title: Prevalence and genetic diversity of Listeria monocytogenes in the tonsils of pigs.
abstract: This study was set up to establish the prevalence of Listeria monocytogenes in the tonsils of sows and fattening pigs from five Finnish slaughterhouses and to evaluate the genetic similarity of L. monocytogenes strains isolated from the tonsils. A total of 271 pig tonsils (132 tonsils from fattening pigs and 139 from sows) from five different slaughterhouses in various parts of Finland were studied from June 1999 to March 2000. Overall, 14 and 4% of pig tonsils harbored L. monocytogenes and Listeria innocua, respectively. The prevalence of L. monocytogenes in tonsils of fattening pigs (22%) was significantly higher than in sows (6%). The isolates (n = 38) recovered from tonsils showed a wide genetic diversity by means of 24 different pulsed-field gel electrophoresis (PFGE) types presented by the strains. Moreover, in numerical analyses of restriction patterns, no association was found between the clustering of strains and the slaughterhouses, and strains showing a similar PFGE type were recovered from pigs of different slaughterhouses. The high prevalence of L. monocytogenes showing various PFGE types in the tonsils of pigs could indicate a potential source of contamination of pluck sets, carcasses, and the slaughterhouse environment and of subsequent processing steps.
authors.affiliation: Department of Food and Environmental Hygiene, Faculty of Veterinary Medicine, P.O. Box 57, FIN-00014 Helsinki University, Finland.
authors.forename: Tiina
authors.initials: T
authors.lastname: Autio
authors.forename: Annukka
authors.initials: A
authors.lastname: Markkula
authors.forename: Sanna
authors.initials: S
authors.lastname: Hellström
authors.forename: Taina
authors.initials: T
authors.lastname: Niskanen
authors.forename: Janne
authors.initials: J
authors.lastname: Lundén
authors.forename: Hannu
authors.initials: H
authors.lastname: Korkeala
mesh_terms: D000003:Abattoirs; D000818:Animals; D015373:Bacterial Typing Techniques; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D005387:Finland / Q000453:epidemiology; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D005798:Genes, Bacterial; D014644:Genetic Variation; D008089:Listeria monocytogenes / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D008297:Male; D014066:Palatine Tonsil / Q000382:microbiology*; D010802:Phylogeny; D015995:Prevalence; D013552:Swine