Identification of mycobacterium species in contaminated cultures by polymerase chain reaction.
OBJECTIVE
The detection of Mycobacterium sp on a culture remains the "gold standard" technique for the diagnosis of mycobacterial infections. A small percentage of these cultures, however, may be contaminated by other nonfastidious microorganisms, making accurate diagnosis difficult. We evaluated the use of a polymerase chain reaction (PCR) protocol that was specific for the genus Mycobacterium, and specifically for Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium intracellulare, for the identification of Mycobacterium sp growing on contaminated cultures.


METHODS
This prospective study was designed to identify Mycobacterium sp growing on mycobacterial cultures contaminated with other microorganisms. Samples and patients: Twenty-six samples, taken from 23 patients with probable mycobacterial disease, that resulted in Mycobacterium growth but were contaminated during their processing were evaluated in this study. Clinical data and the clinical status of each patient were used to ascertain the final diagnosis.


RESULTS
All samples studied here exhibited Mycobacterium growth on solid media but were contaminated by nonfastidious bacteria, compromising the biochemical identification of the Mycobacterium sp. PCR correctly identified the genus Mycobacterium in all samples. M tuberculosis was identified in 14 samples, and M avium in 10 samples. No amplification of M intracellulare was obtained, and in two samples there was amplification only for the genus Mycobacterium. In the cultures of those patients in whom a mycobacterial infection was evident, PCR identified M avium and M tuberculosis in samples from 6 and 12 patients, respectively. However, PCR identified M avium (two patients) and M tuberculosis (two patients) in the cultures of four patients for whom a mycobacterial disease could not be confirmed by our case definition. Finally, in two samples from one patient only the genus Mycobacterium was amplified by PCR.


CONCLUSIONS
PCR, with its advantages of greater speed and effectiveness than conventional detection methods, was successfully used to identify the Mycobacterium sp growing on contaminated cultures.
Lima
Danielle Malta
DM
Departamento de Clínica Médica, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Avenida dos Bandeirantes, 3900, Ribeirão Preto, São Paulo, CEP 14049-900, Brazil.
Bollela
Valdes Roberto
VR
Jácomo
Beatriz Junqueira Tavares
BJ
Martinez
Roberto
R
Lopes da Fonseca
Benedito Antônio
BA
D000328:Adult; D000368:Aged; D001431:Bacteriological Techniques; D002675:Child, Preschool; D003470:Culture Media; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009161:Mycobacterium / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction
D003470:Culture Media