Analyses of livestock production, waste storage, and pathogen levels and prevalences in farm manures

Transmission of foodborne zoonotic pathogens to riparian areas by grazing sheep

The objective of this study was to determine if sheep grazing near riparian areas on pasture in Ontario are an important risk factor for the contamination of water with specific foodborne pathogens. Ten Ontario sheep farms were visited weekly for 12 wk during the summer of 2005. Samples of feces, soil, and water were collected and analyzed for the presence of Escherichia coli O157:H7, Salmonella spp., Campylobacter jejuni and C. coli, and Yersinia enterocolitica, by bacteriological identification and polymerase chain reaction (PCR). The data was analyzed as repeated measures over time using mixed models. No samples were positive for Salmonella, and no samples were confirmed positive for E. coli O157:H7 after PCR. Levels of Campylobacter were highest in the soil, but did not differ between soil where sheep grazed or camped and roadside soil that had never been grazed (P = 0.85). Levels of Yersinia were highest in water samples and were higher in soil where sheep had access (P = 0.01). The prevalence of positive Campylobacter and Yersinia samples were not associated with locations where sheep spent more time (Campylobacter P = 0.46, Yersinia P = 0.99). There was no effect of stocking density on the prevalence of Campylobacter (P = 0.30), but as the stocking density increased the levels of Yersinia increased (P = 0.04). It was concluded that although sheep transmit Yersinia to their environment, pastured sheep flocks are not major risk factors for the transmission of zoonotic pathogens into water.

Distribution, diversity, and seasonality of waterborne salmonellae in a rural watershed

Salmonella outbreaks from contaminated water and nonanimal foods (e.g., produce) are increasingly reported. To address the environment as a potential source of pathogenic Salmonella, we investigated levels of salmonellae and the geographic and temporal variation of Salmonella serotypes from surface waters in a region of Georgia (United States) with a history of high salmonellosis case rates. Monthly water samples were collected from six stations in the Little River (Upper Suwannee Basin) for 12 months (April 2005 to April 2006). Salmonellae were enumerated using a three-step most-probable-number (MPN) assay. Salmonellae were detected in 57 of the 72 water samples collected (79.2%). Monthly Salmonella densities ranged from an MPN of 2.5 liter(-1) in April 2005 to 36.3 liter(-1) in August 2005; concentrations were significantly higher in the summer months compared to other seasons (P<0.05). Concentrations were not significantly different between stations. Levels of salmonellae were correlated with average daily watershed rainfall for the 1 and 2 days preceding each sample collection (r=0.77 and 0.68, respectively; P<0.005). Additionally, water temperature was also positively associated with total Salmonella levels (r=0.44; P<0.05). In total, 13 S. enterica serotypes were identified among 197 Salmonella isolates. Eighty (40.6%) were identified as S. enterica subsp. arizonae. Muenchen and Rubislaw were the most frequently identified serotypes of the remaining 117 isolates (28 and 26 isolates, respectively). Serotype diversity peaked in the summer, with 9 serotypes observed in August compared to only one serotype (S. enterica subsp. arizonae) observed in April (2005 and 2006) (P<0.05). Furthermore, all samples collected in August (6/6) contained multiple serotypes (two to five per sample). The results of this study suggest that Salmonella abundance and diversity in the environment vary temporally and are strongly influenced by seasonal precipitation and water temperature.

Recent advances in the microbial safety of fresh fruits and vegetables

Foodborne illness outbreaks linked to fresh produce are becoming more frequent and widespread. High impact outbreaks, such as that associated with spinach contaminated with Escherichia coli O157:H7, resulted in almost 200 cases of foodborne illness across North America and >$300 m market losses. Over the last decade there has been intensive research into gaining an understanding on the interactions of human pathogens with plants and how microbiological safety of fresh produce can be improved. The following review will provide an update on the food safety issues linked to fresh produce. An overview of recent foodborne illness outbreaks linked to fresh produce. The types of human pathogens encountered will be described and how they can be transferred from their normal animal or human host to fresh produce. The interaction of human pathogens with growing plants will be discussed, in addition to novel intervention methods to enhance the microbiological safety of fresh produce.

Microbial concentrations on fresh produce are affected by postharvest processing, importation, and season

In the United States, the proportion of foodborne illness outbreaks associated with consumption of contaminated domestic and imported fresh fruits and vegetables (produce) has increased over the past several decades. To address this public health concern, the goal of this work was to identify and quantify factors associated with microbial contamination of produce in pre- and postharvest phases of the farm-to-fork continuum. From 2000 to 2003, we collected 923 samples of 14 types of produce (grown in the southern United States or in the northern border states of Mexico) from 15 farms and eight packing sheds located in the southern United States. To assess microbial quality, samples were enumerated for Escherichia coli, total aerobic bacteria, total coliforms, and total Enterococcus. Most produce types had significantly higher microbial concentrations when sampled at the packing shed than when sampled at the farm. In addition, we observed seasonal differences in the microbial concentrations on samples grown in the United States, with higher mean indicator concentrations detected in the fall (September, October, and November). We developed a predictive, multivariate logistic regression model to identify and quantify factors that were associated with detectable concentrations of E. coli contamination on produce. These factors included produce type (specifically, cabbage or cantaloupe), season of collection (harvested in the fall), and packing step (bin, box, conveyor belt, or turntable). These results can be used to identify specific mechanisms of produce contamination and propose interventions that may decrease the likelihood of produce-associated illness.

Comparison of the effectiveness of composting and vermicomposting for the biological stabilization of cattle manure

Cattle manure is produced in large quantities in industrial breeding facilities and the storage and/or spreading of this waste on land may cause contamination of the atmosphere, soil and water. The aim of the present study was to evaluate the effectiveness of the active phases of composting, vermicomposting, and also a combination of composting and vermicomposting for reducing the polluting potential and for stabilizing cattle manure in the short-term. For this, the degree of decomposition as well as the microbial activity and microbial composition of the resulting products after the active phase of composting and vermicomposting were analysed. None of the treatments significantly reduced the dissolved organic carbon and dissolved organic nitrogen contents relative to the control, and therefore more time may be required for stabilization. Nevertheless, the lowest values of microbial biomass and activity corresponded to the earthworm-worked substrates, in which fungal growth was also promoted; the combined treatment (composting + vermicomposting) was the most effective in terms of stabilizing the cattle manure. Moreover, earthworms promoted the retention of nitrogen and gradual release of P, as well as a reduction in electrical conductivity, thereby producing improved substrates for agricultural use.

A framework for valuing the health benefits of improved bathing water quality in the River Irvine catchment

A simple model predicting bathing water concentrations of Escherichia coli from livestock in the Irvine catchment in SW Scotland has been adapted for intestinal enterococci (IE). This has been used to predict risk of bather illness by extrapolation of published data on bather IE exposure vs incidence of gastro-enteritis. Simulated reduction in the risk of illness by reduced faecal loading was multiplied by a willingness to pay for risk reduction to estimate the annual benefits of mitigation. Health benefits of reducing loading by 75% at Irvine Beach were estimated by a willingness to pay method to be about pound 276k pa. Estimated annualised costs of diffuse pollution mitigation measures across the catchment were higher (> pound 1m), and it is very unlikely that 75% mitigation is achievable with current stocking rates. Further work should explore the influence of uncertainty of model parameters, and use emerging epidemiological information on specific zoonotic pathogens such as E. coli O157 and Cryptosporidium. Other components of the value of clean water should also be included to obtain a complete estimate of the cost:benefit of mitigation.

The evaluation of stability and maturity during the composting of cattle manure

We examined chemical, microbiological and biochemical parameters in order to assess their effectiveness as stability and maturity indicators during the composting process of cattle manure. The composting material obtained after 15 d in trenches and at different times during the maturation phase (i.e. 80, 180 and 270 d) were analyzed. We found that the material collected at the end of the active phase was inadequate to be applied to soil as organic amendment due to its high content of NH4+, its high level of phytotoxicity and the low degree of organic matter stability. After a maturation period of 80 d, the stability of the sample increased. This was shown by a reduction in the dissolved organic carbon (DOC) content and NH4+ concentration and also by a reduction in the microbial activity and biomass; however, 180 d of composting were not sufficient to reduce the phytotoxicity to levels consistent for a safe soil application. Among the various parameters studied, the change in DOC with composting time gave a good indication of stability.

Climate and on-farm risk factors associated with Giardia duodenalis cysts in storm runoff from California coastal dairies

Climatic factors and on-farm management practices were evaluated for their association with the concentrations (cyst/liter) and instantaneous loads (cysts/second) of Giardia duodenalis in storm-based runoff from dairy lots and other high-cattle-use areas on five coastal California farms over two storm seasons. Direct fluorescent antibody analysis was used to quantitate cysts in 350 storm runoff samples. G. duodenalis was detected on all five dairy farms, with fluxes of 1 to 14,000 cysts/liter observed in 16% of samples. Cysts were detected in 41% of runoff samples collected near cattle less than 2 months old, compared to 10% of runoff samples collected near cattle over 6 months old. Furthermore, the concentrations and instantaneous loads of cysts were > or =65 and > or =79 times greater, respectively, in runoff from sites housing young calves than in sites housing other age classes of animals. Factors associated with environmental loading of G. duodenalis included cattle age, cattle stocking number, and precipitation but not lot area, land slope, or cattle density. Vegetated buffer strips were found to significantly reduce waterborne cysts in storm runoff: each additional meter of vegetated buffer placed below high-cattle-use areas was associated with reductions in the concentration and instantaneous load of cysts by factors of 0.86 and 0.79 (-0.07 and -0.10 log(10)/m), respectively. Straw mulch, seed application, scraping of manure, and cattle exclusion did not significantly affect the concentration or load of G. duodenalis cysts. The study findings suggest that vegetated buffer strips, especially when placed near dairy calf areas, should help reduce the environmental loading of these fecal protozoa discharging from dairy farms.

Distribution of Escherichia coli 0157 and Salmonella on hide surfaces, the oral cavity, and in feces of feedlot cattle

To determine the distribution of pathogens on cattle hides at the feedlot, samples were collected from six hide surface locations (back, flank, hock, neck, perineum, and ventrum), the oral cavity, the rectal-anal junction, and the feces of feedlot cattle and subjected to Escherichia coli 0157 detection via culture methods and to Salmonella detection via PCR. E. coli 0157 was isolated from one or more of the sampling locations from 31 (42.5%) of the 73 animals sampled. Location-specific prevalence of E. coli 0157 was 5% for back samples, 5% for flank samples, 12% for hock samples, 7% for neck samples, 12% for perineum samples, 8% for ventrum samples, 1% for oral cavity samples, 4% for rectal-anal junction swabs, and 23% for fecal grab samples. Salmonella was isolated from one or more of these sample locations from 100% (50 of 50 samples) of all animals sampled. Location-specific prevalence of Salmonella was 76% for back samples, 74% for flank samples, 94% for hock samples, 76% for neck samples, 88% for perineum samples, 86% for ventrum samples, 94% for oral cavity samples, 64% for rectal-anal junction swabs, and 50% for fecal grab samples. The sampling locations that maximized the likelihood of finding E. coli 0157 and Salmonella (84 and 96%, respectively) if the animal was positive at one sampling location or more were the hock, perineum, and fecal grab. These data suggest that the use of multiple sample locations is useful when isolating these pathogens from feedlot cattle. Focusing on one sampling location may underestimate the prevalence.

Influence of thymol and a urease inhibitor on coliform bacteria, odor, urea, and methane from a swine production manure pit

Pathogens, ammonia, odor, and greenhouse gas emissions are serious environmental concerns associated with swine production. This study was conducted in two manure pits (33,000 L each) to determine the influence of 1.5 or 3.0 g thymol L(-1) and 80 mg L(-1) urease inhibitor amendments on urea accumulation, coliform bacteria, odor, and methane emission. Each experiment lasted 18 or 19 d, during which time 30 to 36 250-mL samples (six per day) were withdrawn from underneath each pit and analyzed for urea, thymol, volatile fatty acids, coliform bacteria, and Campylobacter. At the end of each experiment, six 50-g samples from each pit were placed in serum bottles, and gas volume and composition were determined periodically for 28 d. Compared with the control pit, volatile fatty acids production was reduced 64 and 100% for the thymol amendments of 1.5 and 3.0 g L(-1), respectively. Viable coliform cells were reduced 4.68 and 5.88 log10 colony-forming units kg(-1) of slurry for the 1.5 and 3.0 g thymol L(-1), respectively, and Escherichia coli were reduced 4.67 and 5.01 log10 colony-forming units kg(-1) of slurry, respectively. Campylobacter was not detected in the pits treated with thymol, in contrast to 63% of the samples being positive for the untreated pit. Urea accumulated in the treated pits from Day 3 to 6. Total gas production from serum bottles was reduced 65 and 76% for thymol amendments of 1.5 and 3.0 g L(-1), respectively, and methane was reduced 78 and 93%, respectively. These results suggest that thymol markedly reduces pathogens, odor, and greenhouse gas emissions from a swine production facility. The urease inhibitor produced a temporary response in conserving urea.

Public farms: hygiene and zoonotic agents

In three successive years, we visited petting farms (n=132), care farms (n=91), and farmyard campsites (n=84), respectively, and completed a standard questionnaire with the objective of determining the hygienic status of these farms and describing hygiene measures implemented to reduce the risk of transmission of zoonotic agents from the animals to humans. For at least 85% of the farms, the overall impression of hygiene was recorded as good. However, more attention must be paid to: informing visitors on hygiene and handwashing, provision of handwashing facilities, and a footwear cleaning facility. Examination of samples of freshly voided faeces resulted in the detection of Shiga toxin-producing Escherichia coli O157 and/or Salmonella spp. and/or Campylobacter spp. at almost two-thirds (64.9%) of the petting farms, and around half of the care farms (56.0%) and farmyard campsites (45.2%). These data reinforce the need for control measures for both public and private farms to reduce human exposure to livestock faeces and thus the risk of transmission of zoonotic diseases. Public awareness of the risk associated with handling animals or faecal material should be increased.

Distribution and ecology of campylobacters in coastal plain streams (Georgia, United States of America)

Campylobacter is the leading cause of bacterium-associated diarrhea in the United States and most developed countries. While this disease is considered a food-borne disease, many clinical cases cannot be linked to a food source. In rural and agrarian areas environmental transmission may be an important factor contributing to case loads. Here we investigated the waterborne prevalence of campylobacters in a mixed-use rural watershed in the coastal plain of southern Georgia (United States). Six sites representing various degrees of agricultural and human influence were surveyed biweekly to monthly for 1 year for the presence of culturable thermophilic campylobacters and other measures of water quality. Campylobacters were frequently present in agriculture- and sewage-impacted stretches of streams. The mean campylobacter counts and overall prevalence were highest downstream from a wastewater treatment plant that handled both human and poultry slaughterhouse waste (<or=595 CFU ml-1; 100% positive); the concentrations were significantly higher than those for the four upstream sites (P<0.05). The counts were significantly correlated with the number of fecal coliform bacteria, conductivity, pH, and concentrations of nutrients (NO3-, PO(4)3-, and NH3). Campylobacters were isolated more frequently and larger numbers were present during the summer months, similar to the occurrence of clinical cases of campylobacteriosis in this region. A multivariate model showed that the levels were significantly influenced by increasing precipitation, which also peaked in the summer. The results indicate that loading from both human and domestic animal waste may be high in the watershed studied during the summer months. Mixed-use watersheds supporting agriculture production, human populations, and wildlife may be at risk for contamination by campylobacters and may be an important route for human exposure.

Salmonella survival in manure-treated soils during simulated seasonal temperature exposure

Addition of animal manure to soil can provide opportunity for Salmonella contamination of soil, water, and food. This study examined how exposure of hog manure-treated loamy sand and clay soils to different simulated seasonal temperature sequences influenced the length of Salmonella survival. A six-strain cocktail of Salmonella serovars (Agona, Hadar, Heidelberg, Montevideo, Oranienburg, and Typhimurium) was added to yield 5 log cfu/g directly to about 5 kg of the two soils and moisture adjusted to 60 or 80% of field capacity (FC). Similarly, the Salmonella cocktail was mixed with fresh manure slurry from a hog nursery barn and the latter added to the two soils at 25 g/kg to achieve 5 log cfu/g Salmonella. Manure was mixed either throughout the soil or with the top kilogram of soil and the entire soil volume was adjusted to 60 or 80% FC. Soil treatments were stored 180 d at temperature sequences representing winter to summer (-18, 4, 10, 25 degrees C), spring to summer (4, 10, 25, 30 degrees C), or summer to winter (25, 10, 4, -18 degrees C) seasonal periods with each temperature step lasting 45 d. Samples for Salmonella recovery by direct plating or enrichment were taken at 0, 7, and 15 d post-inoculation and thereafter at 15-d intervals to 180 d. Salmonella numbers decreased during application to soil and the largest decreases occurred within the first week. Higher soil moisture, manure addition, and storage in the clay soil increased Salmonella survival. Salmonella survived longest (> or = 180 d) in both soils during summer-winter exposure but was not isolated after 160 d from loamy sand soil exposed to other seasonal treatments. For all but one treatment decimal reduction time (DRT45d) values calculated from the first 45 d after application were < or = 30 d and suggested that a 30-d delay between field application of manure in the spring or fall and use of the land would provide reasonable assurance that crop and animal contamination by Salmonella would be minimized.

The epidemiology of antibiotic resistance in Campylobacter

Antibiotic resistance, particularly with the fluoroquinolones and macrolide antibiotics, has now emerged globally with thermophilic campylobacters, including Campylobacter jejuni and C. coli, giving rise to concerns about how these organisms have acquired such resistance characteristics, as well as consequences for human and animal treatment. This review examines (i) the clinical epidemiology of antibiotic resistance in human and animal thermophilic campylobacters, (ii) an update on resistance rates globally, (iii) surveillance of antimicrobial resistance in campylobacters originating from animals, particularly poultry, (iv) the role of the environment in the acquisition and transmission of antibiotic-resistant campylobacters, as well as (v) issues of biocide resistance in campylobacters.

Declines of zoonotic agents in liquid livestock wastes stored in batches on-farm

AIM

To measure the decline rates of zoonotic agents introduced into liquid livestock wastes in on-farm storage tanks.

METHODS AND RESULTS

Salmonella spp., Escherichia coli O157, Campylobacter jejuni, Listeria monocytogenes and Cryptosporidium parvum, propagated in laboratory-controlled conditions, were inoculated into 35,000-l volumes of fresh livestock wastes (pig slurries, cattle slurries and dirty waters). D-values for bacteria were six to 44 days, and for C. parvum were 133 to 345 days. Campylobacter jejuni declined significantly more rapidly than the other bacterial pathogens, while E. coli O157 declined significantly more slowly. On average, bacterial declines were not affected by the season of waste deposition and storage or by the dry matter content of the wastes, but were more rapid in dirty waters than in pig slurries. The physiciochemical composition of wastes in each category varied significantly.

CONCLUSIONS

Zoonotic agents can survive for several months during storage of liquid livestock wastes. Livestock wastes should be batch-stored and not subjected to continuous additions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates that batches of liquid livestock waste, if contaminated with bacterial pathogens, should be stored for 6 months to reduce contamination levels. Alternative strategies for reducing C. parvum levels in liquid livestock wastes should be explored.

Decline of zoonotic agents in livestock waste and bedding heaps

AIMS

To measure the rates of decline of zoonotic agents introduced into heaps of spent bedding and faecal wastes generated by commercially farmed livestock and managed in a similar way to that of a working farm.

METHODS AND RESULTS

Livestock isolates of Salmonella, pathogenic Listeria, Campylobacter and Escherichia coli O157 were laboratory cultured and used to inoculate 5 m3 heaps of cattle, sheep or pig wastes mixed with bedding materials. Decline of each of the infectious agents was monitored with time as was the temperature inside each heap. Temperatures of >50 degrees C were typically achieved at the core of the heaps. Pathogen decline was rapid, typically <3 days for a 1-log reduction in levels. The longest time that zoonotic agents were isolated from the heaps was 93 days.

CONCLUSIONS

Movement of heaps of livestock bedding waste from animal pens to a secondary store, and storing them under conditions conducive for increased temperature is a simple and cost-effective treatment for rapidly lowering levels of zoonotic agents in solid farm wastes.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates a simple and cheap treatment that can be used to help prevent the spread of zoonotic agents through agricultural environments.