Comparison of the radiometric BACTEC 460 TB culture system and Lowenstein-Jensen medium for the isolation of mycobacteria in cutaneous tuberculosis and their drug susceptibility pattern.

摘要

BACKGROUND: Mycobacterial isolation from cutaneous tuberculosis on Lowenstein-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.