Effect of water sprinkling on incidence of zoonotic pathogens in feedlot cattle1

Heat stress and dusty conditions are common challenges for cattle during the summer, and a typical method of alleviating these problems involves sprinkling cattle and pens with water. The effect of sprinkling water on the incidence of zoonotic pathogens has not been previously studied. Four pens of heifers (n = 41) were cooled using sprinklers, and four pens (n = 43) served as controls. Heifers were crossbred Charolais, with white and red hair coats. Sprinkling was initiated when cattle were on full concentrate feed (July). Fecal samples, hide swipes, and BW were collected on d 0, 28, 63, 95, and 98. Average daily gain, DMI, and G:F were calculated, and carcass traits were collected 36 h after processing. Performance data were analyzed as a randomized complete block design, and zoonotic pathogen data were analyzed using chi2 analysis. Sprinkling tended (P = 0.054) to increase the incidence of fecal Salmonella spp. populations on d 98, but simultaneously tended to decrease (P = 0.058) the Escherichia coli O157:H7 incidence on hides on d 98. The most prevalent Salmonella serovars in this study were Kentucky, Muenster, Meleagridis, and Cerro. Performance measures and carcass traits did not differ between treatments (P > 0.10). Under our conditions, sprinkling cattle with water did not affect the incidence of zoonotic pathogens in feces or on hides.

Novel preharvest strategies involving the use of experimental chlorate preparations and nitro-based compounds to prevent colonization of food-producing animals by foodborne pathogens

Foodborne diseases caused by enterohemorrhagic Escherichia coli, Salmonella, and Campylobacter species are of public health and economic significance. Shedding of these pathogens during production and slaughter are risks for contamination of products for human consumption. Consequently, strategies are sought to prevent or reduce the carriage of these pathogens in food animals before slaughter. Experimental products containing chlorate salts have been proven efficacious in reducing concentrations of E. coli and Salmonella Typhimurium in the gut of cattle, sheep, swine, and poultry when administered as feed or water additives. Mechanistically, chlorate selectively targets bacteria expressing respiratory nitrate reductase activity, such as most members of the family Enterobacteriaceae, as this enzyme catalyzes the reduction of chlorate to lethal chlorite. Most beneficial gut bacteria lack respiratory nitrate reductase activity, and thus the technology appears compatible with many bacteria exhibiting competitive exclusion capabilities. More recently, select nitrocompounds have been investigated as potential feed additives, and although these nitrocompounds significantly reduce pathogens on their own, evidence indicates that they may most effectively be used to complement the bactericidal activity of chlorate. A particularly attractive aspect of the nitrocompound technology is that, as potent inhibitors of ruminal methanogenesis, they may allow producers the opportunity to recoup costs associated with their use. At present, neither chlorate nor the nitrocompounds have been approved as feed additives by the US Food and Drug Administration, and consequently they are not yet available for commercial use.

Punctate exanthem of West Nile Virus infection: report of 3 cases

The West Nile Virus (WNV) has rapidly emerged as an important etiology of meningoencephalitis in North America since 1999. Diagnosis of this infection on clinical grounds is difficult, as many signs and symptoms of infection are nonspecific. Although cutaneous manifestations are common in WNV-infected patients, these have not been described in detail nor are clinical images widely available. We describe 3 patients with WNV infections, two ambulatory, one hospitalized, who developed punctate erythematous, macular, and papular eruptions, most pronounced on the extremities. Histopathologic findings in one case showed a sparse superficial perivascular lymphocytic infiltrate, a feature commonly seen in viral exanthems but not previously reported with WNV infection. A literature review provides support that this punctate exanthem is a common cutaneous presentation of WNV infection.

X-linked reticulate pigmentary disorder with systemic manifestations: report of a third family and literature review

Three siblings, two boys and one girl, presented with pigmentary abnormalities. The brothers, ages 11 and 6 years, had diffuse reticulate macular hyperpigmentation with onset in early childhood. In addition, these boys had hypohydrosis, coarse hair with an upswept frontal hairline, failure to thrive, and chronic pulmonary disease. The older boy also had corneal dystrophy and marked photophobia. A punch biopsy specimen from the 11-year-old showed melanophages and necrotic keratinocytes. Stains for amyloid were negative. The sister, age 2 years, had congenital linear hyperpigmented patches involving the intertrigenous areas, but was otherwise normal. The clinical findings of these children were consistent with X-linked reticulate pigmentary disorder with systemic manifestations. We present a summary of the clinical manifestations of this rare disorder and discuss efforts to identify the causative gene.

Evaluation of immunosuppressants and dietary mechanisms in an experimental disease model for necrotic enteritis

Clostridium perfringens (CP) is the etiologic agent of necrotic enteritis (NE). Clinical signs of this disease include depression, decreased appetite, diarrhea, and severe necrosis of the intestinal tract. Understanding the disease progression of NE has been difficult due to its complexity and the involvement of multiple factors (dietary components, immunosuppression, and mechanical irritation of the gut) that appear to contribute to this syndrome. In the present investigation, day-of-hatch broilers were fed a 55% wheat diet and randomly assigned to 1 of 8 groups. Treatments included positive control (CP challenge only), commercial coccidia vaccine (CCV), commercial bursal disease vaccine (CBDV), or the combination of CCV and CBDV, and an appropriate negative control for each (vaccinated and not challenged). Challenged treatment groups received 10(7) cfu of CP twice daily. When compared with controls, broilers in each treatment group had increased (P < or = 0.05) lesion scores, with mean scores of 1.05 and 2.05 in the CP and CBDV + CP treatments, respectively. When compared with controls, the incidence of CP increased (P < or = 0.05) in all treatment groups (73 and 100% in the CCV + CP and CBDV + CP treatment groups, respectively). Compared with controls, percentage mortality increased (P < or = 0.05) from 2% to 26 and 34% in the CP and CBDV + CP treatment groups, respectively. Results of this study indicate that the methodology used provides a good model for studying NE.

Comparison of spontaneous antibiotic resistance frequency of Salmonella Typhimurium growth in glucose amended continuous culture at slow and fast dilution rates

The objective of the study was to determine the frequency of spontaneous acquisition of resistance to select antibiotics by Salmonella Typhimurium (ST) when grown in glucose amended continuous flow culture at slow (D = 0.025 h(-1)) or fast (D = 0.27 h(-1)) dilution rates. The bacterium was grown in LB minimal medium (pH 6.25) containing no antibiotics. Upon achieving steady state, samples were plated to tryptic soy agar (TSA) alone or supplemented (per ml) with 2 and 16 microg oxytetracycline, 4 and 16 microg tetracycline, 2 and 64 microg kanamycin, and 0.25 and 2 microg enrofloxacin. Regardless of growth rate, CFU of resistant ST from the TSA containing antibiotics was less than 2 x 10(1) except for 2 microg kanamycin and 0.25 microg enrofloxacin treatments (higher than 1 x 10(9) and 4 x 10(7) CFU of resistant ST for trials 1 and 2, respectively). Frequency of recovering resistant ST from the TSA containing the higher antibiotic concentrations was less than 1 in 10(9) for all antibiotics, but was higher on the media containing 2 microg kanamycin and 0.25 microg enrofloxacin at both slow and fast growth rates. In general, minimal susceptibility differences were detected for isolates from slow and fast dilution rates.

Localization and physical property experiments conducted by Opportunity at Meridiani Planum

The location of the Opportunity landing site was determined to better than 10-m absolute accuracy from analyses of radio tracking data. We determined Rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images. Topographic profiles generated from rover data show that the plains are very smooth from meter- to centimeter-length scales, consistent with analyses of orbital observations. Solar cell output decreased because of the deposition of airborne dust on the panels. The lack of dust-covered surfaces on Meridiani Planum indicates that high velocity winds must remove this material on a continuing basis. The low mechanical strength of the evaporitic rocks as determined from grinding experiments, and the abundance of coarse-grained surface particles argue for differential erosion of Meridiani Planum.

Chemistry of rocks and soils at Meridiani Planum from the Alpha Particle X-ray Spectrometer

The Alpha Particle X-ray Spectrometer on the Opportunity rover determined major and minor elements of soils and rocks in Meridiani Planum. Chemical compositions differentiate between basaltic rocks, evaporite-rich rocks, basaltic soils, and hematite-rich soils. Although soils are compositionally similar to those at previous landing sites, differences in iron and some minor element concentrations signify the addition of local components. Rocky outcrops are rich in sulfur and variably enriched in bromine relative to chlorine. The interaction with water in the past is indicated by the chemical features in rocks and soils at this site.

Utilization of the nitrate reductase enzymatic pathway to reduce enteric pathogens in chickens

Previous reports have shown that some bacteria, including Salmonella, use a dissimilatory nitrate reductase enzyme pathway (NREP) in anaerobic environments. This enzyme reduces nitrate to nitrite and has been shown to cometabolize chlorate to cytotoxic chlorite. The present investigations were performed to evaluate the susceptibility of a competitive exclusion culture (CE) to the experimental chlorate product (ECP). A commercially available CE product was evaluated for its nitrate reductase activity and therefore its chlorate sensitivity. Individual isolates (in triplicate) were cultured in 10 mL of Viande Levure broth containing 5 mM sodium nitrate or 10 mM sodium chlorate. Bacterial growth (optical density at 625 nm) was measured and 1-mL aliquots were removed concurrently for colorimetric determination of nitrate content at 0, 3, 6, and 24 h. Of the 15 different facultative strains, 11 had slight NREP utilization, 3 had moderate NREP utilization, and the remainder were NREP negative (with slight and moderate NREP utilization: >0.1 to <1.0 mM and >1.0 mM nitrate used within 6 h, respectively). Of the obligate anaerobes evaluated, 3 had slight NREP utilization and the remainder were NREP negative. In vivo studies utilizing both products (CE and ECP) in a horizontal transmission challenge model (seeders + contacts) showed significant reductions in Salmonella from 5.37 to 1.76 log10 cfu/g and 3.94 to 0.07 log10 cfu/g, respectively. The combined effect of the CE culture and an ECP are effective in killing these food-borne pathogens.

Soils of Eagle Crater and Meridiani Planum at the Opportunity Rover Landing Site

The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.

Serotyping and Virulence Genes Detection in Escherichia coli Isolated from Fertile and Infertile Eggs, Dead-in-Shell Embryos, and Chickens with Yolk Sac Infection

Escherichia coli is a common avian pathogen mainly associated with extraintestinal infections such as yolk sac infection (YSI). The aim of this study was to determine the serotypes and the presence of some virulence genes of E. coli strains isolated from different samples in a vertically integrated poultry operation in Mexico. Two hundred sixty-seven E. coli isolates from different samples were serotyped using rabbit serum against the 175 somatic (O) and 56 flagellar (H) antigens of the typing schema. Virulence genes were determined by colony blot hybridization, using DNA probes for st, eae, agg1, agg2, bfp, lt, cdt, slt, and ipaH diarrhea-associated virulence factors. The serogroup of 85% of the strains was determined; O19 (12%), 084 (9%), 08 (6%), and 078 (5%) were the most common. Using the complete antigenic formula (O and H), O19:NM (n = 31) was the serotype most frequently isolated from dead-in-shell embryos and in broilers that had died on the fourth, fifth, sixth, and seventh days after hatch. One hundred ten strains (41.2%) hybridized with one or more of the used probes. Of these, ipaH (72%), eae (30%), and cdt (27%) were the most common. Considering the origin of the respective isolates, 40% of the broiler farm strains were positive for at least one probe. Results show that some avian E. coli strains isolated in Mexico are included in avian pathogenic E. coli serotypes not previously reported, suggesting that they could be specific for this geographic area. The wide distribution of the ipaH gene among nonmotile strains suggests that this invasiveness trait could be important in YSI pathogenesis. On the other hand, some other genes could contribute to E. coli virulence during YSI.

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.

METHODS AND RESULTS

Specific growth rates (h(-1)) of S. Typhimurium, E. coli O157:H7 and Ent. faecalis were determined during culture in tryptic soya broth (TSB) supplemented with 0-10 mm 2NPOH. Growth rates were inhibited by 2NPOH, with nearly complete inhibition observed with 10 mm. Studies with S. Typhimurium revealed that its survivability during culture in TSB containing 5 or 10 mm 2NPOH was lower (P < 0.05) under aerobic than anaerobic conditions. The survivability of Salmonella during anaerobic culture in TSB containing 2.5 mm 2NPOH was less at pH 5.6 than at pH 7.0 and 8.0. No Salmonella survived anaerobic incubation in TSB supplemented with 10 mm 2NPOH regardless of pH. When incubated in suspensions of freshly collected populations of ruminal and faecal bacteria, Salmonella concentrations were lower (P < 0.05) in suspensions containing 10 mm 2NPOH than in suspensions containing no 2NPOH.

CONCLUSIONS

2NPOH inhibited S. Typhimurium, E. coli O157:H7 and Ent. faecalis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results suggest that 2NPOH may be a useful antimicrobial supplement to reduce carriage of certain food-borne pathogens in food animals.

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.

Recent pre-harvest supplementation strategies to reduce carriage and shedding of zoonotic enteric bacterial pathogens in food animals

Food-borne bacterial illnesses strike more than 76 million North Americans each year. Many of these illnesses are caused by animal-derived foodstuffs. Slaughter and processing plants do an outstanding job in reducing bacterial contamination after slaughter and during further processing, yet food-borne illnesses still occur at an unacceptable frequency. Thus, it is imperative to widen the window of action against pathogenic bacteria. Attacking pathogens on the farm or in the feedlot will improve food safety all the way to the consumer's fork. Because of the potential improvement in overall food safety that pre-harvest intervention strategies can provide, a broad range of preslaughter intervention strategies are currently under investigation. Potential interventions include direct anti-pathogen strategies, competitive enhancement strategies and animal management strategies. Included in these strategies are competitive exclusion, probiotics, prebiotics, antibiotics, antibacterial proteins, vaccination, bacteriophage, diet, and water trough interventions. The parallel and simultaneous application of one or more preslaughter strategies has the potential to synergistically reduce the incidence of human food-borne illnesses by erecting multiple hurdles, thus preventing entry of pathogens into the food chain. This review emphasizes work with Escherichia coli O157:H7 to illustrate the various strategies.

Prevalence of Escherichia coli O157 in cattle and swine in central Mexico

Escherichia coli O157:H7 is a foodborne pathogenic bacterium that can reside undetected in the gastrointestinal tract of cattle because colonization by this bacterium is asymptomatic. Recent research has indicated that swine can carry and transmit this pathogen as well. The development of more advanced and sensitive detection techniques has improved the limit of detection and increased sensitivity for this important pathogen. This study was undertaken to determine the prevalence of E. coli O157 in cattle and swine in Mexico with the more sensitive detection technique of immunomagnetic bead separation. Samples (n = 60 per farm) were taken from four cattle and four swine farms (n = 240 cattle samples, n = 240 swine samples) located throughout central Mexico in October 2001. The prevalence of E. coli O157 was found to be only 1.25% on cattle farms and 2.1% on swine farms. The prevalence in cattle in this study is lower than that reported in the United States and could be related to the lower reported prevalence of E. coli O157 in humans in Mexico. However, further research is needed to verify prevalence throughout other regions of Mexico, as well as prevalence during other seasons of the year.

Localization and physical properties experiments conducted by Spirit at Gusev Crater

The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.

Chemistry of Rocks and Soils in Gusev Crater from the Alpha Particle X-ray Spectrometer

The alpha particle x-ray spectrometer on the Spirit rover determined major and minor elements of soils and rocks in Gusev crater in order to unravel the crustal evolution of planet Mars. The composition of soils is similar to those at previous landing sites, as a result of global mixing and distribution by dust storms. Rocks (fresh surfaces exposed by the rock abrasion tool) resemble volcanic rocks of primitive basaltic composition with low intrinsic potassium contents. High abundance of bromine (up to 170 parts per million) in rocks may indicate the alteration of surfaces formed during a past period of aqueous activity in Gusev crater.

Examination of Heat Stress and Stage of Lactation (Early versus Late) on Fecal Shedding ofE. coliO157:H7 andSalmonellain Dairy Cattle

Mature, healthy lactating dairy cattle were sampled on two farms in the southwestern United States to examine the effects of heat stress (Experiment I) and stage of lactation (Experiment II) on the fecal shedding of E. coli O157:H7 and Salmonella. To examine the effects of heat stress, fecal samples were collected from 45 cows at 7:00 AM (coolest part of the day) and 5:00 PM (hottest part of the day) in August 2002 on a 250 cow dairy. The study was replicated one month later (n = 170 total samples). A temperature-heat index (THI) was calculated for each sampling time. In Experiment II, stage of lactation was examined by sampling lactating dairy cattle early [< 60 days in milk (DIM)] and late (> 150 DIM) in the lactation cycle in the summer of 2001. The study was replicated the following summer (60 cows/group/replicate; n = 240 total samples). For Experiment I, THI averaged 75 and 82 for the AM and PM samplings, respectively, indicating the cows were beginning to experience heat stress in the morning and by afternoon were in severe heat stress. The shedding of E. coli O157:H7 tended to be higher (p = 0.09) in the afternoon sampling of the first replicate, however was not different in the second replicate or when both replicates were pooled (p > 0.10). Salmonella shedding was not different (p > 0.10) at any sampling time with nearly 100% of the cows positive. Stage of lactation had no effect on the number of cows shedding E. coli O157:H7 (p > 0.10). Salmonella shedding tended to be higher (p = 0.09) in early lactation cows in the first replicate, while in the second replicate more late lactation cows were shedding Salmonella (p < 0.05); however, there were no differences due to stage of lactation when replicates were pooled (p > 0.10). While further research is needed, results of this research highlight the variability in pathogen shedding in healthy dairy cattle and indicate that environmental factors and/or production demands may influence shedding patterns of E. coli O157:H7 and Salmonella.

Variation in the faecal shedding of Salmonella and E. coli O157:H7 in lactating dairy cattle and examination of Salmonella genotypes using pulsed-field gel electrophoresis

AIMS

To examine the variability in faecal shedding of Salmonella and Escherichia coli O157:H7 in healthy lactating dairy cattle and to evaluate the genetic relatedness of Salmonella isolates.

METHODS

Faecal samples were obtained from lactating Holstein dairy cattle on four commercial farms in the southwestern US. All farms were within an 8-km radius and were sampled in August 2001, January 2002 and August 2002 (60 cows per farm per sampling; n = 720 total samples). Samples were cultured for E. coli O157:H7 and Salmonella and a portion of the recovered Salmonella isolates were examined for genetic relatedness using pulsed-field gel electrophoresis (PFGE).

RESULTS

Faecal shedding of E. coli O157:H7 and Salmonella varied considerably between farms and at the different sampling times. Large fluctuations in the percentage of positive animals were observed from summer to summer for both of these pathogens. Similarly, Salmonella serotype and serotype prevalence varied from farm to farm and within farm from one sampling time to another. Multiple Salmonella genotypes were detected for a number of serotypes and identical genotypes were found on different farms with one genotype of Salmonella Senftenberg identified on three of the four farms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated the wide variability in pathogen shedding within and among dairy farms all located in a small geographical region and highlights the complexity of pathogen control at the farm level.

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

Foodborne disease caused by Salmonella 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 10(9)-10(10) colony-forming units of Salmonella serovar Typhimurium. After 24 or 36 h ad 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 challenge Salmonella. Drinking water administration of ECP effectively reduced (p < 0.05) caecal Salmonella concentrations and, with the weaned pigs, tended (p < or = 0.10) to reduce rectal Salmonella 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 caecal Salmonella concentrations occurring within 24 h. These results suggest that ECP administered to pigs just days before slaughter may reduce gut concentrations of Salmonella; however, the impacts of such reductions on slaughter hygiene have yet to be determined.

Effects of sodium chlorate on toxin production by Escherichia coli O157:H7

Chlorate kills E. coli O157:H7 and has been proposed as a feed additive to be included in cattle rations immediately prior to slaughter to reduce E. coli O157: H7 populations in the gut. Antibiotic usage is not recommended in cases of E. coil O157:H7-induced hemorrhagic colitis because some antibiotics stimulate increased toxin production. This study was undertaken to determine if chlorate treatment affected toxin production. Pure cultures of E. coil O157:H7 were treated with 1/4 MIC of antibiotics (ampicillin, tetracycline, ceftiofur, gentamicin, monensin, tylosin, penicillin, ciprofloxacin, and novobiocin); toxin production was significantly increased by some antibiotics, but not by chlorate. Studies with mixed fecal bacteria demonstrated that chlorate killed E. coli O157:H7, but again did not stimulate toxin production. Chlorate appears to be an effective method to reduce shiga toxin-producing E. coil (STEC) populations in food animals, but additional studies are warranted before it is used to control infections.

Antimicrobial Resistance and Serotype Prevalence of Salmonella Isolated from Dairy Cattle in the Southwestern United States

Mature dairy cattle were sampled over a 2-year period (2001-2002) on six farms in New Mexico and Texas. Fecal samples (n = 1560) were collected via rectal palpation and cultured for Salmonella, and one isolate from each positive sample was serotyped. Three isolates of each serotype, with the exception of Salmonella Newport (n = 12), were examined for susceptibility to 17 antimicrobial agents. Twenty-two different serotypes were identified from a total of 393 Salmonella isolates. Montevideo was the predominant serotype (27%) followed by Mbandaka (15%), Senftenberg (11.4%), Newport (6.4%), Anatum (4.8%), and Give (4.8%). Salmonella Typhimurium and Dublin, two frequently reported serotypes, accounted for only 1% of the observed serotypes in this study. Sixty-four percent of the serotypes were susceptible to all 17 antimicrobials, 14% were resistant to a single agent, and 22% were multiresistant (2-11 types of resistance). All isolates tested were susceptible to amikacin, apramycin, imipenem, ceftriaxone, nalidixic acid, and ciprofloxacin. The most frequent types of resistance were to sulfamethoxazole, tetracycline, streptomycin, kanamycin, chloramphenicol, and ampicillin (ranging from 8.9 to 22.4%). Serotypes demonstrating multiple resistance included Dublin and Give (resistant to three or more antibiotics), Typhimurium (resistant to five antibiotics), and Newport (four and two isolates resistant to six and nine antibiotics, respectively). Class 1 integrons were present in only two Salmonella Dublin isolates and one Salmonella Newport isolate. The most prevalent resistance patterns observed in this study were toward antimicrobial agents commonly used in cattle, while all Salmonella isolates were susceptible to ceftriaxone and ciprofloxacin, antibiotics used in human medicine.

Antimicrobial susceptibility and factors affecting the shedding of E. coli O157:H7 and Salmonella in dairy cattle

AIMS

To examine factors affecting faecal shedding of the foodborne pathogens Escherichia coli O157:H7 and Salmonella in dairy cattle and evaluate antimicrobial susceptibility of these isolates.

METHODS

Faecal samples were obtained in replicate from lactating (LAC; n = 60) and non-lactating (NLAC; n = 60) Holstein cattle to determine influence of heat stress, parity, lactation status (LAC vs NLAC) and stage of lactation [</=60 or >60 days in milk (DIM)] and cultured for E. coli O157:H7 and Salmonella. A portion of the recovered isolates were examined for antimicrobial susceptibility using the broth microdilution technique.

RESULTS

No effects of heat stress were observed. Lactating cows shed more (P < 0.01) E. coli O157:H7 than NLAC cows (43% vs 32%, respectively). Multiparous LAC cows tended to shed more (P = 0.06) Salmonella than primiparous LAC cows (39% vs 27%, respectively). Parity did not influence (P > 0.10) bacterial shedding in NLAC cows. Cows </=60 DIM shed more (P < 0.05) Salmonella than cows >60 DIM. Seventeen Salmonella serotypes were identified with the most prevalent being Senftenberg (18%), Newport (17%) and Anatum (15%). Seventy-nine of the Salmonella isolates were resistant to at least one of the seven antibiotics. Escherichia coli O157:H7 isolates were resistant to 11 different antibiotics with multiple resistance to nine or more antibiotics observed in five isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated differences in the shedding patterns of foodborne pathogens due to the stage of the milk production cycle and may help identify times when on-farm pathogen control would be the most effective.

Ionophores: their use as ruminant growth promotants and impact on food safety

Ionophores (such as monensin, lasalocid, laidlomycin, salinomycin and narasin) are antimicrobial compounds that are commonly fed to ruminant animals to improve feed efficiency. These antimicrobials specifically target the ruminal bacterial population and alter the microbial ecology of the intestinal microbial consortium, resulting in increased carbon and nitrogen retention by the animal, increasing production efficiency. Ionophores transport ions across cell membranes of susceptible bacteria, dissipating ion gradients and uncoupling energy expenditures from growth, killing these bacteria. Not all bacteria are susceptible to ionophores, and several species have been shown to develop several mechanisms of ionophore resistance. The prophylactic use of antimicrobials as growth promotants in food animals has fallen under greater scrutiny due to fears of the spread of antibiotic resistance. Because of the complexity and high degree of specificity of ionophore resistance, it appears that ionophores do not contribute to the development of antibiotic resistance to important human drugs. Therefore it appears that ionophores will continue to play a significant role in improving the efficiency of animal production in the future.

Effect of experimental chlorate product administration in the drinking water on Salmonella typhimurium contamination of broilers

The crop is a known source of Salmonella and Campylobacter contamination. Previously, we evaluated lactic acid in the drinking water during a simulated pretransport feed withdrawal (FW) and reported 0.44% lactic acid significantly (P < 0.05) reduced the number of Salmonella recovered in market-age broiler crops. However, total consumption of the organic acid-treated drinking water was reduced. Presently, we evaluated the effect of experimental chlorate product (ECP; 1x ECP is equivalent to a 15 mM chlorate ion concentration) during a 10-h pretransport FW. Market-age broilers were obtained from a commercial processing plant and randomly assigned to ECP-treated or control (nontreated) groups. Broilers were challenged by crop gavage with 10(8) Salmonella Typhimurium (ST) immediately upon arrival and 1 d prior to termination of the experiment. One day later, broilers were killed for ST enumeration (cfu) in the crop and ceca. Broilers provided ECP 24 h prior to slaughter consumed slightly more ECP water than broilers provided distilled water. Treatment with ECP caused a significant decrease (P < 0.05) in the incidence of ST in crop contents (2%) as compared to the controls (36.7%). Similarly, ECP treatment caused a significant decrease (P < 0.05) in number of ST (0.96 log10 ST/g cecal content) detected in the ceca when compared to controls (2.52 log10 ST). This study suggested that incorporation of ECP in the drinking water 24 to 48 h prior to slaughter could reduce Salmonella contamination in broilers.