Molecular Characterization of Diphtheria Toxin Repressor (dtxR) Genes Present in Nontoxigenic Corynebacterium diphtheriae Strains Isolated in the United Kingdom

• Published in: Journal of Clinical Microbiology 2005, Vol.43 (1), p.223-228
• Main Authors: De Zoysa, Aruni, Efstratiou, Androulla, Hawkey, Peter M
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacterial diseases; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Corynebacterium diphtheriae; Corynebacterium diphtheriae - genetics; Corynebacterium diphtheriae - growth & development; Corynebacterium diphtheriae - isolation & purification; Corynebacterium diphtheriae - metabolism; Culture Media; Diphtheria - microbiology; Diphtheria Toxin - antagonists & inhibitors; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Ent and stomatologic bacterial diseases; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Human bacterial diseases; Humans; Infectious diseases; Iron - metabolism; Medical sciences; Microbiology; Molecular Sequence Data; Pharynx - microbiology; Sequence Analysis, DNA; Siderophores - biosynthesis; United Kingdom
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.43.1.223-228.2005

Nontoxigenic strains of Corynebacterium diphtheriae represent a potential reservoir for the emergence of toxigenic C. diphtheriae strains if they possessed functional diphtheria toxin repressor (dtxR) genes. We studied the predominant strain of nontoxigenic C. diphtheriae circulating in the United Kingdom to see if they possessed dtxR genes and ascertain whether they were functional. A total of 26 nontoxigenic C. diphtheriae strains isolated in the United Kingdom during 1995 and 4 nontoxigenic strains isolated in other countries were analyzed by PCR and direct sequencing to determine the presence and intactness of the dtxR genes. The functionality of the DtxR proteins was assayed by testing for the production of siderophore in medium containing high and low concentrations of iron. PCR amplification and sequence analysis of the dtxR genes revealed four variants of the predicted DtxR protein among the nontoxigenic strains isolated in the United Kingdom. Production of siderophore in medium containing a low concentration of iron and repression of siderophore production in medium containing a high concentration of iron demonstrated that in all the strains the dtxR genes were functional. These findings demonstrate that, if lysogenised by a bacteriophage, nontoxigenic strains circulating in the United Kingdom could produce toxin and therefore represent a potential reservoir for toxigenic C. diphtheriae.