In Vitro and In Vivo Invasiveness of Different Pulsed-Field Gel Electrophoresis Types of Listeria monocytogenes

Abstract

The virulence of different pulsed-field gel electrophoresis (PFGE) types of Listeria monocytogenes was examined by monitoring their ability to invade Caco-2 cells. Strains belonging to seven different PFGE types originating from both foods and humans were included. No significant differences in invasiveness were detected between strains isolated from humans and those isolated from food. Strains belonging to PFGE type 1 expressed a significantly lower ability to invade cells compared to strains belonging to other PFGE types. Although strains of PFGE type 2 also seemed to invade at a low level, this was not significant in the present study. PFGE types 1 and 2 as well as type 14 are more frequently found in food than the four other PFGE types examined and moreover have a relatively low prevalence in humans compared to their prevalence in food. Thus, the hypothesis that some PFGE types are less virulent than others is supported by this study showing that certain PFGE types of L. monocytogenes commonly found in food are less invasive than others to Caco-2 cells. In contrast to the differences in invasion, identical intracellular growth rates between the different PFGE types were observed. In vivo studies of the actual ability of the strains to invade the liver and spleen of cimetidinetreated rats following an oral dose of 10 9 L. monocytogenes cells were performed for isolates of PFGE types 1, 2, 5, and 15. After 2 days, equal amounts of bacteria were observed in the liver and spleen of the rats for any of the PFGE types tested.Listeria monocytogenes is an intracellular pathogen of humans and animals that expresses differences in virulence within individual strains (7, 27). Among the 13 serotypes known for this species, most isolates from human cases of listeriosis seem to belong to only three serotypes (1/2a, 1/2b, and 4b). While serotyping has limited application in epidemiological studies, more discriminatory molecular typing methods, such as multilocus enzyme electrophoresis (12, 16), pulsed-field gel electrophoresis (PFGE) (18,20), random amplification of polymorphic DNA (3, 4), ribotyping (23), and phage typing (14), have successfully been used to differentiate among isolates of L. monocytogenes.PFGE has been shown to be highly discriminative for strains of L. monocytogenes (10, 11, 15), either alone or in combination with other methods. PFGE typing of 123 isolates of L. monocytogenes from ready-to-eat foods and 39 isolates from human clinical cases of infection showed a significant difference in the distribution of PFGE types among food isolates compared to human isolates (18), with some types having a higher prevalence among food isolates and vice versa.Individual isolates of L. monocytogenes are known to vary in virulence (7,9). Most earlier studies that have described the association between various subtypes and the virulence of the strains have focused on multiplication inside the host rather than invasion into the intestinal mucosa. The results are not clear, however. By this approach, Nørrung and Anderse...

Comparative Analysis of Multilocus Sequence Typing and Pulsed-Field Gel Electrophoresis for Characterizing Listeria monocytogenes Strains Isolated from Environmental and Clinical Sources

“…During our PFGE analyses, we did not observe subclustering of clinical (and possibly more virulent) or environmental isolates. This observation agrees with a previous report (22) demonstrating no association between various PFGE types of L. monocytogenes and the strains' virulence potential for Caco-2 tissue culture cells. On the other hand, MLST identified three subclusters (A1, B1, and B2 [ Fig.…”

Listeria monocytogenesIsolates from Foods and Humans Form Distinct but Overlapping Populations

“…In addition to ribotypes DUP-1038B and DUP-1042B, which produced significantly larger plaques than other ribotypes, ribotype DUP-1053A was found to have lower infectivity than other ribotypes. These findings are consistent with studies on food and human isolates using chicken embryo and Caco-2 tissue culture infection assays, which also revealed that some subtypes were more virulent than others (19,26). The concept of strain-specific virulence characteristics is also supported by the observation that the correlation between the two measures of cytopathogenicity (plaque size and infectivity) differed among ribotypes.…”

“…Previous studies have also shown that lineage I strains are more common among human listeriosis cases and outbreaks than among animal cases, while lineage III strains are significantly more common among animal listeriosis cases than among human cases (17). From a biological perspective, however, clear correlations between specific genetic types or clonal groups and virulence characteristics remain to be established (19,26,30,42).…”

Role of Flagellin and the Two-Component CheA/CheY System of Listeria monocytogenes in Host Cell Invasion and Virulence

“…Determination of cell association and invasion of L. monocytogenes was performed as described by Larsen et al (32), with some modifications. Enterocyte-like Caco-2 cells obtained from the Deutsche Sammlung von Mikroorganismen und Zellkulturen (Braunschweig, Germany) were cultured in Eagle's minimal essential medium (MEM) enriched with Glutamax and HEPES (Invitrogen, Tåstrup, Denmark) and supplemented with 20% heat-inactivated (30 min at 56°C) fetal calf serum (Invitrogen), 0.1 mM nonessential amino acids (Invitrogen), and 0.5 ml of gentamicin (50 mg/ml) (Invitrogen) at 37°C under 5% CO 2 .…”