Survival of Salmonella Transformed To Express Green Fluorescent Protein on Italian Parsley as Affected by Processing and Storage

Abstract

To study the effect of processing and storage parameters on the survival of Salmonella on fresh Italian parsley, parsley bunches were dipped for 3 or 15 min in suspensions that were preequilibrated to 5, 25, or 35ЊC and inoculated with Salmonella transformed to express enhanced green fluorescent protein. Loosely attached and/or associated, strongly attached and/or associated, and internalized and/or entrapped Salmonella cells were enumerated over 0, 1, and 7 days of storage at 25ЊC and over 0, 1, 7, 14, and 30 days of storage at 4ЊC using surface-plating procedures. Leaf sections obtained from samples after 0, 1, and 7 days of storage were examined using confocal scanning laser microscopy. Temperature of the dip suspension had little effect on the attachment and survival of Salmonella cells on parsley. Regardless of the temperature or duration of dip, Salmonella was internalized. Immersion for longer times resulted in higher numbers of attached and internalized cells. Microscopic observations supported these results and revealed Salmonella cells near the stomata and within cracks in the cuticle. Storage temperature had the greatest impact on the survival of Salmonella cells on parsley. When stored at 25ЊC, parsley had a shelf life of 7 days, and Salmonella populations significantly increased over the 7 days of storage. For parsley stored at 4ЊC, numbers of Salmonella cells decreased over days 0, 1, and 7. After 7 days of storage, there were no viable internalized Salmonella cells detected. Storage temperature represents an important control point for the safety of fresh parsley.Fresh produce is an important source of enteric pathogens in foodborne illness outbreaks. Fruits and vegetables, which are commonly consumed without any cooking treatment, may potentially harbor many foodborne pathogens (12,21). Ingestion of fresh parsley has been associated with Shigella sonnei and enterotoxigenic Escherichia coli infections (23). Salmonellosis outbreaks have been epidemiologically associated with the consumption of cantaloupes, watermelon, tomatoes, lettuce, celery, alfalfa sprouts, parsley, unpasteurized orange juice, and other raw salad vegetables (10,11,15,17,20). To assess the risk factors involved in the contamination of fresh produce with human pathogens, it is important to understand the microbial ecology of the various products and possible vectors during harvesting and processing that may contribute to product contamination.Cultivation, harvesting, and retail preparation of fruits and vegetables provide numerous opportunities for human and equipment contact (5, 18). Typical manual labor operations including picking, sorting, trimming, tying, bunching, and removal of visible soil in rinse water, all of which subject the product to extensive handling and exposure to a variety of microorganisms. Rinse water can be of questionable bacteriological quality (18). Reina et al. (28) found that recycled water developed Enterobacteriaceae populations of up to 10 6 CFU/g during a typical day's operation. Human pat...

Internalization of E. coli O157:H7 and Salmonella spp. in plants: A review

“…and E. coli O157:H7, have been found to be associated with the natural openings in the plant surface in a number of studies (Dong, Iniguez, Ahmer, & Triplett, 2003;Duffy et al, 2005;Gomes et al, 2009;Itoh et al, 1998;Kroupitski et al, 2009;Shaw et al, 2008). The same preferential localization of the bacteria can be found in artificially induced wounds (Burnett, Chen, & Beuchat, 2000) and naturally occurring lesions (Brandl & Mandrell, 2002;Han, Linton, Nielsen, & Nelson, 2000), as well as with physical damage caused by plant pathogens (Beuchat, Scouten, Allen, & Hussey, 2003).…”

Postharvest Handling Conditions Affect Internalization of Salmonella in Baby Spinach during Washing

“…Surface disinfection by immersion in an AgN03 solution has been used to eliminate surface pathogens on leafy greens, enabling assessment of internalization by enrichment and plate counts (12,14). Others have also used chlorinated water for surface disinfection (9,17,26). In our study, compared with AgN03, there was a slight advantage to using chlorinated water because of the lower number of leaves giving positive prints (Table 1) and fewer viable cells detected on leaf surfaces (Fig.…”

“…Takeuchi and Frank (31) demonstrated that soaking freshcut lettuce in a suspension of E. coli 0157:H7 (9 log CFU/ ml) at 4°C resulted in a greater number of cells penetrating into cut surfaces than at higher temperatures. Another report, however, showed that a temperature differential did not promote Salmonella internalization into Italian parsley (9). The issue of internalization is of special concern during postharvest hydrocooling, whereby water is used to cool produce.…”

Fluorescence-based tools for single-cell approaches in food microbiology

“…5 presents a multilabeling example where a mixture of bacteria preferentially occupies the interstitial space between the caseins and the fat in the matrix. Salmonella was shown to preferentially colonize the stomata and cracks of the waxy cuticle of parsley leaf (no pathogens were detected near the leaf edge or on intact leaf surface) (Duffy et al, 2005). In meat products, Yersinia enterolitica was evidenced in deep structure of hair like procine skin follicles (Morild et al, 2011) while E. coli O157:H7 was shown to adhere preferentially to fibril-forming collagens I and IIII of the muscle extracellular matrix (Chagnot et al, 2013).…”