Time course of infection with Salmonella typhimurium and its influence on fecal shedding, distribution in inner organs, and antibody response in fattening pigs

This is the first longitudinal study conducted over the entire 5-month fattening period in pigs to investigate the infection dynamics of Salmonella Typhimurium and the association between antibody response and the prevalence of these bacteria in feces. A total of 16 weaning pigs were infected with Salmonella Typhimurium DT104 followed by clinical examination and blood and fecal sampling until slaughter 138 days postinoculation. To investigate fecal shedding rates and distribution patterns of Salmonella in internal organs regarding premortem stress, one group of swine was transported before slaughter; the other group was slaughtered without being transported. A positive correlation between bacteremia-associated fever and fecal shedding rate was observed, although 69% (11 of 16) of infected pigs had no diarrhea. All animals excreted Salmonella Typhimurium at high levels within 2 weeks postinoculation; thereafter, the number of positive pigs declined and Salmonella shedding became intermittent. In contrast, the proportion of pigs that tested seropositive was higher over the entire fattening period (except during the first 3 weeks postinoculation), revealing the advantage of enzyme-linked immunosorbent assay for Salmonella screening on herd level. Concerning the distribution in internal organs and cross-contamination during slaughter, the highest level of Salmonella was detected in tonsils and jejunal and ileocecal lymph nodes, whereas salmonellae could not be detected in muscle, spleen, and liver. No specific influence of transport-induced stress on Salmonella shedding rates in feces and distribution patterns in organs was observed.     

Unveiling contamination sources and dissemination routes of Salmonella sp. in pigs at a Portuguese slaughterhouse through macrorestriction profiling by pulsed-field gel electrophoresis

Sixty-nine isolates of Salmonella sp. isolated from the ileum, tonsils, carcass and mandibular and ileocolic lymph nodes of individual pigs slaughtered for consumption in one abattoir were analyzed using serotyping and macrorestriction profiling by Pulsed-Field Gel Electrophoresis (RFLP-PFGE), in order to identify clonal relationships. XbaI macrorestriction was able to distinguish 18 genotypes among the eight identified serotypes: Salmonella Typhimurium (4 genotypes), Salmonella Rissen (3), Salmonella Tennessee (2), Salmonella Enteritidis (2), Salmonella 4,[5],12:i:- (4), Salmonella Give (1), Salmonella Anatum (1), and Salmonella Derby (1). Except for one sample, the serotype and the genotype identified in the samples from the same pork were always the same, allowing to unravel possible dissemination routes of Salmonella sp. through these pork tissues and equate presumptive sources of contamination or infection. Highly significant associations (p < 0.001) were observed for the presence of Salmonella sp. in the ileum and in the ileocolic lymph nodes, as well as between the carcass contamination and the presence of Salmonella sp. in others samples of the correspondent slaughtered pig, such as the ileum, the ileocolic and mandibular lymph nodes and the tonsils. Moreover, 80% of the pigs with ileum and ileocolic lymph nodes positive samples also presented the same salmonella genotype in the correspondent tonsils and, among pigs with positive tonsils, 70% also carried the same genotype in the corresponding mandibular lymph nodes. The occurrence of cross-contamination was also detected, since a genotype identified in other pigs slaughtered in the same day was found in 31% of positive carcasses. The global analysis of the genotypes suggested three different sources of pig infection: the farm of origin, the transportation and the lairage. A particular attention should be paid to the last one, since the majority of the isolates from pig samples were related to infection in the lairage. Since the presence of Salmonella sp. in the ileum of pigs and faeces ingestion promotes tonsils infection and internal dissemination of the agent through the mandibular lymph nodes, as well as drainage to the ileocolic lymph nodes, a potential risk exists at slaughter for Salmonella sp. contamination in the carcasses during pork processing. This risk may be increased by incorrect evisceration techniques and by hygienically inappropriate meat inspection procedures, especially those concerned to the mandibular lymph nodes incisions.     

Salmonellosis in finishing pigs in Spain: prevalence, antimicrobial agent susceptibilities, and risk factor analysis

A herd-based survey of Salmonella in pigs was carried in a major pig producing region of Spain. Mesenteric lymph nodes were collected from the carcasses of 25 pigs from each of 80 herds at time of slaughter. Salmonella spp. were isolated from 31% of animals and 94% of herds. Within-herd prevalence ranged from 4 to 88%, with the prevalence in most herds being greater than 10%. A large diversity of Salmonella serotypes was found, with Typhimurium, 4,[5],12:i:-, and Rissen being the most prevalent. Two or more serotypes coexisted in 73% of the herds. Salmonella Typhimurium was present in 68% of the herds. Most (82%) of the Salmonella isolates belonged to serogroups targeted by enzyme-linked immunosorbent assay tests for pig salmonellosis. Resistance to at least one antimicrobial agent was detected in 73% of the strains, and one or more resistant strains were recovered from pigs in 93% of the herds. Antimicrobial agent resistance (AR) was more frequent among the most prevalent than it was among the rarer serotypes. Twenty-five multi-AR patterns were found. Resistance to three or more families of antimicrobial agents was found in 75% of AR strains. The finding that many of the herds yielded isolates of several multi-AR patterns indicates that Salmonella infections were acquired from multiple sources. High prevalence of Salmonella in herds was associated with lack of rodent control programs, herds from farms with only finishing pigs, herds managed by more than one full-time worker, herds for which the source of drinking water was not a city supply, and relatively long fattening times.     

Salmonella status of pigs at slaughter--bacteriological and serological analysis

Apart from Salmonella monitoring of pig herds during the period of growth to evaluate the efficacy of control programmes, monitoring at harvest level is of relevance to assess the Salmonella status of fattening pigs and the associated risk of introducing Salmonella organisms in the slaughter process. Samples from 1830 fattening pigs were gathered at slaughter. Ileocaecal lymph nodes, rectal and caecal content as well as tonsils were collected for bacteriological examinations, and a part of the diaphragm pillar muscle was taken to gain meat-juice for serological analysis. Salmonella spp. was recovered from 13.8% of all pigs examined. Salmonella Typhimurium and Derby were the dominating serovars. The highest detection rates were found in caecal content followed by ileocaecal lymph nodes. By analysing both organs nearly 90% of all Salmonella positive pigs could be identified. Serological examination revealed 9.6% of the pigs as positive using a cut-off value of OD % ≥ 40. Only one quarter of all Salmonella positive pigs showed also a positive serological result. A reduction of the cut-off value does not necessarily result in a higher compliance between bacteriologically and serologically positive slaughter pigs. Detection of antibodies is useful to verify whether pig herds were previously exposed to Salmonella organisms. However, the Salmonella status of pigs at time of slaughter and the associated risk of dissemination of Salmonella organisms can only be assessed by bacteriological examinations which should include both lymph nodes and caecal content.     

Distribution of salmonella strains in farrow-to-finish pig herds: a longitudinal study

The aims of this study were to investigate patterns of Salmonella shedding in finishing pigs and to study the role of the sow in the transmission of Salmonella to her offspring. In each of the three herds (A, B, and C), one cohort of sows (n = 34, n = 40, n = 32, respectively) together with three piglets of their offspring (n = 102, n = 120, n = 96, respectively) were selected. Individual fecal and blood samples were taken from the sows at different times during one production cycle and from the piglets from weaning until slaughter. At slaughter, contents from the jejunum, colon, and mesenteric lymph nodes were collected. Fecal samples, as well as the jejunum, colon, and mesenteric lymph node samples collected at slaughter, were submitted to a qualitative Salmonella analysis. Isolates were characterized by random amplified polymorphic DNA, and if necessary, further characterization was done by pulsed-field gel electrophoresis. In herds A and B, Salmonella shedding began in the nursery. A significant increase in the number of Salmonella shedders was seen after transferring pigs to the growing unit in herd B (P = 0.003) and to the finishing unit in herds A (P < 0.001) and B (P = 0.013). None of the fattening pigs in herd C were shedding Salmonella. This study reveals that transferring pigs is an important trigger to induce Salmonella shedding, leading to horizontal spread. Direct transmission of Salmonella from the sows to their piglets could not be demonstrated, but the similarities between the isolates found in the sows and those found during the nursery and finishing periods and at slaughter suggested indirect transmission.     

Salmonella enterica serovars from pigs on farms and after slaughter and validity of using bacteriologic data to define herd Salmonella status

The primary objective of this study was to evaluate the validity of using data obtained from slaughtered pigs for farm-level epidemiologic studies of Salmonella. The study involved groups of pigs from five farms. Salmonella isolates were obtained from on-farm samples, and a total of 370 on-farm and an additional 486 isolates from samples collected after commercial slaughter were subsequently tested. Preharvest samples included feces of individual animals from defined groups of nursery and finishing pigs on commercial farms and swabs from trucks. Postslaughter samples were cecal contents and mesenteric lymph node samples. The concordance between Salmonella serovars isolated from on-farm samples and those serovars isolated after slaughter varied widely among farms. Results of paired lymph node and cecal cultures were strongly associated (odds ratio, 7.0), but the agreement between on-farm and postslaughter results at the pig level was poor (kappa = 0.34). The results support recent findings that risk of exposure to Salmonella during transport and lairage remains a concern under contemporary industry conditions. The findings further imply that slaughter plant studies based on phenotyping of Salmonella alone (such as serovars) may not reliably indicate the Salmonella status of commercial swine farms.     

Effect of farm type on within-herd Salmonella prevalence, serovar distribution, and antimicrobial resistance

Salmonella represents a major challenge to the pig industry, as pork presents a risk for human salmonellosis. In this study, we have examined the effect of farm type on the prevalence of fattening pigs shedding Salmonella on 12 farms at risk for harboring Salmonella. On six open (grow-to-finish) and six closed (farrow-to-finish) farms, the prevalence of pigs shedding Salmonella was determined on two occasions approximately 2 months apart. The serovar, phage type, and antimicrobial resistance of the obtained Salmonella isolates were determined. On all farms, pigs shedding Salmonella were detected on at least one of the two sampling days. The mean within-herd prevalence was 7.8%. Closed farms were two times less likely to have pigs shedding Salmonella than open farms. On open farms, the odds of finding Salmonella shedding in pigs were 1.9 times higher when sampling was performed at slaughter age than when samples were taken halfway through the fattening period. Salmonella enterica serovar Typhimurium was the most predominant serotype, with a prevalence of 62 to 63% on both farm types. Of all the Salmonella Typhimurium isolates, 65% had the tetraresistant profile ASSuT (ampicillin, streptomycin, sulfonamide, and tetracycline) with or without additional resistance to trimethoprim-sulfonamide. Phage type DT120 seemed to be especially associated with this antimicrobial-resistant profile. The prevalence of Salmonella Typhimurium isolates showing resistance to ampicillin, streptomycin, tetracycline, sulfonamide, trimethoprim-sulfonamide, and lincomycin hydrochloride and spectinomycin sulfate tetrahydrate was significantly higher on open farms than on closed farms.     

Prevalence of Yersinia enterocolitica in fattening pigs

The prevalence of pathogenic Yersinia enterocolitica in pig herds was monitored during six trials (at four different farrow-to-finisher farms). Samples were taken throughout the whole rearing period from birth of the piglets to the final fattening stage, and different samples were taken from these pigs during the slaughter process. Environmental samples also were evaluated to identify potential sources of on-farm infection. Y. enterocolitica was isolated using irgasan-ticarcillin-potassium chlorate broth enrichment and cefsulodin-irgasan-novobiocin agar culture. Colonies were identified using bio- and serotyping methods and by PCR assay. Pathogenic Y. enterocolitica were not isolated from fecal samples from piglets and weaners. The only fecal samples positive for Y. enterocolitica were obtained during the fattening stage. The prevalence of Y. enterocolitica in fattening pig herds ranged between 0 and 65.4%. Y. enterocolitica isolates were detected at the abattoir in 38.4% of the tonsils, in 3.8% of the ileocecal lymph nodes, on 0.3% of the carcass surfaces before chilling, and on 0% of the carcass surfaces after chilling. Almost all isolates belonged to bioserotype 4/O:3. Only one strain was identified as O:9. All isolates contained the ail gene. The yopT gene was found in 99.1% of the farm isolates but in only 76.6% of the isolates found at the abattoir from the corresponding carcasses. Although a direct link between porcine isolates and human infection has not been demonstrated, the similarity of the bioserotypes in infected pigs and humans and the presence of virulence factors in porcine isolates should encourage further studies to determine the risk of transmission of Y. enterocolitica to humans from pigs and pork products.     

Serodiversity and serological as well as cultural distribution of Salmonella on farms and in abattoirs in Lower Saxony, Germany

In this study fattening pigs were monitored on farms and in the abattoir for Salmonella prevalence. The samples with the highest prevalence at slaughter should be identified with special attention to the distribution of Salmonella serovars on farms in comparison to those in slaughtered pigs. Another aim was to monitor whether high serological antibody responses in pigs are in accordance with the specific Salmonella serovars in tissues. From 3418 farm faecal samples, 191 were Salmonella positive (5.58%), whereas from slaughtered pigs 330 out of 2494 analysed samples were Salmonella positive (13.2%) with the highest prevalence in the caecal content (124/499 = 24.9%). The chi-square test for homogeneity between the serovars found on farms and in the different types of samples at slaughter was in most cases negative (p < 0.05). Exceptions were the similar serovars found in samples taken from farm 1 and in the corresponding ileocaecal lymph nodes extracted at slaughter (p = 0.1188); in samples taken from farm 2 and the corresponding tonsils (p = 0.1479) and in samples taken from farm 3 and the corresponding caecal content (p = 0.3230) and ileocaecal lymph nodes (p = 0.1921), respectively. The frequency distribution in different samples was significantly different in most cases. Three exceptions, the distribution between tonsils and caecal content among antibody titre in meat juice (cut off 40) and cultural detection of Salmonella spp. in ileocaecal lymph nodes, as well as between meat juice samples (cut off 20) and caecal content did not differ significantly. The Kappa indices only showed signs of weak concordance according to positive test results (Kappa ≤ 0.4) between different sample types on an animal basis. Pigs harbouring S. Typhimurium 1,4,12:i:1,2; DT104L in tonsils or S. Typhimurium 1,4,12:i:1,2 DT 104B low in caecal content or ileocaecal lymph nodes had the highest optical densities in meat juice. Apart from the different Salmonella prevalences between farms and slaughterhouses and in most cases nonexisting concordance in Salmonella serovar distribution on farms and at slaughter, also in future farm intervention strategies to control Salmonella in the food chain are not dispensable. This is because once introduced into a slaughterhouse via swine the serovars seem to maintain the resident slaughterhouse flora and add to it.     

Prevalence of pigs infected by Salmonella Typhimurium at slaughter after an enterocolitis outbreak

A cross-sectional study was performed to estimate the prevalence of slaughter pigs infected by Salmonella typhimurium after an enterocolitis outbreak in a commercial pig farm, which was characterised by diarrhoea during the growing phase. Anatomopathological and histopathological findings were suggestive of salmonellosis, which was further confirmed by isolation of S. typhimurium from organs and faeces samples from diseased animals. Ileocolic lymph nodes were aseptically collected from 43 pigs during slaughter procedures. The estimated prevalence of Salmonella-infected pigs was 53.48% [confidence interval (CI): 42.94:64.02%]. This finding demonstrates that the carriage of S. typhimurium at slaughter might be high if pigs originate from a batch previously affected by Salmonella-enterocolitis outbreak at the pre-harvest pork production chain.     

Evaluation of subtherapeutic use of the antibiotics apramycin and carbadox on the prevalence of antimicrobial-resistant Salmonella infection in swine.

The antibiotics apramycin and carbadox were fed to growing swine, and the prevalence of Salmonella isolates that are resistant to apramycin and related aminoglycoside antibiotics was examined. Three hundred twelve Salmonella-positive pigs raised on one of five farms in an integrated swine operation and slaughtered at a central plant were used. All farms fed carbadox during the grower phase, and two farms administered apramycin during the first 21 days of age. Ileocolic lymph nodes and cecal contents were sampled at slaughter. One hundred of the 312 pigs were randomly selected to examine apramycin- and carbadox-resistant Salmonella infection, while all 312 pigs were used to evaluate the association between apramycin exposure and infection with Salmonella organisms resistant to amikacin, gentamicin, kanamycin, and streptomycin. Antimicrobial resistance was determined using disk diffusion and breakpoint concentrations. Apramycin treatment appeared to have little effect on apramycin- (12.5 versus 20.9%) or streptomycin- (76.4 versus 73.5%) resistant Salmonella isolates when averaged across farms and compared to control animals. Feeding carbadox resulted in carbadox-resistant Salmonella infection in only 5.3% of the isolates on one farm. The prevalence of amikacin-, gentamicin-, and kanamycin-resistant Salmonella isolates on farms feeding apramycin and carbadox were 0, 0, and 1.8%, respectively. Serogroup B was the most prevalent serogroup isolated, followed by C1 and E1. Apramycin and carbadox treatment did not appear to have any effect on the serogroup isolated. Subtherapeutic use of carbadox and apramycin did not appear to increase the prevalence of antimicrobial-resistant Salmonella in market-age swine.     

The effect of lairage on Salmonella isolation from market swine.

The objective of this paper was to evaluate the effect of lairage (holding >12 h during transport to slaughter) in clean facilities on Salmonella isolation from market swine. We tested 30 market-bound pigs (about 240 lb [110 kg]) on each of 10 occasions from an Iowa farrow-to-finish operation with about 600 sows. All pigs were slaughtered, and samples were collected at a large Midwest abattoir. On the farm, fecal samples were collected for culture of Salmonella. Pigs were alternately assigned to a lairage treatment (holding in a clean, disinfected facility at the National Animal Disease Center) group or a control group (remaining on the farm). After about 18 h, both groups were transported (about 137 km) to a large Midwest abattoir, commingled, and slaughtered. After slaughter, samples were collected for culture of Salmonella (feces from the distal colon, ileocecal lymph nodes, cecal contents, ventral thoracic lymph nodes, subiliac lymph nodes, and carcass swabs). Diaphragm sections were collected for serum ELISA. Salmonella enterica Derby was the only serotype isolated from farm fecal samples (3.4%, 10 of 290). Multiple serotypes (n = 17) were isolated from 71.8% (196 of 273) of the pigs when abattoir-collected samples were cultured: cecal contents (21.2%. 58 of 273), distal colon contents (52%, 142 of 273), and ileocecal lymph nodes (43.6%, 119 of 273). There were lower Salmonella isolation rates from the lairaged pigs (P < 0.05). The predominant serotype isolated at the abattoir varied by week of the study. This study suggests that pigs became internally contaminated with Salmonella after leaving the farm, possibly while in the abattoir holding pens, and that 18 h lairage, in clean facilities, does not increase shedding.     

Associations between on-farm and slaughter plant detection of Salmonella in market-weight pigs

Thirty swine production units in the midwestern United States were studied to assess the relationship of herd-level prevalence of Salmonella on the farm prior to slaughter versus at slaughter. Fecal samples were collected from 30 pigs on each farm within 48 h of slaughter, and 30 ileocecal lymph node samples were collected in the same shipment cohort at slaughter. Samples were cultured by conventional methods, and Salmonella identity was confirmed by serotyping. Overall, 11.7% (n = 105) of the fecal samples and 14.9% (n = 133) of the ileocecal lymph node samples were positive for Salmonella. Seventeen of the farms (56.7%) had one or more positive fecal samples, and 24 (80.0%) had one or more positive ileocecal lymph node samples. Twenty-four recognized serotypes and three additional distinct antigenic types were identified. Among all isolates, 56.5% had serotypes that were duplicated both on the farm and at slaughter for a particular cohort, whereas the remaining samples lacked a duplicate serotype in the other sample type. There was a positive correlation in the prevalence of Salmonella between fecal samples and ileocecal lymph node samples (Spearman's p = 0.75; 95% confidence interval [CI], 0.62 to 0.89). Linear regression analysis was used to identify two farms that biased the regression estimates. Excluding these farms, 62% of the variance in farm slaughter Salmonella prevalence was accounted for by on-farm prevalence. The analyses suggest that the prevalence of Salmonella spp. at slaughter can be predicted from preslaughter on-farm sampling and vice versa.     

Prevalence and genetic diversity of Listeria monocytogenes in the tonsils of pigs

This study was set up to establish the prevalence of Listeria monocytogenes in the tonsils of sows and fattening pigs from five Finnish slaughterhouses and to evaluate the genetic similarity of L. monocytogenes strains isolated from the tonsils. A total of 271 pig tonsils (132 tonsils from fattening pigs and 139 from sows) from five different slaughterhouses in various parts of Finland were studied from June 1999 to March 2000. Overall, 14 and 4% of pig tonsils harbored L. monocytogenes and Listeria innocua, respectively. The prevalence of L. monocytogenes in tonsils of fattening pigs (22%) was significantly higher than in sows (6%). The isolates (n = 38) recovered from tonsils showed a wide genetic diversity by means of 24 different pulsed-field gel electrophoresis (PFGE) types presented by the strains. Moreover, in numerical analyses of restriction patterns, no association was found between the clustering of strains and the slaughterhouses, and strains showing a similar PFGE type were recovered from pigs of different slaughterhouses. The high prevalence of L. monocytogenes showing various PFGE types in the tonsils of pigs could indicate a potential source of contamination of pluck sets, carcasses, and the slaughterhouse environment and of subsequent processing steps.     

Characterization of antimicrobial-resistant phenotypes and genotypes among Salmonella enterica recovered from pigs on farms, from transport trucks, and from pigs after slaughter

The main objectives of this study were to determine antimicrobial resistance patterns among Salmonella serotypes and to evaluate the role of transport trucks in dissemination of antimicrobial-resistant strains of Salmonella. Salmonella from groups of nursery and finishing pigs on farms, from trucks, and from pigs after slaughter were compared using serotyping, patterns of antimicrobial resistance, and pulsed-field gel electrophoresis patterns. The five farms included in the study yielded 858 isolates representing 27 Salmonella serovars. The most common resistance observed (80% of all isolates) was to tetracycline; resistance to ampicillin (42%), chloramphenicol (31%), amoxicillin/clavulanic acid (30%), and piperacillin (31%) also were common. We found a correlation between serovar and antimicrobial resistance. High correlation was found between Salmonella Typhimurium var. Copenhagen and chloramphenicol resistance (Spearman rank correlation, rho = 0.7). Multidrug resistance was observed primarily in Salmonella Typhimurium var. Copenhagen (94%) and Salmonella Typhimurium (93%) and was much less common in the other common serovars, including Salmonella Derby (7%) and Salmonella Heidelberg (8%). Of the 225 isolates exhibiting the most common pentaresistance pattern in this study, amoxicillin/clavulanic acid-ampicillin-chloramphenicol-piperacillin-tetracycline, 220 (98%) were Salmonella Typhimurium var. Copenhagen, and 86% of the isolates of this serovar had this pattern. Isolates from the trucks were similar, based on pulsed-field gel electrophoresis patterns, to those from the cecum and mesenteric lymph nodes of pigs on two of the farms, suggesting the probable infection of pigs during transport. Class I integrons were also common among various serovars.     

Seroprevalence of anti-hepatitis e virus and anti-salmonella antibodies in pigs at slaughter in Switzerland

Hepatitis E virus (HEV) and Salmonella bacteria are zoonotic pathogens that can be acquired by foodborne transmission because food animals, for example pigs, are recognized as a reservoir. The objectives of this study were to determine the seroprevalence of anti-HEV immunoglobulin G (IgG) and anti-Salmonella antibodies from healthy pigs at slaughter in Switzerland, a country with a good health status of pig herds (e.g., eradication of enzootic pneumonia) compared with those of many countries in the European Union, and a rate of importation of live pigs that is very low (<1%). Based on pooled (diaphragm muscles from 3 to 5 animals per producer) meat juice samples, 120 (60%) of 200 and 8 (4%) of 200 samples were positive for anti-HEV IgG and anti-Salmonella antibodies, respectively. HEV seems to be highly prevalent among fattening pigs in Switzerland, whereas the low seroprevalence of anti-Salmonella IgG has not changed in recent years.     

High bacterial contamination of pig tonsils at slaughter

Food-borne zoonoses have a major health impact in industrial countries. Campylobacter spp., Salmonella enterica, Yersinia enterocolitica and Listeria monocytogenes are high-risk food-borne zoonotic hazards in finishing pigs. The objectives of this work were (1) to study the isolation rate of pathogenic Y. enterocolitica, Salmonella spp., Campylobacter spp. and L. monocytogenes in the tonsils and feces and (2) to determine the number of mesophilic aerobic bacteria (MAB) and Escherichia coli in the tonsils of fattening pigs at slaughter. The samples, which were collected from one slaughterhouse on five occasions, originated from 50 pigs and 15 farms. The number of MAB varied from 6.40 to 7.82 log₁₀ CFU/g and E. coli from 4.38 to 6.53 log₁₀ CFU/g. Additionally, 31 (62%) of the tonsils were colonized with Y. enterocolitica and 16 (32%) with L. monocytogenes. Campylobacter spp. were more frequently excreted in feces and only 3 (6%) of the pigs carried Campylobacter spp. in the tonsils. No Salmonella spp. were isolated. The pig tonsils were shown to be colonized with a high number of bacteria including E. coli, which is the most important indicator for fecal contamination, and with Y. enterocolitica and L. monocytogenes, which are important food-borne pathogens. This study demonstrates that the tonsils are highly contaminated with micro-organisms and can be a very important source of contamination in the slaughterhouse.     

Use of a serological approach for prediction of Salmonella status in an integrated pig production system

Relevance of a Salmonella serological detection technique was studied from complete results obtained from 9 pigs fattening units. Feces and overshoes were sampled at different periods after starting fattening (2, 3 and 4 months) while caecal contents were taken on the slaughter line. The bacteriological technique used was based on a Diasalm enrichment and a commercial test was used for serology on an average of ten animals per batch. The aim of this work was to establish a correlation between serological results obtained at slaughter (10 samples/batch) and bacteriological results. In this context, two types of logistic regression models were tested by considering alternatively serology and Salmonella detection in caecal contents as the dependent variables. Firstly, beside the fact that all logistic regression models show weak correlations, the first finding was that positive results in overshoes taken at 2 and 3 months are slightly correlated with serological status of herds (odds-ratios of 4.96 and 2.55). Secondly, when batches were characterized as positive on the basis of serological results, the probability of Salmonella recovery in caecal contents was higher than when the batches were considered as negative (odds-ratios comprised between 4.36 and 5.81). A major conclusion is that serology can be used to follow the improvement of an integrated pig production system, but is not the unique solution for assessing risk of Salmonella shedding from specific herds.     

Relationship between tonsils and mandibular lymph nodes concerning Salmonella sp. infection

Pigs can be orally infected with Salmonella sp. that rapidly (in 30 min) invade the tonsils and subsequently, through lymphatic spread, reach the mandibular lymph nodes. These infected lymphatic tissues may constitute an important reservoir of Salmonella sp. playing a crucial role as a source of contamination during the slaughter process, promoting the introduction of Salmonella into the food chain.The main objective of this work was the study of Salmonella sp. occurrence in mandibular lymph nodes and in tonsils of slaughtered pigs, to define the level of association between these two lymphatic tissues concerning Salmonella infection. For this purpose, RFLP-PFGE was used to identify the clonal relationships between Salmonella sp. strains isolated from the mandibular lymph nodes and from the tonsils. The study revealed the presence of Salmonella in 12.9% of the mandibular lymph nodes and in 9.9% of the tonsils, from which 70% were associated to positive mandibular lymph nodes. This association emphasizes the importance of these lymphatic tissues as Salmonella sp. carriers, and alerts to the fact that particular and additional measures, in the context of the new European Regulation, should be implemented during the slaughter process in order to reduce the level of Salmonella sp. contamination.     

Yersinia pseudotuberculosis with limited genetic diversity is a common finding in tonsils of fattening pigs

A total of 425 pig tonsils, including 210 tonsils from fattening pigs and 215 from sows, from seven different abattoirs in Finland were studied for the occurrence of Yersinia pseudotuberculosis from 1999 to 2000. The mean prevalence of Y. pseudotuberculosis in fattening pig tonsils was 4%, varying from 0 to 10% between slaughterhouses. Y. pseudotuberculosis was not recovered from sow tonsils. All 30 Y. pseudotuberculosis isolates from eight pig tonsils were recovered after cold enrichment. Seventeen isolates from seven tonsils were found after cold enrichment for 14 days, followed by alkali treatment. Y. pseudotuberculosis was not isolated after direct plating, overnight enrichment, or selective enrichment. All 30 isolates belonged to bioserotype 2/0:3 and carried the virF gene in the virulence plasmid. The isolates exhibited calcium dependence and Congo red absorption. The pyrazinamidase test gave variable results. All isolates were characterized with pulsed-field gel electrophoresis (PFGE). Using SpeI, NotI, and XbaI enzymes, seven, five, and two different PFGE patterns were obtained, respectively. A total of 11 genotypes, gI to gXI, identified by a combination of the various SpeI, NotI, and XbaI profiles, were detected. Three pigs were found to carry more than one genotype. Overall, variations between PFGE patterns were small, indicating genetic homogeneity among pig strains of bioserotype 2/0:3.