MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Title: Effect of modified atmosphere on persistence and virulence expression of Escherichia coli O157:H7 on shredded lettuce
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 20, 2010
Publication Date: August 1, 2010
Citation: Lakshman, S., Ferguson, S.E., Ingram, D.T., Patel, J.R., Luo, Y., Sharma, M. 2010. Effect of modified atmosphere on persistence and virulence expression of Escherichia coli O157:H7 on shredded lettuce. [abstract]. IAFP Abstract Book p. 42.
Introduction: Packaged fresh-cut lettuce contaminated with Escherichia coli O157:H7 has caused several outbreaks of infections. The influence of packaging and storage temperature may affect the persistence and expression of virulence factors of the pathogen, affecting the ability of the pathogen to cause illness.
Purpose: To evaluate the influence of packaging material and storage temperature on the behavior of E. coli O157:H7 on shredded lettuce.
Methods: Commercially shredded lettuce was inoculated with 4.07 CFU/g of nalidixic-acid resistant E. coli O157:H7. Inoculated lettuce was packaged under active MA in 110 OTR films using a 2% oxygen flush before sealing (treatment A); passive modified atmosphere (MA) conditions in bags made from films with 110 oxygen transmission rate (OTR) with micro-perforations (treatment B) or in 0 OTR films (treatment C). Inoculated and uninoculated samples were stored at either 4 or 15oC for up to 10 d. Populations of E. coli O157:H7 and total aerobic populations were enumerated on MacConkey agar (MACN) and tryptic soy agar (TSA). RNA from inoculated lettuce stored at 15oC was extracted and levels of expression for 5 virulence factors (VF) - stxII, eae, ehx, iha, and rfbE on each day – were analyzed by reverse transcriptase real –time PCR . Two replicate experiments were performed.
Results: No significant (P < 0.05) differences in E. coli O157:H7 populations were observed in the three MA packaging treatments 4oC. At 15oC, E. coli O157:H7 populations under treatment B were significantly lower than other treatments on day 7. Total aerobic populations from uninoculated lettuce under treatment B were significantly greater than populations from other treatments on day 1 at 4 and 15oC. Expression of stxII, eae, iha, and rfbE under treatment B on day 7 were significantly greater than under other treatments. However, all expression of all VF under treatment B were significantly lower than under treatment C on day 10.
Significance: Different packaging treatments affect the persistence and virulence factor expression of E. coli O157:H7 on lettuce at 15oC, as well as overall bacterial populations at 4 and 15oC. These treatments may affect the ability of the pathogen to cause illness with fresh cut lettuce.