title: Intra-laboratory validation of a concentration method adapted for the enumeration of infectious F-specific RNA coliphage, enterovirus, and hepatitis A virus from inoculated leaves of salad vegetables.
abstract: Salad vegetables exposed to fecal contamination may cause outbreaks of hepatitis or gastro-enteritis if they are eaten raw. A procedure, based on elution with phosphate-buffered saline and concentration by filtration through membrane filters, was developed for the recovery of enteric viruses from salad leaves. The method was evaluated using lettuce leaves inoculated with hepatitis A virus (HAV), poliovirus, and MS2 bacteriophage. In addition, this method was validated by an intra-laboratory study using leaves of various salad vegetables inoculated with MS2 phage. The French standard NF V 03-110 was used to establish the general principle and the technical protocol of the validation procedure. Linear regression models describing the quantitative reactions were good fits to data in the whole range of viral concentrations tested, which was from about 1 to 4 log plaque-forming units (PFU) per 25 g of lettuce. The fractions of inoculated viruses recovered were estimated to be about 64% for HAV, 18% for poliovirus, and 29% for MS2. No significant effect of the food matrix was found using various types of salad vegetable (butter lettuce, iceberg lettuce, romaine lettuce, witloof chicory, curly endive, corn salad, rocket and watercress). Moreover, the variance of the results was constant for all levels of virus contamination within the experimental range. Intermediate reproducibility experiments were also performed to allow calculation of the uncertainty factor, which was found to be 0.58 log PFU/25 g. When used in association with phage enumeration, this validated procedure is rapid enough to be used for screening salad vegetables for evaluation of the efficacy of processes for control of pathogenic microorganisms on such foods.
authors.affiliation: Unité de Virologie des Aliments et de l'Eau, Agence Française de Sécurité Sanitaire des Aliments, 23, avenue du Général de Gaulle, 94706 Maisons-Alfort cedex, France. e.dubois@afssa.fr
authors.forename: Eric
authors.initials: E
authors.lastname: Dubois
authors.forename: Catherine
authors.initials: C
authors.lastname: Hennechart
authors.forename: Nathalie
authors.initials: N
authors.lastname: Deboosère
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Merle
authors.forename: Odile
authors.initials: O
authors.lastname: Legeay
authors.forename: Christian
authors.initials: C
authors.lastname: Burger
authors.forename: Marie
authors.initials: M
authors.lastname: Le Calvé
authors.forename: Bertrand
authors.initials: B
authors.lastname: Lombard
authors.forename: Virginie
authors.initials: V
authors.lastname: Ferré
authors.forename: Ousmane
authors.initials: O
authors.lastname: Traoré
mesh_terms: D019411:Clinical Laboratory Techniques / Q000592:standards*; D003090:Coliphages / Q000302:isolation & purification*; D015169:Colony Count, Microbial / Q000379:methods / Q000592:standards; D004770:Enterovirus / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D030041:Hepatitis A virus / Q000302:isolation & purification*; D016014:Linear Models; D017955:Poliovirus / Q000302:isolation & purification; D012367:RNA, Viral / Q000032:analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014675:Vegetables / Q000821:virology*; D010948:Viral Plaque Assay
chemical_list: D012367:RNA, Viral