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 toward 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 non-pathogenic laboratory strain of against silkworms. The knockout mutant exhibited resistance to the host antimicrobial peptides and antibiotics. Compared with the parent strain, the knockout mutant produced greater amounts of colanic acid, which is involved in 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 null background, the knockout increased resistance to antibiotics and increased the silkworm killing activity of In the null background of the two-component system, which genetically interacts with , the knockout increased the antibiotic resistance and the virulence in silkworms. These findings suggest that the absence of OPG confers antimicrobial resistance and virulence of in a colanic acid-, -, and independent manner. The gene mutation types that increase bacterial virulence of 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 increases 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 , but also support the usefulness of utilizing the bacterial experimental evolution method in the silkworm infection model.