Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae

• Published in: Microbial pathogenesis 1997-06, Vol.22 (6), p.343-351
• Main Authors: Cianciotto, Nicholas P., Groman, Neal B.
• Format: Article
• Language: English
• Subjects: ADP-ribosylation; bacteriophages; Bacteriophages - genetics; Biological and medical sciences; Blotting, Southern; Corynebacterium diphtheriae; Corynebacterium diphtheriae - pathogenicity; Corynebacterium diphtheriae - virology; diphtheria toxin; Diphtheria Toxin - genetics; Fundamental and applied biological sciences. Psychology; Gene Deletion; Humans; Microbiology; Mutation; non-toxigenic strains; Replicative cycle, interference, host-virus relations, pathogenicity, miscellaneous strains; Restriction Mapping; Virology
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1006/mpat.1996.0120

Non-toxigenic strains of Corynebacterium diphtheriaecontinue to cause disease within immunized populations. A subset of these corynebacteria carry the diphtheria toxin gene but in a cryptic form. To determine whether such strains might contribute to the re-emergence of functional toxin genes, the phages and toxmutations within three clone types were examined. tox-containing, β-related phages were isolated from two of the strain types. The third isolate appeared to harbour a defective prophage. One of the tox − phages encoded truncated, yet enzymatically-active, forms of diphtheria toxin, suggesting that it had sustained a point mutation within the latter half of its toxin gene. In contrast, the other mutant phage did not elicit the production of either a cross-reacting material or an ADP-ribosylating activity. Complementation tests employing a series of double lysogens confirmed that the mutations responsible for the non-toxigenic phenotype of all of the phages were cisdominant. Given these findings, it is reasonable to hypothesize that tox + genes can arise within human populations by either homologous recombination between two distinct tox − phages or spontaneous reversion within a single mutant allele.