Salmonella epidemiology and control in pork: questions addressed and questions remaining

To assess trends in Salmonella research in pork production, the listings in a scientific database (CAB, International) were screened for the period 1990-2000. Reported publications increased approximately three fold, from 16 in 1990 to approximately 50 per year from 1997 through 2000. The breakdown of reported research by area of focus was summarized for the period 1995 through 2001 by screening citations reported by three abstracting services (AGRICOLA, CAB International, and MEDLINE). Many important questions remain for further investigation in each area. Judged on numbers of publications, relative strengths were identified in current scientific literature for pre-harvest epidemiology and Salmonella detection, and relative weaknesses were identified in economics and public policy related to control of Salmonella in pork

Chlorate and disinfectant modify Salmonella enterica shedding in weaned pigs

The effects of chlorate administration, age at weaning (10 and 21 days), and topically applied disinfectant on Salmonella enterica shedding were evaluated in 80 weaned pigs naturally exposed to Salmonella positive dams. Salmonella spp were qualitatively detected in samples collected on post-weaning days (PWD) -2, 10 and 14 and the concentration estimated for samples collected PWD 0, 5 and for PWD 14 cecal content

Tetracycline resistance genes in Salmonella from growing pigs and their relationship to antimicrobial use and resistance to other antimicrobials

The aim of this study was to describe the occurrence of three genes coding for tetracycline resistance in Salmonellae isolated from normal slaughter weight pigs, and to test for relationships between the occurrence of these genes, phenotypic resistance, and the use of antimicrobials in feed and water

Cryopreservation of Salmonella enterica in porcine fecal samples

Fecal samples are normally tested for Salmonella soon after collection because storage at any temperature, including refrigeration or freezing, can reduce detection. To evaluate several cryopreservation techniques, autoclaved porcine feces with and without additives were inoculated with 103 CFU S. Derby (UW -9)/g with autoclaved feces pnor to freezing. The mixtures and % of the CFU inoculum that was recovered was as follows: Feces only, 11 %; 50% feces plus 50% glycerol, 45%, 25% feces, 50% glycerol, 25% tetrathionate broth, 63%, 25% feces, 50% glycerol, 25% buffered peptone water (BPW), 66%; 50% feces, 50% glycyceroi/Tris buffer, 58%; 50 % feces, 50% BPW, 30%. When fresh (not autoclaved) feces were used, inoculated with a nalidixic acid resistant S Typhimurium (WI-73), 4% of the inoculum was recovered from undiluted frozen feces wh1le the add1tlon of 50% BPW before freezmg mcreased recovery to 27%

The Occurrence of Salmonella spp. in Superficial Cervical Lymph Nodes of Slaughtered Pigs

Salmonella species are commonly isolated from enteric lymph nodes and intestinal contents. However, Salmonella species have also been isolated from other lymph nodes, including peripheral lymph nodes that may be included in edible product (Wood, et at.). If the occurrence of Salmonella in these lymph nodes occurred at a substantial rate, it could pose a threat to food safety. We designed this study to detect the occurrence of Salmonella spp. in the superficial cervical lymph node group, nodes that can be included in the manufacturer of certain meat products originating from the front leg (picnic)

Farm-level Risk Factor Assessment for Infection with Salmonella spp.

We are focusing on the factors that predispose to Salmonella spp. infection in commercial pig production systems. Our current project aims to accomplish two primary goals. First, we will define the herd-level and pig-level prevalence for Salmonella infection. Second, we will quantify the farm-level risk factors for Salmonella herd- and pig-level prevalence. The determination of Salmonella infection is species and serotype specific. Twenty-five pigs will be sampled on the farm and 15 at slaughter from each of 70 herds that participate in an ongoing slaughter monitoring project (PigMON). Risks will be assessed by a survey of farms at the time of the slaughter inspection

Salmonella prevalence in pigs reared on farms with and without antimicrobials

A convenience sample of farms using antimicrobials (antimicrobial-using, AMU) post-weaning for therapy and/or growth promotion (n=21) were contrasted to a convenience sample of farms not using antimicrobials post-weaning (antimicrobial-free, AMF, n=21) distributed across three US geographic areas

Campylobacter Prevalence and Diversity in Antimicrobial Free and Conventionally Reared Market Swine

The objectives of this study were to determine the prevalence and antimicrobial resistance of Campylobacter spp. among pigs raised antimicrobial free (ABF) and those raised conventionally. Bacterial isolation was done on-farm and at slaughter using conventional methods and antimicrobial susceptibility tests were done for 12 antimicrobials using Kirby-Bauer and epsilometric test (E-test) methods. All 14 herds were positive for Campylobacter. On-farm prevalence among ABF herds was 71% and 81% among conventional herd. In contrast, the prevalence among carcass swabs was higher among ABF herds than conventional herds with 60% and 29% respectively. There was significant reduction after chilling in all groups (p\u3c0.05). On-farm frequency of antimicrobial resistance was significantly higher among isolates from conventional herds than ABF (p\u3c0.05). In contrast frequency of resistance to five of the seven antimicrobials was higher among carcass swabs of ABF herds than conventional herds

Risk factors for the detection of Salmonella in ileocolic lymph nodes in US slaughtered pigs.

Salmonella harborage at slaughter can be viewed as a nsk for human health through contammation of the pork food cham. Better understanding of herd level factors associated with this harborage would be useful to prioritize further study of epidemiology and control of Salmonella in pork production. Ileocolic lymph node samples collected at slaughter from 115 Midwest US sw1ne herds were assayed for Salmonella entenca. A subset of these herds was collected sequentially one or two additional times. Herd characteristics and management factors were assessed by a written survey. Risk factors were screened at the univariate level (p \u3c 0.3), then offered for Inclusion by stepw1se analysis including herd I sample as a random statistical effect. Pigs at increased risk of Salmonella harborage at slaughter included those placed in finisher barns at heaver weights (OR 1.2 per 10 kg Increased we1ght), those from larger herds (OR 2 0 comparing upper quintile to lower quintile of herd size), those from herds that allowed VISitors w1th recent (\u3c8 h) contact with other herds (OR 2.2), or those fed pelleted feeds (OR 2.1 ). Further invest1gat1on of these risk factors and potential biological mechanisms will requ1re further study

Chlorate concentration in the jejunum and cecum in growing pigs when supplemented in feed

Prior research has demonstrated that oral administration of chlorate and nitrate results in reduced risk and/or concentration of Salmonella enterica fecal shedding of infected pigs, poultry and ruminants. The effect of chlorate is concentration dependent in vitro, but the concentration of chlorate in the Gl tract has not been measured in vivo, and consequently the optimal dose of chlorate is poorly defined. We administered three dosages of chlorate (0, 40 and 120 mg/kg/day) and nitrate (0, 2 and 8 mg/kg/day) to 18 growing pigs using a 3 x 3 factorial study design. After 1 or 5 days of treatment subjects were humanely sacrificed to allow collection of jejunal and cecal content samples. The dose of chlorate and nitrate was at or doses associated with suppressed Salmonella shedding in a prior study in our lab. Samples were assayed using LC-MS-MS and chromatographic methods