Submitted to: Zoonoses and Public Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/30/2012
Publication Date: 12/28/2012
Citation: Markland, S., Shortlidge, K., Hoover, D., Yaron, S., Patel, J.R., Singh, A., Sharma, M., Kniel, K. 2012. Survival of pathogenic Escherichia coli on basil, lettuce, and spinach. Zoonoses and Public Health. DOI: 10.1111/zph.12033. Interpretive Summary: Pathogenic E. coli have caused several outbreaks on leafy green commodities over the past several years. Avian pathogenic E. coli (APEC) usually cause illness in poultry birds resulting in severe economic consequences. However, these APEC strains can also affect human health because they share several virulence factors in common with enterohemorrhagic E. coli (EHEC) or shiga-toxin producing E. coli (STEC), and therefore could contribute to the burden of foodborne disease. This study evaluated survival of APEC along with an EHEC strain and E. coli O104:H4, a particularly virulent STEC, strain on basil, spinach and lettuce. The EHEC strain (E. coli O157:H7), in general, survived at lower numbers than the APEC stains or E. coli O104:H4 on all three plants. Overall, the environmental fitness of APEC and E. coli O104:H4 was thought to be enhanced relative to the E. coli O157:H7 strain because of previous exposure to pre-harvest environments (soil, water, feces). This is the first reported work of E. coli O104:H4 survival on a produce commodity. This information should be useful to other scientists, the produce industry and regulatory agencies.
Technical Abstract: The contamination of lettuce, spinach and basil with pathogenic E. coli has caused numerous illnesses over the past decade. E. coli O157:H7, E. coli O104:H4 and avian pathogenic E. coli (APECstx- and APECstx+) were inoculated on basil plants and in promix soiless substrate using drip and overhead irrigation. When overhead-inoculated with 7 log CFU/ml of each strain, E. coli populations were significantly (p=0.03) higher on overhead-irrigated plants than on drip-irrigated plants. APECstx-, E. coli O104:H4 and APECstx+ populations were recovered on plants at 3.6, 2.3, and 3.1 log CFU/g at 10 dpi (days post-inoculation), respectively. E. coli O157:H7 was not detected on basil after 4 dpi. The persistence of E. coli O157:H7 and APECstx- were similar when co-inoculated on lettuce and spinach plants. On spinach and lettuce, E. coli O157:H7 and APEC populations declined from 5.7 - 6.1 log CFU/g amd 4.5 log CFU/g, to undetectable at 3 dpi and 0.6-1.6 log CFU/g at 7 dpi, respectively. The detection of low populations of APEC and E. coli O104:H4 strains 10 dpi indicates these strains may be more adapted to environmental conditions than E. coli O157:H7. This is the first reported study of E. coli O104:H4 on a produce commodity.