Prevalence of human noroviruses in frozen marketed shellfish, red fruits and fresh vegetables.

Noroviruses (NoVs), currently recognised as the most common human food-borne pathogens, are ubiquitous in the environment and can be transmitted to humans through multiple foodstuffs. In this study, we evaluated the prevalence of human NoV genogroups I (GI) and II (GII) in 493 food samples including soft red fruits (n = 200), salad vegetables (n = 210) and bivalve mollusc shellfish (n = 83), using the Bovine Enterovirus type 1 as process extraction control for the first time. Viral extractions were performed by elution concentration and genome detection by TaqMan Real-Time RT-PCR (RT-qPCR). Experimental contamination using hepatitis A virus (HAV) was used to determine the limit of detection (LOD) of the extraction methods. Positive detections were obtained from 2 g of digestive tissues of oysters or mussels kept for 16 h in seawater containing 2.0-2.7 log10 plaque-forming units (PFU)/L of HAV. For lettuces and raspberries, the LOD was, respectively, estimated at 2.2 and 2.9 log10 PFU per 25 g. Of the molluscs tested, 8.4 and 14.4% were, respectively, positive for the presence of GI NoV and GII NoV RNA. Prevalence in GI NoVs varied from 11.9% for the salad vegetables samples to 15.5% for the red soft fruits. Only 0.5% of the salad and red soft fruits samples were positive for GII NoVs. These results highlight the high occurrence of human NoVs in foodstuffs that can be eaten raw or after a moderate technological processing or treatment. The determination of the risk of infection associated with an RT-qPCR positive sample remains an important challenge for the future.

Yeast ecology in French cider and black olive natural fermentations.

In this study, rDNA ITS restriction analysis was used to identify yeasts from two naturally fermented products: French ciders and black olives. In cider musts and bottled ciders, the PCR-RFLP method generated 15 different ITS/RFLP profiles for a total of 208 isolates. The predominant yeasts corresponded to Saccharomyces bayanus, Saccharomyces cerevisiae, Lachancea cidri and Dekkera anomala. Three identified species: Candida sake, Candida tropicalis and Kluyveromyces marxianus had never been described before in ciders. For the black olive fermentation, the method allowed for identification of 11 profiles for a total of 137 isolates. A sequential apparition of yeasts was observed with Pichia anomala, Candida boidinii and Debaryomyces etchellsii being the predominant species. Four isolates did not correspond to any known species based on the sequencing of the D1/D2 region of the 26S rRNA gene. By using the rDNA ITS method, valuable information on yeast population biodiversity and dynamics in the naturally fermented food products studied was obtained.