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

Microbial Pathogenesis
N P Cianciotto, N B Groman

Abstract

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.

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Citations

Feb 5, 2000·The Journal of Infectious Diseases·R K Holmes
Nov 15, 2000·Emerging Infectious Diseases·M ReacherR C George
Dec 6, 2019·Nature Reviews. Disease Primers·Naresh Chand SharmaThandavarayan Ramamurthy

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