Viruses that turn bacteria pathogenic

Abstract

Bacteriophages (bacterial viruses) encode many important bacterial toxins, including diphtheria toxin in Corynebacterium diphtheriae, enterotoxin A and Panton-Valentine leukocidin in Staphylococcus aureus, and cholera toxin in Vibrio cholerae. Only the bacterial strains that have the bacteriophage genome stably inserted into their genome (lysogenic bacteria) encode the toxin genes. A second cluster of genes essential for V. cholerae virulence is now reported to be encoded on a bacteriophage genome 1 Karaolis D.K.R. et al. A bacteriophage encoding a pathogenicity island, a type-IV pilus and a phage receptor in cholera bacteria. Nature. 1999; 399: 375-379 Crossref PubMed Scopus (306) Google Scholar . These genes include the type IV pilus, which is necessary for disease and intestinal colonization. Intriguingly, type IV pilus is also the receptor for the bacteriophage, CTXφ, which carries the cholera toxin gene. Infection of V. cholerae with the CTXφ bacteriophage cannot occur unless the strain is already lysogenic for the pilus-carrying phage, VPIφ . Many bacteria are multiply lysogenic, and these viral genomes probably account for a significant amount of bacterial strain-to-strain variation. Lysogenic bacteria are a source of potential new bacteriophage viruses in the environment, and in the laboratory VPIφ could infect V. cholerae serotypes not normally associated with pathogenicity 1 Karaolis D.K.R. et al. A bacteriophage encoding a pathogenicity island, a type-IV pilus and a phage receptor in cholera bacteria. Nature. 1999; 399: 375-379 Crossref PubMed Scopus (306) Google Scholar . As these pathophages can turn non-pathogenic strains of bacteria into pathogens, we need to be aware of their host ranges, their ability to spread to other strains, and the risks associated with the use of live attenuated bacterial vaccine strains that are susceptible to toxin-carrying bacteri phages.