Quantifying Bacterial Cross-Contamination Rates between Fresh-Cut Produce and Hands

Abstract

ABSTRACT This study quantifies the cross-contamination rates between fresh-cut produce and hands using a nalidixic acid–resistant nonpathogenic Enterobacter aerogenes and cocktails of rifampin-resistant Salmonella or Escherichia coli O157:H7 strains. Volunteers performed the E. aerogenes experiments (n = 20), and one of the authors performed the Salmonella and E. coli O157:H7 experiments multiple times (n =15 and n =10, respectively). Each participant handled 25 g of fresh-cut carrots, celery, or cantaloupe in two different scenarios. In the first scenario, gloved hands were inoculated with 6 log CFU per hand of the bacteria, and in the second scenario, five 25-g pieces of fresh produce were inoculated to a concentration of 6 log CFU/25 g. The glove juice method was used to quantify the bacterial concentration on the gloved hands. About 30% of E. aerogenes on gloved hands was transferred to the carrots and celery, and 18% of E. aerogenes on gloved hands was transferred to the cantaloupe. When carrots or cantaloupe was inoculated with E. aerogenes, 1% was transferred to gloved hands; from inoculated celery, about 0.3% of E. aerogenes was transferred to gloved hands. There was not a significant difference between E. aerogenes and Salmonella cross-contamination rates (P > 0.05). When gloved hands were contaminated with E. coli O157:H7, about 30% was transferred to carrots, about 10% to celery, and about 3% to cantaloupe. When carrots and celery were inoculated with E. coli O157:H7, about 1% was transferred to gloved hands, but from inoculated cantaloupe only about 0.3% was transferred. Direction of transfer (to versus from produce), difference in type of produce, and differences among the bacterial species all had significant effects on the transfer rate. Understanding transfer rates to and from fresh-cut produce will allow for better risk assessment and management of microbial food safety risk related to fresh-cut produce.