Skip to main content
ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Food Safety and Enteric Pathogens Research » Research » Publications at this Location » Publication #118450
Title: APPLICATION OF A MULTIPLEX POLYMERASE CHAIN REACTION (PCR) ASSAY FOR THE SIMULTANEOUS CONFIRMATION OF LISTERIA SPECIES AND LISTERIA MONOCYTOGENES

Author
item WESLEY, IRENE
item HARMON, K - IOWA STATE UNIVERSITY
item RAMOS, A - FOOD SAFETY NET SERVICES

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Listeria monocytogenes is a major human foodborne pathogen which has a case fatality rate of ~ 30%. In 1998 a multistate outbreak occurred, which involved contaminated delicatessen meats, including turkey. Mechanically separated turkey meat consists of turkey skin, trim and dark meat which is ground into a smooth paste and used to make delicatessen meats, such as turkey frankfurters. Products derived from mechanically separated turkey meat are cooked prior to retail sale. We screened mechanically separated turkey meat from a major midwest processor with a newly designed PCR assay. This assay simultaneously detects L. monocytogenes as well as other Listeria species. Using this multiplex PCR test we detected L. monocytogenes in 38% of meat samples and other Listeria species in an additional 18% of samples. In addition 51% of the L. monocytogenes isolates were of serotype 1; 44% were of serotype 4, which is pathogenic for humans. This indicates extensive contamination of this raw product. The PCR assay was highly reliable and may be used by food processors as well as by FSIS as a rapid and highly sensitive means of identifying L. monocytogenes in foods.

Technical Abstract: A multiplex polymerase chain reaction was developed to simultaneously identify species of the genus Listeria and L. monocytogenes. Two sets of primers were used. The first set amplifies a 938-bp region of the 16S rRNA gene which is highly conserved in all Listeria species. The second set amplifies a 174-bp region of the hemolysin (hlyA) gene of L. monocytogenes. Thus, isolates of Listeria spp. yield a single 938-bp product, whereas L. monocytogenes isolates yield both the 938-bp and 174-bp products. The specificity of the assay was verified using all six Listeria species, 11 serotypes of L. monocytogenes as well as non-related bacteria. The multiplex PCR assay was used to determine the incidence of Listeria spp., especially L. monocytogenes, in mechanically separated turkey samples (n = 150 total samples). L. monocytogenes strains were selected by using the University of Vermont (UVM) two-step enrichment protocol and plating to selective Palcam agar. The multiplex PCR assay was used for verification of presumptive Listeria colonies. Approximately 38% of mechanically separated turkey samples (57 of 150) yielded L. monocytogenes; an additional 18% of these samples (27 of 150) harbored Listeria spp. Fifty-one percent (29/57) of the L. monocytogenes isolates were of serotype 1, 44% (25/57) of serotype 4, and 2% (1/57) were assigned to serogroups other than 1 and 4.