Background Mycobacterial isolation from cutaneous tuberculosis on Löwenstein–Jensen (L–J) medium has been reported to be low. The radiometric BACTEC 460 TB culture system (BACTEC system) has shown better isolation rates in pulmonary tuberculosis. There has been a progressive increase in the prevalence of multidrug resistance in pulmonary tuberculosis, but similar studies are lacking for cutaneous tuberculosis. Therefore, this study was undertaken to compare mycobacterial isolation on conventional L–J medium vs. the BACTEC system, and to determine the prevalence of multidrug resistance in cutaneous tuberculosis.
Methods Thirty-five untreated, clinically diagnosed, and histopathologically documented patients with cutaneous tuberculosis constituted the study material. Lesional skin biopsy specimens were cultured on both L–J medium and the BACTEC system. The isolates obtained were identified and subjected to sensitivity to rifampicin, isoniazid, ethambutol, and streptomycin using the BACTEC system.
Results Twenty-six mycobacterial isolates were recovered from 35 patients. Nine isolates (25.7%) grew on L–J medium after a mean period of 31.5 days, and 22 (62.8%) on the BACTEC system in 17.3 days. All of the isolates were identified as Mycobacterium tuberculosis. Drug susceptibility testing demonstrated 12 isolates to be resistant, seven multidrug resistant.
Discussion The BACTEC system demonstrated an improved mycobacterial isolation rate and substantially reduced detection time when compared with L–J medium. The combined isolation rate on both media was 74.3% (26/35), greater than that of either used separately. Drug resistance was observed in 46.2% of isolates.
Conclusion Radiometric liquid culture medium together with conventional L–J medium may be recommended in practice to enable the institution of appropriate antituberculous therapy modifications in drug-resistant cases of cutaneous tuberculosis.