Variation in
            <i>Listeria monocytogenes</i>
            Dose Responses in Relation to Subtypes Encoding a Full-Length or Truncated Internalin A

c Listeria monocytogenes strains belonging to serotypes 1/2a and 4b are frequently linked to listeriosis. While inlA mutations leading to premature stop codons (PMSCs) and attenuated virulence are common in 1/2a, they are rare in serotype 4b. We observed PMSCs in 35% of L. monocytogenes isolates (n ‫؍‬ 54) recovered from the British Columbia food supply, including serotypes 1/2a (30%), 1/2c (100%), and 3a (100%), and a 3-codon deletion (amino acid positions 738 to 740) seen in 57% of 4b isolates from fish-processing facilities. Caco-2 invasion assays showed that two isolates with the deletion were significantly more invasive than EGD-SmR (P < 0.0001) and were either as (FF19-1) or more (FE13-1) invasive than a clinical control strain (08-5578) (P ‫؍‬ 0.006). To examine whether serotype 1/2a was more likely to acquire mutations than other serotypes, strains were plated on agar with rifampin, revealing 4b isolates to be significantly more mutable than 1/2a, 1/2c, and 3a serotypes (P ‫؍‬ 0.0002). We also examined the ability of 33 strains to adapt to cold temperature following a downshift from 37°C to 4°C. Overall, three distinct coldadapting groups (CAG) were observed: 46% were fast (<70 h), 39% were intermediate (70 to 200 h), and 15% were slow (>200 h) adaptors. Intermediate CAG strains (70%) more frequently possessed inlA PMSCs than did fast (20%) and slow (10%) CAGs; in contrast, 87% of fast adaptors lacked inlA PMSCs. In conclusion, we report food chain-derived 1/2a and 4b serotypes with a 3-codon deletion possessing invasive behavior and the novel association of inlA genotypes encoding a full-length InlA with fast cold-adaptation phenotypes.

Section: Discussionmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 59%

Examination of Food Chain-Derived Listeria monocytogenes Strains of Different Serotypes Reveals Considerable Diversity in inlA Genotypes, Mutability, and Adaptation to Cold Temperatures

Kovačević

Arguedas-Villa

Woźniak

et al. 2013

“…The A 6 allele was significantly (P Ͻ 0.0001) overrepresented among food isolates, which is consistent with our previous study (31); conversely, the A 7 allele was significantly (P ϭ 0.0015) underrepresented among these strains. Interestingly, a previous study also showed that the average L. monocytogenes dose per positive serving was 3 ϫ 10 6 CFU/ serving for DUP-1039C with the 5= inlA frameshift mutation (i.e., the A 6 allele), which was Ͼ1,000-fold higher than those for other subtypes, including ribotype DUP-1039C, expressing full-length InlA (2.0 ϫ 10 3 CFU/serving), and ribotype DUP-1042B, representing an epidemic clone (9.0 ϫ 10 2 CFU/serving) (21). This indicates that isolates with the A 6 allele are not only more frequent among RTE food isolates but also typically found at higher levels in RTE foods than other subtypes, including subtypes commonly implicated in sporadic and epidemic listeriosis.…”

Section: Resultsmentioning

confidence: 99%

“…The virulence factor internalin A (InlA; encoded by inlA) facilitates the crossing of the host intestinal barrier, which enables subsequent establishment of a systemic infection by L. monocytogenes (20). L. monocytogenes isolates carrying a PMSC in inlA produce a truncated form of InlA that is secreted rather than anchored to the bacterial cell wall; these strains have been shown to be virulence attenuated in a guinea pig model (17,(21)(22)(23). A number of studies specifically indicate that lineage II strains carry an inlA PMSC more frequently than lineage I strains (18,23,24).…”

mentioning

confidence: 99%

Prevalence and Distribution of Listeria monocytogenes inlA Alleles Prone to Phase Variation and inlA Alleles with Premature Stop Codon Mutations among Human, Food, Animal, and Environmental Isolates

Manuel

Stelten

Wiedmann

et al. 2015

Self Cite

cIn Listeria monocytogenes, 18 mutations leading to premature stop codons (PMSCs) in the virulence gene inlA have been identified to date. While most of these mutations represent nucleotide substitutions, a frameshift deletion in a 5= seven-adenine homopolymeric tract (HT) in inlA has also been reported. This HT may play a role in phase variation and was first identified among L. monocytogenes lineage II ribotype DUP-1039C isolates. In order to better understand the distribution of different inlA mutations in this ribotype, a newly developed multiplex real-time PCR assay was used to screen 368 DUP-1039C isolates from human, animal, and food-associated sources for three known 5= inlA HT alleles: (i) wild-type (WT) (A 7 ), (ii) frameshift (FS) (A 6 ), and (iii) guanine interruption (A 2 GA 4 ) alleles. Additionally, 228 DUP-1039C isolates were screened for all inlA PMSCs; data on the presence of all inlA PMSCs for the other 140 isolates were obtained from previous studies. The statistical analysis based on 191 epidemiologically unrelated strains showed that strains with inlA PMSC mutations (n ‫؍‬ 41) were overrepresented among food-associated isolates, while strains encoding full-length InlA (n ‫؍‬ 150) were overrepresented among isolates from farm animals and their environments. Furthermore, the A 6 allele was overrepresented and the A 7 allele was underrepresented among food isolates, while the A 6 allele was underrepresented among farm and animal isolates. Our results indicate that genetic variation in inlA contributes to niche adaptation within the lineage II subtype DUP-1039C. Listeria monocytogenes is a food-borne pathogen and the etiological agent of listeriosis, a severe invasive disease that can affect both humans and animals (1). More than 99% of human listeriosis cases are estimated to be transmitted through food (2). Despite its presence in a wide range of environments and foods, the majority of human listeriosis infections appear to be linked to consumption of contaminated ready-to-eat (RTE) foods (3) that support L. monocytogenes growth. Numerous studies have indicated that not all L. monocytogenes strains are equally associated with invasive disease. For example, McLauchlin reported that three (1/2a, 1/2b, and 4b) of the 13 serotypes of L. monocytogenes were responsible for 90% of 1,363 listeriosis cases from the United Kingdom (4). Additionally, multiple studies using both DNA band-based and sequence-based subtyping methods have shown that L. monocytogenes forms a structured population composed of at least four divergent lineages (I, II, III, and IV), which in a number of studies have been suggested to differ in their associations with different sources and in their pathogenic potentials (5-9). The majority of L. monocytogenes isolates belong to lineages I and II, which contain the serotypes most commonly associated with human clinical cases; serotypes 1/2b and 4b group into lineage I, while serotypes1/2a and 1/2c group into lineage II. Lineage III and IV strains are rare and usually isolated from ...

“…Specifically, exponential models based on L. monocytogenes concentrations found in samples from retail sources generated mean log 10 r values of Ϫ8.1 and Ϫ10.7 for (i) subtypes encoding a fulllength InlA and (ii) subtypes carrying a PMSC in inlA, respectively. Inclusion of an additional parameter to estimate the increase in L. monocytogenes concentration between that in retail source samples and that from consumption resulted in mean log 10 r values of Ϫ10.44 and Ϫ13.75 for subtypes encoding a full-length InlA and subtypes carrying a PMSC in inlA, respectively (4). Findings from the current study provide further quantitative evidence that L. monocytogenes subtypes vary in their ability to cause a systemic L. monocytogenes infection, which may be mechanistically attributed to a defined genetic marker (i.e., presence of a mutation leading to a PMSC in inlA).…”

Section: Resultsmentioning

confidence: 99%

Significant Shift in Median Guinea Pig Infectious Dose Shown by an Outbreak-AssociatedListeria monocytogenesEpidemic Clone Strain and a Strain Carrying a Premature Stop Codon Mutation ininlA

Stelten

Simpson

Chen

et al. 2011

Listeria monocytogenes contains (i) epidemic clone (EC) strains, which have been linked to the majority of listeriosis outbreaks worldwide and are overrepresented among sporadic cases in the United States, and (ii) strains commonly isolated from ready-to-eat foods that carry a mutation leading to a premature stop codon (PMSC) in inlA, which encodes the key virulence factor internalin A (InlA). Internalin A binds certain isoforms of the cellular receptor E-cadherin to facilitate crossing the intestinal barrier during the initial stages of an L. monocytogenes infection. Juvenile guinea pigs, which express the human isoform of E-cadherin that binds InlA, were intragastrically challenged with a range of doses of (i) an EC strain associated with a listeriosis outbreak or (ii) a strain carrying a PMSC mutation in inlA. Recovery of L. monocytogenes from tissues (i.e., liver, spleen, mesenteric lymph nodes, and ileum) was used to develop strain-specific dose-response curves on the basis of individual and combined organ data. Modeling of individual and combined organ data revealed an approximate 1.2 to 1.3 log 10 increase in the median infectious dose for the strain carrying a PMSC in inlA relative to that for the EC strain. Inclusion of the strain parameter significantly improved the goodness of fit for individual and combined organ models, indicating a significant shift in median infectious dose for guinea pigs challenged with an inlA PMSC strain compared to that for guinea pigs challenged with an EC strain. Results from this work provide evidence that the L. monocytogenes dose-response relationship is strain specific and will provide critical data for enhancement of current risk assessments and development of future risk assessments.