Comparison of Widely Used Listeria monocytogenes Strains EGD, 10403S, and EGD-e Highlights Genomic Differences Underlying Variations in Pathogenicity

Abstract

For nearly 3 decades, listeriologists and immunologists have used mainly three strains of the same serovar (1/2a) to analyze the virulence of the bacterial pathogen Listeria monocytogenes. The genomes of two of these strains, EGD-e and 10403S, were released in 2001 and 2008, respectively. Here we report the genome sequence of the third reference strain, EGD, and extensive genomic and phenotypic comparisons of the three strains. Strikingly, EGD-e is genetically highly distinct from EGD (29,016 single nucleotide polymorphisms [SNPs]) and 10403S (30,296 SNPs), and is more related to serovar 1/2c than 1/2a strains. We also found that while EGD and 10403S strains are genetically very close (317 SNPs), EGD has a point mutation in the transcriptional regulator PrfA (PrfA*), leading to constitutive expression of several major virulence genes. We generated an EGD-e PrfA* mutant and showed that EGD behaves like this strain in vitro, with slower growth in broth and higher invasiveness in human cells than those of EGD-e and 10403S. In contrast, bacterial counts in blood, liver, and spleen during infection in mice revealed that EGD and 10403S are less virulent than EGD-e, which is itself less virulent than EGD-e PrfA*. Thus, constitutive expression of PrfA-regulated virulence genes does not appear to provide a significant advantage to the EGD strain during infection in vivo, highlighting the fact that in vitro invasion assays are not sufficient for evaluating the pathogenic potential of L. monocytogenes strains. Together, our results pave the way for deciphering unexplained differences or discrepancies in experiments using different L. monocytogenes strains.

Comparative Genomic Analysis of Two Serotype 1/2b Listeria monocytogenes Isolates from Analogous Environmental Niches Demonstrates the Influence of Hypervariable Hotspots in Defining Pathogenesis

“…They are thought to promote the cell-to-cell spread of L. monocytogenes by relieving the cortical tension of the host cell and enhancing the ability of the bacterium to protrude into the plasma membrane (52). A fourth type of internalin, which contains an atypical leucine-rich repeat region, has also been recently described (53) with lmo0460 as the sole representative member. The genomes of both strains in this study were examined for the presence of internalin and internalin-like genes.…”

The Listeria monocytogenes Hibernation-Promoting Factor Is Required for the Formation of 100S Ribosomes, Optimal Fitness, and Pathogenesis

“…Because of its ability to shift quickly between saprophytic growth in the environment and potentially lethal pathogenesis upon contacting a host, L. monocytogenes has been referred to as a bacterial "Dr. Jekyll and Mr. Hyde" (3). The ability to tolerate or thrive in a variety of unfavorable conditions, including high salt, low pH, and refrigeration temperatures, has made L. monocytogenes a formidable challenge to the food industry (1,2). Therefore, it is important to understand the set of factors that enable L. monocytogenes to survive so effectively in a wide variety of inhospitable environments.…”

“…isteria monocytogenes is a Gram-positive, food-borne, facultative intracellular pathogen that infects a broad range of vertebrate hosts (1,2). The bacterium leads a saprophytic lifestyle in the environment and is commonly found in soil, water, and decaying organic matter.…”

The roles of noncoding RNA Rli60 in regulating the virulence of Listeria monocytogenes

“…9e11, 15 More than 300 kinds of ncRNA have been found in LM, which include 150 different transencoding small RNA (sRNA) fragments. 16 Small RNA could match the complementary noncontiguous regions of the targeted messenger RNA to regulate the expression of related genes. 17e20 Nielsen et al 21 have found that sRNA LhrA could bind to the 5 0 sequence of chiA messenger RNA, thereby preventing its binding to 30S ribosomes and tRNAf Met and subsequent formation of translation initiation complex, which directly affect the expression of chiA.…”