Survival and colonization of Escherichia coli O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity

Aims: To determine survival and colonization of Escherichia coli O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity (r.h.). Methods and Results: Spinach leaves were inoculated with suspensions of E. coli O157:H7 in distilled water (DW) and 0·1% peptone water (PW) and incubated at 4, 12 and 25°C and 43, 85 and 100% r.h. The number of E. coli O157:H7 on leaves (5·6 or 1·9 log CFU per leaf) inoculated using DW as a carrier medium increased significantly at 25°C and 100% r.h. within 120 h but remained constant or decreased significantly under other test conditions. E. coli O157:H7 on leaves (5·4 log CFU per leaf) inoculated using PW as a carrier increased significantly within 72 and 24 h, respectively, at 12 or 25°C and 100% r.h.; counts using a low inoculum (2·2 log CFU per leaf) increased significantly within 24 h at 25°C. Conclusions: Escherichia coli O157:H7 can colonize on spinach leaves at 12 or 25°C in a 100% r.h. environment. Organic matter in the inoculum carrier may provide protection and nutrients which enhance survival and colonization. Significance and Impact of the Study: Colonization of E. coli O157:H7 on spinach leaves as affected by organic matter in the inoculum, temperature and r.h. was determined. These observations will be useful when developing strategies to prevent growth of E. coli O157:H7 on pre‐ and postharvest spinach.     

Variable agronomic practices, cultivar, strain source and initial contamination dose differentially affect survival of Escherichia coli on spinach

Aims: Greenhouse and field trials were conducted under different agronomic practices and inoculum doses of environmental Escherichia coli and attenuated E. coli O157:H7, to comparatively determine whether these factors influence their survival on leaves and within the rhizosphere. Methods and Results: Hydroponic conditions: E. coli spray‐inoculated at log 4 CFU ml^?1 was recovered from leaf surfaces at a mean population of 1·6 log CFU g^?1 at 15 days. E. coli O157:H7 sprayed at log 2 or 4 CFU ml^?1 levelled off on spinach leaf surfaces at a mean average population of 1·4 log CFU g^?1 after 14 days, regardless of initial dose. Quantitative recovery was inconsistent across leaf developmental age. Field conditions: Average populations of E. coli O157:H7 spray‐inoculated at log 1·45 or 3·4 CFU m^?2 levelled off at log 1·2 CFU g^?1 over a 14‐day period. Pathogen recovery from leaves was inconsistent when compared to regularly positive detection on basal shoot tissue. Pathogen recovery from soil was inconsistent among sampling locations. Moisture content varied up to 40% DW and was associated with 50% (P < 0·05) decrease in positive locations for E. coli O157:H7 but not for E. coli. Conclusions: Overall, similar populations of environmental E. coli and E. coli O157:H7 were recovered from plants despite differences in inoculum dose and agronomic conditions. Strain source had a significant impact on the quantitative level and duration of survival on leaves and in soil. Water availability appeared to be the determinant factor in survival of E. coli and E. coli O157:H7; however, E. coli showed greater environmental fitness. Significance and Impact of the Study: Persistence of surrogate, indicator E. coli and E. coli O157:H7, irrespective of variable growing conditions in spinach is predominantly limited by water availability, strain source and localization within the plant. These findings are anticipated to ultimately be adopted into routine and investigative pathogen testing protocols and mechanical harvest practices of spinach.     

Effect of feeding sun-dried seaweed (Ascophyllum nodosum) on fecal shedding of Escherichia coli O157:H7 by feedlot cattle and on growth performance of lambs

Thirty-two steers orally inoculated with a four-strain mixture (10¹⁰ CFU) of nalidixic acid-resistant Escherichia coli O157:H7 had sun-dried Ascophyllum nodosum seaweed (Tasco-14™) added to their barley-based diet (860 g/kg barley grain and 90 g/kg whole crop barley silage, dry matter basis) to assess its effectiveness in reducing fecal shedding of the pathogen. Steers were housed in four groups of eight and received Tasco-14™ in the diet, in place of barley, at levels (as fed) of 10 g/kg for 14 days (T1-14), 20 g/kg for 7 days (T2-7), 20 g/kg for 14 days (T2-14), or not at all (i.e., control, CON). The dietary treatments commenced 7 days after E. coli O157:H7 inoculation and fecal shedding patterns were examined over 14 weeks. Water, water–trough interface, feed and fecal pat samples were also collected weekly and cultured for E. coli O157:H7. Detection of the pathogen in fecal samples was less frequent (P<0.05) in T1-14 (99/168) and T2-7 (84/168) versus CON (135/168) and T2-14 (115/168), and the concentrations of E. coli O157:H7 recovered in feces from T1-14 and T2-7 steers were lower (P<0.005) than from CON or T2-14 steers. Rates of decline in shedding of E. coli O157:H7 were similar among treatments, but final numbers of E. coli O157:H7 were lower (P<0.05) in T1-14 and T2-7 as compared to T2-14 and CON. Fecal volatile fatty acid concentrations and pH were similar among treatments, suggesting no fecal alterations that were antagonistic to survival. E. coli O157:H7 was present in 1 (from T2-7) of 56 cattle drinking water samples, 2 of 56 (T1-14, CON) feed samples and 32 of 56 fecal pats. A second experiment investigated effects of the dietary treatment on growth performance of non-inoculated sheep. Tasco-14™ was administered to 40 individually fed Canadian Arcott lambs beginning at day 56 of a 105-day finishing period. The lambs received Tasco-14™ at 0 g/kg (control, CON), at 10 g/kg for 14 days (T1-14), 20 g/kg for 14 days (T2-14), 10 g/kg for 28 days (T1-28) or at 20 g/kg for 7 days (T2-7) as a top-dress on their pelleted, barley grain-based diet (n = 8). E. coli O157:H7 was not isolated from fecal samples collected at 4-week intervals, but generic E. coli populations were lower (P<0.05) in T1-28 lambs than in other treatments. Average daily gain, feed intake, feed efficiency and carcass traits did not differ among treatments. Our challenge study supports past studies showing that Tasco-14™ decreases shedding of E. coli O157:H7 by cattle. The lamb study shows that this additive did not directly affect feed intake or animal growth.     

Development of a combined immunochromatographic lateral flow assay for accurate and rapid Escherichia coli O157:H7 detection

Escherichia coli O157:H7 is an important pathogenic Bacterium that threatens human health. A convenient, sensitive and specific method for the E. coli O157:H7 detection is necessary. We developed two pairs of monoclonal antibodies through traditional hybridoma technology, one specifically against E. coli O157 antigen and the other specifically against E. coli H7 antigen. Using these two pairs of antibodies, we developed two rapid test kits to specifically detect E. coli O157 antigen and E. coli H7 antigen, respectively. The detection sensitivity for O157 positive E. coli is 1 × 10³ CFU per ml and for H7 positive E. coli is 1 × 10⁴ CFU per ml. Combining these two pairs of antibodies together, we developed a combo test strip that can specifically detect O157: H7, with a detection sensitivity of 1 × 10⁴ CFU per ml, when two detection lines are visible to the naked eye. This is currently the only rapid detection reagent that specifically detects O157: H7 by simultaneously detecting O157 antigen and H7 antigens of E. coli. Our product has advantages of simplicity and precision, and can be a very useful on-site inspection tool for accurate and rapid detection of E. coli O157:H7 infection.     

Self-Purificatory Ganga Water Facilitates Death of Pathogenic <Emphasis Type="Italic">Escherichia coli</Emphasis> O157:H7

Concern over the prevalence of active pharmaceutical agents and subsequent occurrence of antimicrobial resistance in the environment is increasing. Incorruptible ability of Ganga water was evaluated using fresh, 8-year-old, and 16-year-old Ganga water samples spiked with pathogenic Escherichia coli serotype O157:H7. Survival of E. coli O157:H7 over the course of the experiment was 3, 7, and 15 days for fresh, 8-year-old, and 16-year-old Ganga waters, respectively. On the contrary, in Milli Q water the decline in viable count of E. coli O157:H7 up to 30 days was only 2 log units. Survival of E. coli O157:H7 was greater in boiled water compared with water after passage through a 0.2-μm-pore-size membrane filter, indicating involvement of heat-labile agents influencing survival of E. coli O157:H7 in Ganga water, which seems to indicate the role of antimicrobial peptides. Functional diversity of Ganga water’s native microbial community structure as assessed with Biolog Eco plates was not affected even in the presence of a 5-fold log units higher pathogenic load of E. coli O157:H7. These findings suggest that Ganga water has certain novel antimicrobial attributes, besides its remarkable fluidity, which may provide a much-needed basis for the development of new antimicrobial compounds.     

Fate of Escherichia coli O157:H7 in ground beef following high‐pressure processing and freezing

Aims: The purposes of this study were to evaluate the efficacy of high pressure to inactivate Escherichia coli O157:H7 in ground beef at ambient and subzero treatment temperatures and to study the fate of surviving bacteria postprocess and during frozen storage. Methods and Results: Fresh ground beef was inoculated with a five‐strain cocktail of E. coli O157:H7 vacuum‐packaged, pressure‐treated at 400 MPa for 10 min at ?5 or 20°C and stored at ?20 or 4°C for 5–30 days. A 3‐log CFU g^?1 reduction of E. coli O157:H7 in the initial inoculum of 1 × 10⁶ CFU g^?1 was observed immediately after pressure treatment at 20°C. During frozen storage, levels of E. coli O157:H7 declined to <1 × 10² CFU g^?1 after 5 days. The physiological status of the surviving E. coli was affected by high pressure, sensitizing the cells to pH levels 3 and 4, bile salts at 5% and 10% and mild cooking temperatures of 55–65°C. Conclusions: High‐pressure processing (HPP) reduced E. coli O157:H7 in ground beef by 3 log CFU g^?1 and caused substantial sublethal injury resulting in further log reductions of bacteria during frozen storage. Significance and Impact of the Study: HPP treatment of packaged ground beef has potential in the meat industry for postprocess control of pathogens such as E. coli O157:H7 with enhanced safety of the product.     

Multiple‐locus variable‐nucleotide tandem repeat subtype analysis implicates European starlings as biological vectors for Escherichia coli O157:H7 in Ohio,USA

Aims: To provide molecular epidemiological evidence of avian transmission of Escherichia coli O157:H7 between dairy farms in Ohio, this study was designed to identify genetic relatedness between isolates originating from bovine faecal samples and intestinal contents of European starlings captured on these farms. Methods and Results: During a three‐year period (2007–2009), cattle (n = 9000) and starlings (n = 430) on 150 different dairy farms in northern Ohio were sampled for the presence of E. coli O157:H7. Isolates were subjected to multiple‐locus variable‐nucleotide tandem repeat analysis (MLVA). Distinct allelic groups were identified on most farms; however, isolates clustering into three MLVA groups originated from both cattle and birds on different farms. Conclusions: Sharing of indistinguishable epidemiologically linked E. coli O157 MLVA subtypes between starlings and cattle on different farms supports the hypothesis that these birds contribute to the transmission of E. coli O157:H7 between dairy farms. Significance and Impact of Study: A continued need exists to identify and to improve preharvest measures for controlling E. coli O157:H7. Controlling wildlife intrusion, particularly European starlings, on livestock operations, may be an important strategy for reducing dissemination of E. coli O157:H7 between farms and thereby potentially decreasing the on‐farm prevalence of E. coli O157:H7 and enhancing the safety of the food supply.     

Potential Uptake of Escherichia coli O157:H7 from Organic Manure into Crisphead Lettuce

To investigate the potential transfer of Escherichia coli O157:H7 from contaminated manure to fresh produce, lettuce seedlings were transplanted into soil fertilized with bovine manure which had been inoculated with approximately 10⁴ CFU g⁻¹ E. coli O157:H7. The lettuce was grown for approximately 50 days in beds in climate-controlled rooms in a greenhouse. As the bacterium was not detected in the edible parts of the lettuce, the outer leaves of the lettuce, or the lettuce roots at harvest it was concluded that transmission of E. coli O157:H7 from contaminated soil to lettuce did not occur. The pathogen persisted in the soil for at least 8 weeks after fertilizing but was not detected after 12 weeks. Indigenous E. coli was detected only sporadically on the lettuce at harvest, and enterococci were not detected at all. The numbers of enterococci declined more rapidly than those of E. coli in the soil. Pseudomonas fluorescens, which inhibited growth of E. coli O157:H7 in vitro, was isolated from the rhizosphere.     

Survival of Escherichia coli O157:H7 in Soils from Jiangsu Province,China

Escherichia coli O157:H7 (E. coli O157:H7) is recognized as a hazardous microorganism in the environment and for public health. The E. coli O157:H7 survival dynamics were investigated in 12 representative soils from Jiangsu Province, where the largest E. coli O157:H7 infection in China occurred. It was observed that E. coli O157:H7 declined rapidly in acidic soils (pH, 4.57 – 5.14) but slowly in neutral soils (pH, 6.51 – 7.39). The survival dynamics were well described by the Weibull model, with the calculated t_d value (survival time of the culturable E. coli O157:H7 needed to reach the detection limit of 100 CFU g⁻¹) from 4.57 days in an acidic soil (pH, 4.57) to 34.34 days in a neutral soil (pH, 6.77). Stepwise multiple regression analysis indicated that soil pH and soil organic carbon favored E. coli O157:H7 survival, while a high initial ratio of Gram-negative bacteria phospholipid fatty acids (PLFAs) to Gram-positive bacteria PLFAs, and high content of exchangeable potassium inhibited E. coli O157:H7 survival. Principal component analysis clearly showed that the survival profiles in soils with high pH were different from those with low pH.     

Effect of curli expression and hydrophobicity of Escherichia coli O157:H7 on attachment to fresh produce surfaces

Aim: To investigate the effect of curli expression on cell hydrophobicity, biofilm formation and attachment to cut and intact fresh produce surfaces. Methods and Results: Five Escherichia coli O157:H7 strains were evaluated for curli expression, hydrophobicity, biofilm formation and attachment to intact and cut fresh produce (cabbage, iceberg lettuce and Romaine lettuce) leaves. Biofilm formation was stronger when E. coli O157:H7 were grown in diluted tryptic soy broth (1 : 10). In general, strong curli‐expressing E. coli O157:H7 strains 4406 and 4407 were more hydrophobic and attached to cabbage and iceberg lettuce surfaces at significantly higher numbers than other weak curli‐expressing strains. Overall, E. coli O157:H7 populations attached to cabbage and lettuce (iceberg and Romaine) surfaces were similar (P > 0·05), indicating produce surfaces did not affect (P < 0·05) bacterial attachment. All E. coli O157:H7 strains attached rapidly on intact and cut produce surfaces. Escherichia coli O157:H7 attached preferentially to cut surfaces of all produce types; however, the difference between E. coli O157:H7 populations attached to intact and cut surfaces was not significant (P > 0·05) in most cases. Escherichia coli O157:H7 attachment and attachment strength (S_R) to intact and cut produce surfaces increased with time. Conclusions: Curli‐producing E. coli O157:H7 strains attach at higher numbers to produce surfaces. Increased attachment of E. coli O157:H7 on cut surfaces emphasizes the need for an effective produce wash to kill E. coli O157:H7 on produce. Significance and Impact of the Study: Understanding the attachment mechanisms of E. coli O157:H7 to produce surfaces will aid in developing new intervention strategies to prevent produce outbreaks.     

Interaction between the Microbial Community and Invading Escherichia coli O157:H7 in Soils from Vegetable Fields

The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G⁻) to Gram-positive (G⁺) bacterial PLFAs (G⁻/G⁺ ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G⁻/G⁺ ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.     

Reduction of Escherichia coli O157:H7 on radish seeds by sequential application of aqueous chlorine dioxide and dry‐heat treatment

Aims: To assess the effectiveness of sequential treatments of radish seeds with aqueous chlorine dioxide (ClO₂) and dry heat in reducing the number of Escherichia coli O157:H7. Methods and Results: Radish seeds containing E. coli O157:H7 at 5·5 log CFU g^?1 were treated with 500 μg ml^?1 ClO₂ for 5 min and subsequently heated at 60°C and 23% relative humidity for up to 48 h. Escherichia coli O157:H7 decreased by more than 4·8 log CFU g^?1 after 12 h dry‐heat treatment. The pathogen was inactivated after 48 h dry‐heat treatment, but the germination rate of treated seeds was substantially reduced from 91·2 ± 5·0% to 68·7 ± 12·3%. Conclusions: Escherichia coli O157:H7 on radish seeds can be effectively reduced by sequential treatments with ClO₂ and dry heat. To eliminate E. coli O157:H7 on radish seeds without decreasing the germination rate, partial drying of seeds at ambient temperature before dry‐heat treatment should be investigated, and conditions for drying and dry‐heat treatment should be optimized. Significance and Impact of the study: This study showed that sequential treatment with ClO₂ and dry‐heat was effective in inactivating large numbers of E. coli O157:H7 on radish seeds. These findings will be useful when developing sanitizing strategies for seeds without compromising germination rates.     

Differences in internalization and growth of Escherichia coli O157:H7 within the apoplast of edible plants,spinach and lettuce,compared with the model species Nicotiana benthamiana

Internalization of food‐borne bacteria into edible parts of fresh produce plants represents a serious health risk. Therefore, internalization of verocytotoxigenic E. coli O157:H7 isolate Sakai was assessed in two species associated with outbreaks, spinach (Spinacia oleracea) and lettuce (Lactuca sativa) and compared to the model species Nicotiana benthamiana. Internalization occurred in the leaves and roots of spinach and lettuce throughout a 10 day time‐course. The plant species, tissue type and inoculum dose all impacted the outcome. A combination of low inoculum dose (~10² CFU) together with light microscopy imaging highlighted marked differences in the fate of endophytic E. coli O157:H7 Sakai. In the fresh produce species, bacterial growth was restricted but viable cells persisted over 20 days, whereas there was > 400‐fold (~2.5 Log₁₀) increase in growth in N. benthamiana. Colony formation occurred adjacent to epidermal cells and mesophyll cells or close to vascular bundles of N. benthamiana and contained components of a biofilm matrix, including curli expression and elicitation, extracellular DNA and a limited presence of cellulose. Together the data show that internalization is a relevant issue in crop production and that crop species and tissue need to be considered as food safety risk parameters.     

Fate of manure-borne pathogen surrogates in static composting piles of chicken litter and peanut hulls

The fate of manure-borne pathogen surrogates (gfp-labeled Escherichia coli O157:H7 and Listeria innocua and avirulent Salmonella Typhimurium) in the field was monitored at both sub-surface (30 cm from surface) and surface sites of static composting piles (3.5-m base diameter) composed of chicken litter and peanut hulls. Despite exposure to elevated temperatures, Salmonella was detected by enrichment culture in sub-surface samples following 14 days of composting. In surface samples, pathogen surrogates were detected in the summer after 4 days of composting by enrichment culture only, whereas E. coli O157:H7 and L. innocua remained detectable by direct plating (>2log₁₀ cfu/g) up to 28 days in piles composted during the fall and winter. All three types of bacteria remained detectable by enrichment culture in surface samples composted for 56 days during the winter.     

Leaching of bioluminescent Escherichia coli O157:H7 from sheep and cattle faeces during simulated rainstorm events

Aims: Development of a novel inoculation technique to improve the current methods of determining the leaching of Escherichia coli O157:H7 from faeces. Methods and Results: Ruminant faeces were inoculated with a high [c. 10⁷ colony forming units (CFU) g⁻¹] or low (c. 10⁴ CFU g⁻¹) load of a lux-marked strain of E. coli O157:H7 via injection, and subjected to four simulated heavy rainfall events. The population density and metabolic activity of E. coli O157:H7 recovered within the leachate was determined following each simulated rain event and compared with the indigenous E. coli population. The concentration of E. coli O157:H7 in the leachates followed a similar trend to that of nonpathogenic E. coli. Significantly greater densities of generic and pathogenic E. coli were recovered in the leachates generated from sheep faeces compared with cattle faeces. Pathogen metabolic activity was also significantly greater in sheep faeces. Conclusions: Our findings show that E. coli O157:H7 may readily leach from ruminant faeces during rain events. The bacterium leaches more freely from sheep faeces than from cattle faeces and displays greater metabolic activity within sheep leachate. Significance and Impact of the Study: A novel inoculation technique was developed that allowed the determination of both population density and cellular activity of E. coli O157:H7 in leachate derived from faeces.     

Quantification of Survival of Escherichia coli O157:H7 on Plants Affected by Contaminated Irrigation Water

Enterohemorrhagic E. coli O157: H7 (EHEC) is a major foodborne pathogen capable of causing diarrhea and vomiting, with further complications such as hemolytic‐uremic syndrome (HUS). The aim of this study was to use the real‐time PCR method to quantify the survival of Escherichia coli O157:H7/pGFP in phyllosphere (leaf surface), rhizosphere (volume of soil tightly held by plant roots), and non‐rhizosphere soils (sand and clay) irrigated with contaminated water and compare the results obtained between real‐time PCR method and conventional plate counts. The real‐time PCR probe was designed to hybridize with the (eae) gene of E. coli O157:H7. The probe was incorporated into real‐time PCR containing DNA extracted from the phyllosphere, rhizosphere, and non‐rhizosphere soils irrigated with water artificially contaminated with E. coli O157:H7. The detection limit for E. coli O157:H7 quantification by real‐time PCR was 2.3 × 10³ in the rhizosphere and phyllosphere samples. E. coli O157:H7 survived longer in rhizosphere soil than the non‐rhizosphere soil. The concentration of E. coli O157:H7/pGFP in rhizosphere soils was ≥ 10⁴ CFU/g in both soils at day 12 based on both plate count and real time PCR, with the clay soil significantly (P = 0.05) higher than the sandy soil. This data showed that E. coli O157H:7 can persist in the environment for more than 50 d, and this may pose some risk for both animal and human infection and provides a very significant pathway for pathogen recontamination in the environment.     

Survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in manure and manure‐amended soil under tropical climatic conditions in Sub‐Saharan Africa

Aims: To establish the fate of Escherichia coli O157:H7 and Salmonella Typhimurium in manure and manure‐amended agricultural soils under tropical conditions in Sub‐Saharan Africa. Methods and Results: Survival of nonvirulent E. coli O157:H7 and Salm. Typhimurium at 4 and 7 log CFU g^?1 in manure and manure‐amended soil maintained at ≥80% r.h. or exposed to exclusive field or screen house conditions was determined in the Central Agro‐Ecological Zone of Uganda. Maintaining the matrices at high moisture level promoted the persistence of high‐density inocula and enhanced the decline of low‐density inocula in the screen house, but moisture condition did not affect survival in the field. The large majority of the survival kinetics displayed complex patterns corresponding to the Double Weibull model. The two enteric bacteria survived longer in manure‐amended soil than in manure. The 7 log CFU g^?1E. coli O157:H7 and Salm. Typhimurium survived for 49–84 and 63–98 days, while at 4 log CFU g^?1, persistence was 21–28 and 35–42 days, respectively. Conclusions: Under tropical conditions, E. coli O157:H7 and Salm. Typhimurium persisted for 4 and 6 weeks at low inoculum density and for 12 and 14 weeks at high inoculum density, respectively. Significance and Impact of the Study: Persistence in the tropics was (i) mostly shorter than previously observed in temperate regions thus suggesting that biophysical conditions in the tropics might be more detrimental to enteric bacteria than in temperate environments; (ii) inconsistent with published data isothermally determined previously hence indicating the irrelevance of single point isothermal data to estimate survival under dynamic temperature conditions.     

Effect of Ractopamine HCl Supplementation on Fecal Shedding of Escherichia coli O157:H7 and Salmonella in Feedlot Cattle

The effects of the β-agonist ractopamine, recently approved for use in feedlot cattle to improve carcass quality and performance, on fecal shedding Escherichia coli O157:H7 and Salmonella in feedlot cattle was examined. In the first study, 20 feedlot steers and heifers were randomly assigned to receive ractopamine or no ractopamine (control) by way of oral bolus for 28 days. Fecal samples were collected daily, and shedding of E. coli O157:H7 determined. When examined during the entire 28-day experimental period, ractopamine decreased (P = 0.0006) the percentage of cattle shedding E. coli O157:H7 (58% vs. 42% for control and ractopamine treatments, respectively). A second study was conducted in a commercial feedlot facility in the southwestern United States. Eighteen pens of cross-bred beef heifers (approximately 100 head/pen and 9 pens/treatment) were randomly assigned to receive either 0 (control) or 200 mg ractopamine/head·d^–1. Fresh fecal samples (30/pen) were collected off the pen floor before ractopamine supplementation and again after approximately 28 days of ractopamine supplementation (within a few days of slaughter); the samples were cultured for E. coli O157:H7 and Salmonella. The percentage of animals shedding E. coli O157:H7 was decreased when data were pooled across replicates (P = 0.05) in ractopamine-treated cattle compared with controls. The percentage of animals shedding Salmonella tended to be higher (P = 0.08) with the ractopamine treatment when data were pooled across replicates. Although further research is required to confirm these results, the potential food safety implications of this research are intriguing. Mention of trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the United States Drug Administration and does not imply its approval to the exclusion of other products that may be suitable.     

High concentration of sodium chloride could induce the viable and culturable states of Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis

In the present study, Escherichia coli O157:H7 and Salmonella enterica serovar Enteritidis were transferred into Luria–Bertani medium without NaCl (LBWS) and adjusted to various pHs (4, 5, 6 and 7) with lactic acid containing 0·75, 5, 10 and 30% NaCl, and stored at 25°C until the bacterial populations reached below detectable levels on tryptic soy agar (TSA). Although E. coli O157:H7 and S. Enteritidis did not grow on TSA when incubated in LBWS with 30% NaCl for 35 and 7 days, more than 60 and 70% of the bacterial cells were shown to be viable via fluorescent staining with SYTO9 and propidium iodide (PI), respectively, suggesting that a number of cells could be induced into the viable but nonculturable (VBNC) state. These bacteria that were induced into a VBNC state were transferred to a newly prepared tryptic soy broth (TSB) and then incubated at 37°C for several days. After more than 7 days, E. coli O157:H7 and S. Enteritidis regained their culturability. We, therefore, suggest that E. coli O157:H7 and S. Enteritidis entered the VBNC state under the adverse condition of higher salt concentrations and were revived when these conditions were reversed.     

Vaccination with attenuated Salmonella enterica Dublin expressing E coli O157:H7 outer membrane protein Intimin induces transient reduction of fecal shedding of E coli O157:H7 in cattle

Background  

Escherichia coli serogroup O157:H7 has emerged as an important zoonotic bacterial pathogen, causing a range of symptoms from self-limiting bloody diarrhea to severe hemorrhagic colitis and hemolytic-uremic syndrome in humans. Beef and dairy cattle are considered the most important animal reservoirs for this pathogen. One of the important virulence characteristics of E. coli O157:H7 is the eaeA gene encoding the 97 kDa surface protein intimin. Intimin is required for attachment and effacement during the interaction of enterohemorrhagic E. coli with human and bovine neonatal enterocytes. The present study was undertaken to test the hypothesis that an adaptive mucosal immune response directed against intimin will reduce or prevent enteric colonization and fecal shedding of E. coli O157:H7 in cattle.