Investigation of the gut microbiome, bile acid composition and host immunoinflammatory response in a model of azoxymethane-induced colon cancer at discrete timepoints.

BACKGROUND: Distinct sets of microbes contribute to colorectal cancer (CRC) initiation and progression. Some occur due to the evolving intestinal environment but may not contribute to disease. In contrast, others may play an important role at particular times during the tumorigenic process. Here, we describe changes in the microbiota and host over the course of azoxymethane (AOM)-induced tumorigenesis. METHODS: Mice were administered AOM or PBS and were euthanised 8, 12, 24 and 48 weeks later. Samples were analysed using 16S rRNA gene sequencing, UPLC-MS and qRT-PCR. RESULTS: The microbiota and bile acid profile showed distinct changes at each timepoint. The inflammatory response became apparent at weeks 12 and 24. Moreover, significant correlations between individual taxa, cytokines and bile acids were detected. One co-abundance group (CAG) differed significantly between PBS- and AOM-treated mice at week 24. Correlation analysis also revealed significant associations between CAGs, bile acids and the bile acid transporter, ASBT. Aberrant crypt foci and adenomas were first detectable at weeks 24 and 48, respectively. CONCLUSION: The observed changes precede host hyperplastic transformation and may represent early therapeutic targets for the prevention or management of CRC at specific timepoints in the tumorigenic process.

Examining the efficacy of mushroom industry biocides on Listeria monocytogenes biofilm.

AIMS: The aim of this study was to test the efficacy of new and currently used biocides in the mushroom industry for inactivating Listeria monocytogenes biofilm. METHODS AND RESULTS: A laboratory-scale study was initially carried out to test the efficacy of eleven biocidal products against a cocktail of five L. monocytogenes strains that were grown to 3-day biofilms on stainless steel coupons. Biocidal efficacy was then tested under clean and dirty conditions based on the EN 13697:2015 method. The results for the biocides tested ranged between 1·7-log and 6-log reduction of biofilm, with only the efficacy of the sodium hypochlorite-based biocide being significantly reduced in dirty conditions. A pilot-scale trial was then carried out on a subset of biocides against L. monocytogenes on concrete floors in a mushroom growing room and it was found that biocide efficacy in laboratory-scale did not translate well in pilot-scale. CONCLUSIONS: Biocides that are used in the mushroom industry and potential alternative biocides were determined to be effective against L. monocytogenes biofilm in both laboratory-scale and pilot-scale experiments. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has direct impact for the industry as it provides information on the efficacy of currently used biocides and other biocidal products against L. monocytogenes, an added benefit to their primary use.

Microbial Metabolites as Molecular Mediators of Host-Microbe Symbiosis in Colorectal Cancer.

The symbiosis between the gut microbiota and the host has been identified as an integral part of normal human physiology and physiological development. Research in germ-free or gnotobiotic animals has demonstrated the importance of this symbiosis in immune, vascular, hepatic, respiratory and metabolic systems. Disruption of the microbiota can also contribute to disease, and the microbiota has been implicated in numerous intestinal and extra-intestinal pathologies including colorectal cancer. Interactions between host and microbiota can occur either directly or indirectly, via microbial-derived metabolites. In this chapter, we focus on two major products of microbial metabolism, short-chain fatty acids and bile acids, and their role in colorectal cancer. Short-chain fatty acids are the products of microbial fermentation of complex carbohydrates and confer protection against cancer risk, while bile acids are compounds which are endogenous to the host, but undergo microbial modification in the large intestine leading to alterations in their bioactivity. Lastly, we discuss the ability of microbial modulation to mediate cancer risk and the potential to harness this ability as a prophylactic or therapeutic treatment in colorectal cancer.

The influence of rosuvastatin on the gastrointestinal microbiota and host gene expression profiles.

Statins are the most widely prescribed medications worldwide for the treatment of hypercholesterolemia. They inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R), an enzyme involved in cholesterol synthesis in higher organisms and in isoprenoid biosynthesis in some bacteria. We hypothesized that statins may influence the microbial community in the gut through either direct inhibition or indirect mechanisms involving alterations to host responses. We therefore examined the impact of rosuvastatin (RSV) on the community structure of the murine gastrointestinal microbiota. RSV was orally administered to mice and the effects on the gut microbiota, host bile acid profiles, and markers of inflammation were analyzed. RSV significantly influenced the microbial community in both the cecum and feces, causing a significant decrease in α-diversity in the cecum and resulting in a reduction of several physiologically relevant bacterial groups. RSV treatment of mice significantly affected bile acid metabolism and impacted expression of inflammatory markers known to influence microbial community structure (including RegIIIγ and Camp) in the gut. This study suggests that a commonly used statin (RSV) leads to an altered gut microbial composition in normal mice with attendant impacts on local gene expression profiles, a finding that should prompt further studies to investigate the implications of statins for gut microbiota stability and health in humans.NEW & NOTEWORTHY This work demonstrates that rosuvastatin administration in mice affects the gastrointestinal microbiota, influences bile acid metabolism, and alters transcription of genes encoding factors involved in gut homeostasis and immunity in the gastrointestinal tract.

Analysis of the Impact of Rosuvastatin on Bacterial Mevalonate Production Using a UPLC-Mass Spectrometry Approach.

Statins are widely prescribed cholesterol-lowering medications and act through inhibition of the human enzyme 3-methylglutaryl coenzyme A reductase (HMG-R) which produces mevalonate (MVAL), a key substrate for cholesterol biosynthesis. Some important microbial species also express an isoform of HMG-R; however, the nature of the interaction between statins and bacteria is currently unclear and studies would benefit from protocols to quantify MVAL in complex microbial environments. The objective of this study was to develop a protocol for the analytical quantification of MVAL in bacterial systems and to utilise this approach to analyse the effects of Rosuvastatin (RSV) on bacterial MVAL formation. To determine the effective concentration range of RSV, we examined the dose-dependent inhibition of growth in the HMG-R(+) bacterial pathogens Listeria monocytogenes, Staphylococcus aureus and Enterococcus faecium at various concentrations of pure RSV. Growth inhibition generally correlated with a reduction in bacterial MVAL levels, particularly in culture supernatants at high RSV concentrations, as determined using our ultra-performance liquid chromatography mass spectrometry protocol. This work therefore outlines a refined protocol for the analysis of MVAL in microbial cultures and provides evidence for statin-mediated inhibition of bacterial HMG-R. Furthermore, we show that MVAL is readily transported and secreted from bacterial cells into the growth media.

A five-gene stress survival islet (SSI-1) that contributes to the growth of Listeria monocytogenes in suboptimal conditions.

AIMS: The aim of this study was to examine the contribution of a five-gene islet (lmo0444 - lmo0448) to the growth of Listeria monocytogenes under suboptimal conditions. METHODS AND RESULTS: Bioinformatics and PCR analyses revealed that a five-gene islet is present in c. half of all L. monocytogenes strains examined (66 in total). A deletion mutant that lacks the entire c. 8·7-kb islet was created in L. monocytogenes strain LO28. This mutant was impaired in growth at low pH and at high salt concentrations and demonstrated a decreased ability to survive and grow in a model food system (frankfurters). Transcriptional analysis revealed that the islet is self-regulated in that the product of lmo0445 regulates the expression of the other four genes. A role of the alternative stress sigma factor SigB in regulating the islet was also uncovered. CONCLUSIONS: The five-gene islet (herein designated as SSI-1; stress survival islet 1) contributes to the growth of L. monocytogenes under suboptimal conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: SSI-1 may contribute to the survival of certain strains of L. monocytogenes in food environments.

A significant role for Sigma B in the detergent stress response of Listeria monocytogenes.

AIMS: To investigate the contribution of the alternative sigma factor Sigma B to detergent stress in Listeria monocytogenes upon exposure to the surface-active agents, benzalkoniumchloride (BC), cetylpyridinium chloride (CPC) and sodium docecyl sulfate (SDS). METHODS AND RESULTS: Surfactant/detergent stress in L. monocytogenes 10403S and a DeltasigB mutant of 10403S was investigated by lethality, impact on growth and by transcriptional analysis. We observed a significant 1-2 log decrease in the viability of the DeltasigB mutant in response to lethal levels of surfactants. Transcriptional (reverse transcriptase-PCR) analysis revealed the induction of sigmaB by sublethal levels of surface-active agents. However, Sigma B does not play a significant role in the growth of L. monocytogenes upon exposure to sublethal levels as investigated by growth analysis. CONCLUSIONS: Sigma B is essential for the resistance of L. monocytogenes at lethal levels of BC, CPC and SDS. SIGNIFICANCE AND IMPACT OF THE STUDY: We demonstrate that Sigma B is essential for the resistance of the pathogen to surfactant stress. The findings raise the possibility that induction of Sigma B by sublethal levels of industrial cleaning agents may promote enhanced resistance of further food-processing associated stresses or conditions encountered during infection. Sigma B-regulated mechanisms of detergent resistance may provide targets for the future design of novel cleaning agents.

The glutamate decarboxylase acid resistance mechanism affects survival of Listeria monocytogenes LO28 in modified atmosphere-packaged foods.

AIMS: The contribution of the glutamate decarboxylase (GAD) acid resistance system to survival and growth of Listeria monocytogenes LO28 in modified atmosphere-packaged foods was examined. METHODS AND RESULTS: The survival and growth of the wild-type LO28 and four GAD deletion mutants (DeltagadA, DeltagadB, DeltagadC, DeltagadAB) in packaged foods (minced beef, lettuce, dry coleslaw mix) during storage at 4, 8 and 15 degrees C were studied. Survival and growth patterns varied with strain, product type, gas atmosphere and storage temperature. In minced beef, the wild-type LO28 survived better (P < 0.05) than the GAD mutant strains at 8 and 15 degrees C. In both packaged vegetables at all storage temperatures, the wild-type strain survived better (P < 0.05) than the double mutant DeltagadAB. The requirement for the individual gad genes varied depending on the packaged food. In the case of lettuce, gadA played the most important role, while the gadB and gadC genes played the greatest role in packaged coleslaw (at 15 degrees C). CONCLUSIONS: This work demonstrates that elements of the GAD system play significant roles in survival of L. monocytogenes LO28 during storage in modified atmosphere-packaged foods. SIGNIFICANCE AND IMPACT OF THE STUDY: A better understanding of how L. monocytogenes behaves in modified atmosphere-packaged foods, and how it responds to elevated carbon dioxide atmospheres.

Betaine and carnitine uptake systems in Listeria monocytogenes affect growth and survival in foods and during infection.

AIMS: To establish the relative importance of the osmo- and cryoprotective compounds glycine betaine and carnitine, and their transporters, for listerial growth and survival, in foods and during infection. METHODS AND RESULTS: A set of Listeria monocytogenes mutants with single, double and triple mutations in the genes encoding the principal betaine and carnitine uptake systems (gbu, betL and opuC, respectively) was used to determine the specific contribution of each transporter to listerial growth and survival. Food models were chosen to represent high-risk foods of plant and animal origin i.e. coleslaw and frankfurters, which have previously been linked to major human outbreaks of listeriosis. BALB/c mice were used as an in vivo model of infection. Interestingly, while betaine appeared to confer most protection in foods, the hierarchy of transporter importance differs depending on the food type: Gbu>BetL>OpuC for coleslaw, as opposed to Gbu>OpuC>BetL in frankfurters. By contrast in the animal model, OpuC and thus carnitine, appears to play the dominant role, with the remaining systems contributing little to the infection process. CONCLUSIONS: This study demonstrates that the individual contribution of each system appears dependent on the immediate environment. In foods Gbu appears to play the dominant role, while during infection OpuC is most important. SIGNIFICANCE AND IMPACT OF THE STUDY: It is envisaged that this information may ultimately facilitate the design of effective control measures specifically targeting this pathogen in foods and during infection.