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

Abstract

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.

Listeria monocytogenes Associated with New Zealand Seafood Production and Clinical Cases: Unique Sequence Types, Truncated InlA, and Attenuated Invasiveness

“…Orsi et al (6) also suggest that infrequent reporting of the PMSCs in listeriosis-related strains may have resulted in the overrepresentation of 4b isolates in clinical samples in comparison to 1/2a strains (harboring inlA-PMSC), while the PMSC may have resulted in positive selection for strains with a truncated InlA protein during environmental adaptation. In general, 1/2a strains appear to be more likely to acquire genetic information by horizontal transfer or to undergo recombination events that may afford rapid adaptation to niche-specific stresses (44). The increased mutability of these strains may have led to truncation of InlA as part of their niche adaptation.…”

Characterization of specific alleles in InlA and PrfA of Listeria monocytogenes isolated from foods in Osaka, Japan and their ability to invade Caco-2 cells

“…In the current study, 25.4% of food isolates had inlA PMSC mutations. According to previous reports, inlA PMSC mutations account for 48.5% of RTE isolates in the United States , 35% of isolates from various types of food in France (Jacquet et al, 2004), and 35% of isolates from the Canadian food supply (Kovacevic et al, 2013). Given a previous finding that only 1 of 59 isolates (1.7%) from RTE seafood samples had inlA PMSCs in Japan (Handa-Miya et al, 2007), it appears likely that food isolates with inlA PMSCs may be less widely distributed in Japan than those in the United States, France or Canada.…”

“…Although L. monocytogenes infections are rare in healthy individuals, these infections can cause meningitis and septicemia in neonates and the elderly, as well as miscarriage in pregnant women. Mortality rates for invasive listeriosis range from 20% to 40% (Kovacevic et al, 2013), and of an estimated 1591 listeriosis cases, 255 deaths occur each year in the United States (Scallan et al, 2011). Incidence of human listeriosis cases reportedly varies from 0.2 to 0.8 sporadic cases per 100,000 people per year in Europe and the United States (Vázquez-Boland et al, 2001).…”

“…The Caco-2 cell invasion assay enables assessment of properties of InlA leading to the invasion of host epithelial cells (Kovacevic et al, 2013;Van Stelten et al, 2010). Nightingale et al (2007) reported that L. monocytogenes strains exhibited significantly greater invasion efficiency in a Caco-2 cell invasion assay when grown at 30°C than at 37°C.…”

Invasiveness of Listeria monocytogenes strains isolated from animals in Poland

“…Briefly, 1 μl of appropriate DNA, obtained using DNA extraction kit (Eurx, Gdańsk, Poland), was added to a mix containing 450 nmol l -1 of primers 200 mmol l -1 dNTPs, 10 mol l -1 buffer Tris-HCl of pH 8·3, 50 mnol l -1 KCl, 1·5 mmol l -1 MgCl 2 , 0·1% Triton X-100, and 2U of REDTaq genomic polymerase (Sigma). Primers for inlA were from Kovačević et al (2013).…”