Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery
Highlights
► Pathogen populations declined by 0.5–1 log CFU/g over 7 days on fresh-cut celery at 4 °C ► At 12 °C, Escherichia coli O157:H7 and Salmonella populations remained stable on celery over 7 days. ► At 12 °C, Listeria monocytogenes populations increased over 7 days by 0.5 log CFU/g. ► All pathogen populations increased on fresh-cut–cut celery at 22 °C for 2 days.
Introduction
Celery is commonly consumed in two manners, either as an ingredient or raw, as a snack. The value-added segments of fresh-cut celery sticks are gaining in popularity as part of the growing market for washed, ready-to-eat produce products (Lucier and Jerardo, 2005). Celery has been associated with some documented outbreaks of foodborne disease. In 1899, an outbreak of typhoid fever at a Massachusetts asylum resulting in 40 ill inmates over a 2-week period was linked to celery consumption (Morse, 1899). An outbreak of acute gastroenteritis amongst approximately 1440 cadets at the U.S. Air Force Academy in the early 1990’s was linked to the consumption of chicken salad. Originally attributed to Salmonella, celery exposed to norovirus in nonpotable water and used as an ingredient in the chicken salad was eventually identified as the cause (Warner et al., 1991). In 2010, diced celery, used as ingredient in chicken salad in a hospital, was the cause of a listeriosis outbreak in Texas that led to ten confirmed cases and five deaths in immunocompromised, hospitalized patents. The outbreak strain was isolated from chicken salad, the diced celery ingredient at the hospital and in 19 of >200 surface swabs and 8 of 11 diced celery products at the processing plant (Gaul et al., 2013, Texas DSHS, 2010, US FDA, 2010).
Although no Escherichia coli O157:H7 outbreaks have been associated with fresh-cut celery, this organism has been isolated from 23/89 (27%) vegetable samples (including celery) in Mexico (Zepeda-Lopez et al., 1995). Listeria monocytogenes was isolated from one unprocessed raw celery sample at a health-care food service location in Ontario, Canada (Odumeru et al., 1997), and in 2 of 13 (15.4%) 25 g samples of fresh-cut celery taken from supermarket-prepared salads in Chile (Cordano and Jacquet, 2009). Salmonella was isolated from 2 of 26 (8%) 100-g celery samples obtained from the central market of Granada, Spain (Garcia-Villanova et al., 1987), 5 of 8 (63%) 25-g celery samples from street vendors in Mumbai, India (Viswanathan and Kaur, 2001) and 3 of 100 (3%) 50-g celery samples from a central supply station in Mexico City (Quiroz-Santiago et al., 2009).
Fresh-cut celery is considered to be ready-to-eat without any further preparation by the consumer. Risks from fresh-cut celery consumption may increase from temperature abuse leading to multiplication of pathogens. Data on the survival and growth of pathogens are essentially non-existent for celery, and the influence of consumer handling contribution to risks associated with consumption of fresh-cut celery is unknown. Our objective was to quantify the impacts of time and temperature, and storage container on fate of E. coli O157:H7, L. monocytogenes, and Salmonella on fresh-cut celery under simulated consumer storage conditions.
Section snippets
Fresh-cut celery
Bags of fresh-cut celery advertised as “washed and ready-to-eat,” were purchased from a local supermarket (Winter Haven, FL). Celery was purchased within one day of store delivery and held at 4 ± 2 °C for up to 24 h prior to use in experiments. Immediately prior to inoculation, celery sticks were cut to 10 ± 1 g pieces using a sterile, serrated knife and cutting board.
Strain selection
Cocktails of strains, from produce outbreaks when available, were used as inoculum in all experiments. Five strains of E. coli
Results
No E. coli O157:H7, L. monocytogenes or Salmonella was observed in any of the control samples. No significant differences in growth were observed between any of the strains during cocktail preparation (P ≥ 0.05). Population decreases of up to 1 log CFU/g from initial inoculation levels were observed during air drying. The average log CFU/g populations of E. coli O157:H7 and Salmonella enumerated on nonselective (TSAR) and selective (SMACR for E. coli O157:H7 and BSAR for Salmonella) media on each
Discussion
High levels of organisms naturally occurring on celery were not unexpected; total aerobic counts on 26, 100 g raw celery samples ranged from 2 log CFU/g up to 8.3 log CFU/g (Garcia-Villanova et al., 1987) and fluctuations in the direction of population change during storage is also consistent with previously documented storage studies at 4 and 10 °C for up to 11 days (Odumeru et al., 1997). The large and diverse background populations inherent to celery may have contributed to the behavior of
Acknowledgments
This research was supported by the U.S. Food and Drug Administration, grant 1R01FD003672-01, and a matching assistantship from the University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center. We are grateful for the technical assistance of Rachel McEgan, Pardeepinder Brar, Lorie Friedrich, and Gwen Lundy.
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