Lactiplantibacillus plantarum subsp. plantarum and Fructooligosaccharides Combination Inhibits the Growth, Adhesion, Invasion, and Virulence of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen responsible for many food outbreaks worldwide. This study aimed to investigate the single and combined effect of fructooligosaccharides (FOS) and Lactiplantibacillus plantarum subsp. plantarum CICC 6257 (L. plantarum) on the growth, adhesion, invasion, and virulence of gene expressions of Listeria monocytogenes 19112 serotype 4b (L. monocytogenes). Results showed that L. plantarum combined with 2% and 4% (w/v) FOS significantly (p < 0.05) inhibited the growth of L. monocytogenes (3–3.5 log10 CFU/mL reduction) at the incubation temperature of 10 °C and 25 °C. Under the same combination condition, the invasion rates of L. monocytogenes to Caco-2 and BeWo cells were reduced more than 90% compared to the result of the untreated group. After L. plantarum was combined with the 2% and 4% (w/v) FOS treatment, the gene expression of actin-based motility, sigma factor, internalin A, internalin B, positive regulatory factor A, and listeriolysin O significantly (p < 0.05) were reduced over 91%, 77%, 92%, 89%, 79%, and 79% compared to the result of the untreated group, respectively. The inhibition level of the L. plantarum and FOS combination against L. monocytogenes was higher than that of FOS or L. plantarum alone. Overall, these results indicated that the L. plantarum and FOS combination might be an effective formula against L. monocytogenes.

Virulence potential of Listeria monocytogenes strains recovered from pigs in Spain

BackgroundListeria monocytogenes is a foodborne bacterial pathogen that causes listeriosis, an infectious disease in animals and people, with pigs acting as asymptomatic reservoirs. In August 2019 an outbreak associated with the consumption of pork meat caused 222 human cases of listeriosis in Spain. Determining the diversity as well as the virulence potential of strains from pigs is important to public health.MethodsThe behaviour of 23 L monocytogenes strains recovered from pig tonsils, meat and skin was compared by studying (1) internalin A, internalin B, listeriolysin O, actin assembly-inducing protein and PrfA expression levels, and (2) their invasion and intracellular growth in eukaryotic cells.ResultsMarked differences were found in the expression of the selected virulence factors and the invasion and intracellular replication phenotypes of L monocytogenes strains. Strains obtained from meat samples and belonging to serotype 1/2a did not have internalin A anchored to the peptidoglycan. Some strains expressed higher levels of the studied virulence factors and invaded and replicated intracellularly more efficiently than an epidemic L monocytogenes reference strain (F2365).ConclusionThis study demonstrates the presence of virulent L monocytogenes strains with virulent potential in pigs, with valuable implications in veterinary medicine and food safety.

A Structural Study on the Listeria Monocytogenes Internalin A—Human E-cadherin Interaction: A Molecular Tool to Investigate the Effects of Missense Mutations

Listeria monocytogenes is a widespread foodborne pathogen of high concern and internalin A is an important virulence factor that mediates cell invasion upon the interaction with the host protein E-cadherin. Nonsense mutations of internalin A are known to reduce virulence. Although missense mutations are largely overlooked, they need to be investigated in respect to their effects in cell invasion processes. This work presented a computational workflow to early characterize internalin A missense mutations. The method reliably estimated the effects of a set of engineered missense mutations in terms of their effects on internalin A–E-cadherin interaction. Then, the effects of mutations of an internalin A variant from a L. monocytogenes isolate were calculated. Mutations showed impairing effects on complex stability providing a mechanistic explanation of the low cells invasion capacity previously observed. Overall, our results provided a rational approach to explain the effects of internalin A missense mutations. Moreover, our findings highlighted that the strength of interaction may not directly relate to the cell invasion capacity reflecting the non-exclusive role of internalin A in determining the virulence of L. monocytogenes. The workflow could be extended to other virulence factors providing a promising platform to support a better molecular understanding of L. monocytogenes epidemiology.

Listeriosis: genotyping as a key for identification a possible source of infection

Objective. To perform a comparative analysis of clinical and food isolates of Listeria monocytogenes collected in the European part of Russia in 2018–2019. Materials and Methods. We used multilocus sequencing (MLST), supplemented by virulence loci, including fragments of internalin genes (MvLST, Multi-virulent-locus sequence typing), followed by phylogenetic analysis. Results. The main diagnoses for clinical isolates were prenatal and neonatal listeriosis and meningitis. Clinical isolates predominantly belonged to phylogenetic line II with the predominance of ST7, which was also the most abundant in food isolates. The second most common occurrence in food isolates was ST121, widely distributed in Europe. Isolates of phylogenetic line I in the group of clinical cultures in three cases were represented by ST6, detected during outbreaks of listeriosis in Europe 2015–2018 and South Africa in 2017–2018. Only in one isolate from food belonged to the phylogenetic lineage I. In general, the diversity of food isolate genotypes was significantly higher than clinical isolates. The analysis of virulence loci revealed a new internalin A allele and a new internalin genes profile (IP) in isolate ST7 from food. Conclusions. L. monocytogenes of the most common ST7 is autochthonous in Russia; cases of listeriosis caused by the ST6 bacterium are most likely imported. Based on the analysis of the diversity of ST and IP of L. monocytogenes identified in Russia, a rapid diagnosis scheme for epidemiological investigation is proposed.