Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae.
Non-toxigenic strains of Corynebacterium diphtheriae continue 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 tox mutations within three clone types were examined. tox-containing, beta-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 cis dominant. 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.
Cianciotto
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NP
Department of Microbiology and Immunology, Northwestern University, Chicago, IL 60611, USA.
Groman
N B
NB
D001435:Bacteriophages / Q000235:genetics*; D015139:Blotting, Southern; D003353:Corynebacterium diphtheriae / Q000472:pathogenicity / Q000821:virology*; D004167:Diphtheria Toxin / Q000235:genetics*; D017353:Gene Deletion; D006801:Humans; D009154:Mutation; D015183:Restriction Mapping
D004167:Diphtheria Toxin