The Effect of UV Radiation on Survival of Salmonella enterica in Dried Manure Dust

Introduction: Animal manure has been shown to harbor Salmonella enterica, an enteric pathogen known to be resilient to environmental stresses such as desiccation and solar UV radiation. In farm settings, it has been observed that unintended aerosolization could occur when manure becomes dehydrated, resulting in the exposure of leafy crops to wind-driven manure dust. In order to appraise the risk contributed by aerosolized particulate manure to produce fields, it is important to determine whether these particles can act as a barrier to protect Salmonella from damaging effects of UV light. 

Purpose: This study investigated the effect of UV radiation on the survival of Salmonella when present on dried manure particles.

Methods: In vitro survival under UV-A (365 nm) of Salmonella inoculated into manure dust and dispersed as a thin layer on a petri dish covered with filter paper was compared to exposure under similar conditions using a thin layer of cells that were directly applied to the test surface. The dust was obtained by dehydrating turkey manure to < 5% moisture content and processing until particle sizes of approximately 125 μm were achieved.

Results: Analysis showed that the presence of manure particles significantly (P < 0.05) protected Salmonella from UV exposure. Salmonella cells exposed to UV in a control medium showed a 5-log decline within 80 min compared to the 1.5-log decrease in the manure dust matrix. This was in spite of the higher initial inoculum level of control samples (control inoculum 7.5 x 10¹⁰ CFU/ml; dust inoculum 6.75 x 10⁶ CFU/g).

Significance: These data suggest that manure dust particles can provide protection from lethal UV rays to Salmonella cells, thereby increasing the risk of edible-crop contamination in pre-harvest settings. The ability of manure dust matrix to shield Salmonella from damaging UV effects could increase this pathogen’s survival on leafy greens during cultivation.