To Örebro University

The aim of the present study was to determine whether L. monocytogenes bacteria from an invasive case of listeriosis cultured in a BacT/ALERT FA bottle in 1999 have survived, and if so, whether their pulsed-field gel electrophoresis (PFGE) profiles have changed. In 2024, after more than 25 years in a refrigerator, L. monocytogenes was isolated in pure culture from the BacT/ALERT FA bottle. All 100 selected isolates showed the same by PFGE profile with the restriction enzyme Asc I as the L. monocytogenes isolates did in 1999. L. monocytogenes can apparently survive for a long time in a nutrient-poor environment, and this must be taken into account by the food industry. Persistence in clinical samples has rarely been reported; however, several authors report persistence of L. monocytogenes in the food industry, with bacteria ending up in final products.

Introduction: Listeria monocytogenes causes listeriosis and often exhibits resistance to cadmium. While multiple cadmium resistance genes have been identified, our understanding of the full landscape of cadmium resistance determinants is far from complete.

Purpose: This study aims to investigate cadmium resistance genes via genome-wide screening of cadmium-resistant L. monocytogenes from human listeriosis in Sweden.

Methods: Thirty-two cadmium-resistant isolates were subjected to the whole genome sequencing. Plasmid-borne contigs were identified in silico and cadmium resistance genes were found by BLAST2 with known cadmium resistance genes and pan-genome analysis. These genes were compared and the deduced proteins were aligned with the prototype proteins, bootstrapped, and visualized. To determine the location of the genes, the DNA sequences including flanking regions were compared with each other and, for chromosomal cadmium resistance genes, with the complete genome of strain F2365.

Results: We identified three known cadmium resistance operons (cadA1C1, cadA2C2, and cadA4C4) and two that were novel (cadD8A8 and cadA9C9). cadA1C1 was found most frequently and was plasmid borne, except for one CC101 strain that harbored a cadA1C1-harboring chromosomal island. Chromosomal islands with cadmium resistance genes also included the previously characterized LGI2 (cadA4C4 and arsenic resistance genes) and a novel island harboring cadA9C9 and an arsenic resistance gene. All cadA9C9-positive strains lacked plasmids and other cadmium resistance operons. Our analysis also identified cadA10, which was chromosomally harbored by all strains in our panel and the cadmium-susceptible strain F2365, suggesting that it mediates innate baseline resistance of L. monocytogenes to cadmium.

Significance: Our findings highlight the complex distribution of cadmium resistance genes within L. monocytogenes, which will help us understand the genes that facilitate ecological adaptations, potentially leading to persistence in the environment and increased risk of L. monocytogenes-contaminated foods and foodborne infections.

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.

Mer än 100 små barn har de senaste tolv åren fått svåra njurskador efter att ha smittats av ehec som kan finnas i rå köttfärs. Låt inte barnen vara med och trilla köttbullar, varnar Diana Karpman, specialist på njursjukdomar.

Traditionally, food safety knowledge has been seen as a factor in improving food safety behaviour. However, the relationship between knowledge and behavior is complex. The aim of the present study was to investigate self-reported data from 408 university students regarding food safety background, knowledge, attitudes, and behaviour using Structural Equation Model (SEM) to examine the influence of different factors on food safety behaviour. The SEM was applied to four factors derived from the data: Background, Knowledge, Attitude and Behaviour. The novelty of this current investigation is the inclusion of the Background factor (genus; experience of cooking and handling different food items; experience of a food safety education course; the foremost sources of food safety knowledge). The factors were constructed from variables with sufficient factor loadings and set up in a predetermined structure confirmed to be valid in previous studies. The results, demonstrated as regression coefficients between factors, confirm that the Background factor strongly influenced Knowledge (0.842). The Knowledge factor, in turn, strongly affected Attitude (0.605), while it did not directly affect Behaviour (0.301) in the same way as Attitude. Attitude had a stronger influence on Behaviour (0.438) than Knowledge. Thus, the Attitude factor seemed to play a mediating role between Knowledge and Behaviour. This indicates that students´ attitudes towards the importance of food safety may have an impact on their food safety behavior, which should have implications for the development of food safety education. This warrants further investigation and practical development.