Eric Bush

Prevalence of Pathogenic Yersinia enterocolitica Strains in Pigs in the United States

ABSTRACT Yersinia enterocolitica is considered an important food-borne pathogen impacting the pork production and processing industry in the United States. Since this bacterium is a commensal of swine, the primary goal of this study was to determine the prevalence of pathogenic Y. enterocolitica in pigs in the United Sates using feces as the sample source. A total of 2,793 fecal samples were tested for its presence in swine. Fecal samples were collected from late finisher pigs from 77 production sites in the 15 eastern and midwestern pork-producing states over a period of 27 weeks (6 September 2000 to 20 March 2001). The prevalence of ail-positive Y. enterocolitica was determined in samples using both a fluorogenic 5′ nuclease PCR assay and a culture method. The mean prevalence was 13.10% (366 of 2,793 fecal samples tested) when both PCR- and culture-positive results were combined. Forty-one of 77 premises (53.25%) contained at least one fecal sample positive for the ail sequence. The PCR assay indicated a contamination rate of 12.35% (345/2,793) compared to 4.08% (114/2,793) by the culture method. Of the 345 PCR-positive samples, 252 were culture negative, while of the 114 culture-positive samples, 21 were PCR negative. Among 77 premises, the PCR assay revealed a significantly (P < 0.05) higher percentage (46.75%, n = 36 sites) of samples positive for the pathogen (ail sequence) than the culture method (22.08%, n = 17 sites). Thus, higher sensitivity, with respect to number of samples and sites identified as positive for the PCR method compared with the culture method for detecting pathogenic Y. enterocolitica, was demonstrated in this study. The results support the hypothesis that swine are a reservoir for Y. enterocolitica strains potentially pathogenic for humans.

Use Estimates of In-Feed Antimicrobials in Swine Production in the United States

When considering the development of antimicrobial resistance in food animals, comparing gross use estimates of different antimicrobials is of little value due to differences in potencies, duration of activity, relative effect on target and commensal bacteria, and mechanisms of resistance. However, it may be valuable to understand quantities of different antimicrobials used in different ages of swine and for what applications. Therefore, the objective of this project was to construct an estimate of antimicrobial use through the feed in swine production in the United States. Estimates were based on data from the National Animal Health Monitoring System (NAHMS) Swine 2006 Study and from a 2009 survey of swine-exclusive practitioners. Inputs consisted of number of pigs in a production phase, feed intake per day, dose of the antimicrobial in the feed, and duration of administration. Calculations were performed for a total of 102 combinations of antimicrobials (n=17), production phases (n=2), and reasons for use (n=3). Calculations were first conducted on farm-level data, and then extrapolated to the U.S. swine population. Among the nursery phase estimates, chlortetracycline had the largest estimate of use, followed by oxytetracycline and tilmicosin. In the grower/finisher phase, chlortetracycline also had the largest use estimate, followed by tylosin and oxytetracycline. As an annual industry estimate for all phases, chlortetracycline had the highest estimated use at 533,973 kg. The second and third highest estimates were tylosin and oxytetracycline with estimated annual uses of 165,803 kg and 154,956 kg, respectively. The estimates presented here were constructed to accurately reflect available data related to production practices, and to provide an example of a scientific approach to estimating use of compounds in production animals.

Associations between off-label feed additives and farm size, veterinary consultant use, and animal age

Data from the United States National Swine Survey collected by the National Animal Health Monitoring System were used to describe the use of feed additives in swine feeds. Data were collected from 710 farms. The concentration of feed additives expressed in grams per ton of complete feed was described by stage of production, and the use of feed additives above the labeled treatment levels (i.e. off-label) was identified. Of the 3328 feeds, about 79% contained feed additives used in the labeled manner. For all classes of pigs, the prevalence of labeled feed additive use was greater than 75%. Penicillin was used according to its label most often, followed by apramycin, bacitracin, tetracyclines, lincomycin, and tylosin. Carbadox had the highest prevalence of off-label use. Of the 699 feeds that included feed additives in an off-label manner, about 57% included additives at greater than the recommended concentrations or were fed to an incorrect class of pig. About 56% of the feeds had off-label combinations of additives. Small farms were more likely to use rations with no feed additives than intermediate or large farms (P < 0.001). Of those farms using feed additives, the odds of a small farm using all feed additives in the labeled manner was 7.7 times that of an intermediate or large farm (P < 0.0001). After controlling for herd size, producers who used a veterinary consultant were 2.1 times more likely to use feeds with feed additives (P < 0.0001).

Salmonella prevalence and antimicrobial susceptibility from the National Animal Health Monitoring System Swine 2000 and 2006 studies.

Concern about Salmonella contamination of food is compounded by fear that antimicrobials traditionally used to combat the infection will become useless due to rising antibiotic resistance. Livestock, in particular swine, often are blamed for illnesses caused by Salmonella and for increasing antibiotic resistance due to use of antibiotics in pigs. As part of the National Animal Health Monitoring System Swine 2000 and 2006 studies, swine fecal samples were cultured for Salmonella. These samples were collected from 123 operations in 17 states in 2000 and from 135 operations in 17 states in 2006. At each operation, 50 and 60 fecal samples were collected from late finisher pig pens in 2000 and 2006, respectively. Salmonella isolates were characterized to determine serogroup and serotype and were tested for susceptibility to a panel of 17 and 15 antimicrobial drugs in 2000 and 2006, respectively. A total of 5,470 and 7,788 samples were cultured for Salmonella in 2000 and 2006, respectively. Overall, 6.2% of the samples and 34.2% of the farms were positive for Salmonella in 2000. In 2006, 7.2% of the samples and 52.6% of the farms were positive. Salmonella Derby, Salmonella Typhimurium var. 5- (formerly Salmonella Typhimurium var. Copenhagen), and Salmonella Agona were the three serotypes most often recovered in both study years. The most common antimicrobial resistance pattern for Salmonella Derby in the two study years was resistance to streptomycin, sulfisoxazole, and tetracycline. Most isolates were resistant to tetracycline, sulfisoxazole, and streptomycin in both study years. The proportion of Salmonella isolates that were susceptible to all antimicrobials (pansusceptible) was 38.1% in 2000 and 20.4% in 2006. The proportion of Salmonella isolates that were resistant to three or more antimicrobials (multidrug resistant) was similar in 2000 and in 2006 (52.8 and 57.7%, respectively).

Prevalence of Yersinia enterocolitica in market weight hogs in the United States.

Pigs are the major animal reservoir for Yersinia enterocolitica strains, which are potentially pathogenic for humans. The goals of this study were (i) to estimate the individual animal and on-farm prevalences of Y. enterocolitica in hogs based on tonsil samples collected during National Animal Health Monitoring System Swine 2002 study and (ii) to use these data with data previously published for fecal samples to determine on-farm risk factors for Y. enterocolitica. Tonsil swabs (1,218) and fecal samples (2,847) were collected on 124 farms located in the top 17 pork-producing states. Ten percent of tonsils (122 of 1,218 samples) were positive in irgasan-tiracillin-chlorate (ITC) enrichment broth by real-time PCR, but only 5.6% of samples (68 of 1,218) were positive after subculture on the more selective cefsulodin-irgasan-novobiocin (CIN) agar. For tonsils, the on-farm prevalence based on real-time PCR detection of the ail gene in ITC enrichment broth cultures was 32% (32 of 100 premises sampled); the prevalence based on subculture in CIN agar was 19.6% (20 of 102 premises). Results of bacteriological isolation and real-time PCR analysis of tonsils and feces were combined to estimate prevalence (individual animal and farm), which was subsequently correlated with 40 farm management practices. Four factors and their accompanying odds ratios (ORs) were identified in the final regression model: location in a central state (OR = 0.3), vaccination for Escherichia coli (OR = 3.0), percentage of deaths due to scours (OR = 3.5), and presence of meat or bone meal in grower-finisher diet (OR = 4.1).

Testing of swine feces obtained through the national animal health monitoring system's swine 2000 study for the presence of Escherichia coli O157:H7

Fecal samples collected from healthy pigs from 13 of the top 17 swine-producing states were tested for Escherichia coli O157:H7 as part of the National Animal Health Monitoring System Swine 2000 study. Serogroup O157 strains were isolated from 106 of 2,526 fecal samples. None of the isolates were positive by PCR for the fliCh7 (H7 flagellin) gene or for the hly933 (hemolysin) gene; however, one isolate was positive for the stxl gene (Shiga toxin 1), an additional four isolates were positive for the stx2 gene (Shiga toxin 2), and three isolates possessed the eae gene (intimin).