The role of transport,lairage and slaughter processes in the dissemination of Salmonella spp. in pigs in Ireland

Salmonella is an important foodborne pathogen worldwide and is commonly isolated from pigs and pig products in Ireland. Pigs, reared in an environment free of Salmonella spp. or with low levels of infection, may acquire infection or become contaminated during transport, lairage or post-slaughter. The main objective of this study was to determine the role of the abattoir as a potential factor that contributes to the dissemination of Salmonella spp. in slaughter pigs from herds with a low Salmonella seroprevalence (≤ 10%). A total of 128 pigs from eight herds were monitored from farm through the slaughter process in three separate abattoirs. The prevalence of Salmonella spp. was determined in samples collected from trucks, lairage pens and the slaughterline before pigs entered, from pigs after slaughter (caecal contents and ileocaecal lymph nodes) and carcass surfaces post-evisceration. Isolates were characterised by serotype, phage type and pulsed-field gel electrophoresis (PFGE) patterns. Of the swabs taken from the trucks, lairage and slaughterline, before the pigs entered, 4.3% (3/70), 80% (64/80) and 16.7% (4/27) were positive for Salmonella spp., respectively. The proportion of pigs showing serological evidence of infection was 3.1% (4/128). Salmonella spp. were isolated from the ileocaecal lymph nodes and caecal contents of 14.8% (19/128) and 11.7% (15/128) of pigs, respectively, and 13/128 (10.2%), 5/128 (3.9%), 2/111 (1.8%) and 8/111 (7.2%) carcass swabs pre wash, post wash, post chill and belly-strip samples, respectively, were Salmonella-positive. There was only slight agreement between serological and bacteriological data at the pig level. Salmonella isolates from 45% of all positive pig samples and 82% of positive carcass samples were indistinguishable, based on PFGE patterns, from salmonellae isolated from the lairage and slaughterline. Based on these results it is concluded that the lairage and the slaughterline provide a substantial source for Salmonella contamination of pigs and carcasses.     

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.     

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.     

Prevalence, distribution, and molecular characterization of Salmonella recovered from swine finishing herds and a slaughter facility in Santa Catarina, Brazil

Swine can carry Salmonella strains that may be transmitted to humans by pork products. This investigation determined the distribution and types of Salmonella in 12 swine finishing herds and a slaughter facility in Santa Catarina, Brazil. A total of 1258 samples, consisting of environmental, feed, carcass, lymph node, and fecal material were collected and submitted to bacteriological isolation of Salmonella. From 487 positive samples, 1255 isolates were recovered and confirmed to be Salmonella. The distribution of positive samples was as follows: finishing pen floors 26% (16/61); feed 29% (42/143); feces 44% (52/119); pooled feces 59% (35/59); slaughter holding pens 90% (36/40); lymph nodes 46% (220/478); pre-chilled carcass surfaces 24% (24/98); and post-chilled carcass surfaces 24% (62/260). The most prevalent serovars were Typhimurium, Panama, Senftenberg, Derby, and Mbandaka. By pulsed-field gel electrophoresis, 1071 isolates were subtyped using XbaI, and duplicate isolates were removed. From the remaining 747 isolates, 163 macrorestriction profiles (pulsotypes) were identified. Six pulsotypes were considered very frequent, occurring in 33 isolates or more. The multiple correspondence analyses showed correlations between pulsotypes from shedding pigs (feces), herd environment (pen floors), and subiliac and prescapular lymph nodes and between lairage and carcass surface samples before and after chilling. All sources of Salmonella investigated contributed to the carrier state; however, pre-slaughter contamination at lairage was the variable most strongly associated with carcass contamination. A total of 59 different antimicrobial resistance profiles were observed in 572 Salmonella isolates. From these isolates, 17% (97/572) were susceptible to all 15 antibiotics tested, 83% (475/572) were resistant to at least one, and 43% (246/572) were resistant to four or more antibiotics (multi-resistant). The AmpGenKanTet profile was the most prevalent in carcass isolates and was associated with farm origin.     

Detection and characterization of Salmonella in lairage, on pig carcasses and intestines in five slaughterhouses

In this study, conducted at five slaughterhouses, individual pigs were sampled and followed up from stunning to cooling down of the carcasses. In this way, Salmonella prevalence and possible risk points were described. At the lairage area, pens were sampled using overshoes. At stunning and bleeding, pigs were individually identified and subsequently swabs were taken of the oral cavity and the carcass after polishing, splitting and forced chilling. Additionally, duodenum, ileum, rectum and mesenteric lymph nodes were extracted and samples were taken of the scalding water. All samples were submitted to Salmonella isolation and Salmonella isolates were serotyped and genotyped by pulsed-field gel electrophoresis (PFGE). Of all samples taken (n = 1953), 14.1% were Salmonella positive. The prevalence of S. in the lairage area varied widely (from 0 to 100%) between the slaughterhouses. Of the sampled pigs (n = 226), 48.2% were positive in at least one sample. Statistical analysis revealed that the contamination of the lairage area was related to a higher amount of positive carcasses after polishing. Furthermore, the contamination of the carcasses after splitting and forced chilling was related to the contamination level of the carcass after polishing. A relation between the outer (carcass) contamination and the inner (gut content and lymph nodes) contamination of a pig could not be established. The predominant serotypes were S. Typhimurium (58.7%) and S. Derby (17.4%). Genotyping revealed 46 different PFGE profiles among the 276 Salmonella isolates. The same genotype at the lairage area as in the oral cavity of the pigs was found in 95%. The results indicate that the lairage area is a primary source of Salmonella in slaughter pigs and that carcass contamination originates from the environment rather than from the pig (inner contamination) itself. It further shows that slaughterhouses vary in their capability of dealing with Salmonella positive pigs. A slaughterhouse specific approach is needed, however, general guidelines should be provided to decrease the contamination level of the lairage area and the slaughter environment.     

Investigation of Salmonella enterica in Sardinian slaughter pigs: prevalence, serotype and genotype characterization

In order to improve the knowledge about the presence of Salmonella in pork meat in Sardinia (Italy), the prevalence and the sources of Salmonella at 5 pig slaughterhouses (slaughtered pigs and environment) were investigated and the isolates were characterised. A total of 462 samples were collected, 425 from pigs at slaughter and 41 from the slaughterhouse environment. Salmonella was isolated from 26/85 (30.5%) mesenteric lymph nodes, 14/85 (16.4%) colon contents, and from 12/85 (14.1%) carcasses and livers. Salmonella prevalence was 38% (8/21) in samples from surfaces not in contact with meat, and 35% (7/20) in those from surfaces in contact with meat. Thirty-one pigs were identified as carriers of Salmonella in lymph nodes and/or colon content, but of these, only 8 carcasses were positive. A total of 103 Salmonella isolates were serotyped and genotyped. Eight different serotypes were detected; the most common were S. Derby (44/103, 42.7%) and S. Typhimurium (24/103, 23.3%). The most prevalent S. Typhimurium phage type was DT193. Thirty-two isolates were found to be resistant to more than one antimicrobial (MDR). Pulse-field gel electrophoresis (PFGE) permitted the resolution of XbaI macrorestriction fragments of the Salmonella strains into 20 distinct pulsotypes. Combined application of a plasmid profiling assay (PPA) and PFGE gave useful additional information to assist in tracing the routes of Salmonella contamination in abattoirs. To reduce Salmonella prevalence some preventive measures should be encouraged: the origin of infected slaughter animals should be identified and direct and cross-contamination of carcasses should be avoided by adhering to HACCP principles in association with good hygiene procedures (GHP).     

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.     

Effect of logistic slaughter on Salmonella contamination on pig carcasses

Previous studies have shown that infected pigs are the source of carcass and slaughterhouse environment contamination by Salmonella. The present study tried to evaluate the effect of a logistic slaughter, organised according to Salmonella seroprevalence, on Salmonella contamination on carcasses. The study was performed at the beginning of slaughtering during three consecutive days. Low risk herds (8 batches) were slaughtered on day I, high risk herds (6 batches) on day II, and finally, moderate risk herds (5 batches) were slaughtered on day III. Each slaughtering day, holding pens, five points of the slaughter line, and 80 carcasses were sampled. The number of positive carcasses on days I, II and III was 7 (8.8%), 5 (6.3%) and 19 (24.4%) respectively. The results evidenced no clear effect of the logistic slaughter on carcass contamination, with a three times higher risk of finding a positive carcass when moderate Salmonella risk batches were slaughtered. Carcass contamination in low risk herds was linked to the contamination of holding pens and the slaughter line activities. On the other hand, Salmonella was not detected in any of the sampled carcasses in three out of six high risk Salmonella batches, showing that proper slaughtering practices can prevent carcass contamination. The experience reported here, demonstrates that apart from an accurate batch separation according to their seroprevalence levels, strict measures for cleaning and disinfection in the lairage and the slaughterhouse facilities are needed when logistic slaughter is performed.     

Salmonella contamination in pigs at slaughter and on the farm: a field study using an antibody ELISA test and a PCR technique

An antibody ELISA test and a PCR method for identifying the risk of Salmonella contamination were compared in a field study on the same lots of animals in a slaughterhouse. The results were compared to investigations carried out on two farms with different prevalences of Salmonella antibody-positive animals. Salmonella antibody ELISA testing was carried out on all 383 meat juice samples derived from the diaphragm pillar muscle of each pig. Salmonella DNA analysis was performed by PCR technique on small intestine samples with lymph nodes from all 383 pigs, and on tonsils from the last 129 pigs. The 383 animals tested came from 32 different pig farms. Furthermore, the herd antibody blood serum status against Salmonella spp. of weaners was determined on two selected pig fattening farms, one with low and one with high seroprevalence in meat juice. A total of 7.0% (ELISA cut-off OD% > or =40) of the slaughtered pigs from 6 of 32 fattening farms were seropositive. Salmonella DNA was found in 16.4% of the jejunum/lymph nodes (383 animals) and in 15.5% of the tonsils (129 animals). Salmonella DNA was found in the jejunum/lymph nodes of 41% of the seropositive pigs. However, serotitres were also positive in only 17.5% of all pigs positive in the jejunum DNA test. Two farms were selected for further investigation: farm 13 (F13), with a high prevalence of seropositive pigs, 29.0%, Category II; and F11, with 9.4%, Category I. However, categorization according to the blood serum tests of the fattening pigs after on-farm testing was very different: F13 had 5% positive animals (Category I); and F11, 23.3% (Category II). The study led to the following results and recommendations: First, ELISA tests are useful for the detection of farms that are regularly contaminated with Salmonella, but such tests cannot give information on the infectious status of a single animal (or a group) at the point of slaughter. Second, it is crucial that management measures are taken to prevent the spread of infections by trade and transport: piglets should be supplied exclusively by a single, well-known producer, and finishers should be tested serologically on farm before going to slaughter. Third, ELISA tests and the PCR method are suitable for the detection of Salmonella and are recommended as analytical tools for all pork quality control programmes. Fourth, animals from suspicious farms should always be slaughtered at the end of the slaughter day, followed by thorough cleaning and disinfection.     

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.     

Occurrence of Salmonella spp. in samples from pigs slaughtered for consumption: A comparison between ISO 6579:2002 and 23S rRNA Fluorescent In Situ Hybridization method

Contamination of pork products during slaughter represents an important vehicle for Salmonella spp. dissemination to humans. Salmonellosis poses an important risk for public health and presents an important economic issue to pork producers. This study aimed to evaluate the occurrence of this foodborne pathogen in pork carcasses and risk tissues (ileum, ileocolic and mandibular lymph nodes and tonsils) by two methods: the reference culture method (ISO 6579:2002) and a rapid Fluorescent In Situ Hybridization (FISH) method.The culture method identified the presence of Salmonella spp. in 13.7% of the samples, while the FISH technique revealed that 38.2% of the samples were positive. From these FISH positive samples, only 58 were concordant to the positive results obtained by the culture method.These results confirm the potential risk that pork represents in salmonellosis transmission, suggesting that additional measures should be taken during evisceration practices and extraction of tonsils and mandibular lymph nodes after slaughter, in order to achieve a better control of Salmonella contamination during slaughter. The FISH method showed to be a rapid screening tool for Salmonella spp. detection in pork samples.     

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 surveillance and control for finisher pigs and pork in Denmark — A case study

Salmonella can either be controlled pre-harvest, post-harvest or by a combination of both approaches. This paper describes the lessons learned in Danish Salmonella surveillance and control programme for finisher pigs and pork. Initially, main focus was on pre-harvest initiatives and correct identification of herds with respect to the risk for Salmonella that they represented. However, an analysis of risk-mitigating actions applied along the chain from stable to table showed that it would be more cost-effective to deal with Salmonella on the abattoirs than in the herds. This knowledge moved focus from pre- to post-harvest without giving up on pre-harvest surveillance. First of all, this meant increased attention on slaughter hygiene and individual interventions in the abattoirs. In brief, we learned that for a programme to be successful it must be based on standardised methods for sampling and testing to be able to evaluate and compare performance of the programme. More specifically, meat-juice samples taken from finisher pigs at the time of slaughter are an effective way of identifying high-risk herds for Salmonella. In addition, a penalty system might act as an incentive for farmers to deal with Salmonella in their herd. Additionally, common targets for all abattoirs allowing for unique control solutions should be adapted. Finally, decontamination techniques like hot water decontamination are a feasible way of dealing with high-risk pigs (Level-3 pigs). The current prevalence in Danish pork is around 1.2%, and a target is set to < 1.0% to be reached by the end of 2013. The experience obtained by use of the Danish programme might be used to develop and implement appropriate types of surveillance programs as well as risk-mitigating measures in other countries.     

Risk factors for changing test classification in the Danish surveillance program for Salmonella in dairy herds

A surveillance program in which all cattle herds in Denmark are classified into Salmonella infection categories has been in place since 2002. Dairy herds were considered test negative and thus most likely free of infection if Salmonella antibody measurements were consistently low in bulk tank milk samples collected every 3 mo. Herds were considered test positive and thus most likely infected if the 4-quarter moving average bulk tank milk antibody concentration was high or if there was a large increase in the most recent measurement compared with the average value from the previous 3 samples. The objective of this study was to evaluate risk factors for changing from test negative to positive, which was indicative of herds becoming infected from one quarter of the year to the next, and risk factors for changing from test positive to negative, which was indicative of herds recovering from infection between 2 consecutive quarters of the year. The Salmonella serotypes in question were Salmonella Dublin or other serotypes that cross-react with the Salmonella Dublin antigen in the ELISA (e.g., some Salmonella Typhimurium types). Two logistic regression models that accounted for repeated measurements at the herd level and controlled for herd size and regional effects were used. Data from 2003 was used for the analyses. A change from test negative to positive occurred in 2.0% of the quarterly observations (n = 21,007) from test negative dairy herds. A change from test positive to negative occurred in 10.0% of quarterly observations (n = 6,168) available from test positive dairy herds. The higher the number of test-positive neighbor herds in the previous year-quarter, the more likely herds were to become test positive for Salmonella. The number of purchased cattle from test-positive herds was also associated with changing from test negative to positive. The bigger the herd, the more likely it was to change from negative to test positive. The effect of herd size on recovery was less clear. Large herds consisting mainly of large breeds or having test-positive neighbors in a 2-km radius were less likely to change from test positive to negative, whereas the breed and neighbor factors were not found to be important for small herds. Organic production was associated with remaining test positive, but not with becoming test positive. The results emphasize the importance of external and internal biosecurity measures to control Salmonella infections.     

Epizootiology and Control Measures for Salmonella in Pigs

Pigs and pork meat products are often causes of Salmonella in humans. Salmonella can enter the human food chain at any part of the meat production process. Contamination of pork can be reduced by lowering the contamination of pigs at primary production. Production of “Salmonella free pigs” will reduce the risk of this zoonozis in people. It is possible to determine the serological status of pig farms. Prevention of Salmonella in humans should aim at: prevention of entrance of Salmonella to the pig farm, reduction of the number of infected animals and stopping the spreading of microorganism.     

Prevalence and serovars of Salmonella enterica on pig carcasses,slaughtered pigs and the environment of four Spanish slaughterhouses

The purpose of this study was to investigate the prevalence of Salmonella contamination and main serovars in pig slaughterhouses in Spain including carcasses, live animals and the environment. A total of 896 pig carcasses were randomly selected and swabbed before chilling in 3–5 visits to four pig slaughterhouses (A, B, C and D). Salmonella contamination was detected in 39.7% of the carcasses. The prevalence of positive carcasses was similar amongst slaughterhouses but significant differences were observed when taking sampling day into consideration within each of the slaughterhouses. Furthermore, a significant reduction in the prevalence of Salmonella contaminated carcasses (10.8%) was demonstrated in slaughterhouses C and D after chilling and cooling procedures.Sixteen batches of 10 animals were tracked from farm-to-slaughterhouse in slaughterhouses A and B to investigate the relationship between carcass contamination and contamination in live animals entering the slaughterhouse. No difference was found between infected and uninfected animals with respect to Salmonella contamination of the carcass although an increase in Salmonella contamination during the processing of live pigs into pork carcasses was evident. Regarding contamination in the slaughterhouse environment, Salmonella was isolated from most of the evaluated points in the slaughter line of the four studied slaughterhouses. Holding pens were identified as highly contaminated and what is more the ineffectiveness of the routinely cleaning protocols at this level was demonstrated in slaughterhouses C and D.The predominant Salmonella serovars found in carcasses, live pigs entering the slaughterhouse and the environment of the slaughterhouse were S. Typhimurium, S. Rissen, S. Derby and S. 4,[5],12:i:-. The same serovars were found in all the stages supporting the hypothesis that infected pigs are the main source of Salmonella contamination within slaughterhouses.     

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.     

Introduction of new multidrug-resistant Salmonella enterica strains into commercial dairy herds

A longitudinal observational study of 59 dairy herds was conducted in Washington State to estimate the rate of introduction of new multidrug-resistant (MDR) Salmonella enterica strains onto commercial dairy herds. Samples were collected on these herds over 7 visits separated by intervals of 2 to 4 mo over a period of 15 to 21 mo. Samples were cultured for Salmonella spp. and serogroup, serovar, and antimicrobial susceptibility patterns were identified for MDR Salmonella isolates. Fingerprinting generated by pulsed-field gel electrophoresis (PFGE) using XbaI restriction enzyme digestion generated genotyping profiles for all MDR isolates identified in the study. The rate of new MDR Salmonella strain introduction was 0.9 per herd-year (95% confidence interval: 0.6-1.4). The rates for the most commonly introduced MDR Salmonella serovars were 0.4/herd-year for Typhimurium, 1.2/herd-year for Newport, and 0.1/herd-year for Dublin. Thirty-three of 59 herds (56%) had at least one new MDR Salmonella introduction during the study period. The number of new MDR Salmonella strains acquired by dairy herds ranged from zero to 8. Thirteen of the 59 herds had a history of clinical salmonellosis. Among these 13 herds, 6 herds acquired new MDR Salmonella strains, although these strains were different than historical clinical strains. These data indicate that acquisition of new MDR Salmonella strains by dairy herds was a common event in participating herds, although the number of strains introduced varied greatly among herds.     

Testing of pathogenic Yersinia enterocolitica in pig herds based on the natural dynamic of infection

This study was performed to evaluate testing methods of pathogenic Yersinia enterocolitica in pigs at different ages. Relevant tools and procedures are crucial if pig herds should be declared free from pathogenic Y. enterocolitica. Historical data based on serology showed that the two farms investigated in this study (herds A and B) were contaminated with Y. enterocolitica O:3 since at least 1995. Laboratory investigations of 60 pigs were sampled one to four times (herd A) and 20 pigs were sampled one to three times (herd B) at different ages were the basis for this report. The following testing procedures could be used to conclude that a herd is free from pathogenic Y. enterocolitica:--serological testing of pigs could be performed as a basis for categorisation for all ages from about 100 days including at slaughter when the pigs are 150-180 days old, --bacteriological examination of faeces could be used as a basis for categorisation at all ages from 85 days until about 135 days, --bacteriological examination of tonsils could be used as a basis for categorisation at all ages from 85 days including at slaughter when the pigs are 150-180 days old. However, due to animal welfare aspects, one should avoid sampling of tonsils. Accordingly, the serological method or bacteriological examination of faeces at relevant ages should be preferred. One aspect related to slaughter hygiene is that in pigs slaughtered at the age of 135 days or more, the tonsils may be a more significant source of human pathogenic Y. enterocolitica than faeces.     

Occurrence,Characterization, and Antimicrobial Susceptibility of Salmonella enterica in Slaughtered Pigs in Sardinia

The aim of this study was to determine Salmonella occurrence in slaughtered finishing pigs and piglets and in slaughterhouse environment in order to characterize the isolates with phenotypical (antimicrobial testing) and molecular (PFGE, MLVA) methods. Nine slaughterhouses located in Sardinia were visited. Six hundred and eight samples collected from 106 pigs and 108 environmental samples were collected and analyzed. Salmonella was isolated in 65 of 504 (12.9%) samples from finishing pigs, with an occurrence of 15.1% in colon content, 12.7% in lymph nodes and liver, and 11.1% in carcass surface samples. Salmonella was never detected in piglets. The combined results of serotyping and PFGE showed a possible self‐contamination in 71.5% of Salmonella positive carcasses of lymph nodes and/or colon content carriers, pointing out the role of healthy pigs for carcass contamination. A significantly higher (P < 0.05) occurrence was detected in finishing pigs of EC countries origin (23%) than in pigs of local farms (8%). Salmonella was also detected in 3.7% of environmental samples. The most prevalent serovar was S. Anatum, followed by S. Rissen, S. Derby, and monophasic S. Typhimurium. Resistance to at least 3 antimicrobial was observed in 97.1% of strains and 7 different patterns of multiple resistance were identified. The most common resistance was detected against sulphonamide compounds. A strict slaughterhouse application of hygiene standards is essential to control the risk of Salmonella contamination.