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.

Kinetic model-based prediction of the persistence of Salmonella enterica serovar Typhimurium under tropical agricultural field conditions.

AIM: Present a kinetic model-based approach for using isothermal data to predict the survival of manure-borne enteric bacteria under dynamic conditions in an agricultural environment. METHODS AND RESULTS: A model to predict the survival of Salmonella enterica serovar Typhimurium under dynamic temperature conditions in soil in the field was developed. The working hypothesis was that the inactivation phenomena associated with the survival kinetics of an organism in an agricultural matrix under dynamic temperature conditions is for a large part due to the cumulative effect of inactivation at various temperatures within the continuum registered in the matrix in the field. The modelling approach followed included (i) the recording of the temperature profile that the organism experiences in the field matrix, (ii) modelling the survival kinetics under isothermal conditions at a range of temperatures that were registered in the matrix in the field; and (iii) using the isothermal-based kinetic models to develop models for predicting survival under dynamic conditions. The time needed for 7 log CFU g(-1) Salmonella Typhimurium in manure and manure-amended soil to reach the detection limit of the enumeration method (2 log CFU g(-1) ) under tropical conditions in the Central Agro-Ecological Zone of Uganda was predicted to be 61-68 days and corresponded with observed CFU of about 2·2-3·0 log CFU g(-1) , respectively. The Bias and Accuracy factor of the prediction was 0·71-0·84 and 1·2-1·4, respectively. CONCLUSIONS: Survival of Salm. Typhimurium under dynamic field conditions could be for 71-84% determined by the developed modelling approach, hence substantiating the working hypothesis. SIGNIFICANCE AND IMPACT OF THE STUDY: Survival kinetic models obtained under isothermal conditions can be used to develop models for predicting the persistence of manure-borne enteric bacteria under dynamic field conditions in an agricultural environment.

Transfer and internalisation of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in cabbage cultivated on contaminated manure-amended soil under tropical field conditions in Sub-Saharan Africa.

Surface contamination and internalisation of Escherichia coli O157:H7 and Salmonella Typhimurium in cabbage leaf tissues at harvest (120 days post-transplantation) following amendment of contaminated bovine manure to soil at different times during crop cultivation were investigated under tropical field conditions in the Central Agro-Ecological Zone of Uganda. Fresh bovine manure inoculated with rifampicin-resistant derivatives of non-virulent strains of E. coli O157:H7 and S. Typhimurium was incorporated into the soil to achieve inoculum concentrations of 4 and 7 log CFU/g at the point of transplantation, 56 or 105 days post-transplantation of cabbage seedlings. Frequent sampling of the soil enabled the accurate identification of the survival kinetics in soil, which could be described by the Double Weibull model in all but one of the cases. The persistence of 4 log CFU/g E. coli O157:H7 and S. Typhimurium in the soil was limited, i.e. only inocula applied 105 days post-transplantation were still present at harvest. Moreover, no internalisation in cabbage leaf tissues was observed. In contrast, at the 7 log CFU/g inoculum level, E. coli O157:H7 and S. Typhimurium survived in the soil throughout the cultivation period. All plants (18/18) examined for leaf contamination were positive for E. coli O157:H7 at harvest irrespective of the time of manure application. A similar incidence of leaf contamination was found for S. Typhimurium. On the other hand, only plants (18/18) cultivated on soil amended with contaminated manure at the point of transplantation showed internalised E. coli O157:H7 and S. Typhimurium at harvest. These results demonstrate that under tropical field conditions, the risk of surface contamination and internalisation of E. coli O157:H7 and S. Typhimurium in cabbage leaf tissues at harvest depend on the inoculum concentration and the time of manure application. Moreover, the internalisation of E. coli O157:H7 and S. Typhimurium in cabbage leaf tissues at harvest seems to be limited to the worst case situation, i.e., when highly contaminated manure is introduced into the soil at the time of transplantation of cabbage seedlings.

A rapid monitoring assay for the detection of Salmonella spp. and Salmonella Senftenberg strain W775 in composts.

AIMS: The composting process needs to be validated for its hygienic status in order to ensure that it is free of pathogens. Generally, this is evaluated through temperature monitoring, or additionally through active inoculation and monitoring of indicator organisms. We aimed to develop a monitoring method for the heat-resistant indicator organism Salmonella enterica ssp. enterica serovar Senftenberg strain W775 for detection in composting biowastes. METHODS AND RESULTS: The method development is comprised of: (i) optimization of molecular detection of bacteria belonging to the genus Salmonella; (ii) identification of a DNA marker for Salmonella strain W775; and (iii) development of a multiplex polymerase chain reaction (PCR)-based on both DNA markers. Subsequently, Salmonella strain W775 was inoculated and monitored during composting of biowastes in an industrial composting facility. CONCLUSIONS: A highly sensitive and specific detection of viable cells was obtained by enriching the compost sample prior to multiplex PCR analysis. Complete inactivation of Salmonella strain W775 was obtained within 4 days in an industrial composting facility at temperatures ranging between 41 and 57 degrees C. SIGNIFICANCE AND IMPACT OF THE STUDY: We describe a monitoring method for the simultaneous detection of naturally occurring Salmonella strains and artificially introduced Salmonella strain W775 in composting biowastes that can be applied in routine analysis.

Inactivation of Salmonella Senftenberg strain W 775 during composting of biowastes and garden wastes.

AIMS: Determination of the minimum requirements (time-temperature relationship and moisture content) that are needed for a sufficient eradication of an indicator organism. METHODS AND RESULTS: To determine the hygienic safety of composting processes, the indicator organism Salmonella enterica ssp. enterica serotype Senftenberg strain W 775 (further abbreviated as W 775) was artificially inoculated on a meat carrier and monitored subsequently. Different types of composting processes, e.g. composting in enclosed facilities, in open-air and in-vessel composting, were investigated. The waste feedstocks used in this work were either biowastes (i.e. vegetable, fruit and garden wastes; also called source-separated household wastes) or pure garden wastes. Beside these large-scale trials, we also conducted some lab experiments in order to determine the impact of temperature, moisture content and the presence of an indigenous microflora on the eradication of W 775. We found the temperature to be the most important parameter to eradicate W 775 from compost. When the temperature of the compost heap is 60 degrees C and the moisture content varies between 60-65%, W 775 (10(8) CFU g(-1)) will be inactivated within 10 h of composting. The moisture content is, beside temperature, a second parameter that influences the survival of W 775. When the water content of the composting materials or meat carriers is reduced, a higher survival rate of W 775 was observed (survival rate increases 0.5 log(10) unit when there is a reduction of 5% in moisture content). In addition, other parameters (such as microbial antagonism, toxic compounds, etc.) have an influence on the survival of W 775 as well. CONCLUSIONS: Our study demonstrates that all types of composting processes tested in this work were sufficient to eradicate W 775 providing that they are well managed in terms of temperature and moisture content. SIGNIFICANCE AND IMPACT OF THE STUDY: To give a better view on the parameters of importance for the eradication of W 775 during composting.

Optimalisation and feasability of bioremediation systems for the processing of spray losses of pesticides.

Contamination of ground and surface water puts pressure on the use of pesticides. Pesticide contamination of water can often be linked to point sources rather than to diffuse sources. Examples of such point sources are areas on farms where pesticides are handled, filled into sprayers and where sprayers are cleaned. To reduce contamination from these point sources, different kinds of bio-remediation systems are in various member states of the EU. Bioremediation is the use of living organisms, primarily micro-organisms, to degrade the environmental contaminants into less toxic forms. In this study, the behaviour of six different pesticides with varying physico-chemical properties on substrates used in a bioremediation system is studied. The adsorption of individual pesticides on the substrates is determined. After determination of the adsorption coefficient Kd, it could be concluded for metalaxyl that coco chips had the highest sorption capacity, followed by straw, compost, willow chopping and a sandy loam soil.

Microbiological aspects of biowaste during composting in a monitored compost bin.

AIMS: To determine the microbial succession of the dominating taxa and functional groups of microorganisms and the total microbial activity during the composting of biowaste in a monitored process. METHODS AND RESULTS: Biowaste (vegetable, fruit and garden waste) was composted in a monitored composting bin system. During the process, taxonomic and functional subpopulations of microorganisms were enumerated, and dominating colonies were isolated and identified. All counts decreased during the thermophilic phase of the composting, but increased again when the temperature declined. Total microbial activity, measured with an enzyme activity assay, decreased during the thermophilic phase, increased substantially thereafter, and decreased again during maturation. Bacteria dominated during the thermophilic phase while fungi, streptomycetes and yeasts were below the detection limit. Different bacterial populations were found in the thermophilic and mesophilic phases. In fresh wastes and during the peak-heating phase, all bacterial isolates were bacilli. During the cooling and maturation phase the bacterial diversity increased, including also other Gram-positive and Gram-negative bacteria. Among the fungi, Aspergillus spp. and Mucor spp. were predominant after the thermophilic phase. CONCLUSIONS: The microbial abundance, composition and activity changed substantially during composting and compost maturity was correlated with high microbial diversity and low activity. SIGNIFICANCE AND IMPACT OF THE STUDY: A more complete overview of the whole composting process of biowaste, based on microbial counts, species diversity and functional groups and abiotic parameters is presented, and the potential of a simple enzyme assay to measure total microbial activity was demonstrated.