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

Abstract

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 ...

The Majority of Genotypes of the Virulence Gene inlA Are Intact among Natural Watershed Isolates of Listeria monocytogenes from the Central California Coast

“…monocytogenes have been published, and several types of PMSCs have been described [4–12]. There is less information on inlA alleles in strains from environmental origins, but those published studies indicate that inlA alleles predominantly are intact both in healthy ruminants [8], and farm animals and their environments [10, 13]. …”

Listeria monocytogenes in dairy plants in Southern Brazil: Occurrence, virulence potential, and genetic diversity

“…Some studies showed that inlA PMSC mutations are responsible for attenuated virulence in L . monocytogenes isolates (Manuel et al, ; Nightingale et al, ).…”

“…The inlA gene encodes a product that is responsible for the entry of the bacterium into the host cell, and genes inlB, inlC, and inlJ are directly involved in the subsequent infection stages (Doumith et al, 2004;Liu et al, 2007). Some studies showed that inlA PMSC mutations are responsible for attenuated virulence in L. monocytogenes isolates (Manuel et al, 2015;Nightingale et al, 2008).…”

“…For example, to establish an infection, L. monocytogenes must cross the intestinal barrier, a process that involves the internalin A protein, encoded by inlA gene, which plays a critical role in invasion of intestinal epithelial cells (Lecuit, Ohayon, Braun, Mengaud, & Cossart, 1997). However, previous studies have demonstrated a number of mutations leading to premature stop codons (PMSCs) in inlA resulting in the production of a truncated form of InlA, even in food isolates (Manuel, Stelten, Wiedmann, Nightingale, & Orsi, 2015;Nightingale et al, 2008;Wu, Wu, Zhang, Chen, & Guo, 2016).…”

High resolution melting analysis for the characterization of lineage II Listeria monocytogenes serovars 1/2a and 1/2c based on single nucleotide polymorphisms identification within the Listeria Pathogenicity Island-1 and inlAB operon: a novel approach for

“…Listeria monocytogenes can be categorized into genetic lineages (Manuel et al . ), which are serotype specific. Lineages I and II contain serotypes generally associated with human listeriosis; serovars 1/2b and 4b group in lineage I, and serovars 1/2a and 1/2c in lineage II (Hain et al .…”