Use of Bacteroidales Source-tracking Markers to Evaluate the Effect of Hand Washing or Sanitizing on Fecal Contamination of Produce Workers’ Hands

Introduction: In an earlier study, we investigated the utility of Bacteroidales 16S rDNA source-tracking for identifying fecal contamination, and its source, in the fresh produce production environment. The method was applied to rinses of fresh produce, source and irrigation waters, and harvester hand rinses from farms in Northern Mexico, and results suggested that farm workers’ hands were a risk factor for fecal contamination of produce.

Purpose: As a proxy for fecal contamination, the purpose of this study was to determine if hand hygiene interventions have immediate and/or residual effects on the levels of general and source-specific Bacteroidales on produce workers’ hands.

Methods: The hand rinses of 158 Jalapeño farm workers were collected during the summer of 2013. Workers were divided into 3 intervention groups, control (40), hand washing (60), and sanitizing (60) groups; the latter two of which were subdivided into groups for which samples were collected pre-intervention (20) or post-intervention (40). Bacteria were concentrated from hand rinse samples using a combined centrifugation/filtration method and the DNA extracted using the MP Bio FastSpin kit for soil. Quantification of the universal and human-specific Bacteroidales markers was performed using the AllBac and BFD primers and probes, respectively.

Results: The AllBac marker was detected in 81% (123) of samples, with a geometric mean concentration of 1.6 log genome equivalent copies (GEC) per 100 ml hand rinse sample. The human marker was identified in 46% (69) of samples, with a geometric mean concentration of 2.6 log GEC per 100 ml. There was no significant difference in the AllBac or BFD marker concentrations between intervention groups (P > 0.05).

Significance: Neither intervention had an immediate or a residual effect on the levels of general and source-specific Bacteroidales on produce workers’ hands, suggesting little impact of the intervention on fecal contamination.