The Absence of Osmoregulated Periplasmic Glucan Confers Antimicrobial Resistance and Increases Virulence in Escherichia coli.

Clarifying the molecular mechanisms by which bacteria acquire virulence traits is important for understanding the bacterial virulence system. In the present study, we utilized a bacterial evolution method in a silkworm infection model and revealed that deletion of the operon, encoding synthases for osmoregulated periplasmic glucan (OPG), increased the virulence of a nonpathogenic laboratory strain of Escherichia coli against silkworms. The knockout mutant exhibited resistance to host antimicrobial peptides and antibiotics. Compared with the parent strain, the knockout mutant produced greater amounts of colanic acid, which is involved in E. coli resistance to antibiotics. RNA sequence analysis revealed that the knockout altered the expression of various genes, including the two-component system that functions in antibiotic resistance. In both a colanic acid-negative background and an null background, the knockout increased E. coli resistance to antibiotics and increased the silkworm-killing activity of E. coli. In the null background of the two-component system, which genetically interacts with , the knockout increased antibiotic resistance and virulence in silkworms. These findings suggest that the absence of OPG confers antimicrobial resistance and virulence in E. coli in a colanic acid-, -, and independent manner. The gene mutation types that increase the bacterial virulence of Escherichia coli remain unclear, in part due to the limited number of methods available for isolating bacterial mutants with increased virulence. We utilized a bacterial evolution method in the silkworm infection model, in which silkworms were infected with mutagenized bacteria and highly virulent bacterial mutants were isolated from dead silkworms. We revealed that knockout of OPG synthases increased E. coli virulence against silkworms. The OPG knockout mutants were resistant to host antimicrobial peptides as well as antibiotics. Our findings not only suggest a novel mechanism for virulence acquisition in E. coli but also support the usefulness of the bacterial experimental evolution method in the silkworm infection model.