The manual MGIT system for the detection of M tuberculosis in respiratory specimens: an experience in the University Malaya Medical Centre
- Author:
Fadzilah Mohd Nor
;
Kee Peng Ng
;
Yun Fong Ngeow
- Publication Type:Journal Article
- Keywords:
Mycobacterium tuberculosis diagnosis, manual MGIT system
- From:The Malaysian Journal of Pathology
2009;31(2):93-97
- CountryMalaysia
- Language:English
-
Abstract:
A prospective study was conducted on 510 respiratory specimens for the presence of M. tuberculosis
detected by direct acid-fast bacilli (AFB) smear examination, culture in the Manual Mycobacteria
Growth Indicator Tube (BBL MGIT, Becton-Dickinson) and culture on Lowenstein-Jensen (LJ)
medium. From positive BBL MGIT tubes, Ziehl-Neelsen and Gram stains were performed and
subcultures were put up on LJ medium. A total of 101 (19.8%) specimens were positive by the BBL
MGIT, 60 (11.8%) by primary LJ medium culture, 31 (6.1%) by direct smear examination and 29
(5.7%) by all three methods. Using primary LJ culture as the gold standard, the sensitivity and
specifi city of the BBL MGIT were 90% and 89.6% respectively but the sensitivity of AFB smear
microscopy was only 48.3%. About half (51.1%) of the BBL MGIT false positives were due to
contamination by non-AFB bacteria. The remaining false positives comprised specimens that were
AFB microscopy positive but LJ culture negative. Of the AFB isolates obtained on LJ primary
and sub-cultures, almost all (93.3%) were identifi ed as Mycobacterium tuberculosis complex. The
mean time-to-detection was signifi cantly shorter (p<0.0001) for the BBL MGIT than for LJ culture.
For the former, positive results were available within 14 days for both AFB smear-positive and
AFB smear-negative specimens. On the average, positive results were obtained 1.8 days earlier
for direct AFB smear-positive samples than for AFB smear-negative samples. On the other hand,
positive growth on LJ medium appeared after at least 33 days of incubation. These fi ndings suggest
that the BBL MGIT system will be a suitable alternative to LJ culture for the routine diagnosis
of pulmonary tuberculosis, but a combination of liquid and solid cultures is still required for the
highest diagnostic accuracy.
- Full text:W020151203568154695083.pdf
