Molecular Identification of Corynebacterium minutissimum in Skin Lesions Suspicious for Erythrasma by the PCR method

Erythrasma is a chronic superficial infection of the intertriginous areas. Most laboratories use methylene blue stain and 10% KOH smear to identify Corynebacterium minutissimum (C. minutissimum) by direct observation of filamentous bacilli. Occasionally atypical forms can be seen that create problems in diagnosis. This study aims to use the polymerase chain reaction (PCR) method in order to definitively identify C. minutissimum as an agent of erythrasma. This research was performed during 2013 on 100 skin scrapings suspicious for erythrasmawhich were obtained from various medical mycology laboratories in Tehran. Samples were tested by three methods - direct examination، culture and PCR. DNA was extracted by the modified phenol-chloroform method after which PCR was performed using designed primers. We sequenced some of the PCR products. The sensitivity and specificity of the PCR method was compared to the direct and culture examinations. Of the 100 samples، there were 25 positive samples according to PCR analysis، 13 positive by direct examination and 23 that cultured positive. DNA sequencing results showed the presence of C. minutissimum. The PCR method in comparison with direct examination had a sensitivity of 100% and a specificity of 86. 2%. The study also showed that the PCR method in comparison with culture had a sensitivity of 100% and a specificity of 97. 4%. This study showed that the PCR method in comparison with the direct method and culture had a higher sensitivity in the detection of C. minutissimum. The present PCR method confirmed all typical and some of the atypical forms of C. minutissimum which indicated the importance of this method in the definitive diagnosis of erythrasma.