Enumeration of Salmonella and Escherichia coli O157:H7 in ground beef, cattle carcass, hide and faecal samples using direct plating methods†

Prevalence and Characterization of Salmonella during Pork Sausage Manufacturing

Pork carcasses and meat may harbor Salmonella and may contaminate other products during harvest and fabrication. Sources of contamination include manure on hides, environmental contamination, ingredients from external sources, and lymph nodes. Swine lymph nodes are often incorporated into ground meat, as their anatomical location makes removal labor prohibitive. A sausage processing plant in the midwestern United States was sampled monthly (except for December) from May 2021 to April 2022 to enumerate Salmonella and Enterobacteriaceae (EB) throughout the sausage manufacturing process to determine high-risk stages and efficiency of existing in-plant interventions. Salmonella serotypes and antimicrobial susceptibility were evaluated on a subset of isolates recovered at the end phases of sausage production. In each collection, samples were taken from the carcasses of eight sows through 11 stages of sausage manufacturing. A total of 830 samples were cultured. Thirty-four Salmonella were isolated from the final three production stages; of these, there were eleven serotypes. Three isolates displayed resistance to ampicillin, whereas the remainder of the isolates were pan-susceptible to the antimicrobials tested. Salmonella and EB were significantly reduced (p < 0.001) by acid washes at different stages of production, and the results point to the beneficial effects of interventions to lessen Salmonella concentrations in retail products.

Physicochemical, microbiological, and sensory characteristics of "Sui Wu'u" traditional pork products from Bajawa, West Flores, Indonesia

Background and Aim

Sui Wu'u is a traditional meat preservation product from Bajawa, a region in East Nusa Tenggara. It is made by mixing pork with salt and corn flour, which is then stored in a bamboo container (tuku) for months. After 6 months of storage, this study examined the physicochemical, microbiological, and sensory properties of Sui Wu'u.

Materials and Methods

Sui Wu'u products were prepared using the traditional recipe from the Bajawa community. Fresh pork (pork belly and backfat), corn flour, and salt were purchased from local/traditional markets at proportions of 65%, 30%, and 5%, respectively. The physicochemical, amino acid, fatty acid profile, microbiological, and sensory properties of Sui Wu'u were evaluated after being stored for 6 months in a bamboo container (tuku).

Results

The results indicated that these Sui Wu'u were mainly characterized by high-fat levels, followed by protein. The pH value, salt content, moisture content, and water activity were 4.72%, 1.72%, 6.11%, and 0.62%, respectively. Minerals (K, P, Se, and Zn) and vitamin B6, as well as amino acids, such as leucine, phenylalanine, lysine (essential amino acids), glycine, proline, glutamic acid, and alanine (non-essential amino acids), are present in Sui Wu'u. The fatty acid profile was dominated by monounsaturated fatty acids (MUFA) (21.69%), saturated fatty acids (SFA) (17.78%), and polyunsaturated fatty acids (PUFA) (5.36%). Monounsaturated fatty acids, oleic acid (C18:1n9) was the most abundant fatty acid in Sui Wu'u, followed by palmitic acid SFA (C16:0); MUFA stearic acid (C18:0); and PUFA linoleic (C18:2n-6). The microbiological characteristics of Sui Wu'u showed no detectable microorganisms (<10 CFU/g) for Salmonella, total E. coli and total Staphylococcus, and average values of 4.4 × 105 CFU/g for total microbes, which were still below the maximum limit of microbial contamination according to the regulations of the Food and Drug Supervisory Agency of the Republic of Indonesia. The sensory assessment indicated that panelists highly preferred (rated as very like) Sui Wu'u for all sensory attributes.

Conclusion

The physicochemical, microbiological, and sensory characteristics of Sui Wu'u after 6 months of storage indicated that it still provides essential nutrients for the body and is quite safe for consumption. The stability of Sui Wu'u's shelf life can be attributed to the appropriate combination of pork, salt, corn flour, bamboo packaging (tuku), and storage temperature. The high-fat content in Sui Wu'u can be reduced by increasing the proportion of lean meat. Ensuring strict sanitation during the manufacturing process, using high-quality pork, salt, corn flour, and proper packaging with bamboo can further improve the safety of Sui Wu'u for consumption.

First detection and molecular characteristics of bopivirus from goats in China

A metavirome analysis was performed and detected bopivirus in the diarrhoeal fecal samples of goats in China. A total of 136 fecal samples were collected from yeanlings between the dates of June 2021 and January 2022 in Sichuan province, China. Moreover, "Bopivirus B" strains were detected by a specific RT-PCR targeting the 3D gene of the virus. The results showed that the overall detection rate of "Bopivirus B" was 19.12% (26/136). Additionally, there was a higher detection rate (24.05%, 19/79) in the fecal samples collected from yeanlings with diarrhea compared to those from asymptomatic animals (12.28%, 7/57). In these samples, no other common diarrhea-causing pathogens were detected except for three enteric viruses, namely caprine enterovirus, caprine kobuvirus and caprine hunnivirus (with detection rates of 13.97, 13.97, and 8.82%, respectively). Subsequently, full-length VP4, VP2, VP3, and VP1 genes from "Bopivirus B"-positive samples were amplified, cloned, sequenced, and analyzed. The phylogenetic analysis performed on the VP1 genes revealed that the identified bopivirus belonged to genotype B1 (seven strains) and B2 (three strains) and presented a high genetic diversity. Furthermore, a complete genome sequence of a "Bopivirus B" strain (SWUN/B1/2022) was obtained using PCR from fecal sample of a diarrhoeal yeanling. The complete genome was 7,309 nucleotides in length with a standard picornavirus genome organization, and shares 93.10% and 91.10% nucleotide similarity with bopivirus B1 genotype strain ovine/TB14/2010-HUN and bopivirus B2 genotype strain goat/AGK16/2020-HUN, respectively. According to the species classification criteria put forward by the International Committee on Taxonomy of Viruses and VP1 genotype, the strain SWUN/B1/2022 belongs to the bopivirus B1. This strain has unique amino acid substitutions in the VP4, VP2, VP3, and VP1 genes. Moreover, genomic recombination analysis revealed that this strain may be a minor parental strain of bopivirus B1 ovine/TB14/2010-HUN. Evolutionary analysis based on the 2C and 3CD genes revealed that the new bopivirus B1 strain SWUN/B1/2022 presents a unique evolutionary pattern. This study provided evidence to suggest that "Bopivirus B" is circulating with substantial genetic diversity in goats in China at present, and the mixed infection of "Bopivirus B" with other enteric viruses should be considered to be a composite factor in the occurrence of viral diarrhea in goats.

Association of natural resistance-associated macrophage protein 1 polymorphisms with Salmonella fecal shedding and hematological traits in pigs

Background and Aim

Natural resistance-associated macrophage protein 1 encoding gene (Nramp1) plays a role in immune response and disease resistance. This study aimed to investigate the polymorphisms of Nramp1 intron 6 concerning Salmonella shedding and hematological traits in pigs.

Materials and Methods

A total of 40 commercial pigs (three-way Large White x Landrace x Duroc cross) were genotyped using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method and analyze the relationship between the polymorphisms of the Nramp1 gene and Salmonella fecal shedding and hematological parameters.

Results

Nramp1 was shown to be polymorphic in these pigs. The Nramp1 gene has two alleles (A and B) and two genotypes (AB and BB). The BB genotype had a higher frequency than the AB genotype. A significant relationship between the BB genotype and the number of Salmonella in feces compared to the AB genotype (p < 0.05) on 7 days post-inoculation (DPI) was revealed in the association analysis. The single-nucleotide polymorphism at intron 6 in the Nramp1 gene was linked to white and red blood cells 2 and 7 DPI (p < 0.05).

Conclusion

The Nramp1 gene was suggested by these findings to be potentially used as a molecular marker for the genetic selection of disease susceptibility in pig breeding.

Aichivirus C isolate is a diarrhea-causing pathogen in goats

Aichivirus C is an emerging virus in goats, but its biological significance remains unknown. In this study, 18 diarrheic and 16 non-diarrheic fecal samples of kids were collected from a farm with an ongoing diarrheic outbreak in Sichuan Province, China in May 2021. Of these samples, 77.8% (14/18) of diarrheic samples were detected as Aichivirus C positive by RT-PCR, which was significantly higher than that of non-diarrheic feces (0%, p<0.001); meanwhile, other common diarrhea-causing pathogens in goats were not detected in diarrheic samples, except for two samples that were detected as caprine enterovirus positive, suggesting that Aichivirus C was associated with goat diarrhea. Furthermore, five Aichivirus C strains were successfully isolated from positive samples using Vero cell lines and two isolates further plaque-purified, named SWUN/F5/2021(10^-6.7 TCID₅₀ /0.1ml) and SWUN/F6/2021(10^-7 TCID₅₀ /0.1ml). Interestingly, Aichivirus C strain could cause systemic infection in experimental kids via oral administration, with the main clinical manifestation being severe watery diarrhea. Histopathological changes observed in the duodenum and jejunum were characteristic, with shedding of mucosal epithelial cells. In addition, the virus was detected in tissues of diarrhea kids naturally infected with Aichivirus C, exhibiting pathological changes similar to those of experimental infections. Overall, this study first isolated Aichivirus C and confirmed its pathogenicity on kids, with further study needed to better understand virus pathogenicity. As Aichivirus C has been detected in South Korea, Italy, and the USA and widely prevalent in southwest China, the results obtained here have significant implications for the diagnosis and control of diarrhea in goats. This article is protected by copyright. All rights reserved.

Salmonella Carriage in Peripheral Lymph Nodes and Feces of Cattle at Slaughter Is Affected by Cattle Type, Region, and Season

Salmonella is a significant food safety concern in commercial beef production, and some contamination is thought to occur by inclusion of Salmonella-infected peripheral lymph nodes (LN) in ground beef and through fecal contamination. Surveillance in processing plants assists packers in risk management of Salmonella by understanding seasonal trends and risks associated with different cattle types. Approximately 25 fecal samples and 20 LN were collected from animals representing each of five cattle types (cull beef cattle, cull dairy cows, conventional feedlot cattle, all-natural feedlot cattle raised without pharmaceuticals, and grass-finished cattle) and each of five climate regions (mixed-temperatures and dry, mixed-temperatures and humid, hot and humid, hot and dry, cold) during each of three seasons (summer, fall, winter) to better characterize Salmonella inputs into a commercial cattle processing facility. In total, 1,840 fecal samples and 1,550 LN samples were collected. Fecal samples and LN were cultured for Salmonella, and select isolates were serogrouped and screened for antimicrobial resistance. Conventional feedlot cattle had the highest LN Salmonella concentrations (1.17 log10 CFU/g LN) in this data set, while cull dairy cows had the highest fecal Salmonella concentrations (1.96 log10 CFU/g feces). Conventional feedlot cattle and cull dairy cows had the greatest Salmonella prevalence in both LN (32 and 18%, respectively) and feces (37 and 49%, respectively), while all-natural feedlot cattle had the lowest prevalence in the LN (3%) and feces (7%). As expected, Salmonella prevalence and concentration was lowest for all cattle types during winter compared to warmer seasons. When examined by climate region, a greater Salmonella prevalence in both feces and LN was observed in climate region 4 (hot-dry), than the other regions. Only 21 of 50 Salmonella isolates examined for antimicrobial susceptibility were identified as multidrug resistant (MDR); cull dairy cows were responsible for 48% of MDR isolates, cull beef cattle were responsible for 38%, and conventional feedlot, grass-fed, and all-natural feedlot cattle were each responsible for 4.8%. These results indicate that different production schemes, season, and climate region may influence which cattle are most likely to introduce Salmonella to the abattoir, allowing for greater risk awareness during the slaughter process.

A Farm-to-Fork Quantitative Microbial Exposure Assessment of β-Lactam-Resistant Escherichia coli among U.S. Beef Consumers

Integrated quantitative descriptions of the transmission of β-lactam-resistant Escherichia coli (BR-EC) from commercial beef products to consumers are not available. Here, a quantitative microbial exposure assessment model was established to simulate the fate of BR-EC in a farm-to-fork continuum and provide an estimate of BR-EC exposure among beef consumers in the U.S. The model compared the per-serving exposures from the consumption of intact beef cuts, non-intact beef cuts, and ground beef. Additionally, scenario analysis was performed to evaluate the relative contribution of antibiotic use during beef cattle production to the level of human exposure to BR-EC. The model predicted mean numbers of BR-EC of 1.7 × 10-4, 8.7 × 10-4, and 6.9 × 10-1 CFU/serving for intact beef cuts, non-intact beef cuts, and ground beef, respectively, at the time of consumption. Sensitivity analyses using the baseline model suggested that factors related to sectors along the supply chain, i.e., feedlots, processing plants, retailers, and consumers, were all important for controlling human exposure to BR-EC. Interventions at the processing and post-processing stages are expected to be most effective. Simulation results showed that a decrease in antibiotic use among beef cattle might be associated with a reduction in exposure to BR-EC from beef consumption. However, the absolute reduction was moderate, indicating that the effectiveness of restricting antibiotic use as a standalone strategy for mitigating human exposure to BR-EC through beef consumption is still uncertain. Good cooking and hygiene practices at home and advanced safety management practices in the beef processing and post-processing continuum are more powerful approaches for reducing human exposure to antibiotic-resistant bacteria in beef products.

Application of a Commercial Salmonella Real-Time PCR Assay for the Detection and Quantitation of Salmonella enterica in Poultry Ceca

ABSTRACT

Foodborne salmonellosis is commonly associated with poultry and poultry products, necessitating continued development of pre- and postharvest food safety interventions and risk management strategies. Evaluation of technologies and strategies is limited by availability of cost-effective, rapid laboratory methods. The objective of this study was to evaluate a commercial qualitative PCR assay and its novel quantitative application to detect and enumerate Salmonella in poultry ceca as an analytical matrix. Ceca were collected at harvest, the contents were homogenized, and paired samples were evaluated with buffered peptone water (BPW) and BAX MP + Supplement (MPS) preenrichment broths followed by PCR screening with a BAX System Q7 PCR and by culture isolation. Additional ceca were inoculated with Salmonella to develop a standard curve for the BAX System SalQuant quantitative PCR application (QA), and estimates were obtained by the QA and most-probable-number (MPN) methods. For preenrichment media, PCR outcomes were equivalent to those of culture isolation for detecting Salmonella in ceca with 95.65 and 87.88% sensitivity and 82.00 and 100.00% specificity (P = 0.074) for BPW and MPS, respectively. However, at the sample level, BPW performed significantly worse (47.92%) than did MPS (68.75%) for overall isolation of Salmonella (P < 0.0001). After standard curve development, the mean QA estimates obtained for the inoculated samples were 1.14 (95% confidence interval [CI]: 0.62 to 1.66), 1.79 (1.50 to 2.08), 2.91 (2.65 to 3.17), and 3.76 (3.26 to 4.25) log CFU/mL for each targeted inoculation of 1.0, 2.0, 3.0, and 4.0 log CFU/mL, respectively, and were within or comparable to the 95% CI values of paired MPN estimates. These data support the use of MPS for the detection and isolation of Salmonella enterica from poultry ceca when screening with PCR and indicate that QA may be useful as an alternative tool to estimate Salmonella loads in poultry ceca, which may support preharvest food safety interventions.

HIGHLIGHTS

Dual transcriptomic analysis reveals metabolic changes associated with differential persistence of human pathogenic bacteria in leaves of Arabidopsis and lettuce

Understanding the molecular determinants underlying the interaction between the leaf and human pathogenic bacteria is key to provide the foundation to develop science-based strategies to prevent or decrease the pathogen contamination of leafy greens. In this study, we conducted a dual RNA-sequencing analysis to simultaneously define changes in the transcriptomic profiles of the plant and the bacterium when they come in contact. We used an economically relevant vegetable crop, lettuce (Lactuca sativa L. cultivar Salinas), and a model plant, Arabidopsis thaliana Col-0, as well as two pathogenic bacterial strains that cause disease outbreaks associated with fresh produce, Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium 14028s (STm 14028s). We observed commonalities and specificities in the modulation of biological processes between Arabidopsis and lettuce and between O157:H7 and STm 14028s during early stages of the interaction. We detected a larger alteration of gene expression at the whole transcriptome level in lettuce and Arabidopsis at 24 h post inoculation with STm 14028s compared to that with O157:H7. In addition, bacterial transcriptomic adjustments were substantially larger in Arabidopsis than in lettuce. Bacterial transcriptome was affected at a larger extent in the first 4 h compared to the subsequent 20 h after inoculation. Overall, we gained valuable knowledge about the responses and counter-responses of both bacterial pathogen and plant host when these bacteria are residing in the leaf intercellular space. These findings and the public genomic resources generated in this study are valuable for additional data mining.

Evaluation of public and animal health risks in case of a delayed post-mortem inspection in ungulates

The potential effects of a 24 or 72-h delay in post-mortem inspection (PMI) of ungulates on public health and monitoring of animal health and welfare was evaluated. The assessment used a survey of meat inspectors, expert opinion, literature search and a stochastic model for Salmonella detection sensitivity. Disease detection sensitivity at a delayed PMI is expected to reduce detection sensitivity to a variable extent, depending on the hazard and on the signs/lesions and organs involved. No reduction is expected for Trichinella detection in meat from susceptible animal species and any decrease in detection of transmissible spongiform encephalopathies (TSEs) will not exceed the current tolerance for fallen stock. A 24-h delay in PMI could result in a small reduction in sensitivity of detection for tuberculosis, echinococcosis and cysticercosis. A greater reduction is expected for the detection of pyaemia and Rift valley fever. For the detection of Salmonella, the median model estimates are a reduction of sensitivity of 66.5% (90% probability interval (PI) 0.08-99.75%) after 24-h delay and 94% (90% PI 0.83-100%) after 72-h delay of PMI. Laboratory testing for tuberculosis following a sampling delay of 24-72 h could result in no, or a moderate, decrease in detection depending on the method of confirmation used (PCR, culture, histopathology). For chemical contaminants, a delay in meat inspection of 24 or 72 h is expected to have no impact on the effectiveness of detection of persistent organic pollutants and metals. However, for certain pharmacologically active substances, there will be a reduced effectiveness to detect some of these substances due to potential degradation in the available matrices (tissues and organs) and the non-availability of specific preferred matrices of choice.

Antimicrobial Effects of Zataria multiflora and Ocimum basilicum on Escherichia coli O157:H7 During Ripening of Traditional Lighvan Cheese

Background:

Escherichia coli O157:H7 is one of the most common causes of contamination in Lighvan cheese processing. Using from natural antimicrobial essential oils is applied method to decrease the rate of microbial contamination of dairy products. The present investigation was done to study the antimicrobial effects of Z. multiflora and O. basilicum essential oils on survival of E. coli O157:H7 during ripening of traditional Lighvan cheese.

Methods:

Leaves of the Z. multiflora and O. basilicum plants were subjected to the Clevenger apparatus. Concentrations of 0, 100 and 200 ppm of the Z. multiflora and 0, 50 and 100 ppm of O. basilicum essential oils and also 103 and 105 cfu/ml numbers of E. coli O157:H7 were used. The numbers of the E. coli O157:H7 bacteria were analyzed during the days 0, 30, 60 and 90 of the ripening period.

Results:

Z. multiflora and O. basilicum essential oils had considerable antimicrobial effects against E. coli O157:H7. Using the essential oils caused decrease in the numbers of E. coli O157:H7 bacteria in 90th days of ripening (P <0.05). Using from Z. multiflora at concentration of 200 ppm can reduce the survival of E. coli O157:H7 in Lighvan cheese.

Conclusion:

Using Z. multiflora and O. basilicum essential oils as good antimicrobial agents can reduce the risk of foodborne bacteria and especially E. coli O157:H7 in food products.

Evaluation of the Efficacy of Three Direct Fed Microbial Cocktails To Reduce Fecal Shedding of Escherichia coli O157:H7 in Naturally Colonized Cattle and Fecal Shedding and Peripheral Lymph Node Carriage of Salmonella in Experimentally Infected Cattle

Two experiments were conducted to evaluate the feeding of direct fed microbials (DFMs) on fecal shedding of Escherichia coli O157:H7 in naturally infected cattle (experiment I) and on Salmonella in the feces and peripheral lymph nodes (PLNs) of experimentally infected cattle (experiment II). Thirty cattle, 10 per treatment, were used in each experiment. Treatments in experiment I consisted of a control (lactose carrier only); DFM1, a 1:1 ratio of Enterococcus faecium and Lactobacillus animalis; and DFM2, a 1:1 ratio of Lactobacillus acidophilus and Pediococcus acidilactici. In Experiment II, DFM1 was replaced with DFM3, a 1:2 ratio of Lactobacillus reuteri and other Lactobacillus strains. Additives were mixed in water and applied as a top-dressing to each pen's daily ration for 50 days. Approximately half-way through each experiment, the DFM concentration was doubled for the remainder of the study. Fecal samples were collected throughout experiment I and cultured for E. coli O157:H7. Cattle in experiment II were inoculated intradermally with Salmonella Montevideo on days 32, 37, and 42 and then necropsied on days 49 and 50 (five cattle per treatment on each day). Innate immune function was assessed on days 29, 49, and 50. In experiment I, fecal concentration and prevalence of E. coli O157:H7 were not different (P > 0.10) nor was there an effect (P = 0.95) on the percentage of super shedders (cattle shedding ≥3.0 log CFU/g of feces). In experiment II, no treatment differences (P > 0.05) were observed for Salmonella in the PLNs except for the inguinal nodes, which had a significantly lower Salmonella prevalence in DFM-supplemented cattle than in the controls. Immune function, as measured by monocyte nitric oxide production and neutrophil oxidative burst, was decreased (P < 0.05) in the DFM treatment groups. Although results of this research indicate little to no effect of these DFMs on E. coli O157:H7 or Salmonella in cattle, an increase in the duration of administration to that similar to what is used for commercial cattle might elicit treatment differences.

Quantitative dynamics of Salmonella and E. coli in feces of feedlot cattle treated with ceftiofur and chlortetracycline

Antibiotic use in beef cattle is a risk factor for the expansion of antimicrobial-resistant Salmonella populations. However, actual changes in the quantity of Salmonella in cattle feces following antibiotic use have not been investigated. Previously, we observed an overall reduction in Salmonella prevalence in cattle feces associated with both ceftiofur crystalline-free acid (CCFA) and chlortetracycline (CTC) use; however, during the same time frame the prevalence of multidrug-resistant Salmonella increased. The purpose of this analysis was to quantify the dynamics of Salmonella using colony counting (via a spiral-plating method) and hydrolysis probe-based qPCR (TaqMan® qPCR). Additionally, we quantified antibiotic-resistant Salmonella by plating to agar containing antibiotics at Clinical & Laboratory Standards Institute breakpoint concentrations. Cattle were randomly assigned to 4 treatment groups across 16 pens in 2 replicates consisting of 88 cattle each. Fecal samples from Days 0, 4, 8, 14, 20, and 26 were subjected to quantification assays. Duplicate qPCR assays targeting the Salmonella invA gene were performed on total community DNA for 1,040 samples. Diluted fecal samples were spiral plated on plain Brilliant Green Agar (BGA) and BGA with ceftriaxone (4 μg/ml) or tetracycline (16 μg/ml). For comparison purposes, indicator non-type-specific (NTS) E. coli were also quantified by direct spiral plating. Quantity of NTS E. coli and Salmonella significantly decreased immediately following CCFA treatment. CTC treatment further decreased the quantity of Salmonella but not NTS E. coli. Effects of antibiotics on the imputed log10 quantity of Salmonella were analyzed via a multi-level mixed linear regression model. The invA gene copies decreased with CCFA treatment by approximately 2 log10 gene copies/g feces and remained low following additional CTC treatment. The quantities of tetracycline or ceftriaxone-resistant Salmonella were approximately 4 log10 CFU/g feces; however, most of the samples were under the quantification limit. The results of this study demonstrate that antibiotic use decreases the overall quantity of Salmonella in cattle feces in the short term; however, the overall quantities of antimicrobial-resistant NTS E. coli and Salmonella tend to remain at a constant level throughout.

Population Dynamics of Salmonella enterica within Beef Cattle Cohorts Followed from Single-Dose Metaphylactic Antibiotic Treatment until Slaughter

Antibiotic use in cattle can select for multidrug-resistant Salmonella enterica, which is considered a serious threat by the U.S. Centers for Disease Control and Prevention. A randomized controlled longitudinal field trial was designed to determine the long-term effects of a single dose of ceftiofur or tulathromycin on Salmonella population characteristics in cattle feces and peripheral lymph nodes and on hides. A total of 134 beef cattle from two sources were divided among 12 pens, with cattle in each of the 3-pen blocks receiving a single dose of either ceftiofur or tulathromycin or neither (control) on day 0. Fecal samples were collected before treatment (day 0) and repeatedly following treatment until slaughter (day 99+). Hide and lymph node samples were collected at slaughter age. Salmonella prevalence, phenotypic antimicrobial resistance, serotype, and phylogenetic relationships were examined. Multilevel mixed logistic regression models indicated no significant effects (P ≥ 0.218) of metaphylactic antibiotics on the prevalence of Salmonella across sample types. However, there was a significant time effect observed, with prevalence increasing from spring through the midsummer months (P < 0.0001) in feces. The majority of Salmonella isolates were pansusceptible to a panel of 14 antibiotics both before and after treatment. Highly prevalent Salmonella serotypes were Salmonella enterica serovar Montevideo, Salmonella enterica serovar Anatum, Salmonella enterica serovar Cerro, and Salmonella enterica serovar Lubbock across all sample types. Strong pen and cattle source serotype clustering effects were observed among Salmonella isolates originating from fecal, lymph node, and hide samples; however, the potential role of Salmonella isolates from the pen environment prior to animal placement was not assessed in this study.IMPORTANCE Salmonella is a leading bacterial foodborne pathogen, causing a significant number of human infections and deaths every year in the United States. Macrolides and 3rd-generation cephalosporins play critical roles in the treatment of human salmonellosis. Use of these antibiotics in beef cattle can select for resistant bacteria that may enter the food chain or spread from the farm via manure. There is a lack of longitudinal research concerning the long-term effects of metaphylactic antibiotic administration. Here, we assessed Salmonella population dynamics during the feeding period until slaughter following single-dose antibiotic treatment. We found no long-term effects of antibiotic use early in the cattle-feeding period on Salmonella prevalence and antimicrobial resistance at slaughter. We identified the pens in which cattle were housed as the factor that contributed most to Salmonella serotypes being shared; importantly, the dominant strain in each pen changed repeatedly over the entire feeding period.

Prevalence and concentration of stx+ E. coli and E. coli O157 in bovine manure from Florida farms

Fresh produce outbreaks due to Shiga toxin-producing Escherichia coli (STEC) continue to occur in the United States (US). Manure-amended soils can pose a public health risk when used for growing raw agricultural commodities. Knowing the prevalence and concentration of STEC in untreated biological soil amendments of animal origin (BSAAO) is important to help guide the most appropriate pre-harvest interval(s) following application to limit risks from these soil amendments. Bovine manure samples were collected from 12 farms in Florida, including samples from piles, lagoons, barns, and screened solids. Two methods were used to detect stx1/2 and rfbE genes in samples. A prevalence rate of 9% for stx1 and/or stx2 and 19% for rfbE was observed from the 518 bovine manure samples evaluated. A most probable number (MPN) assay was performed on stx+ samples when applicable. The geometric mean for stx+ samples (n = 20) was 3.37 MPN g^-1 (0.53 log MPN g^-1) with a maximum value of 6,800 MPN g^-1 (3.83 log MPN g^-1). This research was part of a larger nationwide geographical study on the prevalence and concentration of STEC in bovine manure to help guide regulations on feasible pre-harvest intervals for the application of untreated BSAAO.

Prevalence and Characterization of Salmonella Present during Veal Harvest

Beef and veal products have been vehicles implicated in the transmission of Salmonella enterica, a gastroenteritis-causing bacteria. Recent regulatory samples collected from veal have indicated bob veal, or calves harvested within days of birth, have higher rates of Salmonella than samples collected from formula-fed veal, or calves raised 20 weeks on milk replacer formula before harvest. To investigate this problem, we collected samples from veal calf hides, preevisceration carcasses, and final carcasses at five veal processors that harvested bob or formula-fed veal or both. Prevalence and concentrations of Salmonella were determined, and then the isolates were characterized for serovar and antibiotic susceptibility. Salmonella was more prevalent (P < 0.05) among bob veal than formula-fed veal hides, preevisceration carcasses, and final carcass (84.2 versus 15.6%, 62.8 versus 10.1%, and 12.0 versus 0.4%, respectively). Concentrations of Salmonella could be estimated by using regression order statistics on hides and preevisceration carcasses at two veal plants, with one harvesting bob veal and the other bob and formula-fed veal. The concentration of Salmonella on bob veal hides at the plants was 1.45 ± 0.70 and 2.04 ± 1.00 log CFU/100 cm², greater (P < 0.05) than on formula-fed veal hides, which was 1.10 ± 1.51 log CFU/100 cm². Concentrations on carcasses, however, were very low. Seventeen Salmonella serovars were identified among 710 isolates. Salmonella serovars London, Cerro, and Muenster were most common to bob veal and made up 50.7, 18.7, and 6.3% of the isolates, respectively, while serovar Montevideo (6.8% of isolates) was most common to formula-fed veal. Although bob veal had increased prevalence and concentrations of Salmonella, one group of formula-fed veal was found to harbor human disease-related antibiotic-resistant Salmonella serovars Heidelberg and the monophasic variant of Typhimurium (1,4,[5],12:i:-). Veal processors have made changes to improve the safety of veal, but further efforts are necessary from both bob and formula-fed veal to address Salmonella.

A facile signal-on electrochemical DNA sensing platform for ultrasensitive detection of pathogenic bacteria based on Exo III-assisted autonomous multiple-cycle amplification

A facile signal-on electrochemical DNA biosensor has been developed for ultrasensitive detection of pathogenic bacteria using an Exo III-assisted autonomous multiple-cycle amplification strategy. The strategy relies on pathogens and aptamer binding-initiated release of a trigger, which combines with the 3'-protruding terminus of the hairpin probe 1, leading to the formation of double-stranded DNA with a blunt 3' terminus which starts the Exo III-assisted multiple signal amplification reaction. In addition, hairpin probe 2 labeled with an electroactive reporter at the middle of the loop region is ingeniously designed to contain a short hairpin-embedded segment, which can fold into a hairpin structure via an Exo III-assisted cleavage reaction, thus bringing the redox molecule in proximity to the electrode surface for "signal-on" sensing. Under optimal conditions, this biosensor exhibits a very low detection limit as low as 8 cfu mL^-1 and a wide linear range from 1.0 × 10¹ to 1.0 × 10⁷ cfu mL^-1 of target pathogenic bacteria. As far as we know, this is the first time that the Exo III-assisted autonomous multiple-cycle amplification strategy has been used for signal-on electrochemical sensing of pathogenic bacteria. In addition, the proposed sensor can also be used for highly sensitive detection of other targets by changing the aptamer sequence, such as nucleic acids, proteins and small molecules. Therefore, the proposed signal-on electrochemical sensing strategy might provide a simple and practical new platform for detection of pathogenic bacteria and related biological analysis, food safety inspection and environmental monitoring.

Selective and sensitive Escherichia coli detection based on a T4 bacteriophage-immobilized multimode microfiber

Escherichia coli bacteria have been found to be responsible for various health outbreaks caused by contaminated food and water. Accurate and rapid test of E. coli is thus crucial for protecting the public health. A fast-response, label-free bacteriophage-based detection of E. coli using multimode microfiber probe is proposed and demonstrated in this article. Due to the abrupt taper and subwavelength diameter, different modes are excited and guided in the microfiber as evanescent field that can interact with surrounding E. coli directly. The change of E. coli concentration and corresponding binding of E. coli bacteria on microfiber surface will lead to the shift of optical spectrum, which can be exploited for the application of biosensing. The proposed method is capable of reliable detection of E. coli concentration as low as 10³ cfu/mL within the range of 10³ to 10⁷  cfu/mL. Owing to the advantages of high sensitivity and fast response, the microfiber probe has great potential application in the fields of environment monitoring and food safety.

Corn-Based Distillers' Grains in Diets for Feedlot Cattle Are Associated with the Burden of Escherichia coli O157 in Feces

Inclusion of distillers' grains (DGs) has been associated with increased prevalence of Escherichia coli O157:H7 in cattle housed in research settings. Our objective was to quantify the relationship between inclusion of DGs in commercial feedlot rations and the burden of E. coli O157. A convenience sample of 10 feedlots was enrolled based on DG use in finishing diets; 1 cohort included 5 feedlots in which DGs were greater than 15% of the dietary dry matter and the other cohort consisted of 5 feedlots at a concentration less than 8%. Sampling occurred at each feedlot on four occasions at ∼6-week intervals. At each feedlot visit, 4 pens of cattle within 3 weeks of slaughter were selected and 24 freshly voided fecal pats were sampled. Ten-gram samples were enriched in 90 mL of modified tryptic soy broth with novobiocin (20 mg/L) for 14 h at 42°C. Enrichments were subjected to immunomagnetic separation, plating onto chromogenic agar with novobiocin (5 mg/L) and potassium tellurite (2.5 mg/L), incubation for 18 h at 37°C, and latex agglutination of morphologically typical colonies. E. coli O157 was recovered from 16.7% of 3840 samples. Adjusted prevalence was 14.3% after controlling for within-feedlot and within-pen clustering. Prevalence during each sampling period was 19.9% (round 1), 21.0% (round 2), 14.1% (round 3), and 11.7% (round 4). Prevalence varied between cohorts, but this difference varied over time (p = 0.06). Among those with greater than 15% of the diet as DGs, prevalence was greater than those with less than 8% inclusion for all rounds of sampling (p < 0.01). Averaged across time, prevalence was 23.9% and 9.4% for those with greater than 15% and those with less than 8% of DGs, respectively. While observational, these data provide real-world support of reports of increased E. coli O157:H7 burden associated with DG use in cattle diets.

Culture-Based Quantification with Molecular Characterization of Non-O157 and O157 Enterohemorrhagic Escherichia coli Isolates from Rectoanal Mucosal Swabs of Feedlot Cattle

Enterohemorrhagic Escherichia coli (EHEC) strains are foodborne pathogens carried in the intestinal tracts of ruminants and shed in the feces. High concentrations (≥10⁴ colony-forming units [CFU]/g) of EHEC in cattle feces are associated with contamination of hides, and subsequently, carcasses and beef. Several studies using agar media have quantified O157 but few have quantified non-O157 EHEC in samples from cattle. Thus, the objective of this study was to determine the concentration of O157 and non-O157 EHEC in cattle, and to characterize the associated EHEC isolates for their virulence potential. Two hundred feedlot steers were sampled by rectoanal mucosal swab (RAMS) every 35 days over four sampling periods, and a spiral plating method using modified Possé differential agar was used to quantify EHEC organisms in these samples. Bacterial colonies from agar plates were tested by multiplex PCR for Shiga toxin and intimin genes (stx and eae, respectively), and confirmed EHEC isolates (i.e., positive for both stx and eae) were serotyped and characterized for virulence genes using a microarray. Organisms detected in this study included O26, O101, O103, O109, O121, O145, O157, and O177 EHEC, with all except O121 quantifiable and measuring within a range from 9.0 × 10² to 3.0 × 10⁵ CFU/g of RAMS sample. Organisms of the same EHEC serogroup were not detected in quantifiable concentrations from a single animal more than once. EHEC organisms most commonly detected at quantifiable levels were O26, O157, and O177. Interestingly, O26 EHEC isolates tested negative for stx₁ but positive for stx_2a. High concentrations of EHEC were detected in 11 (5.5%) of the steers at least once over the sampling period. These results indicate that in addition to O157, non-O157 EHEC are transiently present in high concentrations in the rectoanal mucosal region of cattle.

Rapid Detection and Classification of Salmonella enterica Shedding in Feedlot Cattle Utilizing the Roka Bioscience Atlas Salmonella Detection Assay for the Analysis of Rectoanal Mucosal Swabs

With an increasing focus on preharvest food safety, rapid methods are required for the detection and quantification of foodborne pathogens such as Salmonella enterica in beef cattle. We validated the Atlas Salmonella Detection Assay (SEN), a nucleic acid amplification technology that targets Salmonella rRNA, for the qualitative detection of S. enterica with sample enrichment using immunomagnetic separation as a reference test, and we further evaluated its accuracy to predict pathogen load using SEN signal-to-cutoff (SCO) values from unenriched samples to classify animals as high or nonhigh shedders. Rectoanal mucosal swabs (RAMS) were collected from 238 beef cattle from five cohorts located in the Midwest or southern High Plains of the United States between July 2015 and April 2016. Unenriched RAMS samples were used for the enumeration and SEN SCO analyses. Enriched samples were tested using SEN and immunomagnetic separation methods for the detection of Salmonella. The SEN method was 100% sensitive and specific for the detection of Salmonella from the enriched RAMS samples. A SEN SCO value of 8, with a sensitivity of 93.5% and specificity of 94.3%, was found to be an optimum cutoff value for classifying animals as high or nonhigh shedders from the unenriched RAMS samples. The SEN assay is a rapid and reliable method for the qualitative detection and categorization of the shedding load of Salmonella from RAMS in feedlot cattle.

The impact of the bovine faecal microbiome on Escherichia coli O157:H7 prevalence and enumeration in naturally infected cattle

AIMS

The objective of this study was to determine if the faecal microbiome has an association with Escherichia coli O157:H7 prevalence and enumeration.

METHODS AND RESULTS

Pyrosequencing analysis of faecal microbiome was performed from feedlot cattle fed one of three diets: (i) 94 heifers fed low concentrate (LC) diet, (ii) 142 steers fed moderate concentrate (MC) diet, and (iii) 132 steers fed high concentrate (HC) diet. A total of 322 585 OTUs were calculated from 2,411,122 high-quality sequences obtained from 368 faecal samples. In the LC diet group, OTUs assigned to the orders Clostridiales and RF39 (placed within the class Mollicutes) were positively correlated with both E. coli O157:H7 prevalence and enumeration. In the MC diet group, OTUs assigned to Prevotella copri were positively correlated with both E. coli O157:H7 prevalence and enumeration, whereas OTUs assigned to Prevotella stercorea were negatively correlated with both E. coli O157:H7 prevalence and enumeration. In both the MC diet group and the HC diet group, OTUs assigned to taxa placed within Clostridiales were both positively and negatively correlated with both E. coli O157:H7 prevalence and enumeration. However, all correlations were weak. In both the MC diet group and the HC diet group, stepwise linear regression through backward elimination analyses indicated that these OTUs were significantly correlated (P < 0·001) with prevalence or enumeration, explaining as much as 50% of variability in E. coli O157:H7 prevalence or enumeration.

CONCLUSIONS

Individual colonic bacterial species have little impact on E. coli O157:H7 shedding but collectively groups of bacteria were strongly associated with pathogen shedding.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial groups in the bovine colon may impact faecal shedding of the zoonotic pathogen E. coli O157:H7, and manipulation of the intestinal microbiota to alter these bacteria may reduce shedding of this pathogen and foodborne illnesses.

Spiral Plating Method To Quantify the Six Major Non-O157 Escherichia coli Serogroups in Cattle Feces

Cattle are a major reservoir of the six major Shiga toxin-producing non-O157 Escherichia coli (STEC) serogroups (O26, O45, O103, O111, O121, and O145) responsible for foodborne illnesses in humans. Besides prevalence in feces, the concentrations of STEC in cattle feces play a major role in their transmission dynamics. A subset of cattle, referred to as super shedders, shed E. coli O157 at high concentrations (≥4 log CFU/g of feces). It is not known whether a similar pattern of fecal shedding exists for non-O157. Our objectives were to initially validate the spiral plating method to quantify the six non-O157 E. coli serogroups with pure cultures and culture-spiked fecal samples and then determine the applicability of the method and compare it with multiplex quantitative PCR (mqPCR) assays for the quantification of the six non-O157 E. coli serogroups in cattle fecal samples collected from commercial feedlots. Quantification limits of the spiral plating method were 3 log, 3 to 4 log, and 3 to 5 log CFU/mL or CFU/g for individual cultures, pooled pure cultures, and cattle fecal samples spiked with pooled pure cultures, respectively. Of the 1,152 cattle fecal samples tested from eight commercial feedlots, 122 (10.6%) and 320 (27.8%) harbored concentrations ≥4 log CFU/g of one or more of the six serogroups of non-O157 by spiral plating and mqPCR methods, respectively. A majority of quantifiable samples, detected by either spiral plating (135 of 137, 98.5%) or mqPCR (239 of 320, 74.7%), were shedding only one serogroup. Only one of the quantifiable samples was positive for a serogroup carrying Shiga toxin (stx1) and intimin (eae) genes; 38 samples were positive for serogroups carrying the intimin gene. In conclusion, the spiral plating method can be used to quantify non-O157 serogroups in cattle feces, and our study identified a subset of cattle that was super shedders of non-O157 E. coli. The method has the advantage of quantifying non-O157 STEC, unlike mqPCR that quantifies serogroups only.

Prevalence of Escherichia coli O157:H7 From House Flies (Diptera: Muscidae) and Dairy Samples in North Central Florida1

La detección de Escherichia coli O157:H7 en las lecherías es importante para mejorar la seguridad de los productos lácteos, y se ha llevado a cabo principalmente mediante el aislamiento de las bacterias a partir de las muestras de estiércol. Sin embargo, los componentes biliares presentes en el estiércol complica la identificación genética utilizando la técnica del PCR, y el aislamiento microbiológico se dificulta por la presencia de bacterias competidoras que comparten características microbiológicas similares. El aislamiento de E. coli O157:H7 a partir de la mosca doméstica evita las dificultades asociadas con el estiércol del ganado. El aislamiento de patógenos a partir de las moscas domésticas proporciona información adicional sobre el potencial impacto epidemiológico de la dispersión de la mosca doméstica en la distribución de patógenos, ya que las moscas domésticas se dispersan desde las lecherías donde la E. coli O157:H7 existe en forma endémica en el ganado. En este estudio, se encontró que las moscas domésticas son 2,6 veces más sensibles para la detección de E. coli O157:H7 en las lecherías. Las moscas son más fáciles de capturar y manejar que el estiércol, y deberían ser utilizadas en cualquier ensayo para detectar E. coli O157:H7 en las lecherías y otros establecimientos.

Characterization of Enterohemorrhagic Escherichia coli on Veal Hides and Carcasses

Enterohemorrhagic Escherichia coli (EHEC) are Shiga toxin-producing E. coli associated with the most severe forms of foodborne illnesses. The U.S. Department of Agriculture, Food Safety and Inspection Service has identified a higher percentage of non-O157 EHEC compared with E. coli O157:H7-positive samples collected from veal trimmings than from products produced from other cattle slaughter classes. Therefore samples were collected from hides and preevisceration carcasses at five veal processors to assess E. coli O157:H7 and non-O157 EHEC contamination during bob veal and formula-fed veal dressing procedures. E. coli O157:H7 prevalence was measured by culture isolation and found to be on 20.3% of hides and 6.7% of carcasses. In contrast, a non-O157 EHEC molecular screening assay identified 90.3% of hides and 68.2% of carcasses as positive. Only carcass samples were taken forward to culture confirmation and 38.7% yielded one or more non-O157 EHEC isolates. The recovery of an EHEC varied by plant and sample collection date; values ranged from 2.1 to 87.8% among plants and from 4.2 to 64.2% within the same plant. Three plants were resampled after changes were made to sanitary dressing procedures. Between the two collection times at the three plants, hide-to-carcass transfer of E. coli O157:H7 and non-O157 EHEC was significantly reduced. All adulterant EHEC serogroups (O26, O45, O103, O111, O121, and O145) were isolated from veal carcasses as well as four other potentially pathogenic serogroups (O5, O84, O118, and O177). Bob veal was found to have a greater culture prevalence of E. coli O157:H7 and greater positive molecular screens for non-O157 EHEC than formula-fed veal (P < 0.05), but the percentage of culture-confirmed non-O157 EHEC was not different (P > 0.05) between the two types of calves. EHEC-O26, -O111, and -O121 were found more often in bob veal (P < 0.05), whereas EHEC-O103 was found more often in formula-fed veal (P < 0.05).

Effects of plant extracts and essential oils as feed supplements on quality and microbial traits of rabbit meat

The effects of dietary supplementation of onion, cranberry,  strawberry and essentials oils on meat quality were analysed. Five groups of 48 Grimaud female weaned rabbits received the supplemented or the control ration; the experimental unit was a cage of 6 rabbits. Each experimental diet contained 10 ppm of added active ingredients.  Rabbits were fed with the experimental diets for 4 wk before determining slaughter and carcass traits and determining the pH at 1 and 24 h post mortem (pHu) of the <em>Longissimus dorsi</em> (LD) and the <em>Biceps femoris</em> (BF) muscle, left and right, respectively. Cooking loss, drip loss and L*, a* and b* color parameters were obtained of the right<em> </em>LD and for ground meat and antioxidant status (TBARS, DNPH, Folin Ciocalteu). Only the pHu of the LD muscle for the strawberry supplemented group was significantly lower when compared to the control group (P=0.04). However, we note that for the pH of the LD, the average was less than 6 for the meat of animals who received a diet enriched in polyphenols, compared to the control group. Plant extract supplementation did not influence meat quality traits, growth performance or oxidative stability. But under aerobic and anaerobic conditions, our results indicate that diet supplementation with extracts rich in polyphenols, especially with essential oils, had a small bot sporadic positive effect in reducing bacterial microflora compared to the control group (P&lt;0.05). In conclusion, plant extracts and essential oils can be used in a rabbit diet without adverse effects on performance and meat quality traits. This effect could be optimized by investigating higher doses.

Diagnostic Accuracy of Rectoanal Mucosal Swab of Feedlot Cattle for Detection and Enumeration of Salmonella enterica

Cattle are noted carriers of the foodborne pathogen Salmonella enterica. The perceived need to decrease the potential human health risk posed by excretion of this pathogen has resulted in numerous studies examining the factors that influence Salmonella shedding in cattle. Fecal grab (FG) samples have been the predominant method used to identify cattle colonized or infected with Salmonella; however, FG sampling can be impractical in certain situations, and rectoanal mucosal swabs (RAMS) are a more convenient sample type to collect. Despite a lack of studies comparing FG and RAMS for the detection and enumeration of Salmonella fecal shedding, RAMS is perceived as less sensitive because a smaller amount of feces is cultured. In a cross-sectional study to address these concerns, paired RAMS and FG samples were collected from 403 adult feedlot cattle approximately 90 days prior to harvest. Samples were processed for Salmonella enumeration (direct plating) and detection (enrichment and immunomagnetic separation). In all, 89.6% of RAMS and 98.8% of FG samples were positive for Salmonella, and concordant prevalence outcomes were observed for 90.8% of samples. Mean enumeration values were 3.01 and 3.12 log CFU/ml for RAMS and FG, respectively. The sensitivity and specificity of RAMS were 91% (95% confidence interval [CI]: 87.5 to 93%) and 100% (95% CI: 48 to 100%), respectively, for Salmonella detection. Furthermore, RAMS Salmonella enumeration was substantially concordant (ρc = 0.89; 95% CI: 0.86 to 0.91) with FG values. We conclude that RAMS are a reliable alternative to FG for assessing cattle Salmonella fecal shedding status, especially for cattle shedding high levels of Salmonella.

Recombinant plasmid-based quantitative Real-Time PCR analysis of Salmonella enterica serotypes and its application to milk samples

The aim of the current study was to develop, a new, rapid, sensitive and quantitative Salmonella detection method using a Real-Time PCR technique based on an inexpensive, easy to produce, convenient and standardized recombinant plasmid positive control. To achieve this, two recombinant plasmids were constructed as reference molecules by cloning the two most commonly used Salmonella-specific target gene regions, invA and ttrRSBC. The more rapid detection enabled by the developed method (21 h) compared to the traditional culture method (90 h) allows the quantitative evaluation of Salmonella (quantification limits of 10(1)CFU/ml and 10(0)CFU/ml for the invA target and the ttrRSBC target, respectively), as illustrated using milk samples. Three advantages illustrated by the current study demonstrate the potential of the newly developed method to be used in routine analyses in the medical, veterinary, food and water/environmental sectors: I--The method provides fast analyses including the simultaneous detection and determination of correct pathogen counts; II--The method is applicable to challenging samples, such as milk; III--The method's positive controls (recombinant plasmids) are reproducible in large quantities without the need to construct new calibration curves.

Enhanced detection sensitivity of Escherichia coli O157:H7 using surface-modified gold nanorods

Escherichia coli O157:H7 (O157) is a Gram negative and highly virulent bacteria found in food and water sources, and is a leading cause of chronic diseases worldwide. Diagnosis and prevention from the infection require simple and rapid analysis methods for the detection of pathogens, including O157. Endogenous membrane peroxidase, an enzyme present on the surface of O157, was used for the colorimetric detection of bacteria by catalytic oxidation of the peroxidase substrate. In this study, we have analyzed the impact of the synthesized bare gold nanorods (AuNRs) and silica-coated AuNRs on the growth of E. coli O157. Along with the membrane peroxidase activity of O157, other bacteria strains were analyzed. Different concentrations of nanorods were used to analyze the growth responses, enzymatic changes, and morphological alterations of bacteria by measuring optical density, 3,3',5,5'-tetramethylbenzidine assay, flow cytometry analysis, and microscopy studies. The results revealed that O157 showed higher and continuous membrane peroxidase activity than other bacteria. Furthermore, O157 treated with bare AuNRs showed a decreased growth rate in comparison with the bacteria with surface modified AuNRs. Interestingly, silica-coated AuNRs favored the growth of bacteria and also increased membrane peroxidase activity. This result can be particularly important for the enzymatic analysis of surface treated AuNRs in various microbiological applicants.

Prevalence of Antimicrobial Resistant and Virulent Salmonella spp. in Treated Effluent and Receiving Aquatic Milieu of Wastewater Treatment Plants in Durban, South Africa

In this study, we evaluated the impact of treated wastewater effluent from two wastewater treatment plants on the physicochemical parameters and Salmonella spp. load of receiving rivers. Presumptive Salmonella spp. were obtained at all sampled points including the discharge points, with counts ranging from 0 to 4.14 log cfu/mL at both plants. Turbidity, chemical and biological oxygen demand were found to be high and mostly above the required limit for treated wastewater discharge. However, recorded nitrate and phosphate values were very low. Of the 200 confirmed Salmonella spp. isolates recovered from the treated effluent and receiving surface waters, 93% harbored the spiC gene, 84% harbored the misL gene, and 87.5% harbored the orfL gene while 87% harbored the pipD gene. The antibiotic resistance profile revealed that the isolates were resistant to sulfamethoxazole, nalidixic acid and streptomycin, but susceptible to quinolones and third generation β-lactams. These results indicate that in South Africa treated effluents are still a major source of contamination of rivers with pathogens such as Salmonella. Appropriate steps by the regulatory authorities and workers at the treatment plants are needed to enforce stipulated guidelines in order to prevent pollution of surface water resources due to the discharge of poorly treated effluents.

A Four-Plex Real-Time PCR Assay, Based on rfbE, stx1, stx2, and eae Genes, for the Detection and Quantification of Shiga Toxin-Producing Escherichia coli O157 in Cattle Feces

Several real-time polymerase chain reaction (PCR) assays have been developed to detect and quantify Shiga toxin-producing Escherichia coli (STEC) O157:H7, but none have targeted the O-antigen specific gene (rfbEO157) in combination with the three major virulence genes, stx1, stx2, and eae. Our objectives were to develop and validate a four-plex, quantitative PCR (mqPCR) assay targeting rfbE(O157), stx1, stx2, and eae for the detection and quantification of STEC O157 in cattle feces, and compare the applicability of the assay to detect STEC O157 to a culture method and conventional PCR (cPCR) targeting the same four genes. Specificity of the mqPCR assay to differentially detect the four genes was confirmed with strains of O157 and non-O157 STEC with different profiles of target genes. In cattle feces spiked with pure cultures, detection limits were 2.8×10(4) and 2.8×10(0) colony-forming units/g before and after enrichment, respectively. Detection of STEC O157 in feedlot cattle fecal samples (n=278) was compared between mqPCR, cPCR, and a culture method. The mqPCR detected 48.9% (136/278) of samples as positive for E. coli O157. Of the 100 samples that were randomly picked from 136 mqPCR-positive samples, 35 and 48 tested positive by cPCR and culture method, respectively. Of the 100 samples randomly chosen from 142 mqPCR-negative samples, all were negative by cPCR, but 21 samples tested positive by the culture method. McNemar's chi-square tests indicated significant disagreement between the proportions of positive samples detected by the three methods. In conclusion, the mqPCR assay that targets four genes is a novel and more sensitive method than the cPCR or culture method to detect STEC O157 in cattle feces. However, the use of real-time PCR as a screening method to identify positive samples and then subjecting only positive samples to a culture method may underestimate the presence of STEC O157 in fecal samples.

Antimicrobial-Resistant Bacterial Populations and Antimicrobial Resistance Genes Obtained from Environments Impacted by Livestock and Municipal Waste

This study compared the populations of antimicrobial-resistant bacteria and the repertoire of antimicrobial resistance genes in four environments: effluent of three municipal wastewater treatment facilities, three cattle feedlot runoff catchment ponds, three swine waste lagoons, and two "low impact" environments (an urban lake and a relict prairie). Multiple liquid and solid samples were collected from each environment. The prevalences and concentrations of antimicrobial-resistant (AMR) Gram-negative (Escherichia coli and Salmonella enterica) and Gram-positive (enterococci) bacteria were determined from individual samples (n = 174). The prevalences of 84 antimicrobial resistance genes in metagenomic DNA isolated from samples pooled (n = 44) by collection date, location, and sample type were determined. The prevalences and concentrations of AMR E. coli and Salmonella were similar among the livestock and municipal sample sources. The levels of erythromycin-resistant enterococci were significantly higher in liquid samples from cattle catchment ponds and swine waste lagoons than in liquid samples from municipal wastewater treatment facilities, but solid samples from these environments did not differ significantly. Similarly, trimethoprim/sulfamethoxazole-resistant E. coli concentrations were significantly higher in swine liquid than in municipal liquid samples, but there was no difference in solid samples. Multivariate analysis of the distribution of antimicrobial resistance genes using principal coordinate analysis showed distinct clustering of samples with livestock (cattle and swine), low impact environment and municipal samples forming three separate clusters. The numbers of class A beta-lactamase, class C beta-lactamase, and fluoroquinolone resistance genes detected were significantly higher (P < 0.05) in municipal samples than in cattle runoff or swine lagoon samples. In conclusion, we report that AMR is a very widespread phenomenon and that similar prevalences and concentrations of antimicrobial-resistant bacteria and antimicrobial resistance genes exist in cattle, human, and swine waste streams, but a higher diversity of antimicrobial resistance genes are present in treated human waste discharged from municipal wastewater treatment plants than in livestock environments.

Prevalence and concentration of Escherichia coli O157 in different seasons and cattle types processed in North America: A systematic review and meta-analysis of published research

Systematic review (SR) and meta-analyses (MA) methodologies were used to identify, critically evaluate and synthesize prevalence and concentration estimates for Escherichia coli O157 contamination along the beef production chain, and to illustrate differences based on cattle types and seasonality in North America from the scientific peer-reviewed literature. Four electronic databases were searched to identify relevant articles. Two independent reviewers performed all SR steps. Random effects MA models were used to estimate the pooled prevalence and concentration of E. coli O157 in feces, hides and carcasses of cattle processed in North America, including their seasonal estimates. The potential sources of between studies heterogeneity were identified using meta-regression and sub-group analysis. Results indicated differences in the fecal prevalence of E. coli O157 among cattle types: 10.68% (95% CI: 9.17-12.28%) in fed beef, 4.65% (95% CI: 3.37-6.10%) in adult beef, and 1.79% (95% CI: 1.20-2.48%) in adult dairy. Fed beef fecal prevalence was 10.65% (95% CI: 8.93-12.49%) during summer and 9.17% (95% CI: 5.24-13.98%) during the winter months. For adult beef, the fecal prevalence was 7.86% (95% CI: 5.43-10.66%) during summer, and 4.21% (95% CI: 1.95-7.13%) during winter. Among adult dairy, the fecal prevalence was 2.27% (95% CI: 1.5-3.18%) during summer, and 0.36% (95% CI: 0.09-0.74%) during winter. There was a significantly higher percentage of hides with E. coli O157 concentration ≥ 40 CFU/100 cm(2) on hides of fed beef sampled at the processing plant (23.81%; 95% CI: 14.79-34.15%) compared to those sampled at the feedlot (1.74%; 95% CI: 0.53-3.44%). Prevalence of E. coli O157 on carcass surfaces differed by season only at the post-evisceration stage, but decreased considerably through the subsequent processing stages. Country, study setting, detection method, hide swab area, and study design were identified as significant sources of heterogeneity among studies reporting prevalence of E. coli O157 along the beef production chain. The pooled prevalence and concentration estimates from this study provide a sound and reliable microbiological basis for risk assessment modeling of E. coli O157 and other pathogens in the food chain.

Quantitative distribution of Salmonella spp. and Escherichia coli on beef carcasses and raw beef at retail establishments

Salmonella is a foodborne pathogen that commonly inhabits the gastrointestinal tract of a healthy feedlot cattle and can be transferred to the carcass surface during hide removal and evisceration procedures. Numerous investigations on Salmonella prevalence throughout different stages of the beef chain have been conducted. In contrast, limited studies are available on quantitative determinations of Salmonella at different steps in raw meat production. Quantitative data, particularly for pathogenic bacteria such as Salmonella are important for quantitative risk assessment. Salmonella spp. and Escherichia coli populations were enumerated on beef carcass samples collected at abattoirs and also in beef chunks and ground beef samples collected from butcher's shops at retail in Jalisco State, Mexico. Sponge samples from beef carcass sides (n=142) were collected immediately after final water wash and before chilling at three non-federally inspected abattoirs following USDA-FSIS sampling protocols. Beef chunks (n=84) and ground beef (n=65) samples were obtained from 86 butcher's shops. Salmonella enumeration was conducted by the Most Probable Number method and E. coli counts were determined using Petrifilm plates. Salmonella was isolated from 18% of beef carcasses, 39% of beef chunks and 71% of ground beef samples. Salmonella mean counts were 1.3±0.9 Log MPN/300 cm(2) on beef carcasses, 1.9±0.9 and 2.3±1.1 Log MPN/25 g in beef chunks and ground beef samples, respectively. Twenty-six Salmonella serotypes and 11 serogroups were identified among 432 isolates recovered. Salmonella typhimurium (14%), Salmonella sinstorf (12%) and S. Group E1 monophasic (10%) were the most frequent. Escherichia coli was present on 97, 84 and 100% of beef carcasses, beef chunks and ground beef samples, respectively. Escherichia coli mean counts were 3.2±0.7 Log CFU/300 cm(2), 3.9±1.1 and 4.5±1.2 Log CFU/25 g on beef carcasses, beef chunks and ground beef, respectively. Salmonella prevalence and mean counts found in raw beef were higher than previously reported in studies from other countries. The data collected in this study show a trend in the prevalence of Salmonella to be higher as meat processing is extended at retail. This, together with the diversity of serotypes found, indicates that raw meat is exposed to multiple contamination sources during slaughter and retail processing and highlights the necessity to implement Sanitation Standard Operating Procedures for those establishments. Finally, this study provides quantitative information for future risk assessments associated with the risk of human salmonellosis.

Highly sensitive bacteria quantification using immunomagnetic separation and electrochemical detection of guanine-labeled secondary beads

In this paper, we report the ultra-sensitive indirect electrochemical detection of E. coli O157:H7 using antibody functionalized primary (magnetic) beads for capture and polyguanine (polyG) oligonucleotide functionalized secondary (polystyrene) beads as an electrochemical tag. Vacuum filtration in combination with E. coli O157:H7 specific antibody modified magnetic beads were used for extraction of E. coli O157:H7 from 100 mL samples. The magnetic bead conjugated E. coli O157:H7 cells were then attached to polyG functionalized secondary beads to form a sandwich complex (magnetic bead/E. coli secondary bead). While the use of magnetic beads for immuno-based capture is well characterized, the use of oligonucleotide functionalized secondary beads helps combine amplification and potential multiplexing into the system. The antibody functionalized secondary beads can be easily modified with a different antibody to detect other pathogens from the same sample and enable potential multiplexing. The polyGs on the secondary beads enable signal amplification up to 10⁸ guanine tags per secondary bead (7.5 x 10⁶ biotin-FITC per secondary bead, 20 guanines per oligonucleotide) bound to the target (E. coli). A single-stranded DNA probe functionalized reduced graphene oxide modified glassy carbon electrode was used to bind the polyGs on the secondary beads. Fluorescent imaging was performed to confirm the hybridization of the complex to the electrode surface. Differential pulse voltammetry (DPV) was used to quantify the amount of polyG involved in the hybridization event with tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)3(2+)) as the mediator. The amount of polyG signal can be correlated to the amount of E. coli O157:H7 in the sample. The method was able to detect concentrations of E. coli O157:H7 down to 3 CFU/100 mL, which is 67 times lower than the most sensitive technique reported in literature. The signal to noise ratio for this work was 3. We also demonstrate the use of the protocol for detection of E. coli O157:H7 seeded in waste water effluent samples.

Comparative analysis of super-shedder strains of Escherichia coli O157:H7 reveals distinctive genomic features and a strongly aggregative adherent phenotype on bovine rectoanal junction squamous epithelial cells

Shiga toxin-producing Escherichia coli O157:H7 (O157) are significant foodborne pathogens and pose a serious threat to public health worldwide. The major reservoirs of O157 are asymptomatic cattle which harbor the organism in the terminal recto-anal junction (RAJ). Some colonized animals, referred to as “super-shedders” (SS), are known to shed O157 in exceptionally large numbers (>104 CFU/g of feces). Recent studies suggest that SS cattle play a major role in the prevalence and transmission of O157, but little is known about the molecular mechanisms associated with super-shedding. Whole genome sequence analysis of an SS O157 strain (SS17) revealed a genome of 5,523,849 bp chromosome with 5,430 open reading frames and two plasmids, pO157 and pSS17, of 94,645 bp and 37,446 bp, respectively. Comparative analyses showed that SS17 is clustered with spinach-associated O157 outbreak strains, and belongs to the lineage I/II, clade 8, D group, and genotype 1, a subgroup of O157 with predicted hyper-virulence. A large number of non-synonymous SNPs and other polymorphisms were identified in SS17 as compared with other O157 strains (EC4115, EDL933, Sakai, TW14359), including in key adherence- and virulence-related loci. Phenotypic analyses revealed a distinctive and strongly adherent aggregative phenotype of SS17 on bovine RAJ stratified squamous epithelial (RSE) cells that was conserved amongst other SS isolates. Molecular genetic and functional analyses of defined mutants of SS17 suggested that the strongly adherent aggregative phenotype amongst SS isolates is LEE-independent, and likely results from a novel mechanism. Taken together, our study provides a rational framework for investigating the molecular mechanisms associated with SS, and strong evidence that SS O157 isolates have distinctive features and use a LEE-independent mechanism for hyper-adherence to bovine rectal epithelial cells.

Shiga toxin-producing Escherichia coli O157, O26 and O111 in cattle faeces and hides in Italy

INTRODUCTION

Ruminants are regarded as the natural reservoir for Shiga toxin-producing Escherichia coli (STEC), especially of serogroup O157.

MATERIALS AND METHODS

During 2011 and 2012, 320 samples (160 faecal samples from the rectum and 160 hide samples from the brisket area) were collected from 160 cattle at slaughter in Northern Italy during warm months (May to October). Cattle were reared in different farms and their age at slaughter ranged between nine months and 15 years, most of them being culled cattle (median age: six years; average age: 4.6 years). Samples were tested by immunomagnetic-separation technique for E coli O157 and O26 and by a screening PCR for stx genes followed by cultural detection of STEC. The virulence genes stx1, stx2, eae, and e-hlyA were detected and among stx2-positive isolates the presence of the stx2a and stx2c variants was investigated.

RESULTS

Twenty-one of 160 cattle (13.1 per cent; 95 per cent CI 8.3 to 19.4 per cent) were found to be faecal carriers of STEC. STEC O157 was found in 10 (6.3 per cent) samples, STEC O26 in six (3.8 per cent) and STEC O111 in one (0.6 per cent). Four isolates (2.5 per cent) were O not determined (OND). Six out of 160 (3.8 per cent; 95 per cent CI 1.4 to 8.0 per cent) hide samples were positive for STEC; four hides (2.5 per cent) were contaminated by STEC O157 and two (1.3 per cent) by STEC O26. In three cattle (1.9 per cent) STEC from both faeces and hides were detected. Among STEC O157, 87.5 per cent of them carried the stx2c gene and 12.5 per cent carried both stx1 and stx2c genes. No O157 isolate harboured stx2a variant. STEC O26 and O111 carried the stx1 gene only. One OND strain carried both the stx2a and stx2c genes.

CONCLUSIONS

This study shows that STEC O157 from cattle can harbour the stx2c variant, which is associated with haemolytic uraemic syndrome in humans, and that cattle hides may be a source of human pathogenic STEC O157 and O26 in the slaughterhouse environment.

Occurrence of Antimicrobial-Resistant Escherichia coli and Salmonella enterica in the Beef Cattle Production and Processing Continuum

Specific concerns have been raised that third-generation cephalosporin-resistant (3GC(r)) Escherichia coli, trimethoprim-sulfamethoxazole-resistant (COT(r)) E. coli, 3GC(r) Salmonella enterica, and nalidixic acid-resistant (NAL(r)) S. enterica may be present in cattle production environments, persist through beef processing, and contaminate final products. The prevalences and concentrations of these organisms were determined in feces and hides (at feedlot and processing plant), pre-evisceration carcasses, and final carcasses from three lots of fed cattle (n = 184). The prevalences and concentrations were further determined for strip loins from 103 of the carcasses. 3GC(r) Salmonella was detected on 7.6% of hides during processing and was not detected on the final carcasses or strip loins. NAL(r) S. enterica was detected on only one hide. 3GC(r) E. coli and COT(r) E. coli were detected on 100.0% of hides during processing. Concentrations of 3GC(r) E. coli and COT(r) E. coli on hides were correlated with pre-evisceration carcass contamination. 3GC(r) E. coli and COT(r) E. coli were each detected on only 0.5% of final carcasses and were not detected on strip loins. Five hundred and 42 isolates were screened for extraintestinal pathogenic E. coli (ExPEC) virulence-associated markers. Only two COT(r) E. coli isolates from hides were ExPEC, indicating that fed cattle products are not a significant source of ExPEC causing human urinary tract infections. The very low prevalences of these organisms on final carcasses and their absence on strip loins demonstrate that current sanitary dressing procedures and processing interventions are effective against antimicrobial-resistant bacteria.

Selected lactic acid-producing bacterial isolates with the capacity to reduce Salmonella translocation and virulence gene expression in chickens

BACKGROUND

Probiotics have been used to control Salmonella colonization/infection in chickens. Yet the mechanisms of probiotic effects are not fully understood. This study has characterized our previously-selected lactic acid-producing bacterial (LAB) isolates for controlling Salmonella infection in chickens, particularly the mechanism underlying the control.

METHODOLOGY/PRINCIPAL FINDINGS

In vitro studies were conducted to characterize 14 LAB isolates for their tolerance to low pH (2.0) and high bile salt (0.3-1.5%) and susceptibility to antibiotics. Three chicken infection trials were subsequently carried out to evaluate four of the isolates for reducing the burden of Salmonella enterica serovar Typhimurium in the broiler cecum. Chicks were gavaged with LAB cultures (10(6-7) CFU/chick) or phosphate-buffered saline (PBS) at 1 day of age followed by Salmonella challenge (10(4) CFU/chick) next day. Samples of cecal digesta, spleen, and liver were examined for Salmonella counts on days 1, 3, or 4 post-challenge. Salmonella in the cecum from Trial 3 was also assessed for the expression of ten virulence genes located in its pathogenicity island-1 (SPI-1). These genes play a role in Salmonella intestinal invasion. Tested LAB isolates (individuals or mixed cultures) were unable to lower Salmonella burden in the chicken cecum, but able to attenuate Salmonella infection in the spleen and liver. The LAB treatments also reduced almost all SPI-1 virulence gene expression (9 out of 10) in the chicken cecum, particularly at the low dose. In vitro treatment with the extracellular culture fluid from a LAB culture also down-regulated most SPI-1 virulence gene expression.

CONCLUSIONS/SIGNIFICANCE

The possible correlation between attenuation of Salmonella infection in the chicken spleen and liver and reduction of Salmonella SPI-1 virulence gene expression in the chicken cecum by LAB isolates is a new observation. Suppression of Salmonella virulence gene expression in vivo can be one of the strategies for controlling Salmonella infection in chickens.