Recovery of Salmonella from Bermudagrass exposed to simulated wastewater
Most confined swine (Sus scrofa) feeding operations in the southeastern United States hold manure in lagoons and apply effluent on bermudagrass [Cynodon dactylon (L.) Pers.] as fertilizer. Salmonella enterica subsp. enterica (ex Kauffman and Edwards) Le Minor and Popoff, has been reported in Mississippi lagoons, but levels and potential for contamination of bermudagrass were unknown. A laboratory method was developed to examine Salmonella contamination of bermudagrass and levels of Salmonella were determined in lagoons. The U.S. Environmental Protection Agency (EPA) worst case water was used to simulate effluent in exposing bermudagrass to Salmonella. Exposed leaves were washed and bacteria enumerated. Contamination of leaves exposed to 106 cfu mL–1 varied from 0 to 104 cfu per leaf within and among eight bermudagrass cultivars and five Salmonella isolates. No differences (P < 0.05) occurred between cultivars (n = 20) or isolates (n = 10). Data fitted (R2 = 0.93) to a contamination equation (y = 5 x 10–6x6.623) described the relationship between levels (Log10 cfu mL–1) of exposure (x) and contamination (y). In fall 2007 Salmonella levels from six lagoons ranged from 1.9 to 2.8 log10 MPN 100 mL–1 and were below the threshold for contamination predicted by the equation. These preliminary results must be tested with effluents in the field, but considered alongside work of others, which report lagoon Salmonella levels to be highest in fall, suggest that Salmonella levels in effluents from these lagoons may be too low to produce measurable contamination on bermudagrass.