title: Genetic Characterization of Listeria monocytogenes Isolates from Industrial and Retail Ready-to-Eat Meat-Based Foods and Their Relationship with Clinical Strains from Human Listeriosis in Portugal.
abstract: Listeria monocytogenes isolates (n = 81) recovered from ready-to-eat meat-based food products (RTEMP) collected in industrial processing plants and retail establishments were genetically characterized for comparison with those from human clinical cases of listeriosis (n = 49). The aim was to assess RTEMP as a possible food source for human infection. L. monocytogenes was detected in 12.5% of the RTEMP samples, and in some cases, counts were above the European food safety criteria. All isolates were assessed by multiplex PCR for serogroup determination and detection of virulence-associated genes inlA, inlB, inlC, inlJ, plcA, hlyA, actA, and iap. Serogroups IIb and IVb dominated in RTEMP and human isolates, and all were positive for the assessed virulence genes. Antibiotic susceptibility testing by the disk diffusion method revealed a low level of resistance among the isolates. Pulsed-field gel electrophoresis (PFGE) of L. monocytogenes isolates, using restriction enzymes ApaI and AscI, revealed genetic variability and differentiated the isolates in five clusters. Although some pulsed-field gel electrophoresis profiles of particular RTEMP and human isolates seemed to be highly related, exhibiting more than 90% similarity, which suggests a possible common source, in most cases the strains were not genetically or temporally matched. The close genetic relatedness of RTEMP and human listeriosis strains stressed the importance of preventive measure implementation throughout the food chain.
authors.affiliation: Centro de Investigação Interdisciplinar em Sanidade Animal, Faculdade de Medicina Veterinária, Universidade de Lisboa, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal.
authors.forename: A R
authors.initials: AR
authors.lastname: Henriques
authors.affiliation: Instituto de Medicina Molecular, Centro Hospitalar de Lisboa Norte, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028 Lisboa, Portugal.
authors.forename: J Melo
authors.initials: JM
authors.lastname: Cristino
authors.affiliation: Centro de Investigação Interdisciplinar em Sanidade Animal, Faculdade de Medicina Veterinária, Universidade de Lisboa, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal.
authors.forename: M J
authors.initials: MJ
authors.lastname: Fraqueza
mesh_terms: D016521:Electrophoresis, Gel, Pulsed-Field; D005516:Food Microbiology; D006801:Humans; D008089:Listeria monocytogenes / Q000302:isolation & purification*; D008088:Listeriosis; D008460:Meat; D011174:Portugal
keywords: Contamination source and route; Listeria monocytogenes; Pulsed-field gel electrophoresis profile; Ready-to-eat meat-based food product; Serogroup; Strain persistence