Multicentre evaluation of an automated BACTEC 960 system for susceptibility testing of Mycobacterium tuberculosis.

SETTING: Three mycobacteria reference laboratories in the south-eastern part of Brazil. OBJECTIVE: To evaluate the automated Mycobacteria Growth Indicator Tube (MGIT) for drug susceptibility testing of Mycobacterium tuberculosis. DESIGN: Performance of the automated BACTEC MGIT 960 (M960) system for testing M. tuberculosis susceptibility to streptomycin (SM), isoniazid (INH), rifampicin (RMP) and ethambutol (EMB) was evaluated with 95 clinical isolates and compared to the results of the radiometric BACTEC 460TB (B460) system, the proportion method (PM), and the resistance ratio method (RRM). Judicial susceptibility profiles of 88 isolates were defined based on two or more concordant results among B460, PM and RRM, and used as a reference for comparison with M960 results. RESULTS: Agreement rates between M960 and conventional methods were 95.2% with B460, 96.6% with the PM and 93.4% with the RRM. The lowest agreement rates were obtained for SM with the RRM and for EMB with B460. When comparing M960 with judicial susceptibility profiles, the agreement rate was 97.9%. The agreement rates obtained for INH and RMP were 99.2% and for SM and EMB they were 96.2% and 96.9%, respectively. The mean time to reporting the M960 results was 6.9 days. CONCLUSION: M960 offers great improvements when compared to the proportion and resistance ratio methods and would benefit patient treatment.

Differentiation of Mycobacterium tuberculosis from other mycobacteria with rho-nitrobenzoic acid using MGIT960.

SETTING: Mycobacteria growth in media with the addition of inhibitory substances has been used in species identification. Growth of the Mycobacterium tuberculosis complex (MTC) is inhibited by rho-nitrobenzoic acid (PNB), whereas non-tuberculous mycobacteria (NTM) are resistant. OBJECTIVE: To develop a rapid PNB test using the automated BACTEC MGIT960 system and to evaluate its usefulness in the screening of mycobacterial isolates. DESIGN: PNB tests were performed in 93 MTC strains and 61 NTM strains from the Instituto Adolfo Lutz Culture Collection. PNB was added to Löwenstein-Jensen (LJ) medium and to BACTEC MGIT960 medium. RESULTS: The MTC strains were all PNB-susceptible, confirming the original identification. Among 10 NTM species, all were found to be resistant to PNB, except for one strain of M. kansasii and another of M. marinum. The median time to obtain presumptive identification of MTC by inhibition test in the BACTEC MGIT960 system was 6.3 days and for NTM it was 2.5 days. The presumptive identification of MTC in LJ was mostly obtained after day 20. CONCLUSION: The key finding of this analysis was the possibility of combining the traditionally accepted method proposed by Tsukamura and Tsukamura in 1964 with the modern, safe and rapid BACTEC MGIT960 methodology.

Decrescimo da populacao bacteriana eliminada por pacientes com tuberculose pulmonar tratados com esquema de curta duracao. / Decrease of bacterial population in patients with pulmonary tuberculosis treated with short-term chemotherapy

Foram estudados 10 pacientes tuberculosos, com baciloscopia e cultura positivas, tratados com esquema de curta duracao constituido de rifampicina, hidrazida e etambutol ou pirazinamida. A avaliacao da populacao bacteriana, antes e depois da quimioterapia foi feita por dois metodos quantitativos: baciloscopia direta do escarro, apos coloracao pelo descontaminacao pelo metodo de Petroff. A populacao bacteriana inicial variou entre 600.000 e 51.200.000 bacilos por ml e 45.450 e 1.511.250 colonias por ml de escarro. O decrescimo desta populacao nos dois subsequentes ao inicio do tratamento nao esta relacionada com a populacao inicial, seja ela alta ou baixa. Entretanto, pela baciloscopia, observa-se que o primeiro exame negativo e o ultimo positivo ocorreram mais precocemente no grupo de populacao baixa do que na alta. Nos primeiros 10 dias de tratamento verificou-se, em media, uma reducao na populacao bacteriana eliminada igual a 33% da inicial, atingindo 2,2% nos primeiros 30 dias a contagem de colonias, nos mesmos periodos, reduziu-se a 31,4% e 1% respectivamente. O percentual de colonicas sobre o numero total de bacilos, expressao da viabilidade bacilar, era de 3,6% antes da medicacao, caindo para 0,3% apos 30 dias de tratamento

Acao da pirazinamida e do etambutol sobre a populacao bacteriana eliminada por pacientes com tuberculose pulmonar tratada com esquema de curta duracao. / Action of the pyrazinamide and ethambutol on the bacterial population from patients with pulmonary tuberculosis treated with short-course chemotherapy

Dez pacientes tuberculosos com baciloscopia e cultura positivas foram divididos em dois grupos quanto ao esquema terapeutico: 1) rifampicina, hidrazida e etambutol; 2) rifampicina, hidrazida e pirazinamida. A avaliacao da populacao bacteriana, antes e depois da quimioterapia, foi feita por dois metodos quantitativos: baciloscopia direta para a determinacao do numero total de bacilos e a cultura para determinacao do numero de unidades viaveis, em dias alternados, ate a negativacao. Confrontando estes dois esquemas verificou-se que eles repercutem de maneira diversa sobre a populacao bacteriana, observada em periodos de dez dias. O esquema com etambutol provoca menor queda no numero total de bacilos nos dez primeiros dias de tratamento do que o da pirazinamida, baixando de 100% para 53,6% e 24,4%, respectivamente. Quanto ao numero de unidades viaveis a situacao e inversa, com 28,3% e 34,6% respectivamente. Nos demais periodos, a pirazinamida provocou menor queda no numero de unidades viaveis do que o etambutol. A negativacao do escarro foi mais precoce com o etambutol do que com a pirazinamida conforme e demonstrado pela analise estatistica. A ultima cultura positiva no grupo do etambutol ocorreu apos 24,8 dias, e com a pirazinamida apos 57,6 dias, em media. O reduzido numero de bacilos viaveis eliminado pelos pacientes submetidos a esses esquemas de tratamento permite inferir que a reintegracao social dos mesmos pode ser precoce, por nao oferecerem risco maior para os comunicantes