COLIWAVE a simulation model for survival of E. coli O157:H7 in dairy manure and manure-amended soil

A Predictive Model for Survival of Escherichia coli O157:H7 and Generic E. coli in Soil Amended with Untreated Animal Manure

This study aimed at developing a predictive model that captures the influences of a variety of agricultural and environmental variables and is able to predict the concentrations of enteric bacteria in soil amended with untreated Biological Soil Amendments of Animal Origin (BSAAO) under dynamic conditions. We developed and validated a Random Forest model using data from a longitudinal field study conducted in mid-Atlantic United States investigating the survival of Escherichia coli O157:H7 and generic E. coli in soils amended with untreated dairy manure, horse manure, or poultry litter. Amendment type, days of rain since the previous sampling day, and soil moisture content were identified as the most influential agricultural and environmental variables impacting concentrations of viable E. coli O157:H7 and generic E. coli recovered from amended soils. Our model results also indicated that E. coli O157:H7 and generic E. coli declined at similar rates in amended soils under dynamic field conditions.The Random Forest model accurately predicted changes in viable E. coli concentrations over time under different agricultural and environmental conditions. Our model also accurately characterized the variability of E. coli concentration in amended soil over time by providing upper and lower prediction bound estimates. Cross-validation results indicated that our model can be potentially generalized to other geographic regions and incorporated into a risk assessment for evaluating the risks associated with application of untreated BSAAO. Our model can be validated for other regions and predictive performance also can be enhanced when data sets from additional geographic regions become available.

Survival of Salmonella enterica Typhimurium in water amended with manure

Outbreaks of Salmonella enterica have been associated with water sources. Survival of S. enterica in various environments has been studied but survival in water has rarely been attempted. In two separate experiments, we examined the survival of S. enterica Typhimurium in clean spring water at various eutrophication levels and temperatures. In the first experiment, lasting for 135 days, survival of S. enterica (10(10) CFU/ml) in water with 0, 50, 100, 500, and 1,000 mg/liter of added carbon at 7, 17, and 27°C was monitored weekly. In the second experiment, lasting for 3 weeks, survival of S. enterica in water at 0, 100, and 200 mg/ liter of added carbon and 27°C was studied daily. Each experiment had four replicates. Dissolved organic carbon was measured daily in each experiment. At the beginning, midpoint, and end of the survival study, microbial communities in both experiments were assessed by denaturing gradient gel electrophoresis (DGGE). Even at minimal carbon concentrations, S. enterica survived for at least 63 d. Survival of Salmonella was highly dependent on eutrophication levels (as measured by dissolved organic carbon) and temperature, increasing at high eutrophication levels, but decreasing at high temperatures. Survival was also strongly affected by microbial competition or predation.

Enteric pathogen survival varies substantially in irrigation water from Belgian lettuce producers

It is accepted that irrigation water is a potential carrier of enteric pathogens, such as Salmonella and E. coli O157:H7 and, therefore, a source for contamination of fresh produce. We tested this by comparing irrigation water samples taken from five different greenhouses in Belgium. The water samples were inoculated with four zoonotic strains, two Salmonella and two E. coli O157:H7 strains, and pathogen survival and growth in the water were monitored up till 14 days. The influence of water temperature and chemical water quality was evaluated, and the survival tests were also performed in water samples from which the resident aquatic microbiota had previously been eliminated by filter sterilization. The pathogen's survival differed greatly in the different irrigation waters. Three water samples contained nutrients to support important growth of the pathogens, and another enabled weaker growth. However, for all, growth was only observed in the samples that did not contain the resident aquatic microbiota. In the original waters with their specific water biota, pathogen levels declined. The same survival tendencies existed in water of 4 °C and 20 °C, although always more expressed at 20 °C. Low water temperatures resulted in longer pathogen survival. Remarkably, the survival capacity of two E. coli 0157:H7 strains differed, while Salmonella Thompson and Salmonella Typhimurium behaved similarly. The pathogens were also transferred to detached lettuce leaves, while suspended in two of the water samples or in a buffer. The effect of the water sample on the pathogen's fitness was also reproduced on the leaves when stored at 100% relative humidity. Inoculation of the suspension in buffer or in one of the water samples enabled epiphytic growth and survival, while the pathogen level in the other water sample decreased once loaded on the leaves. Our results show that irrigation waters from different origin may have a different capacity to transmit enteric pathogens and an important impact on the fitness of the pathogens to sustain and even grow on the leaf surface.

Viability of 'Candidatus Liberibacter asiaticus' prolonged by addition of citrus juice to culture medium

Huanglongbing, or citrus greening disease, is associated with infection by the phloem-limited bacterium 'Candidatus Liberibacter asiaticus'. Infection with 'Ca. L. asiaticus' is incurable; therefore, knowledge regarding 'Ca. L. asiaticus' biology and pathogenesis is essential to develop a treatment. However, 'Ca. L. asiaticus' cannot currently be successfully cultured, limiting its study. To gain insight into the conditions conducive for growth of 'Ca. L. asiaticus' in vitro, 'Ca. L. asiaticus' inoculum obtained from seed of fruit from infected pomelo trees (Citrus maxima 'Mato Buntan') was added to different media, and cell viability was monitored for up to 2 months using quantitative polymerase chain reaction in conjunction with ethidium monoazide. Media tested included one-third King's B (K), K with 50% juice from the infected fruit, K with 50% commercially available grapefruit juice, and 100% commercially available grapefruit juice. Results show that juice-containing media dramatically prolong viability compared with K in experiments reproduced during 2 years using different juice sources. Furthermore, biofilm formed at the air-liquid interface of juice cultures contained 'Ca. L. asiaticus' cells, though next-generation sequencing indicated that other bacterial genera were predominant. Chemical characterization of the media was conducted to discuss possible factors sustaining 'Ca. L. asiaticus' viability in vitro, which will contribute to future development of a culture medium for 'Ca. L. asiaticus'.

Factors affecting the occurrence of Escherichia coli O157 contamination in irrigation ponds on produce farms in the Suwannee River Watershed

Outbreaks of enteritis caused by Escherichia coli O157 associated with fresh produce have resulted in questions about the safety of irrigation water; however, associated risks have not been systematically evaluated. In this study, the occurrence and distribution of the human pathogen E. coli O157 from vegetable irrigation ponds within the Suwannee River Watershed in Georgia were investigated, and the relationship to environmental factors was analyzed. Surface and subsurface water samples were collected monthly from 10 vegetable irrigation ponds from March 2011 to February 2012. Escherichia coli O157 was isolated from enriched filtrates on CHROMagar and sorbitol MacConkey agar media and confirmed by an agglutination test. Presence of virulence genes stx1, stx2 , and eae was tested by polymerase chain reaction. In addition, 27 environmental variables of the sampled ponds were measured. Denaturing gradient gel electrophoresis was conducted for the analysis of bacterial communities in the water samples. Biserial correlation coefficients were calculated to evaluate the log10 colony-forming unit per millilitre correlations between the environmental factors and the occurrence of E. coli O157. Stepwise and canonical discriminant analyses were used to determine the factors that were associated with the presence and absence of E. coli O157 in water samples. All 10 ponds were positive for E. coli O157 some of the time, mainly in summer and fall of 2011. The temporal distribution of this bacterium differed among the 10 ponds. Temperature, rainfall, populations of fecal coliform, and culturable bacteria were positively correlated with the occurrence of E. coli O157 (P < 0.05), while the total nitrogen concentration, oxidation-reduction potential, and dissolved oxygen concentration were negatively correlated with the occurrence of this pathogen (P < 0.05). Temperature and rainfall were the most important factors contributing to the discrimination between samples with and without E. coli O157, followed by bacterial diversity and culturable bacteria population density. Bacterial numbers and diversity, including fecal coliforms and E. coli O157, increased after rainfall (and possibly runoff from pond margins) in periods with relatively high temperatures, suggesting that prevention of runoff may be important to minimize the risk of enteric pathogens in irrigation ponds.

Presence and survival of Escherichia coli O157:H7 on lettuce leaves and in soil treated with contaminated compost and irrigation water

Escherichia coli O157:H7 outbreaks associated with produce consumption have brought attention to contaminated compost manure, and polluted irrigation water as potential sources of pathogens for the contamination of these crops. The aim of this study was to determine the potential transfer of E. coli O157:H7 from soil fertilized with contaminated compost or irrigated with contaminated water to edible parts of lettuce together with its persistence in soil under field conditions in two different seasons (fall and spring). Moreover, its survival on lettuce sprinkled with contaminated irrigation water was evaluated, as well as the prevalence of aerobic mesophilic, Enterobacteriaceae and Pseudomonadaceae in control lettuce samples. Four treatments, contaminated compost, surface and sprinkle irrigation with contaminated water and uninoculated pots, were used in this work. Contaminated compost was applied to soil in the pots before lettuce was transplanted and contaminated irrigation water was applied twice and three times on the plants after the seedlings were transplanted, for sprinkle and surface irrigation, respectively. E. coli O157:H7 survived in soil samples for 9 weeks at levels, 4.50 log cfu gdw(-1) (dw, dry weight) in fall and 1.50 log cfu gdw(-1) in spring. The pathogen survives better in fall, indicating an important influence of environmental factors. E. coli O157:H7 population in lettuce leaves after sprinkle irrigation was very high (between 10(3) and 10(6) cfu g(-1)), but decreased to undetectable levels at field conditions. There was also transfer of E. coli O157:H7 from soil contaminated with compost or irrigated with contaminated water to lettuce leaves, mainly to the outer ones. The mean counts for aerobic mesophilic, Enterobacteriaceae and Pseudomonadaceae populations were also influenced by environmental conditions; higher levels were observed under fall conditions than in spring conditions. Contamination of lettuce plants in the field can occur through both contaminated composted manure and irrigation water and persist for several months.

Variability of Escherichia coli O157 strain survival in manure-amended soil in relation to strain origin, virulence profile, and carbon nutrition profile

The variation in manure-amended soil survival capability among 18 Escherichia coli O157 strains (8 animal, 1 food, and 9 human isolates) was studied using a single sandy soil sample and a single sample of cattle manure as the inoculum carrier. The virulence profiles of E. coli O157 strains were characterized by detection of virulence determinants (73 genes, 122 probes in duplicate) by using the Identibac E. coli genotyping DNA miniaturized microarray. Metabolic profiling was done by subjecting all strains to the Biolog phenotypic carbon microarray. Survival times (calculated as days needed to reach the detection limit using the Weibull model) ranged from 47 to 266 days (median, 120 days). Survival time was significantly higher for the group of human isolates (median, 211 days; minimum [min.], 71; maximum [max.], 266) compared to the group of animal isolates (median, 70 days; min., 47; max., 249) (P = 0.025). Although clustering of human versus animal strains was observed based on pulsed-field gel electrophoresis (PFGE) patterns, no relation between survival time and the presence of virulence genes was observed. Principal component analysis on the metabolic profiling data revealed distinct clustering of short- and long-surviving strains. The oxidization rate of propionic acid, α-ketobutyric acid, and α-hydroxybutyric acid was significantly higher for the long-surviving strains than for the short-surviving strains. The oxidative capacity of E. coli O157 strains may be regarded as a phenotypic marker for enhanced survival in manure-amended soil. The large variation observed in survival is of importance for risk assessment models.

Influence of aerobic and anaerobic conditions on survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in Luria-Bertani broth, farm-yard manure and slurry

The influence of aerobic and anaerobic conditions on the survival of the enteropathogens Escherichia coli O157:H7 and Salmonella serovar Typhimurium was investigated in microcosms with broth, cattle manure or slurry. These substrates were inoculated with a green fluorescent protein transformed strain of the enteropathogens at 10(7) cells g(-1) dry weight. Survival data was fitted to the Weibull model. The survival curves in aerobic conditions generally showed a concave curvature, while the curvature was convex in anaerobic conditions. The estimated survival times showed that E. coli O157:H7 survived significantly longer under anaerobic than under aerobic conditions. Survival ranged from approximately. 2 weeks for aerobic manure and slurry to more than six months for anaerobic manure at 16 °C. On average, in 56.3% of the samplings, the number of recovered E. coli O157:H7 cells by anaerobic incubation of Petri plates was significantly (p < 0.05) higher in comparison with aerobic incubation. Survival of Salmonella serovar Typhimurium was not different between aerobic and anaerobic storage of LB broth or manure as well as between aerobic and anaerobic incubation of Petri dishes. The importance of changes in microbial community and chemical composition of manure and slurry was distinguished for the survival of E. coli O157:H7 in different oxygen conditions.

Survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in manure and manure-amended soil under tropical climatic conditions in Sub-Saharan Africa

AIMS

  To establish the fate of Escherichia coli O157:H7 and Salmonella Typhimurium in manure and manure-amended agricultural soils under tropical conditions in Sub-Saharan Africa.

METHODS AND RESULTS

  Survival of nonvirulent E. coli O157:H7 and Salm. Typhimurium at 4 and 7 log CFU g(-1) in manure and manure-amended soil maintained at ≥80% r.h. or exposed to exclusive field or screen house conditions was determined in the Central Agro-Ecological Zone of Uganda. Maintaining the matrices at high moisture level promoted the persistence of high-density inocula and enhanced the decline of low-density inocula in the screen house, but moisture condition did not affect survival in the field. The large majority of the survival kinetics displayed complex patterns corresponding to the Double Weibull model. The two enteric bacteria survived longer in manure-amended soil than in manure. The 7 log CFU g(-1) E. coli O157:H7 and Salm. Typhimurium survived for 49-84 and 63-98 days, while at 4 log CFU g(-1) , persistence was 21-28 and 35-42 days, respectively.

CONCLUSIONS

  Under tropical conditions, E. coli O157:H7 and Salm. Typhimurium persisted for 4 and 6 weeks at low inoculum density and for 12 and 14 weeks at high inoculum density, respectively.

SIGNIFICANCE AND IMPACT OF THE STUDY

  Persistence in the tropics was (i) mostly shorter than previously observed in temperate regions thus suggesting that biophysical conditions in the tropics might be more detrimental to enteric bacteria than in temperate environments; (ii) inconsistent with published data isothermally determined previously hence indicating the irrelevance of single point isothermal data to estimate survival under dynamic temperature conditions.