OXYRASETM ENZYME AND MOTILITY ENRICHMENT FUNG‐YU TUBE FOR RAPID DETECTION OF LISTERIA MONOCYTOGENES AND LISTERIA SPECIES1

Abstract

ABSTRACT A rapid and simple method using a U‐shaped glass apparatus (Fung‐Yu tube) for early determination of the presence of Listeria monocytogenes and Listeria species in mixed cultures and inoculated meat samples has been developed. This system utilizes unique biochemical and physical properties of Listeria for selective enrichment. Fraser broth was used as a selective enrichment broth especially for observation of esculin hydrolysis (blackening of broth), and semisolid Modified Oxford agar was used for selective detection of motility of Listeria. When Fung‐Yu tubes containing 0.1 unit/mL of OxyraseTM (membrane fractions of Escherichia coli) were inoculated with L. monocytogenes, an enhanced early growth of L. monocytogenes occurred. A presumptive positive result for low numbers of L. monocytogenes (1–100 CFU/g) in the presence of large numbers of competitive microflora in pre‐enriched (24 h) ground beef samples using the Fung‐Yu tube method with the aid of OxyraseTMwas obtainable within 10 h. Using this system, isolation of Listeria in the presence of mixed bacterial flora (44 species), such as Bacillus, Escherichia, Klebsiella, Proteus, Salmonella, Shigella, Staphylococcus, and Streptococcus, and in inoculated ground beef was successful in 24–48 h. The Fung‐Yu tube procedure is a highly sensitive, selective, and easy‐to‐use method to separate and isolate L. monocytogenes and other Listeria spp. from other contaminating microorganisms in meats.