Abstract
The multistate Escherichia coli (E. coli) O157:H7 outbreak associated with in-shell hazelnuts highlights the pathogen’s ability to involve non-traditional vehicles in foodborne infections. Furthermore, it underscores significant gaps in our knowledge of pathogen survivability and persistence on nuts. Therefore, this study investigated the ability of E. coli O157:H7 to attach and survive on in-shell hazelnuts. In-shell hazelnuts were inoculated with a four-strain mixture of E. coli O157:H7 at 7.6 log colony forming units (CFU)/nut by wet or dry inoculation, stored at ambient conditions (24 ± 1 °C; 40% ± 3% relative humidity (RH) and sampled for twelve months. For the attachment assay, in-shell hazelnuts were inoculated and the adherent population was enumerated at 30 s−1 h following inoculation. Irrespective of the inoculation method, ~5 log CFU of adherent E. coli O157:H7 was recovered from the hazelnuts as early as 30 s after inoculation. Conversely, pathogen survival was significantly reduced under dry inoculation with samples being enrichment negative after five months of storage (p < 0.05). On the other hand, wet inoculation led to a significantly longer persistence of the pathogen with ~3 log CFU being recovered from the in-shell nuts at 12 months of storage (p < 0.05). These results indicate that E. coli O157:H7 can survive in significant numbers on in-shell hazelnuts when stored under ambient conditions.
Highlights
Tree nuts have not been associated with a high risk for bacterial foodborne disease.This is mainly due to the hostile environment they provide to the growth and survival of pathogens [1,2].nut-associated outbreaks have been sporadic in the past
Wet inoculation led to a significantly longer persistence of the pathogen with ~3 log CFU being recovered from the in-shell nuts at 12 months of storage (p < 0.05). These results indicate that E. coli O157:H7 can survive in significant numbers on in-shell hazelnuts when stored under ambient conditions
The objective of this study was to evaluate the potential of E. coli O157:H7 to attach and survive on in-shell hazelnuts when stored under ambient conditions using a dry and wet inoculation methods
Summary
Tree nuts have not been associated with a high risk for bacterial foodborne disease.This is mainly due to the hostile environment they provide to the growth and survival of pathogens [1,2].nut-associated outbreaks have been sporadic in the past. Tree nuts have not been associated with a high risk for bacterial foodborne disease. This is mainly due to the hostile environment they provide to the growth and survival of pathogens [1,2]. Recent increases in foodborne illness associated with tree nut consumption have led to an increasing concern regarding the safety of minimally processed foods such as nuts. Traditionally associated with ground beef and leafy green vegetables, the recent outbreak of Escherichia coli (E. coli) O157:H7 in hazelnuts highlights the propensity of the pathogen to colonize diverse surfaces and involve new vehicles that can transmit foodborne infections [8]. According to the Centers for Disease Control and Prevention (CDC) surveillance of foodborne outbreaks in the U.S
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