Retrospective Diagnosis of Diphtheria by Detection of the Corynebacterium diphtheriae tox Gene in a Formaldehyde-Fixed Throat Swab Using PCR and Sequencing Analysis

The tox gene of Corynebacterium diphtheriae was detected in a formaldehyde-fixed throat swab taken from a 68-year-old man who was reported to have died of suffocation due to a pharyngeal tumor. DNA templates prepared from bacterial cells fixed with 10% formaldehyde were subjected to a PCR analysis with tox gene-specific PCR primers. The resultant 112-nucleotide-long PCR product was sequenced using a dye terminator method, and an expected 57-nucleotide-long internal sequence of the tox gene was detected. This method is applicable for retrospective diagnosis in diphtheria cases in which only a formaldehyde-fixed clinical sample is available.