbiome, lipidome, and bile acids. METHODS: Stool samples from 18 patients with CF and gating mutations (ages 6-61 years, 13 pancreatic insufficient) were analyzed for fecal microbiome and lipidome composition as well as bile acid concentrations at baseline and after 3 months of treatment with ivacaftor. Microbiome composition was also assessed in a healthy reference cohort. RESULTS: Alpha and beta diversity of the microbiome were different between CF and reference cohort at baseline, but no treatment effect was seen in the CF cohort between baseline and 3 months. Seven lipids increased with treatment. No differences were seen in bile acid concentrations after treatment in CF. At baseline, 403 lipids and unconjugated bile acids were different between pancreatic insufficient (PI-CF) and sufficient (PS-CF) groups and 107 lipids were different between PI-CF and PS-CF after 3 months of treatment. CONCLUSIONS: The composition and diversity of the fecal microbiome were different in CF as compared to a healthy reference, and did not change after 3 months of ivacaftor. We detected modest differences in the fecal lipidome with treatment. Differences in lipid and bile acid profiles between PS-CF and PI-CF were attenuated after 3 months of treatment.

Effects of prebiotics, probiotics, and synbiotics on the infant gut microbiota and other health outcomes: A systematic review.

The primary aim of this review was to systematically evaluate the literature regarding the effect of pre-, pro-, or synbiotic supplementation in infant formula on the gastrointestinal microbiota. The Cochrane methodology for systematic reviews of randomized controlled trials (RCTs) was employed. Five databases were searched and 32 RCTs (2010-2021) were identified for inclusion: 20 prebiotic, 6 probiotic, and 6 synbiotic. The methods utilized to evaluate gastrointestinal microbiota varied across studies and included colony plating, fluorescence in situ hybridization, quantitative real-time polymerase chain reaction, or tagged sequencing of the 16S rRNA gene. Fecal Bifidobacterium levels increased with supplementation of prebiotics and synbiotics but not with probiotics alone. Probiotic and synbiotic supplementation generally increased fecal levels of the bacterial strain supplemented in the formula. Across all pre-, pro-, and synbiotic-supplemented formulas, results were inconsistent regarding fecal Clostridium levels. Fecal pH was lower with some prebiotic and synbiotic supplementation; however, no difference was seen with probiotics. Softer stools were often reported in infants supplemented with pre- and synbiotics, yet results were inconsistent for probiotic-supplemented formula. Limited evidence demonstrates that pre- and synbiotic supplementation increases fecal Bifidobacterium levels. Future studies utilizing comprehensive methodologies and additional studies in probiotics and synbiotics are warranted.

Lacticaseibacillus rhamnosus Strain GG (LGG) Regulate Gut Microbial Metabolites, an In Vitro Study Using Three Mature Human Gut Microbial Cultures in a Simulator of Human Intestinal Microbial Ecosystem (SHIME).

In the present research, we investigated changes in the gut metabolome that occurred in response to the administration of the Laticaseibacillus rhamnosus strain GG (LGG). The probiotics were added to the ascending colon region of mature microbial communities established in a human intestinal microbial ecosystem simulator. Shotgun metagenomic sequencing and metabolome analysis suggested that the changes in microbial community composition corresponded with changes to metabolic output, and we can infer linkages between some metabolites and microorganisms. The in vitro method permits a spatially-resolved view of metabolic transformations under human physiological conditions. By this method, we found that tryptophan and tyrosine were mainly produced in the ascending colon region, while their derivatives were detected in the transverse and descending regions, revealing sequential amino acid metabolic pathways along with the colonic tract. The addition of LGG appeared to promote the production of indole propionic acid, which is positively associated with human health. Furthermore, the microbial community responsible for the production of indole propionic acid may be broader than is currently known.

Self-Rated Health and Mortality: Moderation by Purpose in Life.

Poor self-rated health consistently predicts reduced longevity, even when objective disease conditions and risk factors are considered. Purpose in life is also a reliable predictor of diverse health outcomes, including greater longevity. Given prior work in which we showed that purpose in life moderated the association between chronic conditions and health-related biological factors, the aim of the current study was to examine the role of purpose in life in moderating the relationship between subjective health and mortality. We also examined potential differences in these associations by race/ethnicity. Data were from two large national longitudinal studies-the Health and Retirement Study (HRS) and the Midlife in the United States (MIDUS) study-with a 12- to 14-year follow-up period for mortality estimates. Results of logistic regression analyses showed that purpose in life and self-rated health were both significantly positively associated with longevity, and that purpose in life significantly moderated the relationship between self-rated health and mortality. Stratified analyses showed similar results across all racial/ethnic groups, with the exception of Black MIDUS participants. These results suggest that greater purpose in life may provide a buffer against the greater probability of mortality associated with poor subjective health.

Dural sinus narrowing in patients with spontaneous anterior skull base cerebrospinal fluid leak.

Objectives: Current evidence suggests a link between idiopathic intracranial hypertension (IIH) and spontaneous cerebrospinal fluid (sCSF) leak, as well as between IIH and dural venous sinus (DVS) narrowing. However, there are limited data linking DVS narrowing and sCSF leak. This study aims to determine the prevalence of DVS narrowing in patients with sCSF leak. Methods: A retrospective review of all patients with sCSF leak that presented to a tertiary academic center from 2008 to 2019. Preoperative imaging was independently reviewed by two neuroradiologists to evaluate for DVS narrowing. Available literature was used to estimate the prevalence of DVS narrowing in the general population to allow for comparison. Data were analyzed using Exact binomial test. Results: Analysis of 25 patients with appropriate imaging revealed the majority were women (21/25, 84%) with a mean age of 51.89 years (SD 13.96). The majority of these patients were found to have narrowing of the DVS (20/25, 80%). In patient with sCSF leaks, there was a significantly higher proportion of patients with DVS narrowing compared with published literature examining this condition in the general population (80% vs. 40%, CI 0.59-0.93, p < .001). Conclusion: The prevalence of DVS narrowing in patients with sCSF leaks is substantial and likely greater than the general population. Moreover, there appears to be narrowing in most patients with sCSF leak. Preoperative radiological evaluation of the DVS using MR venography may be useful in patients with sCSF leaks as DVS stenosis may be an underdiagnosed etiology. Further study is needed to evaluate this. Level of Evidence: IV.

Colonization and Dissemination of Klebsiella pneumoniae is Dependent on Dietary Carbohydrates.

Dysbiosis of the gut microbiota is increasingly appreciated as both a consequence and precipitant of human disease. The outgrowth of the bacterial family Enterobacteriaceae is a common feature of dysbiosis, including the human pathogen Klebsiella pneumoniae . Dietary interventions have proven efficacious in the resolution of dysbiosis, though the specific dietary components involved remain poorly defined. Based on a previous human diet study, we hypothesized that dietary nutrients serve as a key resource for the growth of bacteria found in dysbiosis. Through human sample testing, and ex-vivo , and in vivo modeling, we find that nitrogen is not a limiting resource for the growth of Enterobacteriaceae in the gut, contrary to previous studies. Instead, we identify dietary simple carbohydrates as critical in colonization of K. pneumoniae . We additionally find that dietary fiber is necessary for colonization resistance against K. pneumoniae , mediated by recovery of the commensal microbiota, and protecting the host against dissemination from the gut microbiota during colitis. Targeted dietary therapies based on these findings may offer a therapeutic strategy in susceptible patients with dysbiosis.

An integrated analysis of fecal microbiome and metabolomic features distinguish non-cirrhotic NASH from healthy control populations.

BACKGROUND AND AIMS: There is great interest in identifying microbiome features as reliable noninvasive diagnostic and/or prognostic biomarkers for non-cirrhotic NASH fibrosis. Several cross-sectional studies have reported gut microbiome features associated with advanced NASH fibrosis and cirrhosis, where the most prominent features are associated with cirrhosis. However, no large, prospectively collected data exist establishing microbiome features that discern non-cirrhotic NASH fibrosis, integrate the fecal metabolome as disease biomarkers, and are unconfounded by BMI and age. APPROACH AND RESULTS: Results from shotgun metagenomic sequencing performed on fecal samples prospectively collected from 279 US patients with biopsy-proven NASH (F1-F3 fibrosis) enrolled in the REGENERATE I303 study were compared to those from 3 healthy control cohorts and integrated with the absolute quantification of fecal bile acids. Microbiota beta-diversity was different, and BMI- and age-adjusted logistic regression identified 12 NASH-associated species. Random forest prediction models resulted in an AUC of 0.75-0.81 in a receiver operator characteristic analysis. In addition, specific fecal bile acids were significantly lower in NASH and correlated with plasma C4 levels. Microbial gene abundance analysis revealed 127 genes increased in controls, many involving protein synthesis, whereas 362 genes were increased in NASH many involving bacterial environmental responses (false discovery rate < 0.01). Finally, we provide evidence that fecal bile acid levels may be a better discriminator of non-cirrhotic NASH versus health than either plasma bile acids or gut microbiome features. CONCLUSIONS: These results may have value as a set of baseline characteristics of non-cirrhotic NASH against which therapeutic interventions to prevent cirrhosis can be compared and microbiome-based diagnostic biomarkers identified.

Life-course social connectedness: Comparing data-driven and theoretical classifications as predictors of functional limitations in adulthood.

A life course perspective on social relationships highlights the importance of specific relationships at specific times in life, but analyses that account for life course trajectories in social relationships are rare. This study compares theoretical and data-driven approaches to classifying life course relationships, including multiple dimensions of social connectedness at different time points across the life course. We examine each approach's ability to predict later-life functional limitations, given that functional impairment is prevalent among middle-aged and older adults. Data were from three waves of the Midlife in the United States (MIDUS) study (n = 6909). Relationship variables (parental affection, parental discipline, social support, social strain, and positive relations with others) were from wave 1 or wave 2. Functional limitations were measured at wave 3. Results showed that the data-driven approach had more predictive power than the theoretical approach. Additionally, results suggested that including only positive relationship features was nearly as robust as including both positive and negative relationship features. Overall, the data-driven approach outperformed the theoretical approach and revealed relationship trajectories consistent with life course cumulative processes.

Intestinal epithelial autophagy is required for the regenerative benefit of calorie restriction.

Calorie restriction can enhance the regenerative capacity of the injured intestinal epithelium. Among other metabolic changes, calorie restriction can activate the autophagy pathway. Although independent studies have attributed the regenerative benefit of calorie restriction to downregulation of mTORC1, it is not known whether autophagy itself is required for the regenerative benefit of calorie restriction. We used mouse and organoid models with autophagy gene deletion to evaluate the contribution of autophagy to intestinal epithelial regeneration following calorie restriction. In the absence of injury, mice with intestinal epithelial-specific deletion of autophagy gene Atg7 (Atg7ΔIEC) exhibit weight loss and histological changes similar to wild-type mice following calorie restriction. Conversely, calorie-restricted Atg7ΔIEC mice displayed a significant reduction in regenerative crypt foci after irradiation compared with calorie-restricted wild-type mice. Targeted analyses of tissue metabolites in calorie-restricted mice revealed an association between calorie restriction and reduced glycocholic acid (GCA) in wild-type mice but not in Atg7ΔIEC mice. To evaluate whether GCA can directly modulate epithelial stem cell self-renewal, we performed enteroid formation assays with or without GCA. Wild-type enteroids exhibited reduced enteroid formation efficiency in response to GCA treatment, suggesting that reduced availability of GCA during calorie restriction may be one mechanism by which calorie restriction favors epithelial regeneration in a manner dependent upon epithelial autophagy. Taken together, our data support the premise that intestinal epithelial Atg7 is required for the regenerative benefit of calorie restriction, due in part to its role in modulating luminal GCA with direct effects on epithelial stem cell self-renewal.NEW & NOTEWORTHY Calorie restriction is associated with enhanced intestinal regeneration after irradiation, but the requirement of autophagy for this process is not known. Our data support the premise that intestinal epithelial autophagy is required for the regenerative benefit of calorie restriction. We also report that luminal levels of primary bile acid glycocholic acid are modulated by epithelial cell autophagy during calorie restriction with direct effects on epithelial stem cell function.

Subjective Memory Decline Predicts Incident Cognitive Impairment Among White-But Not Black or Hispanic-Older Adults.

BACKGROUND AND OBJECTIVES: This study investigates whether subjective memory decline (SMD) in a racially diverse sample of older adults without cognitive impairment at baseline is associated with incident cognitive impairment during a 12-year follow-up period. RESEARCH DESIGN AND METHODS: With panel data from a national sample (N = 9,244) of cognitively intact Black, White, and Hispanic Americans 65 years or older in 2004, we examine if SMD is associated with the loss of normal cognition by 2016. Cognitive status was assessed every 2 years with a modified version of the Telephone Interview for Cognitive Status to identify the transition from normal cognition to cognitive impairment. RESULTS: Estimates from Weibull accelerated failure-time models reveal that SMD is associated with earlier incident cognitive impairment (time ratio = 0.96, p < .05). In subsequent models stratified by race-ethnicity, this association was evident among White respondents (time ratio = 0.95, p < .01) but not among Black, U.S.-born Hispanic, or foreign-born Hispanic respondents. DISCUSSION AND IMPLICATIONS: Given that the prognostic validity of SMD differs by race and ethnicity, caution is warranted when using it as a screening or clinical tool in diverse populations.

The Role of the Gut Microbiota in the Relationship Between Diet and Human Health.

The interplay between diet, the gut microbiome, and host health is complex. Diets associated with health have many similarities: high fiber, unsaturated fatty acids, and polyphenols while being low in saturated fats, sodium, and refined carbohydrates. Over the past several decades, dietary patterns have changed significantly in Westernized nations with the increased consumption of calorically dense ultraprocessed foods low in fiber and high in saturated fats, salt, and refined carbohydrates, leading to numerous negative health consequences including obesity, metabolic syndrome, and cardiovascular disease. The gut microbiota is an environmental factor that interacts with diet and may also have an impact on health outcomes, many of which involve metabolites produced by the microbiota from dietary components that can impact the host. This review focuses on our current understanding of the complex relationship between diet, the gut microbiota, and host health, with examples of how diet can support health, increase an individual's risk for disease, and be used as a therapy for specific diseases.

Stable isotope tracing in vivo reveals a metabolic bridge linking the microbiota to host histone acetylation.

The gut microbiota influences acetylation on host histones by fermenting dietary fiber into butyrate. Although butyrate could promote histone acetylation by inhibiting histone deacetylases, it may also undergo oxidation to acetyl-coenzyme A (CoA), a necessary cofactor for histone acetyltransferases. Here, we find that epithelial cells from germ-free mice harbor a loss of histone H4 acetylation across the genome except at promoter regions. Using stable isotope tracing in vivo with 13C-labeled fiber, we demonstrate that the microbiota supplies carbon for histone acetylation. Subsequent metabolomic profiling revealed hundreds of labeled molecules and supported a microbial contribution to host fatty acid metabolism, which declined in response to colitis and correlated with reduced expression of genes involved in fatty acid oxidation. These results illuminate the flow of carbon from the diet to the host via the microbiota, disruptions to which may affect energy homeostasis in the distal gut and contribute to the development of colitis.

Gardnerella vaginalis alters cervicovaginal epithelial cell function through microbe-specific immune responses.

BACKGROUND: The cervicovaginal (CV) microbiome is highly associated with vaginal health and disease in both pregnant and nonpregnant individuals. An overabundance of Gardnerella vaginalis (G. vaginalis) in the CV space is commonly associated with adverse reproductive outcomes including bacterial vaginosis (BV), sexually transmitted diseases, and preterm birth, while the presence of Lactobacillus spp. is often associated with reproductive health. While host-microbial interactions are hypothesized to contribute to CV health and disease, the mechanisms by which these interactions regulate CV epithelial function remain largely unknown. RESULTS: Using an in vitro co-culture model, we assessed the effects of Lactobacillus crispatus (L. crispatus) and G. vaginalis on the CV epithelial barrier, the immune mediators that could be contributing to decreased barrier integrity and the immune signaling pathways regulating the immune response. G. vaginalis, but not L. crispatus, significantly increased epithelial cell death and decreased epithelial barrier integrity in an epithelial cell-specific manner. A G. vaginalis-mediated epithelial immune response including NF-κB activation and proinflammatory cytokine release was initiated partially through TLR2-dependent signaling pathways. Additionally, investigation of the cytokine immune profile in human CV fluid showed distinctive clustering of cytokines by Gardnerella spp. abundance and birth outcome. CONCLUSIONS: The results of this study show microbe-specific effects on CV epithelial function. Altered epithelial barrier function through cell death and immune-mediated mechanisms by G. vaginalis, but not L. crispatus, indicates that host epithelial cells respond to bacteria-associated signals, resulting in altered epithelial function and ultimately CV disease. Additionally, distinct immune signatures associated with Gardnerella spp. or birth outcome provide further evidence that host-microbial interactions may contribute significantly to the biological mechanisms regulating reproductive outcomes. Video Abstract.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens.

The baseline composition of T cells directly affects later response to pathogens, but the complexity of precursor states remains poorly defined. Here, we examined the baseline state of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells in unexposed individuals. SARS-CoV-2-specific CD4+ T cells were identified in prepandemic blood samples by major histocompatibility complex (MHC) class II tetramer staining and enrichment. Our data revealed a substantial number of SARS-CoV-2-specific T cells that expressed memory phenotype markers. Integrated phenotypic analyses demonstrated diverse preexisting memory states that included cells with distinct polarization features and trafficking potential to barrier tissues. T cell clones generated from tetramer-labeled cells cross-reacted with antigens from commensal bacteria in the skin and gastrointestinal tract. Direct ex vivo tetramer staining for one spike-specific population showed a similar level of cross-reactivity to sequences from endemic coronavirus and commensal bacteria. These data highlight the complexity of precursor T cell repertoire and implicate noninfectious exposures to common microbes as a key factor that shapes human preexisting immunity to SARS-CoV-2.