Toni L. Poole

Genotypic variation among arcobacter isolates from a farrow-to-finish swine facility.

Arcobacter spp. were isolated from nursing sows and developing pigs on three farms of a farrow-to-finish swine operation and market-age pigs at slaughter. Isolates were identified by polymerase chain reaction and genotypic fragment patterns were examined by pulsed-field gel electrophoresis (PFGE). Incidences of Arcobacter-positive samples increased progressively as the pigs aged, resulting in all of the pens at the end of the growth cycle in the finishing barn containing Arcobacter-positive feces. However, only 10 of 350 cecal samples from slaughtered pigs were positive. There was little similarity between genotypic patterns for Arcobacter collected from the three farms. The level of genotypic variation revealed by PFGE suggested that pigs in this farrow-to-finish operation were colonized by multiple Arcobacter parent genotypes that may have undergone genomic rearrangement, common to members of Campylobacteraceae, during successive passages through the animals. Additionally, the level of genotypic diversity seen among Arcobacter isolates from farms of a single farrow-to-finish swine operation suggests an important role for genotypic phenotyping as a source identification and monitoring tool during outbreaks.

Escherichia coli O157:H7 populations in sheep can be reduced by chlorate supplementation

Ruminant animals are a natural reservoir of the foodborne pathogen Escherichia coli O157:H7. Some foodborne pathogens (e.g., E. coli) are equipped with a nitrate reductase that cometabolically reduces chlorate. The intracellular reduction of chlorate to chlorite kills nitrate reductase-positive bacteria; however, species that do not reduce nitrate are not affected by chlorate. Therefore, it has been suggested that ruminants be supplemented with chlorate prior to shipment for slaughter in order to reduce foodborne illnesses in human consumers. Sheep (n = 14) were fed a high-grain ration and were experimentally infected with E. coli O157:H7. These sheep were given an experimental product (XCP) containing the equivalent of either 2.5 mM NaNO3 and 100 mM NaCl (control sheep; n = 7) or 2.5 mM NaNO3 and 100 mM NaClO3 (chlorate [XCP]-treated sheep; n = 7). Control and XCP-treated sheep were treated for 24 h; XCP treatment reduced the population of inoculated E. coli O157:H7 (P < 0.05) from 10(2), 10(5), and 10(5) CFU/g in the rumen, cecum, and rectum, respectively, to < 10(1) CFU/g in all three sections of the gastrointestinal tract. The number of sheep testing positive for E. coli O157:H7 was significantly reduced by XCP treatment. In a similar fashion, total E. coli and coliforms were also reduced (P < 0.05) in all three compartments of the intestinal tract. Intestinal pH, total volatile fatty acid production, and the acetate/propionate ratio were unaffected by XCP treatment. On the basis of these results, it appears that chlorate treatment can be an effective method for the reduction of E. coli O157:H7 populations in ruminant animals immediately prior to slaughter.

Conjugative Transferability of the A/C Plasmids from Salmonella enterica Isolates That Possess or Lack blaCMY in the A/C Plasmid Backbone

The objective of this study was to understand the conjugative transmissibility of resistance plasmids present in 205 Salmonella enterica isolates from bovine sources. Polymerase chain reaction (PCR)-based replicon typing was used to type plasmid replicons. Conjugation experiments were preformed in triplicate at 30 degrees C and 37 degrees C on solid medium. PCR mapping of the A/C transfer gene operon was done on 17 Salmonella Newport isolates that were only positive for A/C. Eighty-six percent (n = 177) of the Salmonella isolates were multidrug resistant (MDR) with resistance to 3-12 antimicrobial agents. Of these, 82% (n = 146) were resistant to extended-spectrum cephalosporins and possessed a bla(CMY) gene. A/C was the predominant replicon detected, present in 90% (n = 160) of the MDR isolates. Twenty-three percent (n = 37) of the A/C-positive strains were positive for a second replicon. Replicons coresident with A/C included I1, N, B/O, HI1, and HI2. Only 31% (n = 54) of the MDR isolates produced transconjugants, and most of these donors carried multiple replicons. A/C cotransferred with B/O, N, and I1 at both 30 degrees C and 37 degrees C and with HI2 at 30 degrees C. Seven Salmonella Newport isolates that produced transconjugants possessed only the single A/C replicon and lacked bla(CMY). PCR mapping of the A/C transfer gene operon in ten Salmonella Newport isolates that carried bla(CMY) revealed a bla(CMY) inverted repeat element integrated between the traA and traC genes. These results suggest that A/C may have been a conjugative plasmid before the integration of bla(CMY) into the transfer gene operon. Additionally, transfer deficient A/C replicons may be mobilized in the presence of certain compatible conjugative plasmids.

Competitive Exclusion of Salmonella from the Gut of Neonatal and Weaned Pigs

Our laboratory has developed a bacterial competitive-exclusion (CE) culture against enteropathogens (which are considered human foodborne pathogens) for use in swine. In this article, we document the effects of this CE culture, PCF1, on cecal colonization by and fecal shedding of Salmonella Choleraesuis in neonatal and weaned pigs and its effects on the horizontal transmission of this pathogen between weaned penmates. Piglets treated with the PCF1 culture twice within their first day of life and challenged with Salmonella 48 h after birth shed Salmonella at a significantly (P < 0.05) lower rate than did control pigs in experiment 1. Significant reductions of the pathogen were also observed in the cecum, the cecal contents, the ileocolic junction, and the colon contents (P < 0.05). In experiment 2, culture of the cecal contents and lymph nodes revealed a significant reduction in Salmonella isolated from PCF1-treated pigs (P < 0.05). Pigs in experiment 3 were treated as pigs in experiments 1 and 2 were: however, they were followed through day 10 postweaning. Significant reductions in shedding were noted for treated groups both pre- and postweaning (P < 0.05). Experiments 4 and 5 assessed the effects of PCF1 treatment on the horizontal transmission of Salmonella between littermates that were followed through day 14 postweaning. In these experiments, litters were divided into untreated contacts (UC), untreated seeders (US), treated contacts (TC), and treated seeders (TS). Overall, TC in experiment 4 shed Salmonella at a significantly lower rate than UC and US did (P < 0.05). In experiment 5, the transmission of Salmonella was significantly reduced for litters in which TS or TC were present, as evidenced by reduced shedding of Salmonella by both treated and untreated animals within these litters (P < 0.05). TS shed less often than US did, resulting in reduced levels of Salmonella shedding by both treated and untreated contacts (P < 0.05). Litters containing both TC and UC or both TC and US also shed Salmonella at lower rates than did litters in which only UC and US were present (P < 0.05).

Evaluation of Phage Treatment as a Strategy to Reduce Salmonella Populations in Growing Swine

Salmonella is a foodborne pathogenic bacterium that causes human illnesses and morbidity and mortality in swine. Bacteriophages are viruses that prey on bacteria and are naturally found in many microbial environments, including the gut of food animals, and have been suggested as a potential intervention strategy to reduce Salmonella levels in the live animal. The present study was designed to determine if anti-Salmonella phages isolated from the feces of commercial finishing swine could reduce gastrointestinal populations of the foodborne pathogen Salmonella Typhimurium in artificially inoculated swine. Weaned pigs (n = 48) were randomly assigned to two treatment groups (control or phage-treated). Each pig was inoculated with Salmonella Typhimurium (2 × 10(10) colony forming units/pig) via oral gavage at 0 h and fecal samples were collected every 24 h. Swine were inoculated with a phage cocktail via oral gavage (3 × 10(9) plaque forming units) at 24 and 48 h. Pigs were humanely killed at 96 h, and cecal and rectal intestinal contents were collected for quantitative and qualitative analysis. Fecal Salmonella populations in phage-treated pigs were lower (p < 0.09) than controls after 48 h. Phage treatment reduced intestinal populations of inoculated Salmonella Typhimurium in pigs compared to controls at necropsy. Cecal populations were reduced (p = 0.07) by phage treatment >1.4 log(10) colony forming units/g digesta, and rectal populations were numerically reduced. The number of pigs that contained inoculated Salmonella Typhimurium was reduced by phage treatment, but a significant (p < 0.05) reduction was only observed in the rectum. We conclude that phages can be a viable tool to reduce Salmonella in swine. Further research needs to be performed to determine the most efficacious dosing regimens and the most effective combinations of phages targeting the diverse Salmonella population found in swine before they can enter the food supply.

Effect of Drinking-Water Administration of Experimental Chlorate Ion Preparations on Salmonella enterica serovar Typhimurium Colonization in Weaned and Finished Pigs

Foodborne disease caused bySalmonella is of public health and economic significance. In order to assess the practical effectiveness of a new intervention strategy, experimental chlorate preparations (ECP) were administered via the drinking water to weaned and finished pigs that had been orally challenged the previous day with 109–1010 colony-forming units ofSalmonella serovar Typhimurium. After 24 or 36 had libitum access to 0X, 1X or 2X ECP treatment (where X is the concentration estimated to deliver a minimal daily effective dose), the pigs were euthanized and gut contents and lymph tissue collected at necropsy were cultured for the challengeSalmonella. Drinking water administration of ECP effectively reduced (p<0.05) caecalSalmonella concentrations and, with the weaned pigs, tended (p≤0.10) to reduce rectalSalmonella concentrations. No negative effects of ECP treatment on water intake and animal wellbeing were observed and only marginal effects on gut fermentation characteristics occurred. The bactericidal effect of administering ECP in drinking water was relatively rapid, with reductions in caecalSalmonella concentrations occurring within 24 h. These results suggest that ECP administered to pigs just days before slaughter may reduce gut concentrations ofSalmonella; however, the impacts of such reductions on slaughter hygiene have yet to be determined.

Escherichia coli O157:H7 becomes resistant to sodium chlorate in pure culture, but not in mixed culture or in vivo

Aims: Chlorate kills Escherichia coli O157:H7 and may be an effective feed additive for use in food animals. This study was designed to determine if development of chlorate‐resistant E. coli O157:H7 strains was likely.

Inhibitory activity of 2-nitropropanol against select food-borne pathogens in vitro*

Aims:  To test the inhibitory activity of 2‐nitro‐1‐propanol (2NPOH) against Salmonella Typhimurium, Escherichia coli O157:H7 and Enterococcus faecalis.

Colicin concentrations inhibit growth of Escherichia coli O157:H7 in vitro.

Escherichia coli O157:H7 is a virulent foodborne pathogen that causes severe human illness and inhabits the intestinal tract of food animals. Colicins are antimicrobial proteins produced by E. coli strains that inhibit or kill other E. coli. In the present Study, the efficacy of three pore-forming colicins (El, N, and A) were quantified in vitro against E. coli O157:H7 strains 86-24 and 933. Colicins E1 and N reduced the growth of E. coli O157:H7 strains, but the efficacy of each colicin varied among strains. Colicin E1 was more effective against both strains of E. coli O157:H7 than colicins A and N and reduced (P < 0.05) populations of E. coli O157:H7 at concentrations <0.1 microg/ml. These potent antimicrobial proteins may potentially provide an effective and environmentally sound preharvest strategy to reduce E. coli O157:H7 in food animals.

Characterization of Salmonella enterica isolates from turkeys in commercial processing plants for resistance to antibiotics, disinfectants, and a growth promoter.

Salmonella enterica isolates from turkeys in two commercial processing plants (1 and 2) were characterized for susceptibility to antibiotics, disinfectants, and the organoarsenical growth promoter, 4-hydroxy-3-nitrophenylarsonic acid (3-NHPAA, roxarsone), and its metabolites, NaAsO(2) (As(III)) and Na(2)HAsO(4) • 7H(2)O (As(V)). The 130 Salmonella serovars tested demonstrated a low incidence of resistance to the antibiotics gentamicin (GEN), kanamycin (KAN), sulfamethoxazole (SMX), streptomycin (STR), and tetracycline (TET). Isolates resistant to antibiotics were most often multidrug resistant. Serovars Hadar and Typhimurium were resistant to KAN, STR, and TET and GEN, SMX, and STR, respectively. All isolated Salmonella serovars were resistant to the disinfectant chlorhexidine with minimum inhibitory concentrations (MICs; 1-8 μg/mL), and they were susceptible to triclosan and benzalkonium chloride. The didecyldimethylammonium chloride component was the most active ammonium chloride tested. No cross-resistance was observed between antibiotics and disinfectants. The MICs for 3-NHPAA (4096 μg/mL) were consistent between processing Plant 1 and Plant 2, but MICs for the 3-NHPAA metabolites (As(III) and As(V)) were higher in Plant 1 than in Plant 2. In Plant 1, 76% of the isolates had MICs >256 μg/mL for As(III) and 92% of the isolates had MICs >1024 μg/mL for As(V). In Plant 2, all of the isolates had MICs ≤256 μg/mL for As(III) and 90% of the isolates had MICs ≤1024 μg/mL for As(V). Only 4 Salmonella serovars were isolated from Plant 1, but 10 serovars were isolated from Plant 2. S. enterica serovar Derby from Plant 1 was highly resistant to As(III) and As(V) with MICs >1024 and >8192 μg/mL, respectively, suggesting previous exposure to high arsenic metabolite concentrations. These levels may have been high enough to kill other Salmonella serovars, thus possibly explaining the lack of serovar diversity observed in Plant 1. The application of a growth promoter may affect the serovar diversity in treated birds.