Browsing by Author "Geeraerd, A.H."

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    Kinetic Model-Based Prediction of the Persistence of Salmonella Enterica Serovar Typhimurium under Tropical Agricultural Field Conditions
    (Journal of applied microbiology, 2011) Ongeng, D.; Muyanja, C.; Ryckeboer, J.; Springael, D.; Geeraerd, A.H.
    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. 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−1Salmonella 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. Survival of Salm. Typhimurium under dynamic field conditions could be for 71–84% determined by the developed modelling approach, hence substantiating the working hypothesis.
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    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
    (Journal of applied microbiology, 2011) Ongeng, D.; Muyanja, C.; Geeraerd, A.H.; Springael, D.; Ryckeboer, J.
    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. 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−1E. 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. 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.
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    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
    (International Journal of Food Microbiology, 2011) Ongeng, D.; Vasquez, G.A.; Muyanja, C.; Ryckeboer, J.; Geeraerd, A.H.; Springael, D.
    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.