Tag Archives: Vitamins

Microbiology

New study focuses on genetic diversity of E. coli bacteria in hospitalized patients

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Reviewed by Emily Henderson, B.Sc.Mar 13 2023

The human intestine is an environment inhabited by many bacteria and other microorganisms collectively known as the gut microbiome, gut microbiota or intestinal flora. In most people, it contributes to wellness. A healthy gut indicates a stronger immune system, improved metabolism, and a healthy brain and heart, among other functions.

Escherichia coli is one of the bacteria found in practically everyone’s gut microbiota, where it performs important functions, such as producing certain vitamins.

But there’s a vast amount of genetic diversity in the species. Some of its members are pathogenic and can cause diseases such as urinary tract infections. E. coli is the main agent of this type of infection among both healthy people and hospitalized patients or users of healthcare services.”

Tânia Gomes do Amaral, Head of the Experimental Enterobacterial Pathogenicity Laboratory (LEPE), Federal University of São Paulo’s Medical School (EPM-UNIFESP), Brazil

Amaral is first author of an article published in the journal Pathogens on the virulence of these bacteria and their resistance to antibiotics in hospitalized patients.

“Our study focused on hospitalized patients because patients who stay in hospital for a long period are more likely to undergo various procedures, such as urine catheter insertion or venous access. Although these procedures are performed to assure life support, they may facilitate the entry of bacteria into the organism and cause an infection,” Amaral explained.

She earned a PhD in microbiology from EPM-UNIFESP in 1988, conducting part of her research at New York University Medical School and the Center for Vaccine Development at the University of Maryland, Baltimore (UMB) in the United States.

The article reports the findings of a broader study led by Amaral, with 12 co-authors who are researchers and graduate students, on the virulence and drug resistance of E. coli strains associated with urinary tract infections. The study was supported by FAPESP via three projects (18/17353-7, 19/21685-8 and 17/14821-7).

The main aim of this part of the study, described in the master’s dissertation of José Francisco Santos Neto, was to evaluate the diversity and drug resistance of pathogenic E. coli strains isolated from the gut microbiota of inpatients, and to analyze the frequency of endogenous infection (caused by bacteria from the patient’s own microbiota).

The UNIFESP group first investigated the genetic diversity and drug resistance of E. coli strains isolated from the gut microbiota of hospitalized patients, sequencing these strains as well as others isolated from their urine and comparing the results in order to evaluate dissemination of the bacteria in the hospital environment.

“We also compared the genomes of these strains with those of E. coli strains isolated in different parts of the world in order to see if any globally disseminated pathogenic bacteria were present in the study sample,” said Ana Carolina de Mello Santos, a postdoctoral researcher working on the LEPE team.

Urinary tract infections proved to be endogenous for the vast majority of the patients in the study (more than 70%). The results also showed that the patients’ gut microbiota contained at least two genetically different populations of E. coli and that about 30% were colonized by non-lactose-fermenting E. coli strains, which are less common, with some of the patients studied having only such strains in their gut microbiota.

“This finding is most interesting because previous research conducted in other countries to analyze the composition of human gut microbiota didn’t investigate non-lactose-fermenting E. coli,” Santos said.

The authors also note the presence of bacteria with all the genetic markers required for classification as pathogenic and the detection of pathogenic bacteria in the gut microbiota of all patients that had not yet developed an infection. “Hospitalized patients are more susceptible to infection because by definition they are already unwell. Colonization by pathogens is the first step in the spread of hospital-acquired infections now so frequent worldwide,” Santos said.

With regard to antibiotics and other antimicrobials, the authors stress that drug resistance is also a growing global problem, and enterobacterial resistance to third-generation cephalosporins as well as colistin is critical. In all patients whose gut microbiota was colonized by drug-resistant bacteria, the same bacteria also caused endogenous urinary tract infections. In other words, the multidrug-resistant bacteria colonized the gut and traveled to the urinary tract, where they caused an infection.

“In light of these findings, early assessment of gut microbiota in hospitalized patients, at least in cases of E. coli infection, can facilitate and guide their treatment, while also identifying patients who risk progressing to extra-intestinal diseases such as urinary tract infections, which were part of the focus for our study,” Amaral said. “We don’t yet know whether the findings also apply to other bacteria found in gut microbiota, such as the genera Klebsiella, Enterobacter, Pseudomonas and others that can cause infections when they travel to extra-intestinal sites.”

These bacterial genera tend to be even more drug-resistant than E. coli, representing a major public health problem in the hospital environment. As the researchers noted, the World Health Organization (WHO) considers E. coli strains resistant to cephalosporin and colistin to be a critical global health threat. “The presence in human gut microbiota of drug-resistant bacteria associated with severe infectious disease is a matter of great concern, not least because they could spread to people outside the hospital environment,” Amaral said.

Another point raised by the study is the importance of finding out when colonization of the patient’s gut by drug-resistant virulent bacteria occurred. The authors of the article were unable to determine whether the bacteria resistant to cephalosporins and colistin colonized the patients before or after they were hospitalized.

By analyzing the genomes of the strains, however, the researchers were able to identify global risk clones that can cause severe disease and are associated with antimicrobial resistance. “One such clone found in the gut microbiota of two patients was identical to others isolated from urinary tract infections in Londrina, Paraná [a state in South Brazil], and in the United States, as well as European and Asian countries. This shows that some strains found in the study are clones generally associated with infections in all regions of the world,” Amaral said.

This type of information is important when patients are hospitalized. Knowledge of bacterial virulence and drug resistance can be used to prevent infection in parts of the organism outside the intestine and stop the bacteria from spreading to other patients in the same hospital.

Source:

São Paulo Research Foundation (FAPESP)

Journal reference:

Santos-Neto, J.F., et al. (2023) Virulence Profile, Antibiotic Resistance, and Phylogenetic Relationships among Escherichia coli Strains Isolated from the Feces and Urine of Hospitalized Patients. Pathogens. doi.org/10.3390/pathogens11121528.

Microbiology

Do seasonal changes in food types lead to changes in the composition and structure of gut microbiota?

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Bhavana KunkalikarBy Bhavana KunkalikarMar 6 2023Reviewed by Danielle Ellis, B.Sc.

In a recent study published in the Frontiers in Microbiology, researchers assessed the impact of diet or macronutrient consumption on the function and structure of gut microbiota.

Study: Does diet or macronutrients intake drive the structure and function of gut microbiota? Image Credit: Alpha Tauri 3D Graphics/Shutterstock
Study: Does diet or macronutrients intake drive the structure and function of gut microbiota? Image Credit: Alpha Tauri 3D Graphics/Shutterstock

Background

Shifting ingestive behavior is crucial for animals to adjust to environmental change. Studies have recognized that changes in animal feeding habits lead to gut microbiota structure alterations. However, further research is required to understand the alterations incident in the structure as well as the function of the gut microbiota that occur in response to alterations in nutrient consumption or food types.

About the study

In the present study, researchers explored how animal feeding techniques influence nutrient consumption and further affect the content and digestive function of the gut microbiota.

The study observation site was in the Guanyin Mountain National Natural Reserve in the Qinling Mountains, northwest of Fuping County, Shaanxi Province, China. During a year, this area experiences conventional and four different seasons. According to climate, the seasons are as follows: Spring between March and May, Summer between June and August, Autumn between September and November, and Winter between December and February.

The team compiled feeding information for the four seasonal groupings. For data collection, a month with typical phenological characteristics for each season: March for Spring, June for Summer, October for Autumn, and December for Winter.

All of the 78 golden snub-nosed monkeys in the study group were accustomed to the presence of researchers. The team identified both adult and young individuals in the study cohort. Due to the necessity for quantitative observational data, the natural feeding area of the study animals was restricted. The team provided five kilograms of maize twice daily at 10 am and 3 pm as supplemental nourishment for the group. The feed grounds were evenly strewn with corn kernels.

The team randomly selected one individual per day and observed the subject animal continuously from sunrise to dusk to record data related to its feeding pattern. Furthermore, the type of food, quantity, preset units, and feeding duration were recorded. After the subject had finished eating, food samples were gathered from the leftovers.

Food samples were collected using conventional procedures, their nutritional content was assessed, and their energy content was computed. The lipid, starch, water-soluble carbohydrate (WSC), acid detergent fiber (ADF), neutral detergent fiber (NDF), acid detergent lignin (ADL), ash content of each food, and available protein (AP) were evaluated.

Results

Data related to 96 days of feeding across four months were obtained from the target population. It was discovered that the normal diet of golden snub-nosed monkeys in the wild comprised 24 plant species from 16 families. A total of six plant parts, including branches, buds, seeds, barks, leaves, and stems, were consumed by the subjects.

Throughout the year, wild snub-nosed monkeys eat 33.43% of bark, 3.09% of seed, 1.33% of bud, 3.25% of brunch, 0.17% of the stem, and 58.72% of the leaf. Nonetheless, there were significant variations in the number of plant materials consumed over the four seasons. Herbaceous stems were harvested only in tiny quantities in the Spring. Mostly, seeds were harvested in the Spring and fall. The harvesting of leaves occurred throughout the year. Throughout fall and Winter, when leaves become sparse, especially in Winter, barks, buds, and brunches were the principal sources of nutrition.

The species composition was evaluated to explore seasonal changes in gut microbiota in greater depth. Species annotation revealed that most OTUs could be assigned taxonomically at the phylum and order levels, but assignments reduced dramatically at the genus level.

The top 10 phyla out of 38 phyla recognized dominant phyla, including Bacteroidetes, Firmicutes, Spirochaetes, Proteobacteria, Tenericutes, Planctomycetes, Verrucomicrobia, Epsilonbacteriaeota, Euryarchaeota, and Fibrobacteres comprised 99% of the total abundance ratio. They comprised the majority of the golden snub-nosed monkeys’ gut microbiome.

Three hundred ninety-five metabolic pathways were found based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database’s function prediction. Gut microbes were primarily engaged in the metabolism of nucleotides, carbohydrates, glycans and their production, amino acids, terpenoids, lipids, cofactors, polyketides, and vitamins.

Moreover, some annotated functions pertaining to macronutrients exhibited relatively high abundance, including glycolysis/gluconeogenesis, pyruvate metabolism, sucrose and starch metabolism, glycerolipid metabolism, fatty acid synthesis in lipid metabolism, and pentose phosphate pathway in glycerophospholipid metabolism and carbohydrate metabolism.

Conclusion

The study findings showed a considerable seasonal change in the food consumption and nutritional intake of golden snub-nosed monkeys, with three macronutrients being higher in Autumn and Summer and lower in Winter and Spring. Seasonal dietary changes are the primary source of seasonal shifts in gut microbiota. The results indicated that bacteria in the gut compensate for inadequate macronutrient intake through microbial metabolic functions.

Journal reference:
Microbiology

Differences in gut microbiome diversity attributed to dietary patterns in children with obesity

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Dr. Chinta SidharthanBy Dr. Chinta SidharthanFeb 16 2023Reviewed by Benedette Cuffari, M.Sc.

In a recent study published in Microbiology Spectrum, researchers found that differences in the dietary patterns of children with normal weight and those who were overweight or obese contributed to variations in the gut microbiome diversity, virulence factors of gut bacteria, and metabolic function.

Study: Virulence factors of the gut microbiome are associated with BMI and metabolic blood parameters in children with obesity. Image Credit: Africa Studio / Shutterstock.com

Study: Virulence factors of the gut microbiome are associated with BMI and metabolic blood parameters in children with obesity. Image Credit: Africa Studio / Shutterstock.com

Background

A growing body of evidence indicates that gut microbiota has a significant role in various aspects of host metabolism, including digestion, harvesting of energy, and induction of low-grade inflammation. In addition, the genetic factors of the host, as well as other characteristics such as age, diet, immunity, and gender, influence the gut microbiome composition.

Research shows that bacterial diversity in the gut and the individual’s functional capacity vary between those with normal weight and obese individuals. Gut microbiome profile variations have also been linked to metabolic disorders, lipid accumulation, and inflammation.

Lipogenesis in the liver and the regulation of appetite through hormones are also associated with gut microbiome genes.

Aside from its role in adipogenesis, superoxide reduction, and the metabolism of vitamins, gut microbiota also regulates innate immunity and the systemic, low-grade inflammatory state that can contribute to fat deposition and obesity. Therefore, Dysbiosis, which is the imbalance of gut microbiota, combined with diet, likely has a significant role in the development of obesity.

About the study

In the present study, researchers conducted a cross-sectional analysis of data from 45 children between the ages of six and 12 to determine the association between gut microbiota and obesity.

Questionnaires were used to obtain information on dietary frequencies, gender, age, and body mass index (BMI). Based on the World Health Organization (WHO) z-scores, in which BMI is adjusted for gender and age, the children were classified into two categories of overweight and obese (OWOB) and normal weight (NW).

Data from food frequency questionnaires were used to classify the dietary habits of children into two nutritional patterns. To this end, Pattern 1 was characterized by complex carbohydrates and proteins, whereas Pattern 2 comprised simple carbohydrates and saturated fats.

Shotgun metagenomics was used to assess the taxonomic diversity of the gut microbiota and metabolic capacity from genomic deoxyribonucleic acid (DNA) extracted from fecal samples. Clade-specific markers were used for the taxonomic and functional assessment of the gut bacteria. Additionally, reverse Simpson and Shannon diversity indices were calculated.

The virulence factor database was used to screen for virulence factor genes, whereas multivariate linear modeling was used to determine the association between the taxa, virulence factors, and function of gut microbes and covariates of diet, serology, and anthropometric measurements.

Study findings

Significant differences between the alpha and beta diversity of the gut microbiota were observed between the children in the NW and OWOB groups, thus suggesting that specific phyla of bacteria contribute to higher levels of energy harvest.

Furthermore, species such as Ruminococcus species, Victivallis vadensis, Mitsuokella multacida, Alistipes species, Clostridium species, and Acinetobacter johnsonii were linked to healthier metabolic parameters.

In contrast, an increase in the abundance of bacteria such as Veillonellaceae, Lactococcus, Fusicatenibacter saccharivorans, Fusicatenibacter prausnitzii, Eubacterium, Roseburia, Dialister, Coprococcus catus, Bifidobacterium, and Bilophila was identified in children with pro-inflammatory conditions and obesity.

Bacteria such as Citrobacter europaeus, Citrobacter youngae, Klebsiella variicola, Enterococcus mundtii, Gemella morbillorum, and Citrobacter portucalensis were associated with higher lipid and sugar intake, as well as higher blood biochemistry values and anthropometric measurements.

Diets high in fats and simple carbohydrates have been associated with the abundance of Citrobacter and Klebsiella species in the gut. Moreover, previous studies have indicated that these bacterial species are potential markers of inflammation, obesity, and an increase in fasting glucose.

The metabolism of menaquinones and gamma-glutamyl was negatively associated with BMI. Furthermore, the microbiomes of children in the NW group preserved a more consistent alpha diversity of virulence factors, while OWOB microbiomes exhibited a dominance of virulence factors.

Differences in the metabolic capacities pertaining to biosynthesis pathways of vitamins, carriers, amino acids, nucleotides, nucleosides, amines, and polyamines, as well as the degradation of nucleotides, nucleosides, and carbohydrate-sugars, were also found between the NW and OWOB groups.

Conclusions

Dietary profiles and the diversity of gut microbiota were found to be interconnected and associated with changes in metabolic parameters, the dominance of virulence factors, and obesity. Changes in gut microbiome diversity and relative abundance have been linked to obesity, inflammatory responses, and metabolic disorders.

Taken together, the study findings suggested that the prevalence of virulence factors, as well as the metabolic and genetic roles of gut microbiota in increasing inflammation, can help identify individuals at an increased risk of childhood obesity.

Journal reference:
  • Murga-Garrido, S. M., Ulloa-Pérez, E. J., Díaz-Benítez, C. E., et al. (2023). Virulence factors of the gut microbiome are associated with BMI and metabolic blood parameters in children with obesity. Microbiology Spectrum. doi:10.1128/spectrum.03382-22
Microbiology

Vaccinating against toxin produced by E. coli may protect against malnutrition and stunting

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Reviewed by Emily Henderson, B.Sc.Jan 9 2023

Diarrhea is no longer the killer it was in the mid-20th century, when an estimated 4.5 million children under age 5 died of it every year. While lifesaving oral rehydration therapy turned the tide, it doesn’t prevent infection. Millions of children in low- and middle-income countries still endure repeated bouts of diarrhea that weaken their bodies and leave them vulnerable to malnutrition and stunted growth, and less able to fight off a wide range of infections.

Researchers at Washington University School of Medicine in St. Louis have determined, in studies of human cells as well as mice, how some types of diarrhea-causing Escherichia coli (E. coli) bacteria damage the intestines to cause malnutrition and stunting. And they’ve shown that vaccinating against a toxin produced by E. coli protects infant mice from intestinal damage.

The findings suggest that a vaccine against this kind of E. coli could boost global efforts to ensure that all children not only make it to age 5, but thrive. The study is available online in Nature Communications.

“Ideally, we’d like to have a vaccine that prevents acute diarrhea, which still kills half a million children a year, and that also protects against long-term effects such as malnutrition, which is perhaps the bigger part of the problem now,” said senior author James M. Fleckenstein, MD, a professor of medicine and of molecular microbiology. “When kids become malnourished, their risk of dying from any cause goes up. The World Health Organization is in the process of deciding how to prioritize vaccines for kids in low- and middle-income countries, and I think these data suggest that vaccinating kids against E. coli diarrhea could be hugely beneficial in places that struggle with this.”

Fleckenstein studies a kind of E. coli known as enterotoxigenic E. coli, or ETEC -; so named for the two toxins it produces -; and its effects on children who live where the bacteria run rampant. E. coliis a common cause of diarrhea worldwide, but the strains found in the U.S. and other high-income countries typically don’t carry the same toxins as those in low- and middle-income countries. And that may make all the difference.

A 2020 study by Fleckenstein and Alaullah Sheikh, PhD -; then a postdoctoral researcher in Fleckenstein’s lab and now an instructor in medicine -; indicated that one of ETEC’s two toxins, heat-labile toxin, does more than trigger a case of the runs. The toxin also affects gene expression in the gut, ramping up genes that help the bacteria stick to the gut wall.

As part of the latest study, Fleckenstein and Sheikh discovered that the toxin suppresses a whole suite of genes related to the lining of the intestines, where nutrients are absorbed. The so-called brush border of the intestine is composed of microscopic, finger-like projections called microvilli that are tightly packed over the surface of the intestines like bristles on a brush. When Fleckenstein and Sheikh applied the toxin to clusters of human intestinal cells, the brush border disintegrated.

“Instead of being nice and tight and upright with thousands of microvilli per cell, they are short, floppy and sparse, kind of like if you had plucked out most of the bristles, and what was left was kind of raggedy,” said Sheikh, who led the 2020 and current studies. “That alone would have a negative impact on the body’s ability to absorb nutrients. But on top of that, we found that genes related to absorbing specific vitamins and minerals -; notably vitamin B1 and zinc -; also were downregulated. That could explain some of the micronutrient deficiencies we see in children repeatedly exposed to these bacteria.”

Children in low- and middle-income countries tend to get diarrhea over and over, and the risk of malnutrition and stunting goes up with each bout. Studying infant mice, the researchers found that a single infection with toxin-producing E. coli was sufficient to damage the brush border, while repeated infections led to extensive intestinal damage and growth lag. Pups infected with a strain of E. coli that lacks the toxin showed no such intestinal damage or stunting.

If the toxin is the problem, an immune response neutralizing the toxin may prevent the long-term effects, Fleckenstein and Sheikh reasoned. To find out, they vaccinated nursing mouse mothers with the toxin. Suckling mice are too young to be immunized themselves, but their vaccinated mothers produce antibodies that pass to the pups through breast milk. The researchers found that the intestines of infant mice from vaccinated mothers appeared healthy, suggesting that vaccination can protect against the intestinal damage leading to malnutrition.

“This is an argument for developing a vaccine for this kind of E. coli,” Fleckenstein said. “There are lifelong consequences of getting infected over and over in childhood. Vaccination combined with efforts to improve sanitation and access to clean water could protect children from the long-term effects and give them a better shot at long and healthy lives.”

Source:

Washington University in St. Louis

Journal reference:

Sheikh A, Tumala B, Vickers TJ, Martin JC, Rosa BA, Sabui S, Basu S, Simoes RD, Mitreva M, Storer C, Tyksen E, Head RD, Beatty W, Said HM, Fleckenstein JM. Enterotoxigenic Escherichia coli heat-labile toxin drives enteropathic changes in small intestinal epithelia. Nature Communications. Nov. 12, 2022. DOI: 10.1038/s41467-022-34687-7

Microbiology

Researchers Discover Surprising Risks for COVID-19 Infection + Significant Protection From Vitamin D

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A new paper in Biology Methods & Protocols, published by Oxford University Press, investigated risk factors and protections against contracting COVID-19, and also for suffering from severe COVID. Researchers identified several characteristics – including male sex, lower age, blood group B, and larger household size – that increased the risk of infection and many other characteristics – including mask-wearing and using vitamin D – that decreased it. They also identified the things that increased or decreased the risk of a severe course of COVID-19. Some of these findings are unexpected.

SARS-CoV-2 has infected more than 600 million people worldwide, resulting in 6.57 million confirmed deaths. But information about factors affecting the probability of infection or suffering from a  severe course of the disease remains insufficient and often speculative. Preregistered longitudinal studies about the risk factors of infection are surprisingly rare. Many factors such as contact with animals have been suggested only on a theoretical basis or discussed in non-scientific sources.

Researchers here ran a study on 30 thousand internet users, recruiting participants using sites like Facebook and Twitter, in the Czech Republic who shared information about their exposure to 105 risk factors for COVID-19. Study participants indicated which potential risks and protective factors applied to them. These included health and demographic characteristics as well as information about behaviors, including keeping animals, taking vitamins and supplements, being actively engaged in sports, cold water swimming, frequent singing, marijuana use, tobacco smoking, living alone, walking in nature, and volunteering. 

The study found that, expectedly, some sociodemographic factors had a moderate effect on the risks of COVID-19. People who live in larger cities and people with higher levels of education, especially women, had a lower risk of infection. Larger household sizes and the number of children under 20 years of age (in men), were associated with a higher risk of infection. People living on their own had a much lower risk of infection than those who share the household with someone else. Singles also reported a less severe course of COVID-19. Education level and (in women) also household size had the strongest protective effects against a severe or long course of COVID-19.

Many predictable behaviors appeared to protect people against the infection, while three factors, namely being actively involved in sports, frequent singing, and cold-water swimming, increased the risk of infection. The most substantial protective factor against COVID-19 infection was strict adherence to mask-wearing. The second most substantial protective factor was the consumption of vitamins and supplements. This study found in particular that taking vitamin D provided significant protection against acquiring COVID-19.

Adherence to social distancing and frequent handwashing had only a weak protective effect. This study also indicated that having type B blood increased the risk for COVID-19 infection. Having cats or dogs as pets did not affect the risk of infection and had a mostly insignificant positive effect on the risk of someone experiencing a severe course of the disease.

The study here found that tobacco smoking and also marijuana use (in women) have a relatively strong protective effect against infection. The researchers found that marijuana use and tobacco smoking could also have some protective effects against a severe course of COVID-19. The protective effects of tobacco smoking against infection have been reported in previous studies. However, most studies show adverse effects of smoking on the risk of a severe course of COVID-19.

The most unexpected result of the study was a positive correlation between higher severity of the course of COVID-19 and adherence to wearing masks and respirators and, to a lesser extent, keeping social distance. The investigators speculate this is because people predisposed to a severe course of COVID-19 (those who are overweight, suffer from chronic obstructive pulmonary disease, or have diabetes) tried hard to avoid infection and more strictly adhered to public health recommendations about masks and social distancing. But when they did become infected, they often had a more severe course of the disease due to their underlying health problems.

Reference: “The effects of 105 biological, socioeconomic, behavioral, and environmental factors on the risk of SARS-CoV-2 infection and a severe course of COVID-19: a prospective, explorative cohort study” by Jaroslav Flegr, Pavel Flegr and Lenka Příplatová, 15 December 2022, Biology Methods and Protocols.
DOI: 10.1093/biomethods/bpac030

Oxford University Press USA

Microbiology

Vaccination against E. coli could help prevent some forms of childhood malnutrition, stunting

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Reviewed by Emily Henderson, B.Sc.Dec 7 2022

Diarrhea is no longer the killer it was in the mid-20th century, when an estimated 4.5 million children under age 5 died of it every year. While life-saving oral rehydration therapy turned the tide, it doesn’t prevent infection. Millions of children in low- and middle-income countries still endure repeated bouts of diarrhea that weaken their bodies and leave them vulnerable to malnutrition and stunted growth, and less able to fight off a wide range of infections.

Researchers at Washington University School of Medicine in St. Louis have determined, in studies of human cells as well as mice, how some types of diarrhea-causing Escherichia coli (E. coli) bacteria damage the intestines to cause malnutrition and stunting. And they’ve shown that vaccinating against a toxin produced by E. coli protects infant mice from intestinal damage.

The findings suggest that a vaccine against this kind of E. coli could boost global efforts to ensure that all children not only make it to age 5, but thrive. The study is available online in Nature Communications.

Ideally, we’d like to have a vaccine that prevents acute diarrhea, which still kills half a million children a year, and that also protects against long-term effects such as malnutrition, which is perhaps the bigger part of the problem now. When kids become malnourished, their risk of dying from any cause goes up. The World Health Organization is in the process of deciding how to prioritize vaccines for kids in low- and middle-income countries, and I think these data suggest that vaccinating kids against E. coli diarrhea could be hugely beneficial in places that struggle with this.”

James M. Fleckenstein, MD, senior author, professor of medicine and of molecular microbiology

Fleckenstein studies a kind of E. coli known as enterotoxigenic E. coli, or ETEC -; so named for the two toxins it produces -; and its effects on children who live where the bacteria run rampant. E. coli is a common cause of diarrhea worldwide, but the strains found in the U.S. and other high-income countries typically don’t carry the same toxins as those in low- and middle-income countries. And that may make all the difference.

A 2020 study by Fleckenstein and Alaullah Sheikh, PhD -; then a postdoctoral researcher in Fleckenstein’s lab and now an instructor in medicine -; indicated that one of ETEC’s two toxins, heat-labile toxin, does more than trigger a case of the runs. The toxin also affects gene expression in the gut, ramping up genes that help the bacteria stick to the gut wall.

As part of the latest study, Fleckenstein and Sheikh discovered that the toxin suppresses a whole suite of genes related to the lining of the intestines, where nutrients are absorbed. The so-called brush border of the intestine is composed of microscopic, finger-like projections called microvilli that are tightly packed over the surface of the intestines like bristles on a brush. When Fleckenstein and Sheikh applied the toxin to clusters of human intestinal cells, the brush border disintegrated.

“Instead of being nice and tight and upright with thousands of microvilli per cell, they are short, floppy and sparse, kind of like if you had plucked out most of the bristles, and what was left was kind of raggedy,” said Sheikh, who led the 2020 and current studies. “That alone would have a negative impact on the body’s ability to absorb nutrients. But on top of that, we found that genes related to absorbing specific vitamins and minerals -; notably vitamin B1 and zinc -; also were downregulated. That could explain some of the micronutrient deficiencies we see in children repeatedly exposed to these bacteria.”

Children in low- and middle-income countries tend to get diarrhea over and over, and the risk of malnutrition and stunting goes up with each bout. Studying infant mice, the researchers found that a single infection with toxin-producing E. coli was sufficient to damage the brush border, while repeated infections led to extensive intestinal damage and growth lag. Pups infected with a strain of E. coli that lacks the toxin showed no such intestinal damage or stunting.

If the toxin is the problem, an immune response neutralizing the toxin may prevent the long-term effects, Fleckenstein and Sheikh reasoned. To find out, they vaccinated nursing mouse mothers with the toxin. Suckling mice are too young to be immunized themselves, but their vaccinated mothers produce antibodies that pass to the pups through breast milk. The researchers found that the intestines of infant mice from vaccinated mothers appeared healthy, suggesting that vaccination can protect against the intestinal damage leading to malnutrition.

“This is an argument for developing a vaccine for this kind of E. coli,” Fleckenstein said. “There are lifelong consequences of getting infected over and over in childhood. Vaccination combined with efforts to improve sanitation and access to clean water could protect children from the long-term effects and give them a better shot at long and healthy lives.”

Source:

Washington University School of Medicine

Journal reference:

Sheikh, A., et al. (2022) Enterotoxigenic Escherichia coli heat-labile toxin drives enteropathic changes in small intestinal epithelia. Nature Communications. doi.org/10.1038/s41467-022-34687-7.