A microbiological survey of 50 retail juices was conducted in the fall of 1996. These juices were analyzed for Listeria monocytogenes, Escherichia coli O157:H7, Salmonella, coliforms, fecal coliforms, and pH. Two unpasteurized juices were positive for L. monocytogenes: an apple juice and an apple raspberry blend with a pH of 3.78 and 3.75, respectively. Three L. monocytogenes isolates were characterized. The colonies were typical for Listeria sp. on Oxford and lithium chloride-phenylethanol-moxalactam agars and were beta-hemolytic on sheep blood agar. The isolates required 5 days of incubation at 35 degrees C to produce a positive rhamnose reaction in a phenol red carbohydrate broth. This slow rhamnose utilization resulted in these isolates not being identified using the Micro-ID test strip (Organon Technika). However, the isolates were positive for L. monocytogenes using the API Listeria strip (BioMerieux) and a multiplex polymerase chain reaction for detection of the hemolysis (hyla) and invasion-associated protein (iap) genes.

A multilaboratory study was conducted to compare the VIDAS® LIS immunoassay with the standard cultural methods for the detection of Listeria in foods using an enrichment modification of AOAC Official Method 999.06. The modified enrichment protocol was implemented to harmonize the VIDAS LIS assay with the VIDAS LMO2 assay. Five food types—brie cheese, vanilla ice cream, frozen green beans, frozen raw tilapia fish, and cooked roast beef—at 3 inoculation levels, were analyzed by each method. A total of 15 laboratories representing government and industry participated. In this study, 1206 test portions were tested, of which 1170 were used in the statistical analysis. There were 433 positive by the VIDAS LIS assay and 396 positive by the standard culture methods. A Chi-square analysis of each of the 5 food types, at the 3 inoculation levels tested, was performed. The resulting average Chi square analysis, 0.42, indicated that, overall, there are no statistical differences between the VIDAS LIS assay and the standard methods at the 5% level of significance.