Looking for new approaches for the use of serology in the context of control programmes against pig salmonellosis

Most swine Salmonella national control programmes in Europe have been based on the categorization of herds according to risk levels based on serological results. However, none of the non‐Scandinavian countries have reported of any significant success on Salmonella infection reduction in fattening pigs or the number of human cases attributable to pigs or pork. The limited accuracy of the tests used, the small number of animals sampled and the likely lack of herd representativeness of the samples used could be major factors affecting the suitability of these programmes. Focusing on minimizing Salmonella shedding at slaughter appears more important to prevent human infections than focusing on detection of seropositive pigs/herds at this stage. This study assessed whether performing on‐farm serology may help to predict shedding at slaughter. Between 2010 and 2016, pigs from six cohorts from a Salmonella‐positive herd were bled at 30, 60 and 90 days on fattening and before slaughter, and faecal samples collected at slaughter. Serology on days 60, 90 and before slaughter predicted somewhat shedding at slaughter with no significant differences among them. Pigs with higher OD% values at these point times would have higher risk of shedding when arriving to slaughter. The probability of shedding for a pig sampled on day 90 and showing an OD% value of 10 was 43%, and the risk increased up to 65% if the OD% was 40. Concluding, on‐farm serology may help to determine to some extent the risk of Salmonella shedding at slaughter from seropositive fattening units, which would allow for prompt on‐farm and slaughter interventions to reduce the likelihood of slaughter contamination with Salmonella.     

Epidemiological investigations into the sources of Salmonella contamination of pork

This study was conducted to elucidate which phases of the pork production chain contribute to the Salmonella contamination on pork after slaughter. During 7 sampling days, samples were collected of randomly selected slaughter pigs and of pigs from selected Salmonella-infected and Salmonella-free herds, trucks, lairages, and slaughterlines, in two slaughterhouses. Salmonella genotypes, present on pork after slaughter, were compared with Salmonella types, present on the farm, in the truck, in the lairage, on slaughter equipment, and in pigs from other herds. Results showed that the slaughterline was the most important source of Salmonella contamination of carcasses. The farm was the most important source of contamination of livers, tongues, rectal samples and mesenterial lymphnodes, for pigs originating from sero-positive herds. The lairage was the most important contamination source for pigs originating from sero-negative herds, for all samples, except carcasses. It is recommended to avoid each direct or indirect contact between different herds along the whole pork production chain, especially between Salmonella-infected and Salmonella-free herds.     

Effect of separate transport, lairage, and slaughter on occurrence of Salmonella typhimurium on slaughter carcasses

The study aimed to reduce cross-contamination between finishers from Salmonella-positive and Salmonella-negative herds during transport, lairage, and slaughter, thereby reducing the prevalence of Salmonella Typhimurium on slaughter carcasses. In Phase 1 of the study, pigs from Salmonella-negative herds were kept in lairage for 2-4 hours either in clean pens (intervention group) or pens contaminated with Salmonella-infected faeces (control group). All pigs were slaughtered on the same slaughterline, and carcass swabs 24 hours after slaughter revealed a low degree of cross-contamination in the pens: there was no difference in Salmonella-positive carcasses between intervention (1.7%) and control groups (0.8%). In Phase 2, control pigs from Salmonella-negative herds were mixed with pigs from Salmonella-positive herds during lairage for 2-4 hours, while the intervention group still consisted of pigs from Salmonella-negative herds. All pigs were slaughtered on the same line: first intervention, then control. Carcass swabs taken 24 hours after slaughter failed to show a reduction in Salmonella-positive carcasses in the intervention group (4.5%) compared with the originally Salmonella-negative pigs in the control group (3.6%). In pigs from Salmonella-positive herds the occurrence of Salmonella was substantially higher at 10.4%. When the results were corrected for 6 carcass samples found positive with S. Heidelberg on the same day, which was attributed to a transient hygiene failure, only 2.2% of the carcasses in the intervention group were Salmonella-positive. We conclude that even though cross-contamination occurs in the abattoir pens, its importance on the slaughter line may be greater. However, the final results of this study should be awaited to conclude whether separate slaughter of pigs from Salmonella-positive and Salmonella-negative herds should be recommended.     

Influence of On‐farm pig Salmonella status on Salmonella Shedding at Slaughter

The risk of Salmonella shedding among pigs at slaughter with regard to their previous on‐farm Salmonella status was assessed in a group of pigs from a farm from NE of Spain. A total of 202 pigs that had been serologically monitored monthly during the fattening period and from which mesenteric lymph nodes (MLN) and faecal (SFEC) samples were collected at slaughter for Salmonella isolation were included. A repeated‐measures anova was used to assess the relationship between mean OD% values during the fattening period and sampling time and bacteriology on MLN and SFEC. Pigs were also grouped into four groups, that is pigs seronegative during the fattening period and Salmonella negative in MLN (group A; n = 69); pigs seronegative during the fattening period but Salmonella positive in MLN (B; n = 36); pigs seropositive at least once and Salmonella positive in MLN (C; n = 50); and pigs seropositive at least once but Salmonella negative in (D; n = 47). Pigs shedding at slaughter seroconverted much earlier and showed much higher mean OD% values than non‐shedders pigs. The proportion of Salmonella shedders in groups A and D was high and similar (26.1% and 29.8%, respectively), but significantly lower than that for groups B and C. The odds of shedding Salmonella for groups B and C were 4.8 (95% CI = 1.5–15.5) and 20.9 (3.7–118) times higher, respectively, when compared to A. It was concluded that a large proportion of Salmonella seronegative pigs may shed Salmonella at slaughter, which would be likely associated to previous exposure with contaminated environments (i.e. transport and lairage). For pigs already infected at farm, the likelihood of shedding Salmonella was much higher and may depend on whether the bacterium has colonized the MLN or not. The odds of shedding Salmonella spp. were always much higher for pigs in which Salmonella was isolated from MLN.     

Increasing feed withdrawal and lairage times prior to slaughter decreases the gastrointestinal tract weight but favours the growth of cecal Enterobacteriaceae in pigs

The objective of this study was to evaluate the influence of different feed withdrawal and lairage times prior to slaughter on the gastrointestinal tract (GIT) weight and on the fermentation pattern and numbers of Enterobacteriaceae in the cecum of pigs. A total of 72 finishing pigs (6 pens, 12 animals each) were included in the study and were sent to the slaughterhouse on three consecutive days. On each day pigs from two pens were deprived of feed for either 2 or 12 h before leaving the farm. Pigs from each of the two pens were divided in sub-groups (4 pigs each) on the moment of loading onto the truck and followed the same distribution at the slaughterhouse. Once there, each sub-group corresponding to the same feed withdrawal time was held in different holding pens for 0, 5 or 10 h before slaughter. The weight of the gastro-intestinal tract (GIT) was determined and cecal content was collected to evaluate pH, short chain fatty acids (SCFA) and ammonia (NH₃) concentrations as well as lactobacilli and Enterobacteriaceae numbers. Total GIT weight decreased as feed withdrawal (P < 0.0001) and lairage time (P < 0.001) increased within a range between 6.69 and 4.59 kg. Cecal pH increased with feed withdrawal (P < 0.0001) and lairage time (P = 0.0001) (ranging from 5.79 to 6.79) in parallel to a decrease in the total SCFA concentration (P < 0.005) (from 211 to 100 mM). The percentages of acetic and propionic acid were not modified by the experimental treatments but significant decreases were registered in the percentage of butyric acid with the increased times of both withdrawal (P < 0.0001) and lairage (P < 0.005). The percentage of valeric and branched SCFA and also NH₃ concentration showed an increase with withdrawal (P < 0.005, P < 0.0001 and P < 0.005 respectively) and lairage (P < 0.005, P < 0.0001 and P < 0.001 respectively). Lactobacilli numbers decreased as lairage time increased (from 9.97 to 8.63 log 16S rRNA gene copies/g FM; P < 0.05) and Enterobacteriaceae numbers increased with both, feed withdrawal (P < 0.05) and lairage (P < 0.05) (ranging from 8.53 to 9.95 log 16S rRNA gene copies/g FM).The previous to slaughter increase in feed withdrawal and lairage times decreased the GIT weight but involved changes in the gut microbial ecosystem caused through changes in the fermentation pattern that lead to the increase of Enterobacteriaceae numbers. This increase could represent a higher risk of carcass contamination by the enteropathogens of this group such as Salmonella. However this potential risk should be further investigated.     

Impact of commercial pre-harvest processes on the prevalence of Salmonella enterica in cull sows

This study examined the impact of transport and lairage on Salmonella enterica prevalence in cull sows held under commercial conditions. Five sampling periods over 10 weeks yielded 181 selected culls. Fecal sample positives at the farm and collection point were 2% and 3%, respectively. After transport and lairage 41% of cull sows yielded S. enterica in one or more sampled tissues. A significant increase in cecal isolations was observed. The two S. enterica serotypes found at the production site and collection point were found at the abattoir, as were 13 other serotypes. Transport and lairage practices may contribute to an increased S. enterica contamination immediately prior to slaughter.     

Relationship between Salmonella infection,shedding and serology in fattening pigs in low–moderate prevalence areas

Salmonella is a major foodborne pathogen causing important zoonosis worldwide. Pigs asymptomatically infected in mesenteric lymph nodes (MLN) can be intermittent shedders of the pathogen through faeces, being considered a major source of human infections. European baseline studies of fattening pig salmonellosis are based on Salmonella detection in MLN. This work studies the relationship between Salmonella infection in MLN and intestinal content (IC) shedding at slaughter and the relationship between the presence of the pathogen and the serologic status at farm level. Mean Salmonella prevalence in the selected pigs (vertically integrated production system of Navarra, Spain) was 7.2% in MLN, 8.4% in IC and 9.6% in serum samples. In this low–moderate prevalence context, poor concordance was found between MLN infection and shedding at slaughter and between bacteriology and serology. In fact, most of shedders were found uninfected in MLN (83%) or carrying different Salmonella strains in MLN and in IC (90%). The most prevalent Salmonellae were Typhimurium resistant to ACSSuT ± Nx or ASSuT antibiotic families, more frequently found invading the MLN (70%) than in IC (33.9%). Multivariable analysis revealed that risk factors associated with the presence of Salmonella in MLN or in IC were different, mainly related either to good hygiene practices or to water and feed control, respectively. Overall, in this prevalence context, detection of Salmonella in MLN is an unreliable predictor of faecal shedding at abattoir, indicating that subclinical infections in fattening pigs MLN could have limited relevance in the IC shedding.     

Impact of the Salmonella status of market-age pigs and the pre-slaughter process on Salmonella caecal contamination at slaughter

The aim of this study was to evaluate the impact of the pre-slaughter process on Salmonella caecal contamination of pigs at slaughter. An observational study was carried out in 2001 on 101 conventional farrow-to-finish pig farms. On each farm, one batch of contemporary pigs was followed from the end of the fattening period until slaughter. The Salmonella bacteriological status of the batches was assessed by environmental samples of faecal material. The serological Salmonella status was obtained on 30 individually identified market-age pigs using an indirect ELISA test. At the slaughterhouse, 25 g of caecal contents were taken from 10 of the identified pigs. Faecal and caecal material were analysed according to a classical bacteriological method. A questionnaire was designed to obtain information about the type of feeding during the fattening period (dry versus wet), the duration of fasting on the farm before leaving for the slaughterhouse, the duration of transport between the farm and the slaughterhouse, the holding time in lairage at the slaughterhouse and loading and unloading conditions on the farm and at the slaughterhouse. To assess the relationships between these factors and the Salmonella caecal status of the pigs and the batches, two logistic models were fitted at the individual and at the batch level, respectively. The first analysis was performed using a random effects logistic regression model. The second analysis was based on a cumulative logit model with a positive caecal rate classified into three classes as the outcome variable. The results showed that the Salmonella status of market-age pigs assessed on the farm either by serological or bacteriological examinations and the time spent in lairage before slaughtering played a crucial role on caecal contamination. In the light of these results, actions should be considered both on the farm and at the slaughterhouse to decrease the risk of Salmonella contamination of the caecal contents.     

Evaluation of protection conferred by a Salmonella Typhimurium inactivated vaccine in Salmonella-infected finishing pig farms

The efficacy of an inactivated S. Typhimurium vaccine administered to pigs at the beginning of the fattening period was evaluated in four clinical trials (trials A, B, C and D). Faecal shedding and the systemic antibody response during fattening, as well as, the cecal contents and mesenteric lymph nodes collected after slaughtering were used to assess the outcome. Salmonella shedders prevalence in the control groups was six times higher than in the treated groups in trials A and D, both herds infected by S. Typhimurium. The risk of positive pens was also four or five times higher for the pens housing control pigs in trials A and C. Lower prevalence of Salmonella was observed in the slaughter samples from the vaccinated pigs in trial D and in the cecal content samples in trial A, when just the S. Typhimurium results were compared. The results suggest the effective homologous protection of the vaccinated pigs; however, the high humoral response elicited in the vaccinated pigs complicates their use in farms under serological surveillance programmes.     

Review on the effects of potential prebiotics on controlling intestinal enteropathogens Salmonella and Escherichia coli in pig production

Salmonella enterica serotypes (Salmonella sp.) are the second cause of bacterial foodborne zoonoses in humans after campylobacteriosis. Pork is the third most important cause for outbreak‐associated salmonellosis, and colibacillosis is the most important disease in piglets and swine. Attachment to host cells, translocation of effector proteins into host cells, invasion and replication in tissues are the vital virulence steps of these pathogens that help them to thrive in the intestinal environment and invade tissues. Feed contamination is an important source for Salmonella infection in pig production. Many on‐farm feeding strategies intervene to avoid the introduction of pathogens onto the farm by contaminated feeds or to reduce infection pressure when pathogens are present. Among the latter, prebiotics could be effective at protecting against these enteric bacterial pathogens. Nowadays, a wide range of molecules can potentially serve as prebiotics. Here, we summarize the prevalence of Salmonella sp. and Escherichia coli in pigs, understanding of the mechanisms by which pathogens can cause disease, the feed related to pathogen contamination in pigs and detail the mechanisms on which prebiotics are likely to act in order to fulfil their protective action against these pathogens in pig production. Many different mechanisms involve the inhibition of Salmonella and E. coli by prebiotics such as coating the host surface, modulation of intestinal ecology, downregulating the expression of adhesin factors or virulence genes, reinforcing the host immune system.     

Transmission of methicillin resistant Staphylococcus aureus among pigs during transportation from farm to abattoir

The prevalence of methicillin resistant Staphylococcus aureus (MRSA) in pigs at abattoirs is higher than in pigs sampled on farms. This study investigated whether MRSA negative pigs can become MRSA positive during transportation from the farm to the abattoir after exposure to other pigs and environmental sources of MRSA. Nasal swabs were collected from four batches of pigs during loading at the farm, on arrival at the abattoir and after stunning. Environmental wipes were taken from lorries after transporting pigs and from lairages after holding pigs. All pigs (n = 117) tested MRSA negative before transportation. On arrival at the abattoir, 12/117 (10.3%) pigs in two batches tested MRSA positive. In lorries that tested positive after transportation, the prevalence of MRSA positive pigs was 21.1%, whereas no MRSA was detected in pigs that had been transported in lorries that tested negative after transportation. At stunning, all batches and 70/117 (59.8%) pigs tested MRSA positive. Pigs can become MRSA positive in the short period of time during transportation from the farm to stunning at the abattoir.     

Herd-level risk factors for faecal shedding of Salmonella enterica in Spanish fattening pigs

Herd-level risk factors for faecal shedding of Salmonella enterica were investigated in a cross-sectional study on Spanish finishing units. For this purpose, 10 faecal samples were collected from 10 different pens containing pigs close to market weight in a total of 232 fattening units. The total sample size was proportionally distributed according to the fattener census in each of the regions and provinces of the country in order to ensure a sample representative of the entire swine population. All samples were individually examined by culture of 25 g of faecal material. Data regarding characteristics and management of each fattening unit were collected by means of a questionnaire. Logistic regression was used to detect relationships between the detection of faecal shedding of S. enterica and potential herd-level risk factors. The feeding of pelleted feed was associated with an increased risk of culture-positive faecal samples (OR = 2.28; 95% CI: 1.22, 4.26). The odds of a farm being Salmonella positive were associated with its size. Fattening units that slaughtered more than 3500 pigs per year had a higher risk for Salmonella faecal shedding (OR = 1.78; 95% CI: 0.96, 3.31). Interventions at these two points should be considered when designing or managing growing pig facilities to reduce Salmonella faecal shedding by fatteners.     

A clinical field trial to evaluate the efficacy of vaccination in controlling Salmonella infection and the association of Salmonella-shedding and weight gain in pigs

A clinical field trial was performed to determine the effectiveness of an autogenous Salmonella Typhimurium bacterin compared with a commercial live S. Choleraesuis vaccine in pigs. The association between Salmonella shedding and weight gain was also investigated. Nine cohorts of weaned pigs, (330 to 350 pigs per cohort), were randomly assigned to 1 of 3 treatment groups (injection with S. Typhimurium bacterin, vaccination via water with S. Choleraesuis vaccine, or a control group receiving no vaccine). In each cohort, the average daily gain was calculated for a selected pen throughout the production stage. Pen (pooled) fecal samples were collected bi-weekly and cultured. The odds of Salmonella shedding in both vaccinated groups was higher than in the control group (P < 0.05). The prevalence of Salmonella shedding declined overall as pigs aged (P = 0.04). However, the control pigs showed the smallest decrease in Salmonella shedding over the entire production stage, while prevalence of Salmonella shedding in the vaccinated groups decreased twice as much as the control group over the entire production stage. Salmonella Typhimurium var. Copenhagen DT104, S. Cerro, and S. Agona, which had been isolated on the study farm previously, were recovered from pigs in this study. Shedding of S. Typhimurium var. Copenhagen decreased over time in both vaccine treatment groups. On the other hand, S. Cerro shedding rate was lower in the control pigs compared with vaccinated pigs and S. Agona could be recovered only from the samples collected from S. Choleraesuis vaccinated pigs. The pigs from pens with a higher Salmonella recovery rate experienced slower growth compared with pigs from pens where Salmonella was not isolated. This latter finding indicates that there might be an economic incentive for producers to try to control endemic salmonellosis if effective programs could be developed.     

Effect of withdrawing feed from swine on meat quality and prevalence of Salmonella colonization at slaughter

OBJECTIVE: To determine whether withholding feed from pigs prior to slaughter had any effects on meat quality, percentage of pigs with Salmonella spp in cecal contents during slaughter, or percentage of pigs with lacerations of the gastrointestinal tract during slaughter. DESIGN: Split-plot design. ANIMALS: 873 pigs. PROCEDURES: At the finishing barn, pigs were assigned to 30 pens. Feed withdrawal times were assigned to pens at random, and pigs in each pen were marketed in 3 groups. The first marketing group consisted of the 10 heaviest pigs in each pen, the second consisted of the next 10 heaviest pigs, and the third consisted of all remaining pigs. RESULTS: Withdrawing feed improved the redness score assigned to the meat but did not have any other significant effects on carcass composition or meat quality. The percentage of pigs with Salmonella spp in the cecal contents decreased from the first (73%) to the second (64%) to the third (52%) marketing group. However, isolation of Salmonella spp from cecal contents was not associated with feed withdrawal time or with pen prevalence of Salmonella shedding during the 2 months prior to slaughter. Feed withdrawal time and marketing group did not have any significant effects on overall prevalence of gastrointestinal tract lacerations. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that withdrawal of feed from pigs prior to slaughter does not increase the prevalence of Salmonella colonization or the risk of carcass contamination associated with gastrointestinal tract lacerations during slaughter but only slightly enhances meat quality.     

Longitudinal serological responses to Salmonella enterica of growing pigs in a subclinically infected herd

A longitudinal survey was conducted in France in a subclinically Salmonella-infected farrow-to-finish pig farm to describe the time-course of the serological response to Salmonella enterica in growing pigs. We used three batches of sows and their corresponding litters (n = 31 litters). Among these, 256 pigs randomly selected and individually identified were followed from the first week of age until slaughter. Serial individual blood samples were submitted to indirect Salmonella-ELISA testing. Salmonella shedding was investigated by bacteriological testing of faecal material regularly collected from the sows and pigs and by environment swabs taken from the pens. Caecal contamination was checked at the slaughterhouse. Information about litter composition (filiation), location of the pigs in post-weaning and fattening pens, sanitary events, sex and body weights was recorded. 11.6% of the pigs shed S. enterica; 52% of pigs seroconverted before slaughter. The age-related variation of the natural logarithm of calibrated optical densities (COD) of pigs was described with two linear mixed models. From 8 to 61 days of age, the decrease in COD with age was fitted with a model including random effects of the animal and the dam on the intercept and slope, a batch random effect on the intercept and an individual birth-weight fixed effect on the intercept. The dam random effect was explained by the parity of the sow, Salmonella shedding by the sow during the farrowing phase and the value of the optical density of colostrum collected at parturition. A second model fitting the increase in COD from 61 days of age until slaughter included the random effect on intercept of the batch and the random effects on slope and intercept of the animal, the dam and the pen in which the followed animals were located during the fattening phase and the environmental contamination as fixed effect. In this second model, no relation was found between individual slaughter-bacteriological results and increasing COD values. Considering seroconversion time between 61 days of age and slaughter, survival function were constructed using the Cox proportional-hazards model. Both methods suggested that seroconversions generally occurred during the last third of the fattening phase (from 140 days of age to slaughter), while shedding was observed during the first half of the fattening period. The fitted models suggest the existence of clusters (such as pen and litter of origin).     

Capacity building: benchmark for production of meat with low levels of bacterial contamination in local slaughterhouses in Somaliland

The objective of the study was to investigate and assess the impact of trainings on the levels of meat contamination produced from local livestock slaughter facilities in the North-West region of Somalia (Somaliland). The investigation considered slaughter facilities where workers had been trained or not. The survey was carried out in four local slaughter facilities. A pre-tested questionnaire on abattoir hygiene and food safety standards was administered to International Aid Organizations, government officials, abattoir workers and supervisors. In addition, a total of 320 surface meat swab samples were collected from randomly selected small ruminant carcasses slaughtered from four purposefully selected local slaughter facilities. The samples were analyzed at Analabs laboratories in Nairobi, Kenya, for total viable counts, total coliforms count and presence of Salmonella species. Meat contamination risk factors associated with hygiene practices based on training offered or not was identified. It was noted that slaughter facilities where abattoir workers had not received trainings on minimum meat hygiene standards and quality assurance systems of good hygiene practices and sanitary standard operating procedures produced carcasses with high levels of bacterial contamination in comparison with those where workers had received the said trainings. The laboratory results were in agreement with poor hygiene meat handling practices and lack of compliance with minimum meat hygiene and food safety standards in Berbera and Burao local livestock slaughter facilities where personnel had not been trained.     

Risk factors for Salmonella enterica subsp. enterica contamination in French broiler-chicken flocks at the end of the rearing period

Broiler-chicken are often Salmonella carriers. However, these bacteria are responsible for major food-borne human infection, in which poultry-meat products are frequently implicated. In order to prevent Salmonella spread during the slaughtering process, control measures should be implemented at the farm level to reduce the prevalence before slaughtering. The objective of this study was to identify the risk factors for Salmonella contamination in French commercial broiler flocks at the end of the rearing period. A prospective study was carried out in 1996 and 1997 on 86 broiler flocks located in western France. The Salmonella status of the flocks was assessed by means of litter swabs and dust samples analyzed with classical bacteriological methods. Sixty flocks (70%) had at least one contaminated environmental sample and were classified as Salmonella-contaminated flocks. Logistic regression was used to assess association of managerial practices, general hygiene and results of environmental Salmonella recovery, with the odds that the flock itself would be Salmonella-contaminated at the end of the rearing period. Salmonella contamination of the house before placing day-old chicks and the Salmonella contamination of day-old chicks were significantly related to Salmonella contamination of the flock at the end of the rearing period. The risk for Salmonella contamination of the flock was increased when feed trucks parked near the entrance of the change room and when feed meal, instead of small pellets, was provided at the start.     

Detection of Salmonella in Finishing Pigs on Farm and at Slaughter in Piedmont,Italy

Salmonella is one of the most common causes of human gastroenteritis often associated with pork consumption. The aims of this cross‐sectional study were to collect preliminary data on the presence of Salmonella enterica in pigs in Piedmont (Italy), through sampling on farm and at slaughter and to gather pilot data on serotypes and phagetypes present in the sampled area and distribution of anti‐microbial resistance among isolated strains. Salmonella was detected through culture and identified with Salmonella spp. and Salmonella Typhimurium PCR; positive samples were serotyped, phagetyped and tested for antibiotic susceptibility. Positive samples (from 9% of faeces up to 29% of tonsils) were found in 64% of the herds. Salmonella spp. was retrieved also from scalding water. Most of the isolates were Salmonella Derby, Salmonella Typhimurium and Salmonella 4,5,12:i:‐. The results of Salmonella Typhimurium specific PCR suggested that Salmonella 4,5,12:i:‐ might be unrecognized by serotyping. Anti‐microbial resistance was recorded in 75–100% of the isolates. Phagetyping allowed the identification of DT104B and DT46A strains. These results set the bases for further research studies that would aim to estimate the real herd prevalence in Piedmont and the diffusion of serotypes and anti‐microbial resistant strains within the same region.     

The prevalence of verocytotoxin-producing Escherichia coli and antimicrobial resistance patterns of nonverocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens.

The prevalence of verocytotoxin-producing Escherichia coli and Salmonella in Ontario broiler chickens was determined by culturing cloacal samples from 500 individual birds selected from 50 poultry farms. Resistance to antimicrobials was determined for each of the isolates. In addition, abattoir and farm-level management data were obtained to evaluate variables that may be considered risk factors for infection. The variables selected included: Percentage of birds condemned at slaughter, percentage of birds dead-on-arrival, bird weight, truck number, farm size, hatchery source, litter source and type, feed source, mortality levels, type of water drinker, water sanitization, down time, barn clean out and history of antibiotic treatment. None of the cloacal samples revealed the presence of verocytotoxin-producing E. coli, though 19/500 (3.8%) contained Salmonella organisms. Nine different Salmonella serotypes were isolated; the most common being S. hadar, S. heidelberg and S. mbandaka. Resistance to tetracycline and streptomycin was common among Salmonella (63%) and E. coli (25.2%) isolates. Resistance to two or more antimicrobials occurred in 420/500 (84%) of the E. coli isolates. No statistically significant associations between abattoir or farm-level management variables and the Salmonella-status of farms were demonstrated.     

Salmonella in the mesenteric lymph nodes of healthy sows and hogs

Mesenteric lymph nodes were collected from healthy sow and slaughter hogs that had been kept in holding pens for an average of 10 and 2 days, respectively, before slaughter at an abattoir. Salmonella was isolated from 58.2% (67/115) of the sows and 31.3% (16/51) of the slaughter hogs. This difference in Salmonella prevalence was significant (chi 2 = 10.22, P less than 0.005); therefore, the hypothesis that there would be no significant difference in the infection rates of sows and slaughter hogs was rejected.