Survival of antibiotic resistant and antibiotic sensitive strains of E. coli O157 and E. coli O26 in food matrices

Effects of antibiotic-induced resistance on the growth, survival ability and virulence of Salmonella enterica

Salmonella enterica is an important foodborne pathogen that constitutes a major health hazard. The emergence and aggravation of antibiotic-resistant Salmonella has drawn attention widely around the world. Conducting a risk assessment of antibiotic-resistant foodborne pathogens throughout the food chain is a pressing requirement for ensuring food safety. The growth, survival capability, and virulence of antibiotic-resistant Salmonella represent crucial biological characteristics that play an important role in microbial risk assessment. In this study, eight antibiotic-sensitive S. enterica strains were induced by Ampicillin (Amp) and Ciprofloxacin (CIP), respectively, and AMP-resistant and CIP-resistant mutants were obtained. The growth characteristics under different temperatures (25, 30, 35 °C), viability after exposure to heat (55, 57.5, 60 °C) and acid (HCl, pH = 3.0), the virulence potential (adhesion and invasion to Caco-2 cells, biofilm formation and motility) and the lethality in a model species (Galleria mellonella) were evaluated and compared for S. enterica strains before and after antibiotic exposure. The induction by AMP and CIP are likely to promote cross-antibiotic resistance to their antibiotic classes, β-lactams and quinolones, as well as some compound antibiotics. It was observed that generally the antibiotic-induction-resistant strains showed decreased growth ability and lower heat resistance, although the differences were not significant at all the conditions tested. The AMP-resistant strains were significantly less acid resistance than the sensitive and the CIP-resistant ones, while exhibiting increased biofilm formation ability. In general, the antibiotic-induced resistance did not significantly affect the motility, adherence, or invasion ability of Caco-2 cells. However, CIP-resistant strains displayed lower lethality in G. mellonella infection, whereas AMP-resistant strains did not, and even two strains improved lethality. The study of the biological characteristics of antibiotic-resistant S. enterica is essential in better understanding the microbial risks to both the food chain and human health, thereby facilitating a more accurate risk assessment.

The Heat Is On: Modeling the Persistence of ESBL-Producing E. coli in Blue Mussels under Meal Preparation

Pathways for exposure and dissemination of antimicrobial-resistant (AMR) bacteria are major public health issues. Filter-feeding shellfish concentrate bacteria from the environment and thus can also harbor extended-spectrum β-lactamase—producing Escherichia coli (ESBL E. coli) as an example of a resistant pathogen of concern. Is the short steaming procedure that blue mussels (Mytilus edulis) undergo before consumption enough for food safety in regard to such resistant pathogens? In this study, we performed experiments to assess the survival of ESBL E. coli in blue mussel. Consequently, a predictive model for the dose of ESBL E. coli that consumers would be exposed to, after preparing blue mussels or similar through the common practice of brief steaming until opening of the shells, was performed. The output of the model is the expected number of colony forming units per gram (cfu/g) of ESBL E. coli in a meal as a function of the duration and the temperature of steaming and the initial contamination. In these experiments, the heat tolerance of the ESBL-producing E. coli strain was indistinguishable from that of non-ESBL E. coli, and the heat treatments often practiced are likely to be insufficient to avoid exposure to viable ESBL E. coli. Steaming time (>3.5−4.0 min) is a better indicator than shell openness to avoid exposure to these ESBL or indicator E. coli strains.

Multidrug-resistant enteroaggregative Escherichia coli (EAEC) enters dormant state during heat treatment: A potential hazard in municipal sludge

Reuse of sewage sludge is a general trend and land application is an essential way to reuse sludge. The outbreak of coronavirus disease has raised concerns about human pathogens and their serious threat to public health. The risk of pathogenic bacterial contamination from land application of municipal sludge has not been well assessed. The purpose of this study was to investigate the presence of pathogenic bacteria in municipal sewage sludge and to examine the survival potential of certain multidrug-resistant enteroaggregative Escherichia coli (EAEC) strain isolated from sewage sludge during heat treatment. The sewage sludge produced in the two wastewater treatment plants contained pathogenic bacteria such as pathogenic E. coli, Shigella flexneri, and Citrobacter freundii. The environmental strain of EAEC isolated from the sludge was resistant to eight types of antibiotics. It could also enter the dormant state after 4.5 h of treatment at 55 °C and regrow at 37 °C, while maintaining its antibiotic resistance. Our results indicate that the dormancy of EAEC might be why it is heat-resistant and could not be killed completely during the sludge heat treatment process. Owing to the regrowth of the dormant pathogenic bacteria, it is risky to apply the sludge to land even if the sludge is heat-treated, and there is also a risk of spreading antibiotic resistance.

Antibiotic Resistance Carriage Causes a Lower Survivability Due to Stress Associated with High-Pressure Treatment among Strains from Starter Cultures

Simple Summary

High-pressure processing is one of the most promising novel food preservation methods that is increasingly used in the food industry. It is applied in various food products such as dairy, meat, juices, and jams to improve safety and shelf-life by the inactivation of microorganisms and preserving of quality attributes. It is reported that the level of antibiotic resistance may influence the ability of strains to survive stress conditions. In this study, it was investigated if carrying antibiotic resistance genes affects the survival of lactic acid bacteria (Lactococcus and the former Lactobacillus) strains during high-pressure treatment. It was demonstrated that carrying antibiotic resistance genes strains showed a lower survival in response to pressure than strains carrying up to one resistance gene. The same observations were made for both genera. Appropriately selected parameters of high-pressure treatment may help in the elimination of antibiotic-resistant strains.

Abstract

High-pressure processing is one of the most promising novel food preservation methods that is increasingly used in the food industry. Its biggest advantage is that it is a nonthermal method that ensures the microbiological safety of the product while maintaining other features, including nutritional value. If products made with starter cultures are subjected to high-pressure treatment, the process parameters should be selected so as not to eliminate all microorganisms in the product. The aim of the study was to investigate if carrying antibiotic resistance genes affects the survival of lactic acid bacteria (Lactococcus and the former Lactobacillus) strains during high-pressure treatment. Survival was assessed using the plate count method. It was shown that the strains carrying antibiotic resistance genes showed a lower survival to high pressure. This might be explained by the phenomenon of fitness cost, consisting in a reduced adaptation of antibiotic-resistant strains related to metabolic expenditure. The obtained results indicate the need for further research in this field and the need to select food processing parameters depending on the strains intentionally included in the food.

Assessing the Impact of Heat Treatment of Food on Antimicrobial Resistance Genes and Their Potential Uptake by Other Bacteria-A Critical Review

The dissemination of antibiotic resistance genes (ARGs) is a global health concern. This study identifies and critically reviews the published evidence on whether cooking (heating) food to eliminate bacterial contamination induces sufficient damage to the functionality of ARGs. Overall, the review found that there is evidence in the literature that Antimicrobial Resistant (AMR) bacteria are no more heat resistant than non-AMR bacteria. Consequently, recommended heat treatments sufficient to kill non-AMR bacteria in food (70 °C for at least 2 min, or equivalent) should be equally effective in killing AMR bacteria. The literature shows there are several mechanisms through which functional genes from AMR bacteria could theoretically persist in heat-treated food and be transferred to other bacteria. The literature search found sparce published evidence on whether ARGs may actually persist in food after effective heat treatments, and whether functional genes can be transferred to other bacteria. However, three publications have demonstrated that functional ARGs in plasmids may be capable of persisting in foods after effective heat treatments. Given the global impact of AMR, there is clearly a need for further practical research on this topic to provide sufficient evidence to fully assess whether there is a risk to human health from the persistence of functional ARGs in heat-treated and cooked foods.

Evaluation of the Stress Tolerance of Salmonella with Different Antibiotic Resistance Profiles

Disease caused by antibiotic-resistant Salmonella is a serious clinical problem that poses a great threat to public health. The present study is aimed at assessing differences in bacterial kinetics with different antibiotic resistance profiles under environmental stress and at developing microbial tolerance models in lettuce during storage from 4 to 36°C. The drug-resistance phenotypes of 10 Salmonella Typhimurium (S. Typhimurium) isolates were examined using the broth microdilution method. The results of 10 S. Typhimurium isolates in the suspensions showed that a slow trend towards reduction of drug-sensitive (DS) isolates in relation to the others though without statistical difference. Compared to DS S. Typhimurium SA62, greater bacterial reduction was observed in multidrug-resistant (MDR) S. Typhimurium HZC3 during lettuce storage at 4°C (P < 0.05). It was likely that a cross-response between antibiotic resistance and food-associated stress tolerance. The greater growth in lettuce at 12°C was observed for DS S. Typhimurium SA62 compared to MDR S. Typhimurium HZC3 and was even statistically different (P < 0.05), while no significant difference was observed for bacterial growth between MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 strains in lettuce storage from 16 to 36°C (P > 0.05). The goodness-of-fit indices indicated the Log-linear primary model provided a satisfactory fit to describe the MDR S. Typhimurium HZC3 and DS S. Typhimurium SA62 survival at 4°C. A square root secondary model could be used to describe the effect of temperature (12, 16, 28, and 36°C) on the growth rates of S. Typhimurium HZC3 (adj - R 2 = 0.91, RMSE = 0.06) and S. Typhimurium SA62 (adj - R 2 = 0.99, RMSE = 0.01) derived from the Huang primary model. It was necessary to pay attention to the tolerance of antibiotic resistant bacteria under environmental stress, and the generated models could provide parts of the input data for microbial risk assessment of Salmonella with different antibiotic resistance profile in lettuce.

Characterization and Food Application of the Novel Lytic Phage BECP10: Specifically Recognizes the O-polysaccharide of Escherichia coli O157:H7

Escherichia coli O157:H7 is a global concern that causes serious diseases, such as hemolytic uremic syndrome and bloody diarrhea. To control E. coli O157:H7 in food, a novel siphophage, BECP10, that targets the O157 serotype was isolated and characterized. Unlike other E. coli phages, BECP10 can only infect E. coli O157 strains, and thus, did not infect other strains. The 48 kbp genome of BECP10 contained 76 open reading frames (ORFs), including 33 putative functional ORFs. The phage did not contain lysogeny-related modules or toxin-associated genes, suggesting that the phage might be strictly lytic. The tail spike protein (TSP) sequence had very low homology with the reported T1-like phages, indicating that TSP might be related to this unique host spectrum. The specific O-antigen residue of E. coli O157:H7 may be a key factor for phage infection by adsorption and receptor identification. The phage exhibited strong antibacterial activity against E. coli O157:H7 over a broad pH range and showed little development of phage-insensitive mutants. The phage sustained viability on the burger patties and reduced E. coli O157:H7 to a non-detectable level without the emergence of resistant cells at low temperatures for five days. Therefore, phage BECP10 might be a good biocontrol agent for E. coli O157:H7-contaminated food matrices.

Insights into Emergence of Antibiotic Resistance in Acid-Adapted Enterohaemorrhagic Escherichia coli

The emergence of multidrug-resistant pathogens presents a global challenge for treating and preventing disease spread through zoonotic transmission. The water and foodborne Enterohaemorrhagic Escherichia coli (EHEC) are capable of causing intestinal and systemic diseases. The root cause of the emergence of these strains is their metabolic adaptation to environmental stressors, especially acidic pH. Acid treatment is desired to kill pathogens, but the protective mechanisms employed by EHECs cross-protect against antimicrobial peptides and thus facilitate opportunities for survival and pathogenesis. In this review, we have discussed the correlation between acid tolerance and antibiotic resistance, highlighting the identification of novel targets for potential production of antimicrobial therapeutics. We have also summarized the molecular mechanisms used by acid-adapted EHECs, such as the two-component response systems mediating structural modifications, competitive inhibition, and efflux activation that facilitate cross-protection against antimicrobial compounds. Moving beyond the descriptive studies, this review highlights low pH stress as an emerging player in the development of cross-protection against antimicrobial agents. We have also described potential gene targets for innovative therapeutic approaches to overcome the risk of multidrug-resistant diseases in healthcare and industry.

Antibiotic-resistant bacteria and gut microbiome communities associated with wild-caught shrimp from the United States versus imported farm-raised retail shrimp

In the United States, farm-raised shrimp accounts for ~ 80% of the market share. Farmed shrimp are cultivated as monoculture and are susceptible to infections. The aquaculture industry is dependent on the application of antibiotics for disease prevention, resulting in the selection of antibiotic-resistant bacteria. We aimed to characterize the prevalence of antibiotic-resistant bacteria and gut microbiome communities in commercially available shrimp. Thirty-one raw and cooked shrimp samples were purchased from supermarkets in Florida and Georgia (U.S.) between March-September 2019. The samples were processed for the isolation of antibiotic-resistant bacteria, and isolates were characterized using an array of molecular and antibiotic susceptibility tests. Aerobic plate counts of the cooked samples (n = 13) varied from < 25 to 6.2 log CFU/g. Isolates obtained (n = 110) were spread across 18 genera, comprised of coliforms and opportunistic pathogens. Interestingly, isolates from cooked shrimp showed higher resistance towards chloramphenicol (18.6%) and tetracycline (20%), while those from raw shrimp exhibited low levels of resistance towards nalidixic acid (10%) and tetracycline (8.2%). Compared to wild-caught shrimp, the imported farm-raised shrimp harbored distinct gut microbiota communities and a higher prevalence of antibiotic-resistance genes in their gut. The presence of antibiotic-resistant strains in cooked shrimps calls for change in processing for their mitigation.

Home style frying of steak and meat products: Survival of Escherichia coli related to dynamic temperature profiles

Microbial survival of heating and cross-contamination are the two transmission routes during food preparation in the consumers' kitchen that are relevant for QMRA (Quantitative Microbial Risk Assessment). The aim of the present study was to extend the limited amount of data on microbial survival during real-life preparation of meat and meat products and to obtain accessory temperature data that allow for a more general (product unspecific) approach. Therefore survival data were combined with extensive measurements of time- and location dependent temperature using an infrared camera for the surface and buttons for the inside of the product, supplemented with interpolation modelling. We investigated the survival of heating of Escherichia coli O111:H2 in beefsteak, hamburgers (beef and 50% beef 50% pork (HH)), meatballs (beef and HH) and crumbs (HH). For beefsteak, survival as a whole is dominated by the sides, giving a log reduction of 1-2 (rare), 3-4 (medium) and 6-7 (done). Limited measurements indicated that done preparation gave 5-6 log reduction for crumbs and at least 8-9 log for the other products. Medium preparation gave a higher reduction in hamburgers (2-4 log) than in meatballs (1-2 log) and in beef (3-4) than in HH (2-3) hamburgers. In general, our 'done' results give larger inactivation than found in literature, whereas 'rare' and 'medium' results are similar. The experiments resulted in two types of curves of D₇₀/z-values, dependent on product, doneness and for beefsteaks sides vs. top/bottom. One type of curve agrees reasonably with literature D₇₀/z estimates from isothermal temperature experiments, which supports using these estimates for home style cooking QMRA calculations. In case of the other type of curve, which is mainly found for (near) surface contamination in close contact with the pan, these literature estimates cannot be applied. We also applied a simplified approach, assuming thermal inactivation is dominated by the highest temperatures reached. The time duration of this highest temperature gives accessory D-values which prove to fit with isothermal temperature literature data, thus suggesting application of such data for QMRA is possible by this approach also, which is less labor intensive both in terms of measurements and modelling. In real life, variability in product properties and preparation styles is large. Further studies are needed to analyze the effect on survival, preferably focusing on determining the essential variables. More variation in heating time will allow for estimating D₇₀/z point estimates rather than curves representing possible sets of D₇₀/z-values.

Stress tolerance of Staphylococcus aureus with different antibiotic resistance profiles

Staphylococcus aureus (S. aureus) is a zoonotic bacterium and is among the most important pathogens causing bacterial foodborne diseases. In recent years, disease caused by antibiotic-resistant S. aureus is a serious clinical problem that poses a great threat to public health. In this study, we examined the drug-resistance phenotypes and genotypes of 9 S. aureus strains. One strain was obtained from the China Center for Type Culture Collection (CCTCC), and the remaining eight strains were isolated from food. Two common methods (the Kirby-Bauer disk diffusion and broth microdilution methods) were used to detect bacterial drug resistance. Then, we analysed the relationship between the bacterial drug resistance phenotypes and genotypes. We found that some S. aureus strains isolated from food were drug-resistant or even multi-drug resistant and that there was not a perfect match between resistance phenotypes and genotypes. The viabilities of the drug-sensitive (DS), drug-resistant (DR), and multi-drug resistant (MDR) S. aureus strains were also compared when they were exposed to conditions of acid (HCl, pH = 1.5), heat (63 °C), and osmotic pressure (30% NaCl). The results showed that the DR and MDR bacterial strains had survival rates similar to or higher than those of the DS strains under environmental stress.

Comparative Effect of Heat Shock on Survival of O157:H7 and Non-O157 Shiga Toxigenic Escherichia coli and Salmonella in Lean Beef with or without Moisture-Enhancing Ingredients

Thermal tolerance of pathogenic bacteria has been shown to increase after exposure to sublethal elevated temperatures, or heat shock. We evaluated the effect of heat shock at 48°C on thermal tolerance (D_55°C) of cocktails of O157 and non-O157 Shiga toxigenic Escherichia coli (STEC) and Salmonella in lean ground beef with or without moisture-enhancing ingredients. Beef was moisture enhanced to 110% (w) with a 5% NaCl-2.5% sodium tripolyphosphate (w/w) brine. Meat, with or without added brine, was inoculated (∼10⁸ CFU/g) and heat shocked at 48°C for 0, 5, or 30 min, followed by isothermal heating at 55°C. Inoculated control samples were unenhanced and were not subject to heat shock. From the linear portion of the log CFU per gram surviving cells over time plots, D_55°C-values (minutes) were calculated. D_55°C was 20.43, 28.78, and 21.15 min for O157, non-O157, and Salmonella controls, respectively. Overall, heat shock significantly increased D_55°C, regardless of pathogen (P < 0.05). After 30 min of heat shock, D_55°C increased 89 and 160% for O157 STEC, 32 and 49% for non-O157 STEC, and 29 and 57% for Salmonella, in unenhanced and enhanced samples, respectively, relative to the pathogen control. D_55°C for Salmonella was the same or significantly less than for O157 and non-O157 STEC, regardless of heat shock, and was significantly less than for O157 and non-O157 STEC in all trials with moisture-enhanced meat (P < 0.05). Moisture-enhancing ingredients significantly increased D_55°C, regardless of pathogen (P < 0.05). We suggest that thermal processes validated against Salmonella may not prove effective against STEC in all cases and that regulators of the beef industry should focus attention on STEC in nonintact moisture-enhanced beef products.

The effects of pig manure application on the spread of tetracycline resistance in bulk and cucumber rhizosphere soils: a greenhouse experiment

It is important to understand the dynamics of tetracycline-resistant bacteria (TRB) and tetracycline resistance genes (TRGs) in bulk and rhizosphere soils for evaluating the spread of TRGs from pig manure to human. In this work, a greenhouse experiment was conducted to investigate the difference in abundance of TRB, tetracycline-resistant Escherichia coli (TRE), tetracycline-resistant Pseudomonas spp. (TRP), and TRGs between bulk and cucumber rhizosphere soils. The application of pig manure resulted in the long-term persistence of TRB, TRE, TRP, and TRGs in bulk soil and rhizosphere of cucumber for at least 65 days. Pig manure application dose was the major driving force in altering the abundances of TRB and TRE, whereas TRP was disturbed mainly by compartment (bulk soil or rhizosphere). Both TRE and the percentage of TRE in bulk and rhizosphere soils increased linearly with an increase in dose of pig manure. The exponential relationships between pig manure dose and TRP along with TRP percentage were also noted. There were significant differences in the relative abundances of TRGs between bulk and cucumber rhizosphere soils, suggesting the use of pig manure exerted a more lasting impact on the spread of TRGs in the rhizosphere than in the bulk soil.

Survival of Listeria monocytogenes with different antibiotic resistance patterns to food-associated stresses

The ongoing rise of antibiotic resistant microbial pathogens has become one of the major public health threats worldwide. Despite all the effort and actions taken so far, a proliferation of antibiotic resistant (AR) and multi-antibiotic resistant (MAR) strains is still observed, including in foodborne pathogens. This trend has been also noted recently for isolates of Listeria monocytogenes, a species that, although remaining largely sensitive to clinically relevant antimicrobials, has been reported to develop increased tolerance to antibiotics, particularly in isolates recovered from the food-chain. In this study we compared the ability of MAR (n=8), AR (n=18) and antibiotic susceptible (AS, n=11) L. monocytogenes strains from food and clinical origin to survive to different environmental stress conditions, including temperature (58°C), acidic stress (1% v/v lactic acid, pH3.5), and osmotic stress (37% w/v NaCl). The presence of antibiotic active efflux among MAR and AR strains, and its role on L. monocytogenes tolerance to different antimicrobial compounds was also investigated, namely; hydrogen peroxide; organic acids (acetic, citric and lactic); nisin; benzalkonium chloride (BC); and, sodium nitrite. While no significant differences were observed in the survival of the 37 strains exposed to high temperature (58°C), overall the mean logarithmic reduction of clinical strains was statistically lower after acid and salt exposure than that observed for strains of food origin; but both food and clinical strains resistant to two or three antibiotics were significantly less susceptible to acid (lactic acid 1% v/v) and osmotic stresses (37% w/v NaCl) when compared to AS strains. Using the EtBr-agar Cartwheel method, it was possible to detect efflux pumps in three of the 26 MAR and AR isolates, including one control strain; the active efflux in theses isolates was proven to be associated with fluoroquinolone resistance, and possible extrusion of BC and hydrogen peroxide. The mechanisms responsible for the possible correlation between resistance to antibiotics and to acid or salt stress in L. monocytogenes have yet to be understood.

Escherichia albertii Inactivation following l-Lactic Acid Exposure or Cooking in Ground Beef

Escherichia albertii is an emerging foodborne pathogen recovered from young children and adults exhibiting symptoms of gastroenteritis via pathogenesis factors including attaching and effacing lesions, cytolethal distending toxin, and Shiga toxin variants. Study objectives were to determine E. albertii survival following (i) exposure to lactic acid as a function of solution pH and incubation period and (ii) cooking ground beef patties to different endpoint temperatures. E. albertii was incubated in phosphate buffer containing 3.0% l-lactic acid adjusted to pH 3.0, 4.0, 5.0, or 7.0; survivors were determined every 30 min for 150 min. Ground beef patties (80% lean) were cooked to temperature endpoints simulating undercooking (62°C), the minimum temperature for safe cooking (71.1°C), and cooking to well done (76°C). Maximal pathogen reduction was observed after a 30-min exposure to pH 3.0 l-lactic acid. Reductions of 3.9, 4.4, and 4.9 log CFU/g were obtained following cooking ground beef patties to 62, 71.1, and 76°C, respectively, but the reductions did not differ as a function of the endpoint cooking temperature (P ≥ 0.05). E. albertii may be controlled on beef through the proper application of antimicrobial interventions and cooking.

Growth of Stressed Strains of Four Non-O157 Shiga Toxin-Producing Escherichia coli Serogroups in Five Enrichment Broths

The purpose of this study was to evaluate (i) the behavior of several strains of non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O103, O111, and O145) exposed to different stress conditions and (ii) the growth dynamics of stressed and nonstressed non-O157 STEC cells in five enrichment media. STEC strains were exposed to acid, cold, and freeze stresses. Lethal and sublethal injuries were determined by plating in parallel on selective and nonselective agar media. Freeze stress (8 days, 20°C) caused the most lethal (95.3% ± 2.5%) injury, as well as the most sublethal (89.1% ± 8.8%) injury in the surviving population. Growth of stressed and nonstressed pure cultures of non-O157 STEC on modified tryptic soy broth, buffered peptone water (BPW), BPW with sodium pyruvate, Brila, and STEC enrichment broth (SEB) was determined using total viable counts. To compare growth capacities, growth after 7 and 24 h of enrichment was measured; lag phases and maximum growth rates were also calculated. In general, growth on BPW resulted in a short lag phase followed by a high maximum growth rate during the enrichment of all tested strains when using all three stress types. Furthermore, BPW ensured the highest STEC count after 7 h of growth. Supplementing the medium with sodium pyruvate did not improve the growth dynamics. The two selective media, Brila and SEB, were less efficient than BPW, but Brila's enrichment performance was remarkably better than that of SEB. This study shows that irrespective of the effect of background flora, BPW is still recommended for resuscitation of non-O157 STEC.

Antibiotic-resistant bacteria: prevalence in food and inactivation by food-compatible compounds and plant extracts

Foodborne antibiotic-resistant pathogenic bacteria such as Campylobacter jejuni, Bacillus cereus, Clostridium perfringens, Escherichia coli, Salmonella enterica, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahemolyticus can adversely affect animal and human health, but a better understanding of the factors involved in their pathogenesis is needed. To help meet this need, this overview surveys and interprets much of our current knowledge of antibiotic (multidrug)-resistant bacteria in the food chain and the implications for microbial food safety and animal and human health. Topics covered include the origin and prevalence of resistant bacteria in the food chain (dairy, meat, poultry, seafood, and herbal products, produce, and eggs), their inactivation by different classes of compounds and plant extracts and by the use of chlorine and physicochemical methods (heat, UV light, pulsed electric fields, and high pressure), the synergistic antimicrobial effects of combinations of natural antimicrobials with medicinal antibiotics, and mechanisms of antimicrobial activities and resistant effects. Possible areas for future research are suggested. Plant-derived and other safe natural antimicrobial compounds have the potential to control the prevalence of both susceptible and resistant pathogens in various environments. The collated information and suggested research will hopefully contribute to a better understanding of approaches that could be used to minimize the presence of resistant pathogens in animal feed and human food, thus reducing adverse effects, improving microbial food safety, and helping to prevent or treat animal and human infections.

Thermal tolerance of O157 and non-O157 Shiga toxigenic strains of Escherichia coli, Salmonella, and potential pathogen surrogates, in frankfurter batter and ground beef of varying fat levels

The non-O157 Shiga toxigenic Escherichia coli (STEC) serogroups most commonly associated with illness are O26, O45, O103, O111, O121, and O145. We compared the thermal tolerance (D55°C) of three or more strains of each of these six non-O157 STEC serogroups with five strains of O157:H7 STEC in 7% fat ground beef. D55°C was also determined for at least one heat-tolerant STEC strain per serogroup in 15 and 27% fat ground beef. D55°C of single-pathogen cocktails of O157 and non-O157 STEC, Salmonella, and potential pathogen surrogates, Pediococcus acidilactici and Staphylococcus carnosus, was determined in 7, 15, and 27% fat ground beef and in frankfurter batter. Samples (25 g) were heated for up to 120 min at 55°C, survivors were enumerated, and log CFU per gram was plotted versus time. There were significant differences in D55°C across all STEC strains heated in 7% fat ground beef (P < 0.05), but no non-O157 STEC strain had D55°C greater than the range observed for O157 STEC. D55°C was significantly different for strains within serogroups O45, O145, and O157 (P < 0.05). D55°C for non-O157 STEC strains in 15 and 27% fat ground beef were less than or equal to the range of D55°C for O157. D55°C for pathogen cocktails was not significantly different when measured in 7, 15, and 27% fat ground beef (P ≥ 0.05). D55°C of Salmonella in frankfurter batter was significantly less than for O157 and non-O157 STEC (P < 0.05). Thermal tolerance of pathogen cocktails in ground beef (7, 15, or 27% fat) and frankfurter batter was significantly less than for potential pathogen surrogates (P < 0.05). Results suggest that thermal processes in beef validated against E. coli O157:H7 have adequate lethality against non-O157 STEC, that thermal processes that target Salmonella destruction may not be adequate against STEC in some situations, and that the use of pathogen surrogates P. acidilactici and S. carnosus to validate thermal processing interventions in ground beef and frankfurter batter would be of limited utility to processors.

Escherichia coli O157:H7 in Raw Meat in Addis Ababa, Ethiopia: Prevalence at an Abattoir and Retailers and Antimicrobial Susceptibility

Background

Although raw meat and its products are commonly consumed in traditional Ethiopian diets, E. coli O157: H7 is rarely studied compared to other countries. Thus the present study has been designed to determine the prevalence and assess the antimicrobial susceptibility of E. coli O157: H7 isolated from beef, sheep meat and goat meat at one abattoir and in 48 selected raw meat retail shops in Addis Ababa.

Results

Out of 384 meat samples examined, 10.2% (39/384) were positive to E. coli O157:H7. Among these samples examined, beef was the most frequently contaminated with E. coli O157:H7 with an overall prevalence of 13.3% (17/128) followed by 9.4% (12/128) sheep meat and 7.8% (10/128) goat meat. With regard to meat source, the prevalence rates of E. coli O157:H7 at the abattoir and the selected retail shops were 5.7% (11/192) and 14.6% (28/192), respectively. Significant differences in prevalence was observed among sample sources (p < 0.05). The antimicrobial susceptibility investigation of 39 E. coli O157:H7 isolates using 10 commercially available antimicrobial discs revealed that the isolates were susceptible to nine antimicrobials from 69.3% to 100% except streptomycin which showed susceptibility of 48.7%. An overall resistance of 33.4% and 30.9% was recorded to streptomycin and amikacin, whereas 5.1%, 5.1%, 7.7%, 12.8% and 17.9% resistance rates were recorded against nalidixic acid, tetracycline, amoxacilin-clavulanic acid, cephalothin and ciprofloxacin, respectively. Multidrug resistance was observed among amikacin, amoxycillin-clavulanic acid, cephalothin, ciprofloxacin, streptomycin and tetracycline antimicrobials drugs.

Conclusions

The isolation of E. coli O157:H7 in raw meat and the existence of antimicrobial resistant isolates highlight the potential threat to public health. Hence implementation of E. coli O157:H7 prevention and control strategies from farm production to consumption of meat and meat products are crucial.

A review of factors that affect transmission and survival of verocytotoxigenic Escherichia coli in the European farm to fork beef chain

Verocytotoxigenic Escherichia coli (VTEC) are a significant foodborne public health hazard in Europe, where most human infections are associated with six serogroups (O157, O26, O103, O145, O111 and O104). With the exception of O104, these serogroups are associated with bovine animals and beef products. This paper reviews our current knowledge of VTEC in the beef chain focusing on transmission and the factors which impact on survival from the farm through transport, lairage, slaughter, dressing, processing and distribution, in the context of the European beef industry. It provides new information on beef farm and animal hide prevalence, distribution and virulence factors as well as pre-chilled carcass and ground beef prevalence, generated by the recently completed EU Framework research project, ProSafeBeef. In the concluding section, emerging issues and data gaps are addressed with a view to increasing our understanding of this pathogen and developing new thinking on detection and control.

Effect of stress on non-O157 Shiga toxin-producing Escherichia coli

Non-O157 Shiga toxin-producing Escherichia coli (non-O157 STEC) strains have emerged as important foodborne pathogens worldwide. Non-O157 STEC serogroups O26, O45, O103, O111, O121, and O145 have been declared as adulterants in beef by the U. S. Department of Agriculture Food Safety and Inspection Service. While documentation is limited, treatments including heat and acid that have been shown to inactivate E. coli O157:H7 will likely also destroy non-O157 STEC; however, non-O157 STEC strains show variability in their responses to stress. It has been shown that non-O157 STEC may survive in fermented sausages and cheeses, and treatments such as high pressure may be necessary to eliminate non-O157 STEC from these products. The mechanisms used by non-O157 STEC to resist acid environments are similar to those used by O157:H7 strains and include the acid tolerance response, the oxidative system, and the glutamate and arginine decarboxylase systems. However, one study demonstrated that some non-O157 STEC strains utilize a chaperone-based acid stress response (HdeA and HdeB) to combat acidic conditions, which is lacking in E. coli O157:H7. Genomic studies suggest that while non-O157 STEC can cause diseases similar to those caused by E. coli O157:H7, O157 and non-O157 STECs have different evolutionary histories. Non-O157 STECs are a heterogeneous group of organisms, and there is currently a limited amount of information on their virulence, fitness, and stress responses, rendering it difficult to draw firm conclusions on their behavior when exposed to stress in the environment, in food, and during processing.

Factors influencing the persistence ofEscherichia coliO157:H7 lineages in feces from cattle fed grain versus grass hay diets

Escherichia coli O157:H7 is a pathogenic, gram-negative bacterium that causes diarrhea, hemorrhagic colitis, and can lead to fatal hemolytic uremic syndrome in humans. We examined the persistence of E. coli O157:H7 lineages I and II in feces held at 4, 12, and 25 °C, from animals fed either grain or hay diets. Three strains of each lineage I and II were inoculated into grain-fed or hay-fed feces, and their persistence was monitored over 28 days. No significant differences in E. coli O157:H7 survival between the 2 lineages in both fecal types was found at the examined temperatures. Volatile fatty acids were higher in grain-fed than in hay-fed feces, resulting in consistently lower pH in the grain-fed feces at 4, 12 and 25 °C. Regardless of lineage type, E. coli O157:H7 CFUs were significantly higher in grain-fed than in hay-fed feces at 4 and 25 °C. Escherichia coli O157:H7 survival was highest in grain-fed feces at 25 °C up to 14 days. Our results indicate that the 2 lineages of E. coli O157:H7 do not differ in their persistence; however, it appears that temperature and feces type both affect the survival of the pathogen.

Food as a vehicle for transmission of Shiga toxin-producing Escherichia coli

Contaminated food continues to be the principal vehicle for transmission of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) to humans. A large number of foods, including those associated with outbreaks (alfalfa sprouts, fresh produce, beef, and unpasteurized juices), have been the focus of intensive research studies in the past few years (2003 to 2006) to assess the prevalence and identify effective intervention and inactivation treatments for these pathogens. Recent analyses of retail foods in the United States revealed E. coli O157:H7 was present in 1.5% of alfalfa sprouts and 0.17% of ground beef but not in some other foods examined. Differences in virulence patterns (presence of both stx1 and stx2 genes versus one stx gene) have been observed among isolates from beef samples obtained at the processing plant compared with retail outlets. Research has continued to examine survival and growth of STEC in foods, with several models being developed to predict the behavior of the pathogen under a wide range of environmental conditions. In an effort to develop effective strategies to minimize contamination, several influential factors are being addressed, including elucidating the underlying mechanism for attachment and penetration of STEC into foods and determining the role of handling practices and processing operations on cross-contamination between foods. Reports of some alternative nonthermal processing treatments (high pressure, pulsed-electric field, ionizing radiation, UV radiation, and ultrasound) indicate potential for inactivating STEC with minimal alteration to sensory and nutrient characteristics. Antimicrobials (e.g., organic acids, oxidizing agents, cetylpyridinium chloride, bacteriocins, acidified sodium chlorite, natural extracts) have varying degrees of efficacy as preservatives or sanitizing agents on produce, meat, and unpasteurized juices. Multiple-hurdle or sequential intervention treatments have the greatest potential to minimize transmission of STEC in foods.

Variation in Salmonella resistance to poultry chemical decontaminants, based on serotype, phage type, and antibiotic resistance patterns

Chemical decontaminants are currently under review for final approval by the European Union authorities with the aim of reducing the number and/or prevalence of pathogenic microorganisms on poultry. The purpose of the research being reported here was to determine the association, if any, of decontaminant resistance with the serotype, phage type, and antibiotic resistance of Salmonella strains. Sixty poultry isolates of Salmonella enterica (serotypes Enteritidis: phage types 1, 4, 4b, 6a, 14b, and 35; Typhimurium; Newport; Infantis; Poona; Virchow; Agona; Derby; and Paratyphi B) showing resistance to none (sensitive), one (resistant), two, three, four, five, six, seven, or nine (multiresistant) antibiotics were screened for resistance to 1,000 ppm acidified sodium chlorite, 1.2% trisodium phosphate, or 25% citric acid. D-values (seconds required for 1-log reduction in the number of bacteria) in peptone water, using a linear regression, of Salmonella in the presence of acidified sodium chlorite varied widely with serotype (the highest resistance levels were shown by serotypes Typhimurium, Newport, and Derby) and antibiotic resistance pattern (average values of 8.37 +/- 1.69 s for multiresistant strains as compared with 5.96 +/- 0.54 s for sensitive, P < 0.05). A positive relationship (0.775, P < 0.001) was found between acidified sodium chlorite D-values and the number of antibiotics to which strains were resistant. Both serotype and antibiotic resistance had only a slight influence over Salmonella resistance to trisodium phosphate, with average D-values from 12.44 +/- 0.91 s (sensitive strains) to 13.28 +/- 0.77 s (multiresistant) (P < 0.05). Neither serotype nor antibiotic profile was associated with Salmonella resistance to citric acid (average D-value of 12.20 +/- 0.81 s). Minimal differences in resistance to decontaminants were found among Salmonella Enteritidis phage types. Results in the present study highlight the importance of selecting an adequate strain (serotype and antibiotic resistance pattern) when acidified sodium chlorite and trisodium phosphate are tested against Salmonella to ensure that concentrations capable of inactivating all strains are used.

Tracking emerging zoonotic pathogens from farm to fork

A combination of factors including changes in the agri-food chain, social changes, advances in detection and reporting systems coupled with bacterial adaptation and evolution have in recent years lead to the emergence of a number of zoonotic microorganisms in the food and water chain. These include multi-antibiotic resistant bacteria, verocytotoxigenic Escherichia coli, parasites such as Cyclospora on fruit, and Cyrptosporidium and Giardia in water, Enterobacter sakazakii in infant milk formula, and emergent species of Campylobacteraceae. In this paper, Enterohaemorrhagic E. coli and Campylobacteraceae are taken as examples of emergent pathogens in the meat chain. Specific factors which may have lead to their emergence are deliberated, in addition to an overview of tools for their detection and tracking, and their epidemiology and survival characteristics. Approaches to managing and controlling emergent pathogens in the agri-food chain are also discussed.