Bacterial contamination of tile drainage water and shallow groundwater under different application methods of liquid swine manure.

A 2 year field experiment evaluated liquid manure application methods on the movement of manure-borne pathogens (Salmonella sp.) and indicator bacteria (Escherichia coli and Clostridium perfringens) to subsurface water. A combination of application methods including surface application, pre-application tillage, and post-application incorporation were applied in a randomized complete block design on an instrumented field site in spring 2007 and 2008. Tile and shallow groundwater were sampled immediately after manure application and after rainfall events. Bacterial enumeration from water samples showed that the surface-applied manure resulted in the highest concentration of E. coli in tile drainage water. Pre-tillage significantly (p < 0.05) reduced the movement of manure-based E. coli and C. perfringens to tile water and to shallow groundwater within 3 days after manure application (DAM) in 2008 and within 10 DAM in 2007. Pre-tillage also decreased the occurrence of Salmonella sp. in tile water samples. Indicator bacteria and pathogens reached nondetectable levels within 50 DAM. The results suggest that tillage before application of liquid swine manure can minimize the movement of bacteria to tile and groundwater, but is effective only for the drainage events immediately after manure application or initial rainfall-associated drainage flows. Furthermore, the study highlights the strong association between bacterial concentrations in subsurface waters and rainfall timing and volume after manure application.

Evaluation of Petrifilm EC method for enumeration of E. coli from soil.

AIMS: To evaluate the suitability of commercially available Petrifilm EC plates for enumeration of Escherichia coli from soil. METHODS AND RESULTS: A confirmed E. coli strain isolated from liquid swine manure was inoculated into sterilized sandy clay loam and loam soils at the concentrations of 10(2), 10(3), 10(5) CFU g(-1) of soil. The efficiency of recovery on Petrifilm EC plates for soils spiked with E. coli was compared with standard membrane filtration techniques on m-FC basal medium supplemented with 3-bromo-4-chloro-5-indoyl-beta-D-glucopyranoside (BCIG) and most probable numbers (MPN) techniques in E. coli medium with 4-methylumbelliferyl-beta-D-glucuronide (EC-MUG) broth. Petrifilm EC and m-FC (BCIG) methods were then assessed for the ability to recover E. coli from field soils applied with swine manure. No significant differences (P > 0.05) were observed between Petrifilm EC, m-FC (BCIG) and MPN methods for the recovery of E. coli from spiked samples, irrespective of soil type. However, recovery of E. coli from manure-applied field soil samples showed a significant difference (P < 0.05) between the Petrifilm EC method and the m-FC method in enumerating E. coli possibly as a result of false positives on m-FC. CONCLUSION: The Petrifilm EC method is suitable for the enumeration of E. coli from soil with a detection limit of 10 CFU g(-1) soil. SIGNIFICANCE AND IMPACT OF THE STUDY: The commercially available Petrifilm EC method is comparatively low cost, easy to use method for the enumeration of E. coli from soil without the need for further confirmation tests.