Dietary protein changes the way cholera bacteria colonize the intestines

Dietary protein changes the way cholera bacteria colonize the intestines

New research shows that what we eat, down to the type of dietary protein, can influence the balance between Vibrio cholerae and the gut microbiota, altering bacterial competition and disease potential during cholera infection.

A recent study published inCell host and microbe examines the role of dietary components and the intestinal microbiotaVibrio choleraeInfection, commonly referred to asas cholera.

Cholera risk is influenced by interactions between diet and microbiota

Cholera is a serious diarrheal disease that affects over 2.9 million people worldwide, with 95,000 dying from this infection each year. The virulence of V. cholerae is determined by the coordinated expression of multiple virulence factors amid the destruction attempts of microorganisms in the gastrointestinal tract aimed at preventing the colonization of pathogens.

The effectiveness of this host defense against V. cholerae infection is determined by the composition of the gut microbiome, which is influenced by daily dietary habits and affects its diversity and quantity. For example, consuming fiber leads to the production of short-chain fatty acids (SCFAs), which prevent diarrhea by facilitating sodium and water absorption.

The central role of diet in the prevalence and severity of cholera is illustrated by its strong association with malnutrition, a common comorbidity in cholera-endemic areas. Nevertheless, it remains unclear how diet influences gene expression, fitness, and competition with the gut microbiome of V. cholerae during infection.

The macronutrient-specific effects on V. cholerae colonization

The current study examined how macronutrients in the host diet are involved in intestinal colonization and competition by V. cholerae. For this purpose, specific pathogen-free (SPF) mice were infected with V. cholerae while consuming a diet high in carbohydrates, proteins, or fats, with all minerals and vitamins similar between groups.

Mice that consumed a high-protein (casein-based) diet showed significantly lower colonization with V. cholerae compared to mice that consumed other refined diets or control foods. V. cholerae accounted for 99.9% of the bacteria present in the gastrointestinal tract of these mice, suggesting that reduced colonization is unlikely to be explained by residual intestinal commensals following antibiotic treatment.

Casein, the main protein component of this refined diet, has previously been shown to inhibit cholera toxin (CT) binding in vitro. To clarify this possible connection, the researchers repeated their experiment using a high-protein refined diet containing soybean protein or wheat gluten. Compared to mice fed casein or wheat gluten, high soy protein intake was associated with greater V. cholerae colonization.

A total of 202, 1,288 and 678 genes were differentially expressed in fecal DNA samples from mice consuming high-protein soybean, wheat gluten and casein diets compared to controls. Consumption of casein and wheat gluten diets resulted in a greater degree of similarity in up- or down-regulated gene expression compared to the soy protein diet.

More specifically, consumption of diets refined with casein or wheat gluten reduced the expression of genes involved in oxidative phosphorylation, tricyclic acid cycle (TCA), and carbon metabolism, suggesting that casein or wheat gluten may influence the metabolism of V. cholerae during infection. Significant upregulation of sulfur-related signaling pathways has also been associated with casein and wheat gluten compared to soybean protein.

All protein sources resulted in high protein diets Trends toward decreased expression of the CT genes ctxAB, toxin co-regulated pilus (TCP) genes, and accessory colonization factors, although most of these changes, with the exception of tcpF, did not reach statistical significance. The casein-rich diet downregulated genes involved in class II and IV flagellar genes, which encode the body hook, flagellin, and specific motor components. Casein and wheat gluten were found to significantly regulate the genes encoding elements of the type VI secretion system (T6SS) involved in intrabacterial competition compared to soy protein and control diet.

Host diet can largely influence V. cholerae gene expression related to metabolism, motility and virulence expression.

The researchers then conducted genetic screening using transposon insertion site sequencing (TN-seq) to identify mutant strains of V. cholerae that were more effective at colonizing the mouse gastrointestinal tract compared to wild-type strains. To this end, 3,061 were identified, pooled and introduced into mice consuming either a high casein diet or a control diet.

After deletion, a total of 40 genes were identified that support V. cholerae colonization in mice consuming a casein-rich diet, 16 of which were involved in flagella assembly. Ribonucleic acid sequencing (RNA-seq) data suggest that V. cholerae downregulates downstream flagellar structural genes following high casein intake.

V. cholerae with a mutation in the flagellar master regulatory gene flrA significantly outcompeted the wild-type strain in mice consuming a casein-rich diet, increasing the colonization rate four days after infection. The presence of flrA mutations also restored T6SS pathway gene expression, which was previously suppressed in wild-type strains after ingestion of a casein-rich diet. Notably, the effects of flrA mutations on colonization rates were not observed when the high-protein soybean diet was consumed.

Further experiments demonstrated that these diet-induced changes in T6SS activity altered the competitive interactions between V. cholerae and intestinal commensals, including a human Escherichia coli isolate, thereby remodeling the structure of the microbiota during infection.

These results suggest dietary interventions to limit V. cholerae and highlight the importance of diet in pathogen-commensal interactions.

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