To Örebro University

Premature stop codons in the internalin virulence determinant inlA are common in serotype 1/2a Listeria monocytogenes from food/food processing environments but rare among human clinical isolates. Here, we report the genome sequences of serotype 1/2a (STs 121 and 3258) human listeriosis isolates from Sweden harboring such mutations in inlA.

Listeria monocytogenes of clonal complex 14 (CC14) is a potentially hypervirulent clone of serotype 1/2a but remains poorly characterized. We report the genome sequences of five sequence type 14 (ST14) (CC14) strains from human listeriosis cases in Sweden, which harbor a chromosomal heavy metal resistance island that is generally uncommon in serotype 1/2a.

Listeria monocytogenes is a Gram-positive pathogen responsible for the severe foodborne disease listeriosis. A chromosomal hotspot between lmo0301 and lmo0305 has been noted to harbor diverse restriction modification (RM) systems. Here, we analyzed 872 L. monocytogenes genomes to better understand the prevalence and types of RM systems in this region, designated the immigration control region (ICR). Type I, II, III and IV RM systems were found in 86.1% of strains inside the ICR and in 22.5% of strains flanking the ICR. ICR content was completely conserved within the same multilocus sequence typing-based sequence type (ST), but the same RM system could be identified in diverse STs. The intra-ST conservation of ICR content suggests that this region may drive the emergence of new STs and promote clone stability. Sau3AI-like, LmoJ2 and LmoJ3 type II RM systems as well as type I EcoKI-like, and type IV AspBHI-like and mcrB-like systems accounted for all RM systems in the ICR. A Sau3AI-like type II RM system with specificity for GATC was harbored in the ICR of many STs, including all strains of the ancient, ubiquitous ST1. The extreme paucity of GATC recognition sites in lytic phages may reflect ancient adaptation of these phages to preempt resistance associated with the widely distributed Sau3AI-like systems. These findings indicate that the ICR has a high propensity for RM systems which are intraclonaly conserved and may impact bacteriophage susceptibility as well as ST emergence and stability.

Listeriosis is a foodborne disease with a high fatality rate, and infection is mostly transmitted through ready-toeat(RTE) foods contaminated with Listeria monocytogenes, such as gravad/smoked fish, soft cheeses, andsliced processed delicatessen (deli) meat. Food products/dishes stored in vacuum or in modified atmospheresand with extended refrigerator shelf lives provide an opportunity for L. monocytogenes to multiply to largenumbers toward the end of the shelf life. Elderly, pregnant women, neonates, and immunocompromisedindividuals are particularly susceptible to L. monocytogenes. Listeriosis in humans manifests primarily assepticemia, meningitis, encephalitis, gastrointestinal infection, and abortion. In the mid 1990s and early 2000s ashift from L. monocytogenes serovar 4b to serovar 1/2a causing human listeriosis occurred, and serovar 1/2a isbecoming more frequently linked to outbreaks of listeriosis, particularly in Europe and Northern America.Consumer lifestyle has changed, and less time is available for food preparation. Modern lifestyle has markedlychanged eating habits worldwide, with a consequent increased demand for RTE foods; therefore, more RTE andtake away foods are consumed. There is a concern that many Listeria outbreaks are reported from hospitals.Therefore, it is vitally important that foods (especially cooked and chilled) delivered to hospitals and residentialhomes for senior citizens and elderly people are reheated to at least 72C: cold food, such as turkey deli meatand cold-smoked and gravad salmon should be free from L. monocytogenes. Several countries have zerotolerance for RTE foods that support the growth of Listeria.

Among 504 clinical lineage II isolates of Listeria monocytogenes isolated during 1958-2010 in Sweden, 119 pulsed-field gel electrophoresis (PFGE) types (AscI) have been identified based on the number and distribution of all banding patterns in each DNA profile. In this study, these types were further divided into PFGE groups based on the configuration of small bands with sizes <145.5 kb. The 504 isolates included 483 serovar 1/2a isolates distributed into 114 PFGE types and 21 serovar 1/2c isolates distributed into 9 PFGE types; these were further divided into 21 PFGE groups. PFGE group, that is, configuration of small bands below 145.5 kb, and serovars were correlated. L. monocytogenes isolates belonging to PFGE groups A, B, C, E, F, H, K, L, M, S, V, W, Y, and Ö-6 to Ö-12 shared serovar 1/2a, with one exception. PFGE group E also included two PFGE types sharing serovar 1/2c and four PFGE types belonging to either serovar 1/2a or 1/2c. Isolates belonging to PFGE group N shared serovar 1/2c. In contrast to lineage I isolates, small fragments <33.3 kb were visible in all L. monocytogenes isolates belonging to lineage II. In the results from both the present and previous studies, the genomic region of small bands was genetically more conservative than in large bands. The distribution of these small bands established the relatedness of strains and defined a genetic marker for both lineages I and II, while also establishing their serogroup. The division of L. monocytogenes PFGE types into PFGE groups is advantageous as the profile of every new isolate can be identified easily and quickly through first studying the PFGE group affiliation of the isolate based on the smaller band patterns <145.5 kb, and then identifying the PFGE type based on the band patterns >145.5 kb.

Microbiological and sensory methods were used to analyze 22 soft cheeses, of which 19 were made from raw milk, one was made from both raw and pasteurized milk and two were made from pasteurized milk. Moderate correlations (r-value 0.5–0.6 and p-value <0.01–0.05) were found between the levels of Enterobacteriaceae 37°C and the intensity of the sensory characteristics “bitter”, “metallic”, “pungent”, “manure” and “ammonia”. The present study indicates that it is possible to predict high levels of Enterobacteriaceae in soft cheeses made from raw milk using only the human senses (odor and taste).

The 63 pulsed-field gel electrophoresis (PFGE) types identified among 427 clinical isolates of Listeria monocytogenes that were characterized in a previous study by serotyping and PFGE (AscI) could be further divided into 17 PFGE groups. While the 63 PFGE types, all part of lineage I, were established based on the number and distribution of all bands in each DNA profile, the 17 PFGE groups were based on the configuration of small bands with sizes L. monocytogenes serovar 4b isolates (n=334) were divided into 8 PFGE groups; the 32 PFGE types of serovar 1/2b isolates (n=90) and the serovar 3b isolates (n=3, 1 PFGE type) were divided into 9 PFGE groups. An association was observed between PFGE groups and serovars. L. monocytogenes isolates belonging to PFGE groups I, J, Q, R, X, Z, o-4, and o-5 all shared serovar 4b, whereas isolates from PFGE groups D, G, O, P, T, U, o-1, o-2, and o-3 shared serovar 1/2b. Small fragments L. monocytogenes isolates. From the results of the present study, a procedure for accelerating the identification of PFGE types when analyzing new PFGE profiles can be suggested. Therefore, we propose a stepwise procedure to PFGE profiling by first identifying the PFGE group using the smaller band patterns <145.5 kb, and then determining PFGE types based on the band patterns >145.5 kb.