Survival of Escherichia coli, Enterococci, and Campylobacter spp. in sheep feces on pastures.

The survival of enteric bacteria in 10 freshly collected sheep fecal samples on pastures was measured in each of four seasons. Ten freshly collected feces were placed on pasture, and concentrations of Escherichia coli, enterococci, and Campylobacter spp. were monitored until exhaustion of the fecal samples. In all four seasons, there was an increase in enterococcal concentrations by up to 3 orders of magnitude, with peak concentrations recorded between 11 and 28 days after deposition. E. coli concentrations increased in three out of four seasons by up to 1.5 orders of magnitude, with peak concentrations recorded between 8 and 14 days after deposition. The apparent growth of E. coli and enterococci was strongly influenced by the initial water content of the feces and the moisture gained during periods of rehydration following rainfalls. Conversely, the results suggested that dehydration promoted inactivation. Campylobacter spp. did not grow and were rapidly inactivated at a rate that tended to be faster at higher temperatures. Pulsed-field gel electrophoresis (PFGE) of a selection of Campylobacter spp. suggested that these survival data are applicable to a range of Campylobacter spp., including the most frequently isolated PFGE genotype from sheep in New Zealand, and to genotypes previously observed to cause disease in humans. The results of this study are currently being incorporated into a fecal microbe reservoir model that is designed to assist water managers' abilities to estimate microbial loads on pastures grazed by sheep, including the influence of factors such as rainfall and temperature.

Transport of Escherichia coli and F-RNA bacteriophages in a 5m column of saturated pea gravel.

The relative transport and attenuation of bacteria, bacteriophages, and bromide was determined in a 5m long x 0.3m diameter column of saturated pea gravel. The velocity (V), longitudinal dispersivity (alpha(x)) and total removal rate (lambda) were calculated from the breakthrough curves at 1m, 3m, and 5m, at a flow rate of 32Lh(-1). Inactivation (mu) rates were determined in survival chambers. Two pure culture experiments with Escherichia coli J6-2 and F-RNA phage MS2 produced an overall V ranking of E. coli J6-2>MS2>bromide, consistent with velocity enhancement, whereby larger particles progressively move into faster, central streamlines of saturated pores. Removal rates were near zero for MS2, but were higher for E. coli J6-2. In two sewage experiments, E. coli and F-RNA phage Vs were similar (but > bromide). This was attributed to phage adsorption to colloids similar in size to E. coli cells. Sewage phage removal rates were higher than for the pure MS2 cultures. The application of filtration theory suggested that, whereas free phage were unaffected by settling, this was the primary removal mechanism for the colloid-associated phage. However, cultured and sewage E. coli removal rates were similar, suggesting the dominance of free E. coli cells in the sewage. When MS2 was attached to kaolin particles, it was transported faster than free MS2, but at similar rates to sewage phage. The mu values indicated little contribution of inactivation to removal of either cultured or sewage microorganisms. The results showed the importance of association with colloids in determining the relative transport of bacteria and viruses in gravels.

Survival of indicator and pathogenic bacteria in bovine feces on pasture.

The survival of enteric bacteria was measured in bovine feces on pasture. In each season, 11 cow pats were prepared from a mixture of fresh dairy cattle feces and sampled for up to 150 days. Four pats were analyzed for Escherichia coli, fecal streptococci, and enterococci, and four inoculated pats were analyzed for Campylobacter jejuni and Salmonella enterica. Two pats were placed on drainage collectors, and another pat was fitted with a temperature probe. In the first 1 to 3 weeks, there were increases (up to 1.5 orders of magnitude) in the counts of enterococci (in four seasons), E. coli (three seasons), fecal streptococci (three seasons), and S. enterica (two seasons), but there was no increase in the counts of C. jejuni. Thereafter, the counts decreased, giving an average ranking of the times necessary for 90% inactivation of C. jejuni (6.2 days from deposition) < fecal streptococci (35 days) < S. enterica (38 days) < E. coli (48 days) < enterococci (56 days). The pat temperature probably influenced bacterial growth, but the pattern of increases and decreases was primarily determined by desiccation; growth occurred when the water content was greater than 80%, but at a water content of 70 to 75% counts decreased. E. coli and enterococcus regrowth appeared to result from pat rehydration. Of 20 monthly leaching losses of E. coli, 16 were <10% of the total counts in the pat, and 12 were <1%. Drainage losses of C. jejuni (generally <1%) were detected for only 1 to 2 months. Although enterococci exhibited the best survival rate, higher final counts suggested that E. coli is the more practical indicator of bovine fecal pollution.