The lysogenization of the non-O157 Escherichia coli strains by stx-converting bacteriophage phi24B is associated with the O antigen loss and reduced fitness

Abstract

Acquisition of new prophages that are able to increase the bacterial fitness by lysogenic conversion is believed to be important strategy of bacterial adaptation to changing environment. However, in contrast to the factors determining the range of bacteriophage lytic activity, little is known about the factors that define the lysogenization host range. Bacteriophage phi24B is the paradigmal model of stx-converting phages, encoding the toxins of the Shiga-toxigenic E. coli (STEC). This virus has been shown to lysogenize the wide range of E. coli strains that is much broader than the range of the strains supporting its lytic growth. Therefore, phages produced by the STEC population colonizing the small intestine are potentially able to lysogenize symbiotic E. coli in the hindgut, and these secondary lysogens may contribute to the overall patient toxic load and to lead to the emergence of new pathogenic STEC strains. We demonstrate, however, that O antigen effectively limit the lysogenization of the wild E. coli strains by phi24B phage. The lysogens are formed from the spontaneous rough mutants and therefore have increased sensitivity to other bacteriophages and to the bactericidal activity of the serum if compared to their respective parental strains.

RB49-like Bacteriophages Recognize O Antigens as One of the Alternative Primary Receptors

“…The latter function appears to be essential in many phages of the Gram-negative hosts, where O antigen efficiently shields the cells against phages, not possessing O antigen-specific adhesins/depolymerases (reviewed in [ 3 ]). Therefore, the O antigen is one of the major determinants of the actual cell sensitivity to bacteriophages [ 7 , 11 , 12 , 13 ], either making for a protective layer masking the cell surface or serving as a tag marking the susceptible host cell for phage docking.…”