Biomedical subjects

Christopher D Clegg

Publications and source records attributed to Christopher D Clegg.

3 recordsLinked to original sources

PubMed2006

Differential E. coli die-off patterns associated with agricultural matrices.

The investigation of fecal bacterial die-off in various agricultural and catchment related matrices remains important because of the growing concern over pathogens in agricultural environments and watercourses. The aim of this research was to investigate the die-off of Escherichia coli within cattle manure (both slurry [liquid mix of excrement and urine produced by housed livestock] and feces), soil, and runoff water and to determine if cell numbers would be influenced by the presence of cattle manure within soil and runoff water. E. coli survived better within feces than in slurry; cells within feces declined from 7.5 to 3.3 log CFU g(-1) in 76 days. Within slurry, cells fell from 8.5 log CFU g(-1) to below levels of detection by day 42. E. coli died off more quickly within manure and slurry than in soil amended with the same fecal material, and declined significantly faster within microcosms when introduced to the soil via sterile water rather than cattle manure. E. coli was found to decline more rapidly within wet (50% moisture w/w), rather than dry (25% moisture w/w), soil. Conversely, in runoff water, die-off of E. coli was increased in the presence of feces. Overall, E. coli die-off was most rapid in water incorporated with cattle manure > unincorporated cattle manure > soil incorporated with cattle manure. The derived die-off characteristics including half-life and decimal reduction times can now provide (i) input for predictive models and (ii) information upon which to consider mitigation strategies associated with both manure and land management.

Agriculture↗

PubMed2005

Transfer of Escherichia coli to water from drained and undrained grassland after grazing.

The aim of this study was to determine the load of Escherichia coli transferred via drainage waters from drained and undrained pasture following a grazing period. Higher concentrations (ranging between 10(4) and 10(3) colony forming units [CFU] g(-1)) of E. coli persisted in soil for up to 60 d beyond the point where cattle were removed from the plots, but these eventually declined in the early months of spring to concentrations less than 10(2) CFU g(-1). The decline reflects the combined effect of cell depletion from the soil store through both wash-out and die-off of E. coli. No difference (P > 0.05) was observed in E. coli loads exported from drained and undrained plots. Similarly, no difference (P > 0.05) was observed in E. coli concentrations in drainage waters of mole drain flow and overland plus subsurface interflow. Intermittent periods of elevated discharge associated with storm events mobilized E. coli at higher concentrations (e.g., in excess of 400 CFU mL(-1)) than observed during low flow conditions (often <25 CFU mL(-1)). The combination of high discharge and cell concentrations resulted in the export of E. coli loads from drained and undrained plots exceeding 10(6) CFU L(-1) s(-1). The results highlight the potential for drained land to export E. coli loads comparable with those transferred from undrained pasture.

Agriculture↗

PubMed2005

Influence of inorganic nitrogen management regime on the diversity of nitrite-oxidizing bacteria in agricultural grassland soils.

To assess links between the diversity of nitrite-oxidizing bacteria (NOB) in agricultural grassland soils and inorganic N fertilizer management, NOB communities in fertilized and unfertilized soils were characterized by analysis of clone libraries and denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. Previously uncharacterized Nitrospira-like sequences were isolated from both long-term-fertilized and unfertilized soils, but DGGE migration patterns indicated the presence of additional sequence types in the fertilized soils. Detailed phylogenetic analysis of Nitrospira-like sequences suggests the existence of one newly described evolutionary group and of subclusters within previously described sublineages, potentially representing different ecotypes; the new group may represent a lineage of noncharacterized Nitrospira species. Clone libraries of Nitrobacter-like sequences generated from soils under different long-term N management regimes were dominated by sequences with high similarity to the rhizoplane isolate Nitrobacter sp. strain PJN1. However, the diversity of Nitrobacter communities did not differ significantly between the two soil types. This is the first cultivation-independent study of nitrite-oxidizing bacteria in soil demonstrating that nitrogen management practices influence the diversity of this bacterial functional group.

Bacteria↗