Super shedding of Escherichia coli O157:H7 by cattle and the impact on beef carcass contamination

Beef carcass contamination is a direct result of pathogen transfer from cattle hides harboring organisms such as enterohemorrhagic Escherichia coli. Hide contamination occurs from direct and indirect fecal contamination in cattle production and lairage environments. In each of these environments, individual animals shedding E. coli O157:H7 at high levels (> 10⁴ CFU/g of feces, hereafter referred to as “super shedders”) can have a disproportionate effect on cattle hide and subsequent carcass contamination. It is not known what criteria must be met to cause an animal to shed at levels exceeding 10⁴ CFU/g. Understanding the factors that play a role in super shedding will aid in minimizing or eliminating the super shedding population. Interventions that would prevent supershedding in the cattle population should reduce E. coli O157:H7 transmission in the production and lairage environments resulting in reduced risk of beef carcass contamination and a safer finished product.     

Survival of Escherichia coli O157:H7 and non-pathogenic E. coli on irradiated and non-irradiated beef surfaces

This study examined changes in numbers of pathogenic (PEC) and non-pathogenic (NPEC) Escherichia coli during storage at 10 °C on the surfaces of irradiated (IR) and non-irradiated (NIR) meat pieces excised from the neck, brisket and rump of beef carcasses and in Brain Heart Infusion Broth (BHI) and Maximum Recovery Diluent (MRD). On irradiated meat pieces, there were significant differences between mean PEC and NPEC counts at all sites. Differences in counts were also observed between IR and NIR surfaces and among the three meat sites for both E. coli types. These differences occurred only on IR samples, suggesting that the irradiation associated reductions in normal beef surface flora influenced survival of both E. coli types. PEC and NPEC counts increased during storage in BHI, but only NPEC counts increased in MRD. The results of this study highlight the impact of meat surface type and the presence/absence of the normal beef carcass surface flora on E. coli survival and/or growth during meat storage. Such previously unreported effects, and their precise mechanisms, have direct implications in the development and application of accurate models for the prediction of the safety and shelf life of stored meat.     

Prevalence and antimicrobial susceptibility of Escherichia coli O157:H7 on beef cattle slaughtered in Amman abattoir

Cattle are the main asymptomatic reservoir of Escherichia coli O157:H7 which can cause illness to human. The objectives of the study were to measure the prevalence of E. coli O157:H7 on cattle slaughtered in Amman abattoir, detect virulence factors in the isolates, determine antibacterial resistance of the isolates, and know how the isolates are different or similar when compared to characterized isolates from developed countries.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Salmonella, Escherichia coli O157:H7 and E. coli biotype 1 in a pilot survey of imported and New Zealand pig meats

A pilot survey for the pathogens Salmonella and Escherichia coli O157:H7, and E. coli biotype 1 was conducted on 100 New Zealand-produced (domestic) pig carcasses and 110 imported pig meat samples over an 8-month period to assess the likelihood of introduction of novel pathogen strains into New Zealand (NZ), and as a guide for development of a domestic pork National Microbiological Database programme. Salmonella was not isolated from domestic pig carcasses or from pig meat imported from Canada and the USA. The prevalence of Salmonella in imported pig meat was 3.6% (95% CI 1.0–9.0) with positive samples detected from Australian pig meat. The prevalence of E. coli O157:H7 on domestic pig carcasses was 1% (95% CI 0.03–5.4) while the overall prevalence of E. coli O157:H7 in imported pig meat was 1.8% (95% CI 0.2–6.4), detected mainly from Australian but not from Canadian or US pork. All except three samples have an E. coli biotype 1 count of <100 CFU cm⁻² or g⁻¹, indicating good hygiene quality of domestic and imported pig meat. The results demonstrated that importation of uncooked pig meat is a potential route for the introduction of new clones of Salmonella and E. coli O157:H7 into New Zealand.     

Synergistic antimicrobial effect of pyrophosphate on Listeria monocytogenes and Escherichia coli O157 in modified atmosphere packaged and refrigerated seabass slices

Effect of pyrophosphate (PP) in combination with modified atmosphere (MAP) (80% CO₂, 10% O₂ and 10% N₂) on the survival of Listeria monocytogenes and Escherichia coli O157 inoculated on seabass slices stored at 4 °C was investigated. PP pretreatment showed the synergistic effect on microbiological inhibition with MAP as evidenced by the lowered TVC and LAB counts, compared with samples stored in air and those kept under MAP. Microbiological changes of seabass slices inoculated with different levels of L. monocytogenes or E.coli O157 (10³ and 10⁵ cfu/g) were monitored during storage. PP pretreatment reduced colony count of E. coli O157 and extended the lag phase of L. monocytogenes. Therefore, MAP in combination with PP pretreatment not only retarded microbiological deterioration of seabass slices but also reduced or inactivated some pathogenic bacteria to some extent.     

The growth,survival and thermal inactivation of Escherichia coli O157:H7 in a traditional South African sausage

This study investigated the growth and survival of Escherichia coli O157:H7 inoculated into boerewors models with (B + P) and without (B − P) sulphur dioxide preservative at a low (L) and high (H) inoculum followed by storage at 0, 4 and 10 °C for 10 days. The pathogen’s thermal inactivation at 50, 60, 65 and 70 °C was also evaluated in B + P. The B − P at both low and high inocula had significantly higher recoveries at all temperatures compared to B + P. The BL + P and BH + P had significant reductions in recoveries at 0 °C, declining to below detectable limits at days 8 and 10, respectively. At 4 °C, the BL + P and BH + P recoveries declined significantly at day 10. At 10 °C, significant increases were observed from days 0 to day 10 in both models and at low and high inocula. At 0 °C, the BL − P and BH − P treatments had significant declines in recoveries. The combination of sulphur dioxide preservative and low temperature demonstrated the best efficacy against E. coli O157:H7 survival. Thermal inactivation of E. coli O157:H7 was 60 min at 60 °C, 80 s at 65 °C and 60 s at 70 °C. This study demonstrated that E. coli O157:H7 can survive in boerewors with and without preservative and is more sensitive to heat treatment at 70 °C.     

Inactivation of Salmonella and Escherichia coli O157:H7 on artificially contaminated alfalfa seeds using high hydrostatic pressure

Alfalfa sprouts contaminated with Salmonella and Escherichia coli O157:H7 have been implicated in several outbreaks of foodborne illnesses in recent years. The seed used for sprouting appears to be the primary source of pathogens. Seed decontamination prior to sprouting presents a unique challenge for the sprouting industry since cells of the pathogenic survivors although undetectable after sanitizing treatments, can potentially multiply back to hazardous levels. The focus of this study was to therefore test the efficacy of high hydrostatic pressure to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Pressure treatment of 600 MPa for up to 25 min at 20 °C could not result in complete inactivation of Salmonella. High-pressure treatment was then carried out either at sub-ambient (4 °C) or elevated (40, 45 and 50 °C) temperatures to test the ability of high pressure to eliminate Salmonella. Pressure treatment at 4 and 20 °C did not deliver any satisfactory inactivation of Salmonella while high pressure at elevated temperatures achieved complete kill. Pre-soaking seeds prior to high-pressure treatment also enhanced pressure inactivation of Salmonella but at the expense of seed viability. High-pressure treatment of 500 MPa for 2 min at 45 °C was able to eliminate wild-type Salmonella and E. coli O157:H7 strains without bringing about any appreciable decrease in the seed viability.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Transfer of verocytotoxigenic Escherichia coli O157, O26, O111, O103 and O145 from fleece to carcass during sheep slaughter in an Irish export abattoir

The purpose of this study was to investigate carriage and transfer of verocytotoxigenic Escherichia coli (VTEC) O157, O26, O111, O103 and O145 from fleece to dressed carcasses of 500 sheep, and to establish the virulence potential of recovered VTEC. Individual sheep were tracked and sampled (10 g fleece, full carcass swab) through the slaughter process. Samples were examined for the presence of verotoxin (vt1 and vt2) genes using a duplex real-time PCR assay and positive samples were further screened for the presence of the above five serogroups by real-time PCR. VTEC cells were recovered from PCR positive samples by serogroup specific immunomagnetic separation and confirmed by serogroup specific latex agglutination and PCR. Isolates were subject to a virulence screen (vt1, vt2, eaeA and hlyA) by PCR and isolates carrying vt genes were examined by Pulsed-Field Gel Electrophoresis (PFGE). VTEC O26 was recovered from 5/500 (1.0%) fleece and 2/500 (0.4%) carcass samples. VTEC O157 was isolated from 4/500 (0.8%) fleece samples and 3/500 (0.6%) carcass samples. E. coli O103 was recovered from 84/500 (16.8%) fleece and 68/500 (13.6%) carcasses, but only one E. coli O103 isolate (0.2%) carried vt genes. E. coli O145 was recovered from one fleece sample, but did not carry vt genes. E. coli O111 was not detected in any samples. For the four serogroups recovered, the direct transfer from fleece to carcass was not observed with PFGE showing that VTEC O26 isolates from a matched fleece/carcass “pair” were not identical. This study shows that while VTEC O157 are being carried by sheep presented for slaughter in Ireland, other potentially clinically significant verotoxin producing strains (particularly VTEC O26) are emerging.     

Survival of Escherichia coli O157:H7 in channel catfish pond and holding tank water

Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond and holding tank water was investigated. Water from three channel catfish ponds was inoculated with ampicillin/nalidixic acid-resistant E. coli O157:H7 transformed with a plasmid encoding for green fluorescent protein at 10⁵, 10⁶, and 10⁷ CFU/ml. Samples were taken from surface, internal organs, and skin scrape of fish and pond water for E. coli O157:H7 enumeration on brain heart infusion (BHI) agar containing ampicillin and nalidixic acid. To determine the survival of E. coli O157:H7 in catfish holding tank water from two farmers markets, the water was inoculated with 10⁷E. coli O157:H7 CFU/ml. E. coli O157:H7 were detected by direct plating for 33 and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first 2 weeks to reach 2 log CFU/ml. When E. coli O157:H7 was not recovered by direct plating, the pathogen was isolated by enrichment in TSB for approximately another 30 d from pond and holding tank water. The populations of E. coli O157:H7 found in the internal organs and skin scrape were 5.5 log and 2.5 log CFU/ml, respectively. E. coli O157:H7 from internal organs and water were recovered for at least 12 d. Results suggest that E. coli O157:H7 can survive in channel catfish pond and holding tank water and channel catfish may become a potential carrier of the pathogen.     

Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi

Acid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 °C) and commercial Amasi fermented at 30 °C for 24 h and stored at 7 °C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log₁₀ cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p ? 0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p ? 0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.     

Antibacterial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on beef

This study determined the efficacy of actinidin and papain on reducing Listeria monocytogenes and three mixed strains of Escherichia coli O157:H7 populations on beef. The average reduction of E. coli O157:H7 was greater than that of L. monocytogenes and higher concentrations of either protease yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml meat rinse after 3 h at 25 & 35 °C, and by 1.45 log cfu/ml rinse after 24 h at 5 °C, while the same actinidin concentration significantly reduced the populations of three mixed strains of E. coli O157:H7 by 1.81 log cfu/ml rinse after 3 h at 25 & 35 °C, and 1.94 log cfu/ml rinse after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteolytic enzymes can enhance meat safety when stored at suitable temperatures.     

Effect of cooking procedures of kiymali pide,a traditional Turkish fast-food,on destruction of Escherichia coli O157:H7

The objective of the present study was to obtain data about cooking time and temperature of kiymali pide in the restaurants and to investigate thermal inactivation of E. coli O157:H7 during experimental kiymali pide making. A field study was conducted in randomly selected 23 of 87 pide restaurants. Processing parameters including oven temperature, cooking period and post-cooking temperature were determined. Kiymali pide samples were prepared using ground beef filling experimentally inoculated with E. coli O157:H7 (7.6 log₁₀ CFU/g). Pide samples were cooked at a conventional oven at 180 °C for 180, 240, 270, 300 and 330 s. Results of the current study suggest that cooking kiymali pide at 180 °C for at least 330 s (5.5 min) may provide sufficient food safety assurance (≥ 6 log₁₀ CFU/g) for E. coli O157:H7.     

Enhancing the thermal destruction of Escherichia coli O157:H7 in ground beef patties by trans-cinnamaldehyde

The effect of trans-cinnamaldehyde (TC) on the inactivation of Escherichia coli O157:H7 in undercooked ground beef patties was investigated. A five-strain mixture of E. coli O157:H7 was inoculated into ground beef (7.0 log CFU/g), followed by addition of TC (0, 0.15, and 0.3%). The meat was formed into patties and stored at 4 °C for 5 days or at −18 °C for 7 days. The patties were cooked to an internal temperature of 60 or 65 °C, and E. coli O157:H7 was enumerated. The numbers of E. coli O157:H7 did not decline during storage of patties. However, cooking of patties containing TC significantly reduced (P < 0.05) E. coli O157:H7 counts, by >5.0 log CFU/g, relative to the reduction in controls cooked to the same temperatures. The D-values at 60 and 65 °C of E. coli O157:H7 in TC-treated patties (1.85 and 0.08 min, respectively) were significantly lower (P < 0.05) than the corresponding D-values for the organism in control patties (2.70 and 0.29 min, respectively). TC-treated patties were more color stable and showed significantly lower lipid oxidation (P < 0.05) than control samples. TC enhanced the heat sensitivity of E. coli O157:H7 and could potentially be used as an antimicrobial for ensuring pathogen inactivation in undercooked patties. However detailed sensory studies will be necessary to determine the acceptability to consumers of TC in ground beef patties.     

The physiologic state of Escherichia coli O157:H7 does not affect its detection in two commercial real-time PCR-based tests

Multiplex real-time PCR detection of Escherichia coli O157:H7 is an efficient molecular tool with high sensitivity and specificity for meat safety assurance. The Biocontrol GDS^® and DuPont Qualicon BAX^®-RT rapid detection systems are two commercial tests based on real-time PCR amplification with potential applications for quantification of specific E. coli O157:H7 gene targets in enriched meat samples. However, there are arguments surrounding the use of these tests to predict pre-enrichment concentrations of E. coli O157:H7, as well as arguments pertaining to the influence of non-viable cells causing false positive results. The present study attempts to illustrate the effects of different bacterial physiologic states and the presence of non-viable cells on the ability of these systems to accurately measure contamination levels of E. coli O157:H7 in ground beef. While the PCR threshold cycle (C_T) values of these assays showed a direct correlation with the number of bacteria present in pure cultures, this was not the case for ground beef samples spiked with various levels of injured or healthy cells. Furthermore, comparison of post-enrichment cell densities of bacteria did not correlate with injured or healthy cell numbers inoculated before enrichment process. Ground beef samples spiked with injured or healthy cells at different doses could not be distinguished by C_T values from either assay. In addition, the contribution of nonviable cells in generating positive real-time PCR signals was investigated using both assays on pre-enriched and post-enriched beef samples, but only if inoculated at levels of 10⁶ cells/sample or higher, which are levels not typically seen in ground beef.     

Multiplex fiber optic biosensor for detection of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica from ready-to-eat meat samples

Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica are the most common foodborne bacterial pathogens and are responsible for many outbreaks. Therefore, multiplex detection of these three using a single assay platform is highly desirable. The objective was to develop and optimize a fiber optic sensor for simultaneous detection of these three from food. The streptavidin coated optical waveguides were immobilized with biotinylated polyclonal antibodies and exposed to the bacterial suspensions or enriched food samples for 2 h. Pathogens were detected after reacting with Alexa-Fluor 647-labeled monoclonal antibodies. Ready-to-eat beef, chicken and turkey meats were inoculated with each pathogen (∼100 cfu/25 g), enriched in SEL (Salmonella, E. coli, Listeria), a multipathogen selective enrichment broth for 18 h and tested with the biosensor. The biosensor was able to detect each pathogen, individually or in a mixture with very little cross-reactivity. The limit of detection for the sensor was ∼10³ cfu/ml for all three pathogens. Furthermore, the biosensor successfully detected each pathogen, grown in a mixture from enriched meat samples under 24 h. The pathogen presence was further verified by PCR and immunofluorescence assay. The multiplex fiber optic sensor shows promise for detection of the three pathogens if present in the same sample eliminating the use of multiple single pathogen detection platforms.     

Antimicrobial activity of lactic acid and copper on growth of Salmonella and Escherichia coli O157:H7 in laboratory medium and carrot juice

Outbreaks of food-borne pathogens, such as Escherichia coli O157:H7 and Salmonella, continue to draw public attention to food safety. Several reports have demonstrated the efficacy of using natural ingredients to control the growth of food-borne pathogens. The objective of this study was to investigate antimicrobial effects of lactic acid and copper, alone and in combination, on the survival and growth of Salmonella spp. and E. coli O157:H7 in laboratory medium and carrot juice. Survival and growth of 38 Salmonella spp. and six E. coli O157:H7 strains were compared when grown in brain heart infusion (BHI) broth and carrot juice under conditions including either lactic acid (0.2%) alone, copper sulfate (50 ppm) alone or the combination of the two. The growth inhibition was negligible when copper sulfate was added to BHI broth and carrot juice. Lactic acid (0.2%) retarded the growth of bacterial strains. However, the growth of bacterial strains was significantly inhibited when both lactic acid and copper were in BHI broth and carrot juice within the time frame of this study. These findings indicated that lactic acid, in combination with copper sulfate, could be used to inhibit the growth of pathogens. Natural ingredients, such as lactic acid and low dose of copper ions, can be used to improve the safety of food products.     

Application of caffeine, 1,3,7-trimethylxanthine,to control Escherichia coli O157:H7

The objective of this research was to determine the effectiveness of caffeine on inactivation of Escherichia coli O157:H7 in brain heart infusion (BHI) broth. Overnight samples of five E. coli O157:H7 strains of (E0019, F4546, H1730, 944 and Cider) were used in this study. These strains were individually inoculated at an initial inoculum level of 2 log CFU/ml into BHI broth containing caffeine at different concentrations (0.00%, 0.25%, 0.50%, 0.75%, 1.00%, 1.25%, 1.50%, 1.75%, and 2.00%). Samples were then incubated at 37 °C for 24 h. Bacterial growth was monitored at different time intervals by measuring turbidity at 610 nm using a spectrophotometer. Results revealed that the addition of caffeine inhibited the growth of E. coli O157:H7. Significant growth inhibition was observed with concentration levels of 0.50% and higher. These results indicate that caffeine has potential as an antimicrobial agent for the treatment of E. coli O157:H7 infection and should be investigated further as a food additive to increase biosafety of consumable food products.     

Modelling of Escherichia coli O157:H7 growth at various storage temperatures on beef treated with electrolyzed oxidizing water

The influence of storage temperature (4, 10, 15, 20, 25, and 30 °C) on the growth of Escherichia coli O157:H7 in beef untreated (control) and treated by acidic electrolyzed oxidizing water (AcEOW) or slightly acidic electrolyzed oxidizing water (SAcEOW) was examined. A Baranyi model was employed to describe growth parameters such as specific growth rate (SGR) and lag time (LT) as a function of storage temperature. SGR increased and LT declined with rising temperatures in all samples. There were no significant differences between the SGR and LT values obtained from beef treated with AcEOW or SAcEOW. Secondary models were established for SGR and LT to evaluate the effects of storage temperature on the growth kinetics of E. coli O157:H7 in treated and untreated beef. Mathematical evaluation was carried out to validate the performance of the developed models.