Editorial: Shiga Toxin-Converting Bacteriophages

Gut phageome in Mexican Americans: a population at high risk for metabolic dysfunction-associated steatotic liver disease and diabetes

Mexican Americans are disproportionally affected by metabolic dysfunction-associated steatotic liver disease (MASLD), which often co-occurs with diabetes. Despite extensive evidence on the causative role of the gut microbiome in MASLD, studies determining the involvement of the gut phageome are scarce. In this cross-sectional study, we characterized the gut phageome in Mexican Americans of South Texas by stool shotgun metagenomic sequencing of 340 subjects, concurrently screened for liver steatosis by transient elastography. Inter-individual variations in the phageome were associated with gender, country of birth, diabetes, and liver steatosis. The phage signatures for diabetes and liver steatosis were subsequently determined. Enrichment of Inoviridae was associated with both diabetes and liver steatosis. Diabetes was further associated with the enrichment of predominantly temperate Escherichia phages, some of which possessed virulence factors. Liver steatosis was associated with the depletion of Lactococcus phages r1t and BK5-T, and enrichment of the globally prevalent Crassvirales phages, including members of genus cluster IX (Burzaovirus coli, Burzaovirus faecalis) and VI (Kahnovirus oralis). The Lactococcus phages showed strong correlations and co-occurrence with Lactococcus lactis, while the Crassvirales phages, B. coli, B. faecalis, and UAG-readthrough crAss clade correlated and co-occurred with Prevotella copri. In conclusion, we identified the gut phageome signatures for two closely linked metabolic diseases with significant global burden. These phage signatures may have utility in risk modeling and disease prevention in this high-risk population, and identification of potential bacterial targets for phage therapy.IMPORTANCEPhages influence human health and disease by shaping the gut bacterial community. Using stool samples from a high-risk Mexican American population, we provide insights into the gut phageome changes associated with diabetes and liver steatosis, two closely linked metabolic diseases with significant global burden. Common to both diseases was an enrichment of Inoviridae, a group of phages that infect bacterial hosts chronically without lysis, allowing them to significantly influence bacterial growth, virulence, motility, biofilm formation, and horizontal gene transfer. Diabetes was additionally associated with the enrichment of Escherichia coli-infecting phages, some of which contained virulence factors. Liver steatosis was additionally associated with the depletion of Lactococcus lactis-infecting phages, and enrichment of Crassvirales phages, a group of virulent phages with high global prevalence and persistence across generations. These phageome signatures may have utility in risk modeling, as well as identify potential bacterial targets for phage therapy.

Host-derived O-glycans inhibit toxigenic conversion by a virulence-encoding phage in Vibrio cholerae

Pandemic and endemic strains of Vibrio cholerae arise from toxigenic conversion by the CTXφ bacteriophage, a process by which CTXφ infects nontoxigenic strains of V. cholerae. CTXφ encodes the cholera toxin, an enterotoxin responsible for the watery diarrhea associated with cholera infections. Despite the critical role of CTXφ during infections, signals that affect CTXφ-driven toxigenic conversion or expression of the CTXφ-encoded cholera toxin remain poorly characterized, particularly in the context of the gut mucosa. Here, we identify mucin polymers as potent regulators of CTXφ-driven pathogenicity in V. cholerae. Our results indicate that mucin-associated O-glycans block toxigenic conversion by CTXφ and suppress the expression of CTXφ-related virulence factors, including the toxin co-regulated pilus and cholera toxin, by interfering with the TcpP/ToxR/ToxT virulence pathway. By synthesizing individual mucin glycan structures de novo, we identify the Core 2 motif as the critical structure governing this virulence attenuation. Overall, our results highlight a novel mechanism by which mucins and their associated O-glycan structures affect CTXφ-mediated evolution and pathogenicity of V. cholerae, underscoring the potential regulatory power housed within mucus.

Immunogenicity of inactivated Escherichia coli O157:H7 with Stx2B microparticle in mice

Objectives

Vaccination using inactivated bacteria is one of the most effective ways to protect against EHEC infection. Escherichia coli O157:H7 infections are mainly influenced by Shiga toxins (Stx) and attaching/effacing factors. Among various factors, Stx2B is gaining much attention as a vaccine candidate. Formulating an inactivated bacteria with a suitable adjuvant increases vaccine efficacy and antibody production and can lead to a lasting immune response and protection against O157:H7.

Materials and Methods

To assess vaccine efficacy, in this study, we have considered heat and formalin-inactivated bacteria along with chitosan-coated Stx2B/ Stx2B in a mouse model. Ionotropic gelation via tripolyphosphate anions was used to coat Stx2B on chitosan. Subcutaneous injection or oral gavage was used to immunize mice, which were then challenged with E. coli O157:H7.

Results

Immunity and protection against E. coli O157:H7 were achieved by all forms of the vaccine. Inactivated E. coli O157:H7 formulated with chitosan-coated Stx2B effectively evoked humoral and mucosal immune responses. However, minimum shedding appeared with the mice groups orally immunized with formalin-inactivated bacteria sublimated with chitosan-coated Stx2B and heat-inactivated bacteria plus Stx2B in subcutaneous immunization.

Conclusion

Administration of inactivated whole-cell and toxin was synergistic and increased the protection capacity with both parenteral and oral immunization routes.

A Validation System for Selection of Bacteriophages against Shiga Toxin-Producing Escherichia coli Contamination

Shiga toxin-producing Escherichia coli (STEC) can cause severe infections in humans, leading to serious diseases and dangerous complications, such as hemolytic-uremic syndrome. Although cattle are a major reservoir of STEC, the most commonly occurring source of human infections are food products (e.g., vegetables) contaminated with cow feces (often due to the use of natural fertilizers in agriculture). Since the use of antibiotics against STEC is controversial, other methods for protection of food against contaminations by these bacteria are required. Here, we propose a validation system for selection of bacteriophages against STEC contamination. As a model system, we have employed a STEC-specific bacteriophage vB_Eco4M-7 and the E. coli O157:H7 strain no. 86-24, bearing Shiga toxin-converting prophage ST2-8624 (Δstx2::cat gfp). When these bacteria were administered on the surface of sliced cucumber (as a model vegetable), significant decrease in number viable E. coli cells was observed after 6 h of incubation. No toxicity of vB_Eco4M-7 against mammalian cells (using the Balb/3T3 cell line as a model) was detected. A rapid decrease of optical density of STEC culture was demonstrated following addition of a vB_Eco4M-7 lysate. However, longer incubation of susceptible bacteria with this bacteriophage resulted in the appearance of phage-resistant cells which predominated in the culture after 24 h incubation. Interestingly, efficiency of selection of bacteria resistant to vB_Eco4M-7 was higher at higher multiplicity of infection (MOI); the highest efficiency was evident at MOI 10, while the lowest occurred at MOI 0.001. A similar phenomenon of selection of the phage-resistant bacteria was also observed in the experiment with the STEC-contaminated cucumber after 24 h incubation with phage lysate. On the other hand, bacteriophage vB_Eco4M-7 could efficiently develop in host bacterial cells, giving plaques at similar efficiency of plating at 37, 25 and 12 °C, indicating that it can destroy STEC cells at the range of temperatures commonly used for vegetable short-term storage. These results indicate that bacteriophage vB_Eco4M-7 may be considered for its use in food protection against STEC contamination; however, caution should be taken due to the phenomenon of the appearance of phage-resistant bacteria.