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Pathogen Inactivation on Gloves

July 2013

Preharvest contamination of produce with enteric pathogens can result in outbreaks of infections associated with fresh-cut products. To minimize this risk, field workers commonly wear gloves during harvesting produce in an attempt to minimize cross-contamination via hand contact. We did a study to determine the effectiveness of chlorine, Purell® hand sanitizer, and a mixture of levulinic acid (LVA) and sodium dodecyl sulfate (SDS) to inactivate green-fluorescent labeled Escherichia coli O157:H7 and Salmonella on gloves (12-mil disposable textured latex, 7-mil disposable nitrile, and 20-mil reusable Ansell Canner’s® latex).

In preliminary studies, glove-use practices of iceberg lettuce harvesting crews were observed for one week. Disposable gloves were generally worn continuously throughout the day (up to 10 hours) but during breaks they were tied up along with aprons. Gloves collected from field workers revealed the presence of varying amounts of lettuce debris, soil, lettuce sap, and water, depending on environmental conditions at the time of harvest. This information was the basis for creating worst-case “dirty” gloves experiments in our lab.

Clean latex and nitrile glove pieces (4 cm2 inoculation zone) were spot inoculated with E. coli O157:H7 (3.7 - 4.7 log CFU) or Salmonella (3.6 - 3.8 log CFU), dried for 60 - 75 min, and then exposed to Purell or chlorine (50 µg/ml) disinfectant for 15 sec. With Purell, 79 - 100% of the glove pieces were still positive for E. coli O157:H7, whereas 0 - 10% and 10 - 30% of the glove pieces treated with chlorine were positive for E. coli O157:H7 and Salmonella, respectively. Prevalence for Salmonella as high as 40% was observed on glove pieces on which soil had been rubbed on the inoculation zone and lettuce sap was applied prior to application of the inoculum. Elimination of Salmonella did occur on clean nitrile gloves inoculated at lower levels (ca. 3 log CFU/piece) and soaked in 75 µg/ml chlorine.

To determine whether effectiveness of chlorine would improve if gloves were immersed sequentially in two buckets of disinfectant versus one bucket, dirty E. coli O157:H7-contaminated Canner’s and nitrile gloves were immersed in a bucket(s) containing 8 L of either 50 or 100 µg/ml chlorine and hand rubbed in an up and down motion for 10 - 15 sec. In a one-bucket system, 25% of the gloves remained positive for the pathogen. After immersion and rubbing of gloves in a two-bucket system, 12 - 18% of the gloves were positive for E. coli O157:H7.

In contrast, scrubbing gloves with non-abrasive pads during immersion in chlorinated water resulted in an increase in the percentage of gloves that were positive for E. coli O157:H7 compared to the percentage on rubbed gloves. It is believed that the pathogen was protected from chlorine when lodged in abrasions created when gloves were rubbed with soil or brushed during disinfection. In support of this explanation, contaminated gloves on which parallel lines were scored contained fluorescent E. coli O157:H7 at those locations on agar prints.

Another relatively new disinfectant that has shown promise in killing enteric bacterial pathogens is LVA in combination with SDS. Given that LVA is more expensive than chlorine, we devised a wash system whereby gloved hands were immersed in 150 ml of disinfectant (5% LVA/0.1% SDS or 200 µg/ml chlorine) in a one-gallon plastic bag and rubbed for 10 - 15 sec. Using this system, 64% and 53% of Canner’s and nitrile gloves (4.6 - 4.8 log CFU Salmonella/glove) (n = 36), respectively, were positive for the pathogen after treatment with 200 µg/ml chlorine. In contrast, after disinfection in LVA/SDS solution, only 14% and 3% of Canner’s and nitrile gloves, respectively, were positive for the pathogen. Salmonella was also eliminated on 12 gloves by immersing in a LVA/SDS solution previously used to disinfect 18 gloves one week earlier.

Based on the higher effectiveness and stability of LVA/SDS compared to chlorine, this alternative disinfectant could be a viable option in the field when used at low volumes. If each field worker harvesting lettuce had access to a wash bag containing 200-300 ml of the disinfectant near their work station, gloved hands could be repeatedly dipped in the solution during the work day at a cost of about $1.00 per worker.