Identification of Listeria monocytogenes from unpasteurized apple juice using rapid test kits

Abstract

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 chloridephenylethanol-moxalactam agars and were β-hemolytic on sheep blood agar. The isolates required 5 days of incubation at 35°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.