Influence of intestinal decontamination using metronidazole on the detection of methanogenic Archaea in bone marrow transplant recipients

Small Intestinal Bacterial Overgrowth and Non-Alcoholic Fatty Liver Disease: What Do We Know in 2023?

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease associated with the pathological accumulation of lipids inside hepatocytes. Untreated NAFL can progress to non-alcoholic hepatitis (NASH), followed by fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). The common denominator of the above-mentioned metabolic disorders seems to be insulin resistance, which occurs in NAFLD patients. Obesity is the greatest risk factor for lipid accumulation inside hepatocytes, but a part of the NAFLD patient population has a normal body weight according to the BMI index. Obese people with or without NAFLD have a higher incidence of small intestinal bacterial overgrowth (SIBO), and those suffering from NAFLD show increased intestinal permeability, including a more frequent presence of bacterial overgrowth in the small intestine (SIBO). The health consequences of SIBO are primarily malabsorption disorders (vitamin B12, iron, choline, fats, carbohydrates and proteins) and bile salt deconjugation. Undetected and untreated SIBO may lead to nutrient and/or energy malnutrition, thus directly impairing liver function (e.g., folic acid and choline deficiency). However, whether SIBO contributes to liver dysfunction, decreased intestinal barrier integrity, increased inflammation, endotoxemia and bacterial translocation is not yet clear. In this review, we focus on gut–liver axis and discuss critical points, novel insights and the role of nutrition, lifestyle, pre- and probiotics, medication and supplements in the therapy and prevention of both SIBO and NAFLD.

The impact of antimicrobials on the efficiency of methane fermentation of sewage sludge, changes in microbial biodiversity and the spread of antibiotic resistance

The study was designed to simultaneously evaluate the influence of high doses (512-1024 µg/g) the most commonly prescribed antimicrobials on the efficiency of anaerobic digestion of sewage sludge, qualitative and quantitative changes in microbial consortia responsible for the fermentation process, the presence of methanogenic microorganisms, and the fate of antibiotic resistance genes (ARGs). The efficiency of antibiotic degradation during anaerobic treatment was also determined. Metronidazole, amoxicillin and ciprofloxacin exerted the greatest effect on methane fermentation by decreasing its efficiency. Metronidazole, amoxicillin, cefuroxime and sulfamethoxazole were degraded in 100%, whereas ciprofloxacin and nalidixic acid were least susceptible to degradation. The most extensive changes in the structure of digestate microbiota were observed in sewage sludge exposed to metronidazole, where a decrease in the percentage of bacteria of the phylum Bacteroidetes led to an increase in the proportions of bacteria of the phyla Firmicutes and Proteobacteria. The results of the analysis examining changes in the concentration of the functional methanogen gene (mcrA) did not reflect the actual efficiency of methane fermentation. In sewage sludge exposed to antimicrobials, a significant increase was noted in the concentrations of β-lactam, tetracycline and fluoroquinolone ARGs and integrase genes, but selective pressure was not specific to the corresponding ARGs.

Metronidazole: an update on metabolism, structure-cytotoxicity and resistance mechanisms

Metronidazole, a nitroimidazole, remains a front-line choice for treatment of infections related to inflammatory disorders of the gastrointestinal tract including colitis linked to Clostridium difficile. Despite >60 years of research, the metabolism of metronidazole and associated cytotoxicity is not definitively characterized. Nitroimidazoles are prodrugs that are reductively activated (the nitro group is reduced) under low oxygen tension, leading to imidazole fragmentation and cytotoxicity. It remains unclear if nitroimidazole reduction (activation) contributes to the cytotoxicity profile, or whether subsequent fragmentation of the imidazole ring and formed metabolites alone mediate cytotoxicity. A molecular mechanism underpinning high level (>256 mg/L) bacterial resistance to metronidazole also remains elusive. Considering the widespread use of metronidazole and other nitroimidazoles, this review was undertaken to emphasize the structure-cytotoxicity profile of the numerous metabolites of metronidazole in human and murine models and to examine conflicting reports regarding metabolite-DNA interactions. An alternative hypothesis, that DNA synthesis and repair of existing DNA is indirectly inhibited by metronidazole is proposed. Prokaryotic metabolism of metronidazole is detailed to discuss new resistance mechanisms. Additionally, the review contextualizes the history and current use of metronidazole, rates of metronidazole resistance including metronidazole MDR as well as the biosynthesis of azomycin, the natural precursor of metronidazole. Changes in the gastrointestinal microbiome and the host after metronidazole administration are also reviewed. Finally, novel nitroimidazoles and new antibiotic strategies are discussed.

Infection dynamics of Toxoplasma gondii in gut-associated tissues after oral infection: The role of Peyer's patches

Toxoplasma gondii is a common perorally transmitted parasite; however, its immunopathogenesis in gut-associated tissues remains unclear. Here, we compared disease manifestation in C57BL/6 immunocompetent wild type (WT) mice and immunocompromised interferon (IFN)-γ-deficient (GKO) mice after peroral infection (PI) with T. gondii cysts (Fukaya strain). Strong PI-induced Th1 cytokine expression was detected in WT mice. Moreover, bradyzoite-specific T.g.HSP30/bag1 mRNA was detected in the ileum parenchyma and Peyer's patches (PP), but not in the mesenteric lymph nodes, at 7 days post-infection in WT mice, and was significantly higher than that in GKO mice. Nested PCR showed that parasites existed in ileum parenchyma at days 1 and 1.5 post-PI in GKO and WT mice, respectively. In addition, quantitative competitive-PCR indicated that T. gondii first colonized the PP (day 3 post-PI), followed by the ileum parenchyma and mesenteric lymph nodes, spleen, and portal and aortic blood (day 7 post-PI). Although parasites were consistently more abundant in GKO mice, similar invasion and dissemination patterns were observed in the two hosts. Collectively, these data suggest that some zoites differentiate from tachyzoites to bradyzoites in the ileum and that T. gondii initially invades the ileum parenchyma, and then accumulates and proliferates in the PP before disseminating through the lymphatic systems of both GKO and WT hosts.

Effectiveness of trimethoprim-sulfamethoxazole and metronidazole in the treatment of small intestinal bacterial overgrowth in children living in a slum

Trimethoprim-sulfamethoxazole and metronidazole were used for 14 days to treat 20 children with small intestine bacterial overgrowth (SIBO). SIBO was diagnosed using the lactulose hydrogen breath test. The breath test was repeated 1 month after treatment, and 19 (95.0%) of 20 children showed no evidence of SIBO (P < 0.001). The area under the individual curves showed that children with SIBO exhibited greater hydrogen production before treatment in both the first hour and between 60 and 180 minutes after the breath test. The treatment did not decrease methane production. In conclusion, trimethoprim-sulfamethoxazole and metronidazole was effective in treating children with SIBO.

Hydrophobicity of imidazole derivatives correlates with improved activity against human methanogenic archaea

Methanogenic archaea are involved in periodontitis in humans. They have also been implicated in digestive tract pathologies and obesity. These microorganisms are broadly resistant to antibiotics, except for metronidazole and ornidazole. In this study, eight imidazole derivatives were synthesised and their in vitro cytotoxicity and activity against six species of methanogenic archaea, including Methanobrevibacter smithii, Methanobrevibacter oralis, Methanosphaera stadtmanae, Methanobacterium beijingense, Methanosaeta concilii and Methanomassiliicoccus luminyensis, were tested. Whilst the effective half-maximum cytotoxic concentrations (EC50 values) of all compounds were ≤50 mg/L, minimum inhibitory concentrations (MICs) were 0.05-0.8 mg/L for most methanogenic archaea and 0.1-1mg/L for M. stadtmanae. These results indicated a >20-400 therapeutic index (EC50/MIC) for these compounds, which compared with metronidazole exhibited 1-log increased activity against methanogenic archaea cultured from the human microbiota. These compounds are therefore promising molecules for the treatment of methanogenic archaea-related infections.

Effects of treatment with antimicrobial agents on the human colonic microflora

Antimicrobial agents are the most valuable means available for treating bacterial infections. However, the administration of therapeutic doses of antimicrobial agents to patients is a leading cause of disturbance of the normal gastrointestinal microflora. This disturbance results in diminishing the natural defense mechanisms provided by the colonic microbial ecosystem, making the host vulnerable to infection by commensal microorganisms or nosocomial pathogens. In this minireview, the impacts of antimicrobials, individually and in combinations, on the human colonic microflora are discussed.

Archaea in protozoa and metazoa

The presence of Archaea is currently being explored in various environments, including extreme geographic positions and eukaryotic habitats. Methanogens are the dominating archaeal organisms found in most animals, from unicellular protozoa to humans. Many methanogens can contribute to the removal of hydrogen, thereby improving the efficiency of fermentation or the reductive capacity of energy-yielding reactions. They may also be involved in tissue damage in periodontal patients. Recent molecular studies demonstrated the presence of Archaea other than methanogens in some animals-but so far, not in humans. The roles of these microorganisms have not yet been established. In the present review, we present the state of the art regarding the archaeal microflora in animals.