RESUMO
Low-colony-number counts on solid media are considered characteristic of cross-contamination, although they are normally observed in true-positive cultures from some groups of patients. The aim of this study was to evaluate low-yield growth cultures as a microbiological marker for cross-contamination. We evaluated 106 cultures with <15 colonies from 94 patients, and the proportions of false-positive cultures were 0.9% per sample and 1.1% per patient, which indicates that low-yield growth is not a reliable marker of cross-contamination.
Assuntos
Mycobacterium tuberculosis/isolamento & purificação , Tuberculose/diagnóstico , Adulto , Idoso , Técnicas de Tipagem Bacteriana , Análise por Conglomerados , Contagem de Colônia Microbiana , Impressões Digitais de DNA , DNA Bacteriano/genética , Reações Falso-Positivas , Feminino , Genótipo , Humanos , Masculino , Polimorfismo de Fragmento de Restrição , Sensibilidade e EspecificidadeRESUMO
SETTING: A tuberculosis clinic associated with a university hospital in Monterrey, Mexico, an urban community with high tuberculosis incidence. OBJECTIVE: To determine the diversity of DNA fingerprint patterns and the extent of drug resistance of Mycobacterium tuberculosis isolates from patients who attended the clinic. DESIGN: Isolates of M. tuberculosis obtained from 186 patients during the period from 31 January 1996 to 31 March 1998 were tested for susceptibility to isoniazid, rifampicin, ethambutol and streptomycin. Demographic data and the social history of each patient were obtained prospectively by interview. The IS6110 DNA fingerprints were obtained for 166 of the 186 isolates. Secondary typing was carried out on isolates with fewer than six copies of IS6110. RESULTS: Thirty-two per cent of the tested isolates (60/ 186) were drug-resistant, and 18% (33/186) were multidrug-resistant. Approximately 55% of the resistant isolates (33/60) were attributed to acquired resistance. A total of 106 different IS6110 fingerprint patterns were observed among the 166 fingerprinted isolates. Based on both IS6110 and pTBN12 fingerprinting, 65 (39%) of the 166 isolates were part of 22 DNA fingerprint clusters. Various drug susceptibility patterns were seen in most clusters. CONCLUSION: Fingerprint clustering indicates extensive recent transmission of tuberculosis in patients attending the clinic. The prevalence of drug-resistant tuberculosis is high.