Human listeriosis : Grouping of human Listeria monocytogenes isolates with PFGE and AscI restriction enzyme

• Main Author: Lopez Valladares, Gloria
• Other Authors: Påhlson, Carl, University of Helsinki, Faculty of Veterinary Sciences, Doctoral Programme in Food Chain and Health, Helsingin yliopisto, eläinlääketieteellinen tiedekunta, Ruokaketjun ja terveyden tohtoriohjelma, Helsingfors universitet, veterinärmedicinska fakulteten, Doktorandprogrammet i livsmedelskedjan och hälsa, Tham, Wilhelm, Danielsson-Tham, Marie-Louise, Korkeala, Hannu
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Helsingin yliopisto 2019
• Subjects: Faculty of Veterinary Medicine; Salmo salar
• Online Access: http://hdl.handle.net/10138/301659

Isolates of Listeria monocytogenes (N=932) collected from human cases of invasive listeriosis in Sweden between 1958 and 2010 were serotyped and characterised with pulsed-field gelelectrophoresis (PFGE) and AscI restriction enzyme. The genotype diversity of L. monocytogenes isolates was investigated and related to genotypic results from epidemiological information on human infection, in order to detect possible clustering of L. monocytogenes genotypes over time, season, location, age, or gender (Paper I). From 1972 to 1995, serovar 4b was the predominant serovar; however, in 1996, serovar 1/2a became the major serovar among human listeriosis cases in Sweden. Based on the number and distribution of all bands in the profile, 63 PFGE types belonging to serovars 1/2b, 3b and 4b and 119 PFGE types belonging to serovars 1/2a and 1/2c were identified (Paper I). The PFGE types were further assembled into PFGE groups, based on the number and distribution of small bands below 145.5 kb (Papers II and III). As the genomic region of small bands is genetically more conservative than in large bands, the distribution of small bands establishes relatedness of strains and defines genetic markers for both lineages. Cold-smoked salmon (Salmo salar) and gravad salmon packed under modified atmosphere or vacuum from three manufacturers were purchased in Sweden and Germany in 2005 and the occurrence and levels of L. monocytogenes were analysed (Paper IV): 56 products were analysed and eleven harboured L. monocytogenes. From the positive samples, 56 isolates were analysed with AscI, and 11 isolates were further analysed with ApaI: five AscI PFGE types were identified, four belonging to serovar 1/2a and one to 4b. Forty-three (n=43: 76.8%) isolates shared serovar 1/2a and 13 (23.2%) shared serovar 4b and all AscI types were identified among human clinical strains in Sweden. Moreover, three gravad salmon samples harboured two PFGE types each from different lineages, serovar 1/2a and serovar 4b. Although, in most of the products, the level ...