MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Title: Epiphytic survival of Shiga-toxigenic Escherichia coli O145 on baby spinach plants
Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2011
Publication Date: March 20, 2011
Citation: Ingram, D.T., Roberts, C.L., Ferguson, S.E., Lakshman, S., Sharma, M. 2011. Epiphytic survival of Shiga-toxigenic Escherichia coli O145 on baby spinach plants. [abstract] International Association for Food Protection Proceedings. P2-78.
Introduction: Non-O157 Shiga-toxigenic E. coli (STEC) have contaminated leafy greens. In early 2010, 26 confirmed illnesses were traced to a multi-state outbreak involving shredded romaine lettuce contaminated with E. coli O145, a STEC. It is possible that the O145 serotype may be suited for growth and/or survival on leafy green surfaces.
Purpose: This study examined the epiphytic survival of O145 STEC on the surfaces of baby spinach leaves.
Methods: An inoculum containing four isolates of E. coli O145 were adapted for growth in a diluted dairy manure slurry and spot inoculated onto two-week old baby spinach plants maintained in a growth chamber (14h photopheriod, 18oC, 75% humidity). At time 0 (0 h), immediately after inoculation, 19h and 24h, the aerial tissue from plants (n=3) was homogenized in 40ml buffered peptone water before spiral plating onto MacConkey agar. On days 2 through 8, three plants were harvested daily to determine E. coli O145 counts via standard 3-tube MPN analysis.
Results: At time 0, 6.20 log CFU/plant E. coli O145 was recovered from the plants. E. coli O145 populations declined by almost 4 log CFU after only 19 hours to 2.33 log CFU/plant. After 24h E. coli O145 populations were 1.94 log CFU/plant with continued reduction on day 2 and 3 with resulting recoveries of 1.15 log and 1.09 log MPN/plant, respectively. Subsequent analyses on days 4 through 8 did not recover E. coli O145 from spinach plants.
Significance: E. coli O145 declined rapidly on the epiphytic surface of baby spinach plants under controlled growth chamber conditions. Even when inoculated at 6 log CFU/plant, there is no evidence of E. coli O145 populations surviving for more than three days. Data suggest that E. coli O145 isolates do not appear to persist for durations longer than other STEC on leafy green foliar surfaces.