We compared rectal swab nucleic acid amplification testing (NAAT) with stool culture to detect Clostridioides difficile colonization and correlated results with environmental contamination. Rectal swab NAAT sensitivity (43%) for detecting toxigenic C. difficile colonization was low. Toxigenic culture-positive patients were more likely to have C. difficile detected in the hospital environment.

Engineered probiotics are an emerging platform for in situ delivery of therapeutics to the gut. Herein, we developed an orally administered, yeast-based therapeutic delivery system to deliver next-generation immune checkpoint inhibitor (ICI) proteins directly to gastrointestinal tumors. We engineered Saccharomyces cerevisiae var. boulardii (Sb), a probiotic yeast with high genetic tractability and innate anticancer activity, to secrete “miniature” antibody variants that target programmed death ligand 1 (Sb_haPD-1). When tested in an ICI-refractory colorectal cancer (CRC) mouse model, Sb_haPD-1 significantly reduced intestinal tumor burden and resulted in significant shifts to the immune cell profile and microbiome composition. This oral therapeutic platform is modular and highly customizable, opening new avenues of targeted drug delivery that can be applied to treat a myriad of gastrointestinal malignancies.

Gastrointestinal colonization by Clostridioides difficile is common in healthcare settings and ranges in presentation from asymptomatic carriage to lethal C. difficile infection (CDI). We used a systems biology approach to investigate why patients colonized with C. difficile have a range of clinical outcomes. Microbiota humanization of germ-free mice with fecal samples from toxigenic C. difficile carriers revealed a spectrum of virulence among clinically prevalent clade 1 lineages and identified candidate taxa, including Blautia, as markers of stable colonization. Using gnotobiotic mice engrafted with defined human microbiota, we validated strain-specific CDI severity across clade 1 strains isolated from patients. Mice engrafted with a community broadly representative of colonized patients were protected from severe disease across all strains without suppression of C. difficile colonization. These results underline the capacity of gut community structure to attenuate a diversity of pathogenic strains without inhibiting colonization, providing insight into determinants of stable C. difficile carriage.

The history of clinical resistance to tetracycline antibiotics is characterized by cycles whereby the deployment of a new generation of drug molecules is quickly followed by the discovery of a new mechanism of resistance. This suggests mechanism-specific selection by each tetracycline generation; however, the evolutionary dynamics of this remain unclear. Here, we evaluate 24 recombinant Escherichia coli strains expressing tetracycline resistance genes from each mechanism (efflux pumps, ribosomal protection proteins, and enzymatic inactivation) in the context of each tetracycline generation. We employ a high-throughput barcode sequencing protocol that can discriminate between strains in mixed culture and quantify their relative abundances. We find that each mechanism is preferentially selected for by specific antibiotic generations, leading to their expansion. Remarkably, the minimum inhibitory concentration associated with individual genes is secondary to resistance mechanism for inter-mechanism relative fitness, but it does explain intra-mechanism relative fitness. These patterns match the history of clinical deployment of tetracycline drugs and resistance discovery in pathogens.

Pyridoxine-unresponsive homocystinuria has lifelong implications for health. In this issue, Perreault and colleagues present evidence that orally delivered engineered probiotic Escherichia Coli Nissle SYNB1353 is a promising candidate in reducing homocysteine, with successful trials in mice, monkeys, and humans. However, further probiotic optimization and safety assessments are required.

Background and Aims:Diagnostic differentiation between Crohn's disease (CD) and ulcerative colitis (UC) is crucial for timely and suitable therapeutic measures. The current gold standard for differentiating between CD and UC involves endoscopy and histology, which are invasive and costly. We aimed to identify blood plasma proteomic signatures using a Protein-Wide Association Study (PWAS) approach to differentiate CD from UC and evaluate the efficacy of these signatures as features in machine learning (ML) classifiers. Methods:Among participants (n=1,106; nCD=636; nUC=470) of the Study of a Prospective Adult Research Cohort with IBD (SPARC), plasma protein (n=2,920) levels were estimated using Olink proteomics. A PWAS with Bonferroni correction for multiple testing was used to identify proteins associated with disease states after controlling for age, sex, and disease severity. ML classifiers examined the diagnostic utility of these models. Feature importance was determined via SHapley Additive exPlanations (SHAP) analysis. Results:Thirteen proteins which were significantly differentially abundant in CD vs UC (all |β|s > 0.22, all adjusted p values < 8.42E-06). Random forest models of proteins differentiated between CD and UC with models trained only on PWAS identified proteins (Average ROC-AUC 0.73) outperforming models trained of the full proteome (Average ROC-AUC 0.62). SHAP analysis revealed that Granzyme B, insulin-like peptide 5 (INSL5), and interleukin-12 subunit beta (IL-12B) were the most important features. Conclusions:Our findings demonstrate that PWAS-based feature selection approaches are a powerful method to identify features in complex, noisy datasets. Importantly, we have identified novel peptide based biomarkers such as INSL5, that can be potentially used to complement existing strategies to differentiate between CD and UC.

Aberrant preterm infant gut microbiota assembly predisposes to early-life disorders and persistent health problems. Here, we characterize gut microbiome dynamics over the first 3 months of life in 236 preterm infants hospitalized in three neonatal intensive care units using shotgun metagenomics of 2,512 stools and metatranscriptomics of 1,381 stools. Strain tracking, taxonomic and functional profiling, and comprehensive clinical metadata identify Enterobacteriaceae, enterococci, and staphylococci as primarily exploiting available niches to populate the gut microbiome. Clostridioides difficile lineages persist between individuals in single centers, and Staphylococcus epidermidis lineages persist within and, unexpectedly, between centers. Collectively, antibiotic and non-antibiotic medications influence gut microbiome composition to greater extents than maternal or baseline variables. Finally, we identify a persistent low-diversity gut microbiome in neonates who develop necrotizing enterocolitis after day of life 40. Overall, we comprehensively describe gut microbiome dynamics in response to medical interventions in preterm, hospitalized neonates.

Clostridioides difficile infection (CDI) is a major cause of healthcare-associated diarrhea, despite the widespread implementation of contact precautions for patients with CDI. Here, we investigate strain contamination in a hospital setting and the genomic determinants of disease outcomes. Across two wards over 6 months, we selectively cultured C. difficile from patients (n = 384) and their environments. Whole-genome sequencing (WGS) of 146 isolates revealed that most C. difficile isolates were from clade 1 (131/146, 89.7%), while only one isolate of the hypervirulent ST1 was recovered. Of culture-positive admissions (n = 79), 19 (24%) patients were colonized with toxigenic C. difficile on admission to the hospital. We defined 25 strain networks at ≤2 core gene single nucleotide polymorphisms; two of these networks contain strains from different patients. Strain networks were temporally linked (P < 0.0001). To understand the genomic correlates of the disease, we conducted WGS on an additional cohort of C. difficile (n = 102 isolates) from the same hospital and confirmed that clade 1 isolates are responsible for most CDI cases. We found that while toxigenic C. difficile isolates are associated with the presence of cdtR, nontoxigenic isolates have an increased abundance of prophages. Our pangenomic analysis of clade 1 isolates suggests that while toxin genes (tcdABER and cdtR) were associated with CDI symptoms, they are dispensable for patient colonization. These data indicate that toxigenic and nontoxigenic C. difficile contamination persist in a hospital setting and highlight further investigation into how accessory genomic repertoires contribute to C. difficile colonization and disease. IMPORTANCE:Clostridioides difficile infection remains a leading cause of hospital-associated diarrhea, despite increased antibiotic stewardship and transmission prevention strategies. This suggests a changing genomic landscape of C. difficile. Our study provides insight into the nature of prevalent C. difficile strains in a hospital setting and transmission patterns among carriers. Longitudinal sampling of surfaces and patient stool revealed that both toxigenic and nontoxigenic strains of C. difficile clade 1 dominate these two wards. Moreover, quantification of transmission in carriers of these clade 1 isolates underscores the need to revisit infection prevention measures in this patient group. We identified unique genetic signatures associated with virulence in this clade. Our data highlight the complexities of preventing transmission of this pathogen in a hospital setting and the need to investigate the mechanisms of in vivo persistence and virulence of prevalent lineages in the host gut microbiome.

Antibiotic-mediated perturbation of the gut microbiome is associated with numerous infectious and autoimmune diseases of the gastrointestinal tract. Yet, as the gut microbiome is a complex ecological network of microorganisms, the effects of antibiotics can be highly variable. With the advent of multi-omic approaches for systems-level profiling of microbial communities, we are beginning to identify microbiome-intrinsic and microbiome-extrinsic factors that affect microbiome dynamics during antibiotic exposure and subsequent recovery. In this Review, we discuss factors that influence restructuring of the gut microbiome on antibiotic exposure. We present an overview of the currently complex picture of treatment-induced changes to the microbial community and highlight essential considerations for future investigations of antibiotic-specific outcomes. Finally, we provide a synopsis of available strategies to minimize antibiotic-induced damage or to restore the pretreatment architectures of the gut microbial community.

Abstract Background Clostridioides difficile (CD) colonization is common among hospitalized patients. Screening for toxigenic CD (TCD) colonization with rectal swab nucleic acid amplification tests (NAAT) may identify people at risk for CDI and help prevent onward TCD transmission, especially in immunocompromised patients with long hospitalizations. The study objective was to test whether rectal swab NAAT could detect TCD colonized patients and whether NAAT results identify patients that contribute to environmental contamination. Methods This was a prospective cohort study on two BMT/Leukemia units. Stool specimens, rectal swabs, and environmental swabs (bedrail, room sink, keyboard) were collected from patients at admission and weekly and cultured semi-quantitatively for TCD. NAAT (Cepheid) was performed on rectal swabs (eSwabs; Copan Diagnostics). The relationship between stool TCD concentration, NAAT Ct, and a positive environmental culture was evaluated using univariate logistic regression. Bleach was used for daily and terminal discharge cleaning of all rooms. Toxigenicity was determined by detection of tcdA or tcdB by whole genome sequencing (WGS). Results From January 2019 - July 2019, 659 stool specimens and 495 rectal swabs were collected from 384 patients. Specimens from 554 patient-days were cultured and 126 (23%) were positive. Of those, 88 (70%) were TCD. 21 of 987 (2%) environmental swabs were TCD positive; 18 (86%) were from bedrails. Among 61 unique patient calendar days with paired rectal swab NAAT and stool culture results (paired samples), overall sensitivity of rectal swab NAAT to detect toxigenic CD colonization compared to culture was 44%, with 4/16 (25%) of people colonized with > 0 - < 10,000 CFU/g of TCD and 7/9 (78%) with ≥ 10,000 CFU/g TCD (Figure 1). There was no relationship between stool culture or rectal swab NAAT result and risk of a positive environmental swab (Figure 2). Figure 1. Toxigenic C. difficile semi-quantitative culture and rectal swab NAAT on paired patient-day of specimen collection (N=61 patient-days) Figure 2. Toxigenic C. difficile semi-quantitative stool and rectal swab NAAT results and environmental contamination by paired patient-day of specimen collection Conclusion Rectal swab NAAT may not be sufficiently sensitive to screen for TCD colonization that contributes to environmental contamination. Disclosures Erik R. Dubberke, MD, MSPH, Abbott: Advisor/Consultant|AstraZeneca: Advisor/Consultant|Ferring Pharmaceuticals: Advisor/Consultant|Ferring Pharmaceuticals: Grant/Research Support|Merck and Co.: Advisor/Consultant|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Seres Therapeutics: Advisor/Consultant|Summit: Advisor/Consultant|Theriva Biologics: Grant/Research Support

BACKGROUND:Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and an increasingly frequent cause of opportunistic infections. Mycobacterium abscessus complex (MABC) is one of the major NTM lung pathogens that disproportionately colonize and infect the lungs of individuals with cystic fibrosis (CF). MABC infection can persist for years, and antimicrobial treatment is frequently ineffective.METHODS:We sequenced the genomes of 175 isolates longitudinally collected from 30 patients with MABC lung infection. We contextualized our cohort amidst the broader MABC phylogeny and investigated genes undergoing parallel adaptation across patients. Finally, we tested the phenotypic consequences of parallel mutations by conducting antimicrobial resistance and mercury-resistance assays.RESULTS:We identified highly related isolate pairs across hospital centers with low likelihood of transmission. We further annotated nonrandom parallel mutations in 22 genes and demonstrated altered macrolide susceptibility co-occurring with a nonsynonymous whiB1 mutation. Finally, we highlighted a 23-kb mercury-resistance plasmid whose loss during chronic infection conferred phenotypic susceptibility to organic and nonorganic mercury compounds.CONCLUSIONS:We characterized parallel genomic processes through which MABC is adapting to promote survival within the host. The within-lineage polymorphisms we observed have phenotypic effects, potentially benefiting fitness in the host at the putative detriment of environmental survival.

AbstractClostridioides difficileinfection (CDI) is a major cause of healthcare-associated diarrhea, despite the widespread implementation of contact precautions for patients with CDI. Here, we investigate strain contamination in a hospital setting and genomic determinants of disease outcomes. Across two wards over six months, we selectively culturedC. difficilefrom patients (n=384) and their environments. Whole-genome sequencing (WGS) of 146 isolates revealed that mostC. difficileisolates were from clade 1 (131/146, 89.7%), while only one isolate of the hypervirulent ST1 was recovered. Of culture-positive admissions (n=79), 19 (24%) of patients were colonized with toxigenicC. difficileon admission to the hospital. We defined 25 strain networks at ≤ 2 core gene SNPs; 2 of these networks contain strains from different patients. Strain networks were temporally linked (p<0.0001). To understand genomic correlates of disease, we conducted WGS on an additional cohort ofC. difficile(n=102 isolates) from the same hospital and confirmed that clade 1 isolates are responsible for most CDI cases. We found that while toxigenicC. difficileisolates are associated with the presence ofcdtR, nontoxigenic isolates have an increased abundance of prophages. Our pangenomic analysis of clade 1 isolates suggests that while toxin genes (tcdABER and cdtR) were associated with CDI symptoms, they are dispensable for patient colonization. These data indicate toxigenic and nontoxigenicC. difficilecontamination persists in a hospital setting and highlight further investigation into how accessory genomic repertoires contribute toC. difficilecolonization and disease.

We report the draft genome sequence of an unusual Mycobacterium isolate recovered from a patient's arm tissue. The 4,025,753-bp draft genome exhibits a GC content of 71.02%, and a 16S rRNA gene analysis found that the closest relative was Mycobacterium grossiae.

Clostridioides difficile infection (CDI) imposes a substantial burden on the health care system in the United States. Understanding the biological basis for the spectrum of C. difficile-related disease manifestations is imperative to improving treatment and prevention of CDI. Here, we investigate the correlates of asymptomatic C. difficile colonization using a multi-omics approach. We compared the fecal microbiome and metabolome profiles of patients with CDI versus asymptomatically colonized patients, integrating clinical and pathogen factors into our analysis. We found that CDI patients were more likely to be colonized by strains with the binary toxin (CDT) locus or strains of ribotype 027, which are often hypervirulent. We find that microbiomes of asymptomatically colonized patients are significantly enriched for species in the class Clostridia relative to those of symptomatic patients. Relative to CDI microbiomes, asymptomatically colonized patient microbiomes were enriched with sucrose degradation pathways encoded by commensal Clostridia, in addition to glycoside hydrolases putatively involved in starch and sucrose degradation. Fecal metabolomics corroborates the carbohydrate degradation signature: we identify carbohydrate compounds enriched in asymptomatically colonized patients relative to CDI patients. Further, we reveal that across C. difficile isolates, the carbohydrates sucrose, rhamnose, and lactulose do not serve as robust growth substrates in vitro, consistent with their enriched detection in our metagenomic and metabolite profiling of asymptomatically colonized individuals. We conclude that pathogen genetic variation may be strongly related to disease outcome. More interestingly, we hypothesize that in asymptomatically colonized individuals, carbohydrate metabolism by other commensal Clostridia may prevent CDI by inhibiting C. difficile proliferation. These insights into C. difficile colonization and putative commensal competition suggest novel avenues to develop probiotic or prebiotic therapeutics against CDI.

Microbial biocontainment is an essential goal for engineering safe, next-generation living therapeutics. However, the genetic stability of biocontainment circuits, including kill switches, is a challenge that must be addressed. Kill switches are among the most difficult circuits to maintain due to the strong selection pressure they impart, leading to high potential for evolution of escape mutant populations. Here we engineer two CRISPR-based kill switches in the probiotic Escherichia coli Nissle 1917, a single-input chemical-responsive switch and a 2-input chemical- and temperature-responsive switch. We employ parallel strategies to address kill switch stability, including functional redundancy within the circuit, modulation of the SOS response, antibiotic-independent plasmid maintenance, and provision of intra-niche competition by a closely related strain. We demonstrate that strains harboring either kill switch can be selectively and efficiently killed inside the murine gut, while strains harboring the 2-input switch are additionally killed upon excretion. Leveraging redundant strategies, we demonstrate robust biocontainment of our kill switch strains and provide a template for future kill switch development.

Clostridioides difficile infection (CDI) imposes a substantial burden on the health care system in the United States. Understanding the biological basis for the spectrum of C. difficile -related disease manifestations is imperative to improving treatment and prevention of CDI. Here, we investigate the correlates of asymptomatic C. difficile colonization using a multi-omics approach, comparing the fecal microbiome and metabolome profiles of patients with CDI versus asymptomatically-colonized patients. We find that microbiomes of asymptomatic patients are significantly enriched for species in the class Clostridia relative to those of symptomatic patients. Asymptomatic patient microbiomes were enriched with fucose, rhamnose, and sucrose degradation pathways relative to CDI patient microbiomes. Fecal metabolomics corroborates this result: we identify carbohydrate compounds enriched in asymptomatic patients relative to CDI patients, and correlated with a number of commensal Clostridia. Further, we reveal that across C. difficile isolates, the carbohydrates rhamnose and lactulose do not serve as robust growth substrates in vitro , corroborating their enriched detection in our metagenomic and metabolite profiling of asymptomatic individuals. We conclude that in asymptomatically-colonized individuals, carbohydrate metabolism by other commensal Clostridia may prevent CDI by inhibiting C. difficile proliferation. These insights into C. difficile colonization and putative commensal competition suggest novel avenues to develop probiotic or prebiotic therapeutics against CDI.

The mycobacterial cell wall is a promising target for new antibiotics due to the abundance of important membrane-associated proteins. Defining mechanisms of synthesis of the membrane proteome will be critical to uncovering and validating drug targets.

A gold standard diagnostic for Clostridioides difficile infection (CDI) does not exist. An area of controversy is how to manage patients whose stool tests positive by nucleic acid amplification tests but negative by toxin enzyme immunoassay.

Antimicrobial resistance is one of the largest threats to global health and imposes substantial burdens in terms of morbidity, mortality, and economic costs. The gut is a key conduit for the genesis and spread of antimicrobial resistance in enteric bacterial pathogens. Distinct bacterial species that cause enteric disease can exist as invasive enteropathogens that immediately evoke gastrointestinal distress, or pathobionts that can arise from established bacterial commensals to inflict dysbiosis and disease. Furthermore, various environmental reservoirs and stressors facilitate the evolution and transmission of resistance. In this review, we present a comprehensive discussion on circulating resistance profiles and gene mobilization strategies of the most problematic species of enteric bacterial pathogens. Importantly, we present emerging approaches toward surveillance of pathogens and their resistance elements as well as promising treatment strategies that can circumvent common resistance mechanisms.