Depuration of Aliarcobacter butzleri and Malaciobacter molluscorum in Comparison with Escherichia coli in Mussels (Mytilus galloprovincialis) and Oysters (Crassostrea gigas)

Abstract

Arcobacter-related species are considered emerging food-borne and waterborne pathogens, with shellfish being a suggested reservoir. In a published study that investigated 204 shellfish samples and 476 isolates, the species Arcobacter butzleri (now known as Aliarcobacter butzleri) and Arcobacter molluscorum (now known as Malaciobacter molluscorum) have been isolated as the most dominant species. However, the efficiency of depuration for eliminating A. butzleri and M. molluscorum in comparison with Escherichia coli from mussels and oysters is unknown and is therefore the objective of this investigation. The shellfish depuration process was evaluated in the laboratory, in summer and winter, using mussels and oysters collected from the Ebro Delta harvesting areas after performing a natural contamination and an artificial contamination using the same conditions for both mollusk and seasons. The natural contamination was performed by exposing the shellfish to a freshwater channel that receives untreated sewage from the village of Poble Nou (PNC) and that had a salinity of 10.7–16.8‰. The artificial contamination exposed the shellfish to A. butzleri and E. coli (in one tank) and to M. molluscorum and E. coli in another tank under controlled conditions of salinity (34.5‰) and temperature (20 °C summer and 14 °C winter). When evaluating the reduction in the bacteria load (every 24 h) throughout 120 h, the naturally contaminated shellfish at the PNC showed a higher reduction than the shellfish contaminated at the laboratory, with the exception of M. molluscorum, that at 24 h could not be detected in summer, neither in mussels nor in oysters. This may be attributed to the fact that the bacteria from the PNC were less adapted to the conditions of high salinity (34.5‰) in which the depuration process was performed. Although temperature did not statistically make a difference in depuration, at 20 °C a higher elimination of all bacteria was recorded relative to 14 °C. In general, E. coli survived more in mussels than in oysters, and M. molluscorum suffered in both mollusks a higher reduction than A. butzleri. New studies are required to determine further the safety of bivalves regarding the presence of Arcobacter-related species.