Diagnosis of cutaneous tuberculosis in biopsy specimens by PCR and Southern blotting

Abstract

Aims - To evaluate the use of a gene amplification and hybridisation method for detecting mycobacterial nucleic acid as a possible diagnostic method for cutaneous tuberculosis infection. Methods - Biopsy specimens from 20 patients with various skin conditions of possible tuberculous aetiology were studied. Six patients had ulcerative nodules, seven lupiform lesions, two non-necrotic granulomas, one scrofulous lichen, one impetigo, one erythematosus lesions, one warty lesions, and one suspected tuberculous lipoma. Biopsy specimens were stained using Ziehl-Neelsen stain and cultured in Lowenstein-Jensen medium. DNA was extracted and then amplified by PCR using primers specific for the Mycobacterium tuberculosis complex. Specificity was confirmed by Southern blotting. Results - Of the specimens, 30% were positive for mycobacteria on staining with Ziehl-Neelsen stain, 60% were culture positive and 85% PCR positive. Only 35.2% of specimens were positive with all three techniques. A further 32.5% were both culture and PCR positive. All PCR negative samples were also negative when cultured or stained with Ziehl-Neelsen stain. Of the PCR positive specimens, 29.4% were negative when cultured or stained. Conclusions - PCR, using suitable primers, is an efficient and sensitive method for the diagnosis of cutaneous tuberculosis.