Evaluation of glove type on survival and transfer of Escherichia coli in model systems and during hand harvesting of lettuce

Abstract

Background: Both reusable and single-use gloves can be employed during hand harvesting of lettuce and leafy greens. The impact of glove type on survival and transfer of Escherichia coli was evaluated using agar or lettuce in a laboratory setting and during simulated lettuce harvesting in the field.

Results: Textured and smooth reusable latex and smooth disposable latex gloves inoculated with E. coli were sequentially touched to 10 or 20 agar plates or 20 lettuce leaves (n = 6; laboratory) or used to sequentially harvest 20 heads of lettuce (n = 6; field). E. coli was recovered by enrichment from significantly fewer leaves (46%; 55 of 120) or heads (26%; 31 of 120) of lettuce when inoculated reusable textured gloves were used compared with disposable gloves (leaves: 98%; 118 of 120, or heads: 74%; 89 of 120). In contrast, when a single head of lettuce was the point source for glove contamination, there was no significant difference in the number of E. coli-positive lettuce heads harvested with reusable textured (71%; 85 of 120) or disposable gloves (75%; 90 of 120). In either field-contamination scenario, at the 20th head of lettuce harvested with a single glove (final sample point), E. coli was recovered from one to five of six lettuce heads across experimental trials.

Conclusion: Contamination of a glove from a single point source can lead to subsequent contamination of multiple heads of lettuce during hand harvesting, showing the importance of policies to manage hand hygiene and glove use for harvest crews.

Keywords: STEC; cross contamination; gloves; harvest; leafy greens; lettuce.

FIGURE 1

Mean populations of E. coli TVS 354 sequentially transferred to agar plates from the outer palm surface of reusable textured latex (), reusable smooth latex (), disposable smooth latex (), or disposable nitrile () gloves inoculated at 4.5 log CFU glove⁻¹. Counts were above the upper limit of quantification (2.48 log CFU plate⁻¹) in all cases for plates 1 through 5. Error bars indicate standard deviation (n = 6)

FIGURE 2

Mean populations of E. coli TVS 354 sequentially transferred to agar plates from the outer palm surface of reusable textured latex (), reusable smooth latex (), or disposable smooth latex () gloves inoculated at 3.5 log CFU glove⁻¹. Error bars indicate standard deviation (n = 6)

FIGURE 3

The number of lettuce leaves positive by enrichment for E. coli TVS 354 out of six independent replicates after sequential transfer from reusable textured latex () or disposable smooth latex () gloves inoculated with E. coli TVS 354 at 4.5 log CFU glove⁻¹ under laboratory conditions

FIGURE 4

Mean populations of E. coli TVS 354 transferred from ~5.0 log CFU leaf⁻¹ inoculated lettuce leaves to various latex gloves after contact with 200 g weight for 5 s, under laboratory conditions. Each data point represents a single glove applied once to a single lettuce leaf (n = 6). Limit of detection (LOD) = 0.30 log CFU glove⁻¹. Horizontal lines represent mean values, and vertical lines indicate standard deviation. Mean E. coli populations transferred to glove types or between drying times were not significantly different (p > 0.05)

FIGURE 5

Number of lettuce heads positive for E. coli TVS 354 out of six independent replicates after sequential harvest in the field using reusable textured latex (; 26% positive out of 120) or disposable smooth latex (; 74% positive out of 120) gloves inoculated at 4.5 log CFU glove⁻¹ and then dried for 2 min under ambient field conditions

FIGURE 6

Number of lettuce heads positive for E. coli TVS 354 after harvest using the same reusable textured latex (; 71% positive out of 120) or disposable smooth latex (; 75% positive out of 120) glove (n = 6) used to first harvest a single inoculated head of lettuce (inoculated at 7.0 log CFU lettuce⁻¹ and dried for 2 h under field conditions)