Effect of type of mulch on microbial food safety risk on cucumbers irrigated with contaminated water.

Mulches are used to block light and retain soil moisture which may affect the survival of bacterial pathogens on soil. This study examined the effectiveness of different types of mulches to minimize microbial risk from contaminated water used for irrigation of cucumbers. A production bed of 120 ft with 18 beds (30 ft long) covered with five different types of m'ulch (paper, paper with fertilizer incorporated (PF), maize based mulch, biodegradable plastic covering, and conventional plastic) including three beds with no cover were planted with Dasher 2 Variety cucumber. Soil samples from each bed were collected for first five weeks to examine natural E. coli and coliforms. Well water contaminated with or without nalidixic acid resistant mutant of E. coli (8 Log CFU/mL) was used for drip irrigation for 7 days before harvesting. Prior to irrigation with contaminated water, naturally present E. coli and coliform in the soil samples with or without mulch were in the range of 3.45-3.78 Log CFU/g and 4.18-5.31 Log CFU/g respectively. E. coli levels on cucumbers harvested from mulched beds and irrigated with contaminated irrigation water had significantly higher (P<0.05) levels of E. coli as compared with samples from similar beds irrigated with non-contaminated water. However, Cucumber, harvested within each irrigation water quality were not significantly difference regardless of the type of mulch with E. coli levels from 1.72 - 3.30 Log CFU/cm (contaminated water) and 0.28 - 1.86 Log CFU/cm (Non-contaminated water).. A significant die-off of inoculated E. coli was observed on cucumber within 3 days (>1.17 Log CFU/cm) and >1.38 Log CFU/cm after 4 days. Beds with maize mulch were effective on minimizing E. coli contamination on cucumber from contaminated irrigation water.