A hypermutator phenotype attenuates the virulence of Listeria monocytogenes in a mouse model

• Published in: Molecular microbiology Vol. 44; no. 3; pp. 877 - 887
• Main Authors: Mérino, Delphine, Réglier‐Poupet, Hélène, Berche, Patrick, Charbit, Alain
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.05.2002; Blackwell Publishing Ltd
• Subjects: Adenosine Triphosphatases - genetics; Adenosine Triphosphatases - physiology; Animals; Bacillus subtilis - genetics; Bacterial Proteins - genetics; Bacterial Proteins - physiology; Base Pair Mismatch; DNA Repair - genetics; DNA Repair - physiology; DNA, Bacterial - genetics; DNA, Bacterial - metabolism; DNA-Binding Proteins; Escherichia coli Proteins - genetics; Escherichia coli Proteins - physiology; Female; Listeria monocytogenes; Listeria monocytogenes - genetics; Listeria monocytogenes - pathogenicity; Listeriosis - microbiology; Mice; mutL gene; MutL protein; MutL Proteins; MutS DNA Mismatch-Binding Protein; mutS gene; MutS protein; Phenotype; Sequence Deletion; Sequence Homology, Amino Acid; Species Specificity; Specific Pathogen-Free Organisms; Streptococcus pneumoniae - genetics; Virulence
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2002.02929.x

Summary The integrity of the genetic material of bacteria is guaranteed by a set of distinct repair mechanisms. The participation of these repair systems in bacterial pathogenicity has been addressed only recently. Here, we study for the first time the participation in virulence of the MutSL mismatch repair system of Listeria monocytogenes. The mutS and mutL genes, which are contiguous in the L. monocytogenes chromosome, were identified after in silico analysis. The deduced MutS shares 62% identity with MutS of Bacillus subtilis and 50% identity with HexA, its homologue in Streptococcus pneumoniae; MutL shares 59% identity with MutL of B. subtilis and 47% identity with HexB of S. pneumoniae. Functional analysis of the mutSL locus was studied by constructing a double knock‐out mutant. We showed that the deletion ΔmutSL induces: (i) a 100‐ to 1000‐fold increase in the spontaneous mutation rate; and (ii) a 10‐ to 15‐fold increase in the frequency of transduction, thus demonstrating the role of mutSL of L. monocytogenes in both mismatch repair and homologous recombination. We found that the deletion ΔmutSL moderately affected bacterial virulence, with a 1‐log increase in the lethal dose 50% (LD50) in the mouse. Strikingly, repeated passages of the mutant strain in mice reduced virulence further. Competition assays between wild‐type and mutant strains showed that the deletion ΔmutSL reduced the capacity of L. monocytogenes to survive and multiply in mice. These results thus demonstrate that, for the intracellular pathogen L. monocytogenes, a hypermutator phenotype is more deleterious than profitable to its virulence.