Enumeration and survival of salmonella enterica in live oyster shellstock harvested from Canadian waters

Abstract

Since 2015, 11 recalls of live oyster shellstock have been issued in Canada due to the presence of Salmonella enterica. Six of those recalls took place in 2018. To understand this increase, fundamental information is needed on the relationship between S. enterica and oysters. The aims of this study were to address important data gaps concerning the levels of Salmonella in naturally contaminated oysters and the ability of this pathogen to survive in live oyster shellstock. Enumeration data were evaluated for five oyster and clam samples collected from the east coast of Canada from 2015 to 2018. The reported levels were,0.0015 to 0.064 most probable number per g of oyster tissue. The S. enterica isolates recovered from these animals belonged to serovars Typhimurium, Infantis, Enteritidis, and I 4,5:i:-. Filter feeding by the oysters was exploited to assess the Salmonella accumulation that would occur following a natural contamination event. Detectable levels of the pathogen were observed after 30 min of exposure and began to plateau at 60 min. A survival study in live oyster shellstock indicated that after 4 days of storage at ambient temperatures, the Salmonella level declined slightly from 4.3 to 3.7 log CFU/g. These data indicate that the levels of Salmonella found in naturally contaminated oysters are low and are not expected to increase between the point of harvest and the point of consumption. The changing ecology of shellfish environments requires continued monitoring and testing to safeguard public health. The data presented here will be useful for the evaluation and design of sampling plans and risk management approaches for the control of Salmonella in live oyster shellstock.