Acid-sensitive enteric pathogens are protected from killing under extremely acidic conditions of pH 2.5 when they are inoculated onto certain solid food sources

Mechanisms of Pathogenic Escherichia coli Attachment to Meat

Escherichia coli are present in the human and animal microbiome as facultative anaerobes and are viewed as an integral part of the whole gastrointestinal environment. In certain circumstances, some species can also become opportunistic pathogens responsible for severe infections in humans. These infections are caused by the enterotoxinogenic E. coli, enteroinvasive E. coli, enteropathogenic E. coli and the enterohemorrhagic E. coli species, frequently present in food products and on food matrices. Severe human infections can be caused by consumption of meat contaminated upon exposure to animal feces, and as such, farm animals are considered to be a natural reservoir. The mechanisms by which these four major species of E. coli adhere and persist in meat postslaughter are of major interest to public health and food processors given their frequent involvement in foodborne outbreaks. This review aims to structure and provide an update on the mechanistic roles of environmental factors, curli, type I and type IV pili on E. coli adherence/interaction with meat postslaughter. Furthermore, we emphasize on the importance of bacterial surface structures, which can be used in designing interventions to enhance food safety and protect public health by reducing the burden of foodborne illnesses.

Heat Resistance, Virulence, and Gene Expression of Desiccation-Adapted Salmonella Enteritidis During Long-Term Storage in Low-Water Activity Foods

Desiccation stress could induce crossprotection and even affect virulence of Salmonella enterica. However, the influence of food matrices with low-water activity on desiccation adaptation of Salmonella still remains unclear. This study investigated the survival and adaptation of Salmonella Enteritidis in skim milk powder, ginger powder, and chocolate powder under desiccation storage conditions for a total of 12 weeks. High survival rates of Salmonella Enteritidis in all food matrices maintained over the long-term desiccation storage. Desiccation-adapted Salmonella Enteritidis enhanced heat resistance (p < 0.05) with the increase of storage time. Food composition plays an important role in the induction of crossresistance of desiccation-adapted Salmonella. After desiccation storage, Salmonella Enteritidis in ginger powder was most tolerant to heat treatment. Salmonella Enteritidis in skim milk powder was most resistant to the gastrointestinal simulation environment, and had strongest adhesion to Caco-2 cells. The effects of food composition on gene expression (rpoS, proV, otsA, otsB, grpE, dnaK, rpoH, and sigDE) in desiccation-adapted Salmonella Enteritidis were not significant (p > 0.05). At initial desiccation storage, osmotic protection-related genes (fadA, proV, otsA, and otsB), stress response regulator (rpoS), and heat-resistance-related genes (grpE, dnaK, and rpoH) were all significantly upregulated (p < 0.05). However, after 4-week storage, the expression level of desiccation-related genes, proV, otsA, otsB, grpE, dnaK, and rpoH, significantly decreased (p < 0.05). This study enables a better understanding of Salmonella's responses to long-term desiccation stress in different kinds of low-water activity foods.

Cold tolerance in Campylobacter jejuni and its impact on food safety

Campylobacter jejuni is a major cause of foodborne illnesses worldwide and is primarily transmitted to humans through contaminated poultry meat. To control this pathogen, it is critical to understand its cold tolerance because poultry products are usually distributed in the cold chain. However, there is limited information regarding how this thermotolerant, microaerophilic pathogen can survive in cold and aerobic environments in the poultry cold chain. In this study, we investigated the cold tolerance of C. jejuni by measuring the viability of 90 C. jejuni strains isolated from retail raw chicken at 4 °C under aerobic and microaerobic conditions. Despite the microaerophilic nature of C. jejuni, under aerobic conditions, C. jejuni exhibited higher viability at 4 °C and required an extended inactivation time compared to microaerobic conditions. Some strains were highly tolerant to refrigeration temperatures and exhibited increased survival at 4 °C. These cold-tolerant strains mostly belonged to multilocus sequence typing (MLST) clonal complex (CC)-21 and CC-443, indicating that cold tolerance is associated with the phylogeny of C. jejuni. Notably, cold-tolerant strains had an increased probability of illness and were more likely to cause human infections due to their extended survival on refrigerated chicken meat compared to those sensitive to cold stress. Furthermore, the majority of cold-tolerant strains exhibited elevated aerotolerance, indicating that cold tolerance is related to aerotolerance. These findings suggest that refrigeration of chicken meat under aerobic conditions may not be effective at controlling C. jejuni and that cold-tolerant C. jejuni can pose an increased risk to food safety.

Proton Pump Inhibitor Use Before and After a Diagnosis of Inflammatory Bowel Disease

BACKGROUND

Proton pump inhibitors (PPIs) have an impact on the gut microbiome. We investigated whether increased use of PPIs was associated with a diagnosis of inflammatory bowel disease (IBD).

METHODS

The University of Manitoba IBD Epidemiology Database includes all Manitobans diagnosed with IBD between 1984 and 2018 with age-, sex-, and geography-matched control subjects and comprehensive prescription drug data from April 1995. Subjects were considered to be users if they received 2 PPI prescriptions. We assessed PPI prescriptions prediagnosis and for 3 years postdiagnosis of IBD. The absolute and relative rates were calculated and compared for PPI use pre- and post-IBD diagnosis.

RESULTS

A total of 5920 subjects were diagnosed with IBD after April 1996. Rates of PPI use in control subjects increased gradually from 1.5% to 6.5% over 15 years. Persons with IBD had a higher rate of PPI use, peaking up to 17% within 1 year of IBD diagnosis with a rate ratio (RR) of 3.1 (95% confidence interval [CI], 2.9-3.3). Furthermore, persons with Crohn's disease (RR, 4.2; 95% CI, 3.7-4.6) were more likely to have been PPI users prediagnosis than persons with ulcerative colitis (RR, 2.4; 95% CI, 2.2-2.7). Important predictors of increased PPI use were older age, year of data collection, and Crohn's disease diagnosis.

CONCLUSIONS

Persons with IBD have higher PPI use preceding their diagnosis. Possibly, the use of a PPI alters the gut microbiome, increasing the risk for IBD diagnosis; or persons with IBD have increased rates of dyspepsia, warranting PPI use; or some IBD symptoms are treated with PPIs whether warranted or not.

Salmonella spp. in poultry production-A review of the role of interventions along the production continuum

Salmonella is a significant pathogen of human and animal health and poultry are one of the most common sources linked with foodborne illness worldwide. Global production of poultry meat and products has increased significantly over the last decade or more as a result of consumer demand and the changing demographics of the world's population, where poultry meat forms a greater part of the diet. In addition, the relatively fast growth rate of birds which is significantly higher than other meat species also plays a role in how poultry production has intensified. In an effort to meet the greater demand for poultry meat and products, modern poultry production and processing practices have changed and practices to target control and reduction of foodborne pathogens such as Salmonella have been implemented. These strategies are implemented along the continuum from parent and grandparent flocks to breeders, the farm and finished broilers to transport and processing and finally from retail to the consumer. This review focuses on common practices, interventions and strategies that have potential impact for the control of Salmonella along the poultry production continuum from farm to plate.

Gut microbiota of the small intestine as an antimicrobial barrier against foodborne pathogens: Impact of diet on the survival of S. Typhimurium and L. monocytogenes during in vitro digestion

The human gastrointestinal tract employs an assortment of chemical, enzymatic and immune barriers to impede pathogen colonization. An essential component of these barriers is the gut microbiota, which infers protection against ingested pathogens through its colonization resistance mechanisms. Specifically, the gut microbiota of the distal small intestine (ileum) renders a crucial line of defense, given that this location is regarded as an important interaction site. This study aimed to evaluate the impact of the ileal microbiota on the survival of the foodborne pathogens Salmonella enterica serotype Typhimurium and Listeria monocytogenes, utilizing an in vitro digestion model system. Moreover, the effect of diet on the gut microbiota colonization resistance mechanisms was assessed, by comparing a healthy (high fiber/low sugar) and a western diet (low fiber/high sugar). For S. Typhimurium, the results revealed that the digestion of a healthy diet led to a similar inactivation compared to the western diet, with the values of total log reduction being 0.83 and 0.82 log(CFU), respectively; yet the lack of readily accessible nutrients in the healthy diet combined with the acidic shock during gastric digestion caused the induction of stress tolerance to the pathogen. This resulted in increased pathogen survival in the presence of gut microbiota, with S. Typhimurium proliferating during the ileal phase with a maximum specific growth rate of 0.16 1/h. On the contrary, for L. monocytogenes, the healthy diet was associated with a greater inactivation than the western diet (total log reduction values: 3.08 and 1.30 log(CFU), respectively), which appeared strongly influenced by the encounter of the pathogen with the gut microbiota. Regarding the latter, the species Escherichia coli and Bacteroides thetaiotaomicron appeared to be the most prevalent in most cases. Finally, it was also demonstrated that the ileal microbiota colonization resistance mechanisms largely relied on competitive responses. The obtained knowledge of this research can contribute to the development and/or complementation of defensive strategies against pathogen infection, while also underlining the value of in vitro approaches.

Impact of Acidulants on Salmonella and Escherichia coli O157:H7 in Water Microcosms Containing Organic Matter

As demands for fresh water become more competitive between the processing plant and other consumers of water such as municipalities, interest has grown in recycling or reusing water for food processing. However, recycling the processing water from a poultry plant, for example, represents challenges due to increased organic loads and the presence of bacterial contaminants including foodborne pathogens. The objective in the current study was to evaluate the inactivation of Salmonella and E. coli O157:H7 using combinations (0.5% and 1%) of sodium bisulfate (SBS) and 1% lactic acid (LA) in water and water with organic matter in the form of horse blood serum (0.3%) with exposure times of 1 min and 5 min. Pathogen reductions after a 5 min exposure time were greater than corresponding reductions after a 1 min exposure time for all acid solutions. The Salmonella counts were significantly reduced (i.e., ≥1 log-unit) in all acid solutions after a 5 min exposure time with the combination of LA + SBS acid solutions being more effective than the corresponding 2% LA solutions. None of the acid solutions were effective in reducing the E. coli O157:H7 after a 1 min exposure time. The 1% LA + 1% SBS solution was the most effective acid solution against both pathogens and was the only acid solution effective in reducing E. coli O157:H7 by at least one log unit after 5 min of exposure.

The hidden risk of microplastic-associated pathogens in aquatic environments

Increasing studies of plastisphere have raised public concern about microplastics (MPs) as vectors for pathogens, especially in aquatic environments. However, the extent to which pathogens affect human health through MPs remains unclear, as controversies persist regarding the distinct pathogen colonization on MPs as well as the transmission routes and infection probability of MP-associated pathogens from water to humans. In this review, we critically discuss whether and how pathogens approach humans via MPs, shedding light on the potential health risks involved. Drawing on cutting-edge multidisciplinary research, we show that some MPs may facilitate the growth and long-range transmission of specific pathogens in aquatic environments, ultimately increasing the risk of infection in humans. We identify MP- and pathogen-rich settings, such as wastewater treatment plants, aquaculture farms, and swimming pools, as possible sites for human exposure to MP-associated pathogens. This review emphasizes the need for further research and targeted interventions to better understand and mitigate the potential health risks associated with MP-mediated pathogen transmission.

In vitro digestion of ESC-resistant Escherichia coli from poultry meat and evaluation of human health risk

Introduction

The spread of antimicrobial resistance (AMR) has become a threat against human and animal health. Third and fourth generation cephalosporins have been defined as critically important antimicrobials by The World Health Organization. Exposure to Extended spectrum cephalosporin-resistant E. coli may result in consumers becoming carriers if these bacteria colonize the human gut or their resistance genes spread to other bacteria in the gut microbiota. In the case that these resistant bacteria at later occasions cause disease, their resistance characteristics may lead to failure of treatment and increased mortality. We hypothesized that ESC-resistant E. coli from poultry can survive digestion and thereby cause infections and/or spread their respective resistance traits within the gastro-intestinal tract.

Methods

In this study, a selection of 31 ESC-resistant E. coli isolates from retail chicken meat was exposed to a static in vitro digestion model (INFOGEST). Their survival, alteration of colonizing characteristics in addition to conjugational abilities were investigated before and after digestion. Whole genome data from all isolates were screened through a custom-made virulence database of over 1100 genes for virulence- and colonizing factors.

Results and discussion

All isolates were able to survive digestion. Most of the isolates (24/31) were able to transfer their bla _CMY2-containing plasmid to E. coli DH5-á, with a general decline in conjugation frequency of digested isolates compared to non-digested. Overall, the isolates showed a higher degree of cell adhesion than cell invasion, with a slight increase after digestion compared non-digested, except for three isolates that displayed a major increase of invasion. These isolates also harbored genes facilitating invasion. In the virulence-associated gene analysis two isolates were categorized as UPEC, and one isolate was considered a hybrid pathogen. Altogether the pathogenic potential of these isolates is highly dependent on the individual isolate and its characteristics. Poultry meat may represent a reservoir and be a vehicle for dissemination of potential human pathogens and resistance determinants, and the ESC-resistance may complicate treatment in the case of an infection.

Effect of food structure and buffering capacity on pathogen survival during in vitro digestion

Even though a plethora of barriers are employed by the human gastrointestinal tract (GIT) to cope with invading pathogens, foodborne diseases are still a common problem. The survival of food pathogens in the GIT is known to depend on food carrier properties. The aim of this study was to investigate the influence of food buffering capacity and food structure on the survival of Salmonella Typhimurium and Listeria monocytogenes during simulated digestion, following contamination of different food model systems that had different combinations of fat and protein content. The results illustrated the strong protective properties of proteins, acting either as a strong buffering agent or as a physical barrier against gastric acidity, for both pathogens. In comparison, fat manifested a lower buffering capacity and weaker protective effects against the two pathogens. Intriguingly, a low fat content was often linked with increased microbial resistance. Nonetheless, both pathogens survived their transit through the simulated GIT in all cases, with S. Typhimurium exhibiting growth during intestinal digestion and L.monocytogenes demonstrating a healthy residual population at the end of the intestinal phase. These results corroborate the need for a deeper understanding regarding the mechanisms with which food affects bacterial survival in the human GIT.

Roles of Aerotolerance, Biofilm Formation, and Viable but Non-Culturable State in the Survival of Campylobacter jejuni in Poultry Processing Environments

Campylobacter jejuni is one of the most common causes of foodborne human gastroenteritis in the developed world. This bacterium colonizes in the ceca of chickens, spreads throughout the poultry production chain, and contaminates poultry products. Despite numerous on farm intervention strategies and developments in post-harvest antimicrobial treatments, C. jejuni is frequently detected on broiler meat products. This indicates that C. jejuni is evolving over time to overcome the stresses/interventions that are present throughout poultry production and processing. The development of aerotolerance has been reported to be a major survival strategy used by C. jejuni in high oxygen environments. Recent studies have indicated that C. jejuni can enter a viable but non-culturable (VBNC) state or develop biofilm in response to environmental stressors such as refrigeration and freezing stress and aerobic stress. This review provides an overview of different stressors that C. jejuni are exposed to throughout the poultry production chain and the genotypic and phenotypic survival mechanisms, with special attention to aerotolerance, biofilm formation, and development of the VBNC state.

The Role of Egg Yolk in Modulating the Virulence of Salmonella Enterica Serovar Enteritidis

Contribution of food vehicles to pathogenicity of disease-causing microorganisms is an important but overlooked research field. The current study was initiated to reveal the relationship between virulence of Salmonella enterica serovar Enteritidis and egg yolk as a hosting medium. Mice were orally challenged with Salmonella Enteritidis cultured in egg yolk or tryptic soy broth (TSB). Additionally, mice were challenged with Salmonella Enteritidis cultured in TSB, followed by administration of sterile egg yolk, to discern the difference between pre-growth of the pathogen and its mere presence in egg yolk during infection. The pathogen’s Lethal dose 50 (LD₅₀) was the lowest when grown in yolk (2.8×10² CFU), compared to 1.1×10³ CFU in TSB, and 4.6×10³ CFU in TSB followed by administration of sterile yolk. Additionally, mice that orally received Salmonella Enteritidis grown in egg yolk expressed a high death rate. These findings were supported by transcriptional analysis results. Expression of promoters of virulence-related genes (sopB and sseA) in genetically modified Salmonella Enteritidis reporter strains was significantly higher (p < 0.05) when the bacterium was grown in the yolk, compared to that grown in TSB. Sequencing of RNA (RNA-seq) revealed 204 differentially transcribed genes in Salmonella Enteritidis grown in yolk vs. TSB. Yolk-grown Salmonella Enteritidis exhibited upregulated virulence pathways, including type III secretion systems, epithelial cell invasion, and infection processes; these observations were confirmed by RT-qPCR results. The transcriptomic analysis suggested that upregulation of virulence machinery of Salmonella Enteritidis grown in egg yolk was related to increased iron uptake, biotin utilization, flagellar biosynthesis, and export of virulence proteins encoded on Salmonella pathogenicity island 1, 2, 4, and 5. These biological responses may have acted in concert to increase the virulence of Salmonella infection in mice. In conclusion, growth in egg yolk enhanced Salmonella Enteritidis virulence, indicating the significance of this food vehicle to the risk assessment of salmonellosis.

Investigation of an international outbreak of multidrug-resistant monophasic Salmonella Typhimurium associated with chocolate products, EU/EEA and United Kingdom, February to April 2022

An extensive multi-country outbreak of multidrug-resistant monophasic Salmonella Typhimurium infection in 10 countries with 150 reported cases, predominantly affecting young children, has been linked to chocolate products produced by a large multinational company. Extensive withdrawals and recalls of multiple product lines have been undertaken. With Easter approaching, widespread product distribution and the vulnerability of the affected population, early and effective real-time sharing of microbiological and epidemiological information has been of critical importance in effectively managing this serious food-borne incident.

Survival capability of Campylobacter upsaliensis under environmental stresses

Objective

Campylobacter upsaliensis has been recognized as an emerging pathogen. However, little is known about its survival in the environment. To evaluate its survival capability, we estimated the reduction in viable counts of C. upsaliensis after aerobic exposure to starvation in phosphate-buffered saline (PBS), acidity (pH = 4.3), high osmolarity (4% NaCl), and dryness in wet pulp disks at different temperatures. Also, survival in dog feces and dog food at variable temperate was assessed.

Results

Campylobacter upsaliensis remained culturable under starvation for 4 days at 25 °C and for 10 weeks at 4 °C. C. upsaliensis was also recoverable after exposure to high osmolality for 9 days, dryness for 5 days, and acidity for 2 days, respectively. Similarly, C. upsaliensis survived in dog feces and dog food for several days at 25 °C and weeks at 4 °C. The survival capability of the organism was dependent on the water content, and also temperature. Notably, the tested C. upsaliensis strain was less resilient under all tested conditions than a C. jejuni strain used as a control. The findings showed that C. upsaliensis is able to survive under various environmental stresses, suggesting that it could pose a potential threat to public health.

Experimentally observed Campylobacter jejuni survival kinetics in chicken meat products during model gastric digestion tended to be lower than model predictions

Campylobacter jejuni-related foodborne diseases are mainly attributed to the consumption of undercooked chicken meat and cross-contaminated produce. This study aimed to develop a survival kinetics model, based on the Weibull model, for predicting foodborne C. jejuni survival during gastric digestion in a model stomach. We previously confirmed that C. jejuni can survive temperatures up to 62 °C; therefore, certain types of grilled chicken skewers (yakitori) were examined for C. jejuni survival during simulated gastric digestion. C. jejuni survival on a chicken thigh following grilling was examined to confirm the foods for digestion experiments. Further, C. jejuni survival during model digestion was investigated through simultaneous digestion of raw chicken and cross-contaminated iceberg lettuce. The model stomach pH increased from 1.5 to 6.0 immediately after yakitori ingestion and did not decrease below 4.0 within 3 h of digestion. Gastric digestion did not significantly contribute to C. jejuni inactivation (<1.5 log reduction after 3 h digestion). Our model could predict C. jejuni survival kinetics in simulated gastric fluid under varying pH during model digestion. This approach can be used to predict C. jejuni survival rates following digestion to improve food safety and reduce Campylobacter-related disease outbreaks.

Thyme Oil Enhances the Inactivation of Salmonella enterica on Raw Chicken Breast Meat During Marination in Lemon Juice With Added Yucca schidigera Extract

Enteric pathogens such as Salmonella enterica can survive in low pH conditions and pose a food safety threat during marinating of raw poultry meat. A study was conducted to investigate the effectiveness of thyme oil for killing S. enterica on raw chicken during marination in lemon juice containing yucca extract. Samples of raw chicken breast were inoculated with a five-serovar mixture of S. enterica (~10⁸ CFU/mL) and immersed for 2, 4, 6, and 8 h in four lemon-based marinades at 22°C: lemon juice alone (L), L with added 0.5% yucca extract (L + Y), L + Y and 0.5% thyme oil (L + Y + 0.5% TO) and L + Y + 1.0% TO. The L and L + Y served as controls. Survivors were determined by surface plating chicken homogenates on xylose-lysine tergitol-4 (XLT4) agar and XLT4 agar overlaid with non-selective agar (TAL) and counting bacterial colonies after 48 h of incubation (35°C). Marinades containing Y and TO significantly reduced initial viable populations of S. enterica compared to control (L and L + Y) solutions (P < 0.05). Based on S. enterica survivors on TAL medium, the L and L + Y reduced initial populations by 1.12 and 1.42 Log CFU/sample, respectively, after 8 h whereas, Log reductions caused by L + Y + 0.5% TO and L + Y + 1.0% TO, respectively, were 2.62 and 3.91 (P < 0.05). Numbers of survivors were higher on TAL compared to XLT4 agar (P < 0.05); however, the extent of sub-lethal injury caused by the marinades was not statistically significant (P > 0.05). The death rate of S. enterica increased significantly (P < 0.05) in the marinades containing TO (0.5 or 1.0%) compared to control (L + Y). Based on these results, thyme oil has good potential to increase the antimicrobial efficacy of lemon juice marinade against Salmonella on raw chicken breast and enhance the microbial safety of this popular poultry product.

Short communication: Evaluating the recovery potential of injured cells of Listeria innocua under product temperature-abuse conditions and passage through simulated gastrointestinal fluids

Ice cream handling and serving conditions on the consumer side may result in temperature abuse before consumption. Under some extreme conditions, even the sporadic presence of injured bacterial cells might pose a health risk due to the possibility of recovery of those cells. We conducted this investigation to evaluate the potential of injured cells of Listeria innocua to recover under ice cream temperature abuse conditions and on exposure to simulated gastrointestinal (GI) fluids. Ice cream mix samples (42% total solids), spiked with 4 log₁₀ cfu/g of Listeria innocua, were thermally treated at 69°C for 30 min. Potential heat-injured cells were recovered in buffered Listeria broth (BLEB), followed by isolation on Listeria-specific modified Oxford agar (MOX). The ice cream mix samples, containing potentially injured cells of Listeria innocua, were followed through overnight aging (7°C), freezing (-3.3°C), and overnight hardening (-40°C) steps to obtain the final ice cream samples. To simulate temperature abuse conditions, the samples were held for 12 h at 4.4°C, followed by 30 min at room temperature (22°C); this treatment was considered the first cycle of temperature abuse. To generate a worst-case scenario, the samples were exposed to 3 such consecutive temperature abuse cycles. At the end of each cycle, direct plating was done on MOX to recover viable cells, and BLEB enrichment verified the presence of potential injured cells. In addition, the ice cream samples, containing potential injured cells, were passed through simulated GI fluids. As a first step, samples were mixed (1:1) with simulated gastric fluids (pH 1.0 and 2.0 before mixing) and held at 37°C in a shaker incubator. Samples drawn at 15, 30, and 60 min were analyzed for viable and potential injured cells. To study the effect of sequential transit through simulated intestinal fluid, a mixture of ice cream and gastric fluid (1:1) from the gastric fluid experiment above was added to simulated intestinal fluid (pH 6.8) and held at 37°C. Samples were analyzed at 30 and 360 min for viable and potential injured cells. Three trials were conducted and the samples collected in duplicates. The temperature abuse or GI fluid exposure studies did not result in the recovery of potential injured cells of Listeria innocua in the ice cream samples under the conditions tested. Exposure to gastric fluids, however, did not eliminate the potential injured cells. Further studies are necessary to understand the exact risk implications of these findings.

The lipoprotein NlpD in Cronobacter sakazakii responds to acid stress and regulates macrophage resistance and virulence by maintaining membrane integrity

Cronobacter sakazakii, an emerging opportunistic pathogen, is implicated in severe foodborne outbreak infections in premature and full-term infants. Generally, acid tolerance is vital for the pathogenesis of foodborne pathogens; however, its role in C. sakazakii virulence remains largely unknown. To screen out acid-tolerance determinants from transposon mutants, anovel counterselection method using gentamicin and acid was developed. Using the counterselection method and growth assay, we screened several acid-sensitive mutants and found that nlpD encodes an acid-resistance factor in C. sakazakii. 

Compared to the wild-type strain, the nlpD mutant exhibited attenuated virulence in a rat model. Using macrophage THP-1 cells and a pH probe, we verified that nlpD enables bacteria to resist macrophages by resisting acidification. Finally, we confirmed that nlpD maintains C. sakazakii membrane integrity in acid using propidium iodide permeabilization assays via flow cytometry. Our results confirm that nlpD is a novel virulence factor that permits C. sakazakii to survive under acid stress conditions. Considering that NlpD is a conserved lipoprotein located in the bacterial outer membrane, NlpD could be used as a target for drug development.

Acid tolerance response of Salmonella during simulated chilled beef storage and its regulatory mechanism based on the PhoP/Q system

To investigate the persistence of acid tolerance response (ATR) and the regulatory mechanism during chilled storage, Salmonella ATCC 14028 and the △phoP mutant were acid adapted and then incubated in meat extract at 4 °C for 24 days as simulated beef storage. The bacterial population, D values and expression of PhoP/PhoQ linked genes of both strains were determined at 6-day intervals. Although a mild suppression effect on the D values of adapted Salmonella was found during the long-time storage in meat extract at 4 °C, the D value of adapted strains was significantly higher than non-adapted strains, indicating the persistence of ATR during the whole aging and distribution of beef posing a threat to food safety. The fact that low temperature inhibits the formation of ATR at the early adapted stage emphasizes the importance of keeping a low-temperature environment during slaughter. An interaction between the acidic adaptation and phoP gene on D values was found and the expression levels of adiA, adiY, cadA and cadB genes was significantly reduced in the △phoP mutant, suggesting that PhoP/Q system plays an important role in the ATR by sensing the pH and regulating lysine and arginine decarboxylation directly or indirectly.

Sublethal concentrations of undissociated acetic acid may not always stimulate acid resistance in Salmonella enterica sub. enterica serovar Enteritidis Phage Type 4: Implications of challenge substrate associated factors

Acid adaptation enhances survival of foodborne pathogens under lethal acid conditions that prevail in several food-related ecosystems. In the present study, the role of undissociated acetic acid in inducing acid resistance of Salmonella Enteritidis Phage Type 4 both in laboratory media and in an acid food matrix was investigated. Several combinations of acetic acid (0, 15, 25, 35 and 45 mM) and pH values (4.0, 4.5, 5.0, 5.5, 6.0) were screened for their ability to activate acid resistance mechanisms of pathogen exposed to pH 2.5 (screening assay). Increased survival was observed when increasing undissociated acetic acid within a range of sublethal concentrations (1.9–5.4 mM), but only at pH 5.5 and 6.0. No effect was observed at lower pH values, regardless of the undissociated acetic acid levels. Three combinations (15mM/pH5.0, 35mM/pH5.5, 45mM/pH6.0) were selected and further used for adaptation prior to inoculation in commercial tarama (fish roe) salad, i.e., an acid spread (pH 4.35 ± 0.02), stored at 5°C. Surprisingly and contrary to the results of the screening assay, none of the acid adaptation treatments enhanced survival of Salmonella Enteritidis in the food matrix, as compared to non-adapted cells (control). Further examination of the food pH value, acidulant and storage (challenge) temperature on the responses of the pathogen adapted to 15mM/pH5.0, 35mM/pH5.5 and 45mM/pH6.0 was performed in culture media. Cells adapted to 35mM/pH5.5 were unable to induce acid resistance when exposed to pH 4.35 (tarama salad pH value) at 37°C and 5°C, whereas incubation under refrigeration (5°C) at pH 4.35 sensitized 45mM/pH6.0 adapted cells against the subsequent acid and cold stress. In conclusion, pre-exposure to undissociated acetic acid affected the adaptive responses of Salmonella Enteritidis Phage Type 4 in a concentration- and pH-dependent manner, with regard to conditions prevailing during acid challenge.

Membrane modification as a survival mechanism through gastric fluid in non-acid adapted enteropathogenic Escherichia coli (EPEC)

In bacterial cells, the cytoplasmic membrane forms a barrier between the environment and the cell's cytoplasm. This barrier regulates which substances (and the amount) that leave and enter the cell, to maintain homeostasis between the cytoplasm and the external environment. One of the mechanisms employed to maintain structure and functionality during exposure to environmental stress is adaptation of the membrane lipids. The aim of this study was to investigate membrane alteration as a possible survival method of non-acid adapted enteropathogenic Escherichia coli (E. coli) (EPEC) (as could be found in contaminated water or unprocessed food) through simulated gastric fluid (SGF). Enteropathogenic E. coli was grown in nutrient-rich media and then exposed to SGF of various pH (1.5, 2.5, 3.5, or 4.5) for 180 min. Flow cytometry was utilised to examine membrane integrity; and morphological changes were investigated using transmission electron microscopy (TEM). Gas chromatography-mass spectrometry (GC-MS) was used to assess the membrane lipid composition. The results of this study showed that SGF treatment caused membrane damage, as well as cell wall thickening and irregular plasma membranes. The morphological changes were accompanied by membrane lipid changes indicative of decreased membrane fluidity and increased rigidity. The findings suggest that non-acid adapted EPEC can perceive pH change in the environment and adapt accordingly.

The Phylogeny and Biological Function of Gastric Juice-Microbiological Consequences of Removing Gastric Acid

Gastric juice is a unique combination of hydrochloric acid (HCl), lipase, and pepsin. Acidic gastric juice is found in all vertebrates, and its main function is to inactivate microorganisms. The phylogenetic preservation of this energy-consuming and, at times, hazardous function (acid-related diseases) reflects its biological importance. Proton pump inhibitors (PPIs) are one of the most widely used drugs in the world. Due to the reduced prevalence of Helicobacter pylori infection as well as the increased use of inhibitors of gastric acid secretion, the latter has become the most important cause of gastric hypoacidity. In the present manuscript, we review the microbiological consequences of removing gastric acidity. The resulting susceptibility to infections has not been studied extensively, and focus has mainly been restricted to bacterial and parasitic agents only. The strongest evidence concerning the relationship between hypochlorhydria and predisposition to infections relates to bacterial infections affecting the gastrointestinal tract. However, several other clinical settings with increased susceptibility to infections due to inhibited gastric acidity are discussed. We also discuss the impact of hypochlorhydria on the gut microbiome.

The Fate of Bacteria in Human Digestive Fluids: A New Perspective Into the Pathogenesis of Vibrio parahaemolyticus

Vibrio parahaemolyticus causes the most seafood-attributed gastroenteritis outbreaks worldwide and studies on its pathogenesis during passage through the human digestive fluids are limited. An in vitro continuous model system mimicking passage through saliva, gastric and intestinal fluid was used to study the survival, morphology and virulence-related gene expression of a total of sixty pathogenic, and non-pathogenic V. parahaemolyticus strains. The changes to these three characteristics for the sixty V. parahaemolyticus strains were minimal on passage through the saliva fluid. No V. parahaemolyticus strains survived passage through gastric fluid with low pH values (2.0 and 3.0) and the cells, examined microscopically, were severely damaged. However, when the pH of gastric fluid increased to 4.0, the bacterial survival rate was 54.70 ± 1.11%, and the survival rate of pathogenic strains was higher when compared to non-pathogenic strains. Even though the bactericidal effect of intestinal fluid was lower than gastric fluid, virulence-related gene expression was enhanced in the intestinal fluid. Seafood matrices can significantly raise the pH level of gastric fluid and thus aid the survival of V. parahaemolyticus through passage from human gastric acid and progression of pathogenesis in the intestinal fluid. We confirmed these phenomena in the in vitro continuous digestion model.

Unveiling the acid stress response of clinical genotype Vibrio vulnificus isolated from the marine environments of Mangaluru coast, India

Gastric acidity is one of the earliest host defences faced by ingested organisms, and successful pathogens need to overcome this hurdle. The objective of this study was the systematic assessment of acid-stress response of Vibrio vulnificus isolated from coastal regions of Mangaluru. Acid-shock experiments were carried out at pH 4.0 and pH 4.5, with different experimental conditions expected to produce a varied acid response. Exposure to mild acid before the acid shock was favourable to the bacteria but was dependent on cell population and pH of the media and was independent of the strains tested. Lysine-dependent acid response was demonstrated with reference to the previously identified lysine decarboxylase system. Additionally, the results showed that inoculation into oysters provided some level of protection against acid stress. Increased expression of lysine/cadaverine genes was observed upon the addition of ground oyster and was confirmed by quantitative real-time PCR. The potential role of ornithine was analyzed with regard to acid stress, but no change in the survival pattern was observed. These findings highlight the physiology of bacteria in acid stress.

Acid-happy: Survival and recovery of enteropathogenic Escherichia coli (EPEC) in simulated gastric fluid

BACKGROUND

Gastric fluid pH serves an important function as an ecological filter to kill unwanted microbial taxa that would otherwise colonise the intestines, thereby shaping the diversity and composition of microbial communities found in the gut. The typical American-based diet causes the gastric pH to increase to pH 4 to 5, and it takes ∼2 h to return to pH 1.5 (normal). This window of increased gastric pH may allow potential pathogens to negotiate the hostile environment of the stomach. Another factor to consider is that in developing countries many people experience hypochlorhydria related to malnutrition and various gastric diseases. Enteropathogenic E. coli (EPEC) is a leading cause of infantile diarrhoea and has a high incidence in the developing world. The aim of this study was to assess the survival and recovery of non-acid adapted EPEC exposed to simulated gastric fluid (SGF) over a period of 180 min.

RESULTS

EPEC were grown in nutrient-rich medium and acid challenged in SGF at pH 1.5, 2.5, 3.5 and 4.5. Culturability was evaluated using a standard plate count method, and metabolic viability was assessed via cellular energy (adenosine triphosphate [ATP] assay) and respiratory activity (3-bis(2-methyloxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide [XTT] assay), and recovery and proliferation by means of optical density in liquid cultures. Sampling was performed at 0, 30, 60, 120, and 180 min post-SGF exposure. The results of this study showed that EPEC is remarkably acid resistant and was able to survive a simulated gastric environment for up to 3 h (180 min) at various pH (1.5, 2.5, 3.5, and 4.5). EPEC was culturable at all pH (1.5, 2.5, 3.5 and 4.5) at the higher inoculum size of 5.4-7.1 × 10⁶ CFU/ml, and at all pH except pH 1.5 at the lower inoculums of 5.4-7.1 × 10³ CFU/ml or 5.4-7.1 × 10¹ CFU/ml. The organism remained metabolically viable at pH 1.5, 2.5, 3.5, and 4.5 and was able to recover and proliferate once placed in a neutral, nutrient-rich environment.

CONCLUSION

In this study, EPEC demonstrated remarkable acid resistance and recovery at low pH without prior acid adaptation, which could prove to be problematic even in healthy people. In individuals with decreased gastric acidity, there is a higher probability of pathogen colonization and a resulting change in the gut microbiome. The results highlight the potential increase of food- and waterborne diseases in persons with compromised gastric function, or who are malnourished or immunocompromised. The data herein may possibly help in calculating more precisely the risk associated with consuming bacterial contaminated food and water in these individuals.

pH plays a role in the mode of action of trimethoprim on Escherichia coli

Metabolomics-based approaches were applied to understand interactions of trimethoprim with Escherichia coli K-12 at sub-minimum inhibitory concentrations (MIC≈0.2, 0.03 and 0.003 mg L-1). Trimethoprim inhibits dihydrofolate reductase and thereby is an indirect inhibitor of nucleic acid synthesis. Due to the basicity of trimethoprim, two pH levels (5 and 7) were selected which mimicked healthy urine pH. This also allowed investigation of the effect on bacterial metabolism when trimethoprim exists in different ionization states. UHPLC-MS was employed to detect trimethoprim molecules inside the bacterial cell and this showed that at pH 7 more of the drug was recovered compared to pH 5; this correlated with classical growth curve measurements. FT-IR spectroscopy was used to establish recovery of reproducible phenotypes under all 8 conditions (3 drug levels and control in 2 pH levels) and GC-MS was used to generate global metabolic profiles. In addition to finding direct mode-of-action effects where nucleotides were decreased at pH 7 with increasing trimethoprim levels, off-target pH-related effects were observed for many amino acids. Additionally, stress-related effects were observed where the osmoprotectant trehalose was higher at increased antibiotic levels at pH 7. This correlated with glucose and fructose consumption and increase in pyruvate-related products as well as lactate and alanine. Alanine is a known regulator of sugar metabolism and this increase may be to enhance sugar consumption and thus trehalose production. These results provide a wider view of the action of trimethoprim. Metabolomics indicated alternative metabolism areas to be investigated to further understand the off-target effects of trimethoprim.

Diffusiophoretic exclusion of colloidal particles for continuous water purification

It has been observed that colloidal particles are anomalously repelled from the interface of nanoporous materials and water by up to hundreds of micrometers even if there is no additional external field present. Recently, the physical origin of this anomalous repulsion has turned out to be diffusiophoretic migration triggered by an ion exchange process through the interface. Since the repulsive force is induced by a salt gradient only, the phenomenon can be applied to a microscale water purification platform without the need for any external power sources. In this work, we suggest a micro/nanofluidic device for continuous water purification utilizing long-range diffusiophoretic migration around ion exchangeable surfaces. An ion concentration boundary layer was characterized by the Sherwood number (Sh) which is a key dimensionless number to describe the purification process. Depending on Sh, we have theoretically and experimentally demonstrated that long-range diffusiophoretic exclusion can be used for continuous water purification. Finally, our platform can be used as a highly energy-efficient and portable water treatment option for operations such as purification, disinfection, water softening, etc.

Salmonella Cold Stress Response: Mechanisms and Occurrence in Foods

Since bacteria in foods often encounter various cold environments during food processing, such as chilling, cold chain distribution, and cold storage, lower temperatures can become a major stress environment for foodborne pathogens. Bacterial responses in stressful environments have been considered in the past, but now the importance of stress responses at the molecular level is becoming recognized. Documenting how bacterial changes occur at the molecular level may help to achieve the in-depth understanding of stress responses, to predict microbial fate when they encounter cold temperatures, and to design and develop more effective strategies to control pathogens in food for ensuring food safety. Microorganisms differ in responding to a sudden downshift in temperature and this, in turn, impacts their metabolic processes and can cause various structural modifications. In this review, the fundamental aspects of bacterial cold stress responses focused on cell membrane modification, DNA supercoiling modification, transcriptional and translational responses, cold-induced protein synthesis including CspA, CsdA, NusA, DnaA, RecA, RbfA, PNPase, KsgA, SrmB, trigger factors, and initiation factors are discussed. In this context, specific Salmonella responses to cold temperature including growth, injury, and survival and their physiological and genetic responses to cold environments with a focus on cross-protection, different gene expression levels, and virulence factors will be discussed.

The Risk of Community-Acquired Enteric Infection in Proton Pump Inhibitor Therapy: Systematic Review and Meta-analysis

BACKGROUND

Previous meta-analyses suggest that users of proton pump inhibitors (PPIs) have a higher risk of developing enteric infections compared with nonusers. These previous meta-analyses have considerable heterogeneity, and it is not clear whether the effect of PPIs is different for different types of microorganisms.

OBJECTIVE

The aim of this study is to update previous meta-analyses, concentrating on enteric infection in community settings and exploring potential sources of heterogeneity.

METHODS

A systematic search was conducted on electronic databases (all available years until November 2017). PubMed, EMBASE, Cochrane, and Web of Science were searched using specific keywords related to PPI therapy and community-acquired enteric infection. Eligible studies were selected based on prespecified criteria.

RESULTS

A total of 9 observational studies evaluating community-acquired enteric infection were eligible, including 12 separate analyses. The meta-analysis showed that PPI users have an increased risk of developing community-acquired enteric infection (pooled odds ratio [OR] = 4.28; 95% CI = 3.01-6.08). There was significant heterogeneity between the studies ( I² = 85%; P < 0.001), which was partly explained by type of microorganism. The strength of the association was similar for Salmonella (pooled OR = 4.84; 95% CI = 2.75-8.54; I² = 58.7%; P = 0.064) and Campylobacter (pooled OR = 5.09; 95% CI = 3-8.64; I² = 81%; P < 0.001) but lower for studies that combined all bacteria (pooled OR = 2.42; 95% CI = 0.96-6.14; I² = 94.3%; P < 0.001).

CONCLUSION

PPI users have an increased risk of developing community-acquired enteric infections compared with nonusers. The heterogeneity was partially explained by type of microorganism; the association is stronger for Salmonella and Campylobacter than for all bacteria combined.

Characterization of Enterotoxigenic Bacillus cereus sensu lato and Staphylococcus aureus Isolates and Associated Enterotoxin Production Dynamics in Milk or Meat-Based Broth

Bacillus cereus sensu lato species, as well as Staphylococcus aureus, are important pathogenic bacteria which can cause foodborne illness through the production of enterotoxins. This study characterised enterotoxin genes of these species and examined growth and enterotoxin production dynamics of isolates when grown in milk or meat-based broth. All B. cereus s. l. isolates harboured nheA, hblA and entFM toxin genes, with lower prevalence of bceT and hlyII. When grown at 16 °C, toxin production by individual B. cereus s. l. isolates varied depending on the food matrix; toxin was detected at cell densities below 5 log₁₀(CFU/mL). At 16 °C no staphylococcal enterotoxin C (SEC) production was detected by S. aureus isolates, although low levels of SED production was noted. At 30 °C all S. aureus isolates produced detectable enterotoxin in the simulated meat matrix, whereas SEC production was significantly reduced in milk. Relative to B. cereus s. l. toxin production, S. aureus typically required reaching higher cell numbers to produce detectable levels of enterotoxin. Phylogenetic analysis of the sec and sel genes suggested population evolution which correlated with animal host adaptation, with subgroups of bovine isolates or caprine/ovine isolates noted, which were distinct from human isolates. Taken together, this study highlights the marked differences in the production of enterotoxins both associated with different growth matrices themselves, but also in the behaviour of individual strains when exposed to different food matrices.

Gastric Mixing During Food Digestion: Mechanisms and Applications

Gastric mixing is a complex process that is governed by meal properties, such as food buffering capacity, physical properties, and the rate of breakdown as well as physiological factors, such as the rate of gastric secretions, gastric emptying, and gastric motility. Gastric mixing processes have been studied through the use of experimental and computational methods. Gastric mixing impacts the intragastric pH distribution and residence time in the stomach for ingested materials. Development of a fundamental understanding of the advective and diffusion processes and their roles in gastric mixing will be important in furthering our understanding of food breakdown, microbial survival, and drug dissolution during gastric digestion.

Preventing infection in the home

F undamental to controlling infection transmission in the home is the need to recognise it as an environment where all human activities occur, including food hygiene, hand hygiene and hygiene related to care of vulnerable groups. In recent years the concept of a risk assessment/risk reduction approach to hygiene has successfully controlled microbial risks in food and other manufacturing environments.

To deliver hygiene policy with real health benefits it is now accepted that a risk-based approach must also be developed for the home. The first step, hazard characterisation, involves identifying sites and surfaces where pathogens most frequently occur, and whether they are likely to be present in numbers that represent an infectious dose. A risk assessment is then made by considering this information together with an assessment of the probability of human exposure to the hazard. Risk reduction is achieved by application of a suitable hygiene procedure at the appropriate time.

Ecological Dynamics of Campylobacter in Integrated Mixed Crop-Livestock Farms and Its Prevalence and Survival Ability in Post-Harvest Products

This study investigated the ecological distribution of zoonotic bacterial pathogen, Campylobacter, in mixed crop-livestock (MCL) farms compared to conventional farms and their products at pre- and post-harvest levels. A total of 222 Campylobacter isolates were identified. At pre-harvest level, a total of 1287 samples from seven MCL farms, four conventional poultry farms, four organic produce-only and five conventional produce-only farms from Maryland and the DC metropolitan area were analysed from 2012 to 2014. Campylobacter was detected in 11.16% and 3.6% of MCL and conventional farm samples, respectively, but none from produce-only farm samples. Tetracycline resistance was observed in 51.02% of MCL farm isolates but none among conventional farm isolates. For post-harvest analysis, a total of 1281 food products from seven farmers markets, three organic retail supermarkets and three conventional retail supermarkets were collected from the same area. Campylobacter was isolated in 87.5%, 71.43% and 33.33% of whole chicken carcasses in farmers markets, organic and conventional retail supermarkets, respectively. No Campylobacter was detected in post-harvest produce samples due in part to the inability of Campylobacter to survive in absence of sufficient water activity. Overall, this study reveals public health concerns regarding the MCL farm environment and their products that are sold in retail and farmers markets.

Surviving the acid barrier: responses of pathogenic Vibrio cholerae to simulated gastric fluid

When bacteria are subjected to low acidic pHs of the gastric environment, they may enter the viable but nonculturable (VBNC) state of survival. In this state, bacteria cannot be cultured on solid media, still exhibit signs of metabolic activity (viability). In this study, the response of pathogenic Vibrio cholerae O1 and O139 to low pH-simulated environments of the human stomach was evaluated for their survival by culturability (plate count) and viability (flow cytometry-FC) assays. Bacteria were acid challenged with simulated gastric fluid (SGF) at pH 1.5, 2.5, 3.5 and 4.5 over a period of 180 min. Exposure to SGF up to 120 min increased acid tolerance of the Vibrios up to pH 3.5 with acid challenge occurring at pH 4.5. Bacteria were culturable from pH 2.5 to 4.5 up to 60 min SGF exposure. The stationary-phase cultures of Vibrio were able to survive SGF at all pHs in an 'injured' state with FC. This could possibly mean that the bacteria have entered the VBNC stage of survival. This is a worrying public health concern due to the fact that once favourable conditions arise (intestines), these Vibrios can change back to an infectious state and cause disease.

Characterization of the Invasive, Multidrug Resistant Non-typhoidal Salmonella Strain D23580 in a Murine Model of Infection

A distinct pathovar of Salmonella enterica serovar Typhimurium, ST313, has emerged in sub-Saharan Africa as a major cause of fatal bacteremia in young children and HIV-infected adults. D23580, a multidrug resistant clinical isolate of ST313, was previously shown to have undergone genome reduction in a manner that resembles that of the more human-restricted pathogen, Salmonella enterica serovar Typhi. It has since been shown through tissue distribution studies that D23580 is able to establish an invasive infection in chickens. However, it remains unclear whether ST313 can cause lethal disease in a non-human host following a natural course of infection. Herein we report that D23580 causes lethal and invasive disease in a murine model of infection following peroral challenge. The LD₅₀ of D23580 in female BALB/c mice was 4.7 x 10⁵ CFU. Tissue distribution studies performed 3 and 5 days post-infection confirmed that D23580 was able to more rapidly colonize the spleen, mesenteric lymph nodes and gall bladder in mice when compared to the well-characterized S. Typhimurium strain SL1344. D23580 exhibited enhanced resistance to acid stress relative to SL1344, which may lend towards increased capability to survive passage through the gastrointestinal tract as well as during its intracellular lifecycle. Interestingly, D23580 also displayed higher swimming motility relative to SL1344, S. Typhi strain Ty2, and the ST313 strain A130. Biochemical tests revealed that D23580 shares many similar metabolic features with SL1344, with several notable differences in the Voges-Proskauer and catalase tests, as well alterations in melibiose, and inositol utilization. These results represent the first full duration infection study using an ST313 strain following the entire natural course of disease progression, and serve as a benchmark for ongoing and future studies into the pathogenesis of D23580.

A deadly form of non-typhoidal Salmonella has emerged as a major cause of invasive disease in sub-Saharan Africa. Initial genomic profiling of this novel Salmonella sequence type, ST313, indicated that although it is technically classified as S. Typhimurium (a serovar characterized by a broad host range), it may be evolving towards becoming a more human-specific, ‘typhoid-like’ pathogen. However, it was recently demonstrated that ST313 strains were indeed able to establish an invasive and damaging infection in chickens. Despite these important findings, it remains unclear whether ST313 is able to cause lethal disease in a non-human host, since no study has yet followed the entire natural course of disease progression. As such, there are no data available concerning the median lethal dose (LD₅₀) of any ST313 strain. This is an important metric, as the LD₅₀ value will serve as a benchmark for mechanistic studies focused on understanding the relationship between virulence and the phenotypic and molecular genetic attributes associated with ST313 infections. Here we report that D23580 causes lethal disease in BALB/c mice and determined the LD₅₀ following peroral challenge. Phenotypic characterization revealed distinct differences in tissue distribution, acid stress resistance, and biochemical utilization between D23580 and the ‘classic’ Typhimurium strain SL1344.

Use of Ensure® nutrition shakes as an alternative formulation method for live recombinant Attenuated Salmonella Typhi vaccines

Background

To be effective, orally administered live Salmonella vaccines must first survive their encounter with the low pH environment of the stomach. To enhance survival, an antacid is often given to neutralize the acidic environment of the stomach just prior to or concomitant with administration of the vaccine. One drawback of this approach, from the perspective of the clinical trial volunteer, is that the taste of a bicarbonate-based acid neutralization system can be unpleasant. Thus, we explored an alternative method that would be at least as effective as bicarbonate and with a potentially more acceptable taste. Because ingestion of protein can rapidly buffer stomach pH, we examined the possibility that the protein-rich Ensure® Nutrition shakes would be effective alternatives to bicarbonate.

Results

We tested one Salmonella enterica serovar Typhimurium and three Salmonella Typhi vaccine strains and found that all strains survived equally well when incubated in either Ensure® or bicarbonate. In a low gastric pH mouse model, Ensure® worked as well or better than bicarbonate to enhance survival through the intestinal tract, although neither agent enhanced the survival of the S. Typhi test strain possessing a rpoS mutation.

Conclusions

Our data show that a protein-rich drink such as Ensure® Nutrition shakes can serve as an alternative to bicarbonate for reducing gastric pH prior to administration of a live Salmonella vaccine.

Survival after cryogenic freezing of Campylobacter species in ground Turkey patties treated with polyphosphates

The use of polyphosphate-based marinades in the processing of poultry has been previously shown to increase the survival of Campylobacter species present in the exudates derived from these products. This study investigates the effects that some of the same polyphosphates have on the survival of Campylobacter species within a ground turkey product subjected to cryogenic freezing. Ground turkey patties with two different polyphosphate formulations added in two different concentrations were artificially contaminated with known concentrations of Campylobacter jejuni or Campylobacter coli. The patties were cryogenically frozen at -80°F (-62.2°C) with liquid nitrogen vapor and held at -20°C for 7 or 33 days, after which the number of Campylobacter surviving in the patties was determined. On average the cryogenic freezing resulted in a 2.5-log decrease in the survival of C. jejuni cells and a 2.9-log decrease in C. coli cells present in the turkey patties. Additionally, the presence of polyphosphates in the turkey patties had no effect on Campylobacter survival up to the maximum allowed concentration (0.5%) for polyphosphates in poultry marinades. Finally, it was determined that the added polyphosphates had little effect on the pH of the ground turkey meat; an effect which previously had been implicated in the enhancement of Campylobacter survival due to the presence of polyphosphates.

Metal ions, not metal-catalyzed oxidative stress, cause clay leachate antibacterial activity

Aqueous leachates prepared from natural antibacterial clays, arbitrarily designated CB-L, release metal ions into suspension, have a low pH (3.4–5), generate reactive oxygen species (ROS) and H₂O₂, and have a high oxidation-reduction potential. To isolate the role of pH in the antibacterial activity of CB clay mixtures, we exposed three different strains of Escherichia coli O157:H7 to 10% clay suspensions. The clay suspension completely killed acid-sensitive and acid-tolerant E. coli O157:H7 strains, whereas incubation in a low-pH buffer resulted in a minimal decrease in viability, demonstrating that low pH alone does not mediate antibacterial activity. The prevailing hypothesis is that metal ions participate in redox cycling and produce ROS, leading to oxidative damage to macromolecules and resulting in cellular death. However, E. coli cells showed no increase in DNA or protein oxidative lesions and a slight increase in lipid peroxidation following exposure to the antibacterial leachate. Further, supplementation with numerous ROS scavengers eliminated lipid peroxidation, but did not rescue the cells from CB-L-mediated killing. In contrast, supplementing CB-L with EDTA, a broad-spectrum metal chelator, reduced killing. Finally, CB-L was equally lethal to cells in an anoxic environment as compared to the aerobic environment. Thus, ROS were not required for lethal activity and did not contribute to toxicity of CB-L. We conclude that clay-mediated killing was not due to oxidative damage, but rather, was due to toxicity associated directly with released metal ions.

Efficacy of Acetic Acid against Listeria monocytogenes Attached to Poultry Skin during Refrigerated Storage

This work evaluates the effect of acetic acid dipping on the growth of L. monocytogenes on poultry legs stored at 4 °C for eight days. Fresh inoculated chicken legs were dipped into either a 1% or 2% acetic acid solution (v/v) or distilled water (control). Changes in mesophiles, psychrotrophs, Enterobacteriaceae counts and sensorial characteristics (odor, color, texture and overall appearance) were also evaluated. The shelf life of the samples washed with acetic acid was extended by at least two days over the control samples washed with distilled water. L. monocytogenes counts before decontamination were 5.57 log UFC/g, and after treatment with 2% acetic acid (Day 0), L. monocytogenes counts were 4.47 log UFC/g. Legs washed with 2% acetic acid showed a significant (p < 0.05) inhibitory effect on L. monocytogenes compared to control legs, with a decrease of about 1.31 log units after eight days of storage. Sensory quality was not adversely affected by acetic acid. This study demonstrates that while acetic acid did reduce populations of L. monocytogenes on meat, it did not completely inactivate the pathogen. The application of acetic acid may be used as an additional hurdle contributing to extend the shelf life of raw poultry and reducing populations of L. monocytogenes.