15D-3 |
Microscopic examination of Shigella boydii 18 on parsley and cilantro |
M. E. AGLE1, S. Raengpradub, S. J. Robinson3, and H. P. Blaschek. (1) Food Science and Human Nutrition, University of Illinois Urbana-Champaign, 492 ASL, 1207 West Gregory Drive, Urbana, IL 61801, (2) Beckman Institute for Advanced Science and Technology, University of Illinois Urbana-Champaign, 405 North Matthews Avenue, Urbana, IL 61801 Produce-related outbreaks have increased drastically over the past twenty years. Shigella boydii 18 was isolated from a 1999 Chicago area foodborne outbreak involving contaminated bean salad that contained fresh parsley and cilantro. Cilantro and parsley were also implicated as the food vehicles in a 1998 multi-state outbreak of Shigella sonnei. We have previously shown that S. boydii 18 is capable of surviving on parsley treated with commercial produce wash or with water. When parsley was inoculated with 106 CFU/g S. boydii 18, water or produce wash yielded 1.38 and 1.36 log reductions, respectively. Alternatively, when produce wash was inoculated with S. boydii no organisms were detected after one or five minutes. The objective of this work is to explain the reduced efficacy of produce wash on Shigella on produce. Scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM) were used to observe S.boydii 18 on parsley and cilantro samples treated with produce wash and water. Parsley and cilantro samples were inoculated by dipping into a Shigella horse serum suspension (optical density=1.5). Samples were allowed to dry in a laminar flow hood for 1.5 hrs and then were treated with water or produce wash for five minutes. Samples were fixed with 2% glutaraldehyde, and stained with 2% osmium tetroxide, dehydrated using a graded ethanol series and critical point dried using hexamethyldisilazane. Samples were sputter coated with gold/palladium and imaged using a Philips XL30 ESEM-FEG microscope. Evidence of biofilm formation by S. boydii was observed on the parsley and cilantro samples. Cells in biofilms have been found to be more resistant to antibiotics and disinfectants. This may explain the decreased efficacy of produce wash on parsley and cilantro samples.
Session 15D, Food Microbiology: Fruits and vegetables
|