584. Differentiating Rapid- and Slow-growing Mycobacterium by the Difference in Time to Growth Detection in Liquid Broth Medium
Session: Poster Abstract Session: Mycobacterial Diagnostics
Friday, October 21, 2011
Room: Poster Hall B1
Background:

Non-tuberculous mycobacteria (NTM) are classified into two categories based on the interval to colony formation by subculture on solid medium: slow-growing mycobacteria (SGM) and rapid-growing mycobacteria (RGM). However, little is known about the differences in the time to detection between clinical specimens of RGM and SGM in liquid broth medium. We evaluated the differences in the time to growth detection (TGD) according to species and the results of acid-fast staining in actual clinical situations.

Methods:

Microbiologic data for 1210 NTM that were cultured in BBL mycobacteria growth indicator tubes (MGIT) in a tertiary hospital over a 2-year period were reviewed. The time to growth detection (TGD) was defined as the interval between inoculation and growth detection. The species of NTM were identified using the 16S rRNA polymerase chain reaction and restriction fragment length analysis. The cases were classified into two groups: the acid-fast bacilli (AFB) smear-negative or trace group and the AFB-positive group. The receiver operating characteristic (ROC) curve was used to evaluate the predictive value of the TGD at differentiating RGM from SGM.

Results:

Of the 1210 NTM, 776 NTM isolates were identified to the species level. Of these isolates, 218 (28%) were RGM and 558 (72%) were SGM. In the AFB-negative or trace group, the mean TGD was 133 hours for RGM and 271 hours for SGM (p<0.001). In the AFB-positive group, the mean TGD was 112 hours for RGM and 153 hours for SGM (p=0.043). In the AFB-negative or trace group, a cut-off value of 6 days was the most effective for distinguishing RGM from SGM (sensitivity 82%, specificity 73%). In the AFB-positive group, an appropriate cut-off value could not be decided for the TGD only.

Conclusion:

The TGD in liquid broth medium can be useful for distinguishing RGM from SGM in AFB-negative specimens, although the overlap may be too great to differentiate between RGM and SGM in AFB-positive specimens.


Subject Category: D. Diagnostic microbiology

Chung-Jong Kim, MD1, Jeong-Hwan Hwang, MD2, Pyoeng Gyun Choe, MD3, Kyoung-Ho Song, MD2, Eu Suk Kim, MD, PhD2, Sang-Won Park, MD3, Hong Bin Kim, MD, PhD2, Nam-Joong Kim, MD3, Wan Beom Park, MD, PhD3 and Myoung-don Oh, MD, PhD2, (1)National Evidence-based Healthcare Collaborating Agency, Seoul, South Korea, (2)Department of Internal Medicine, Seoul National University College of Medicine, Seoul, South Korea, (3)Internal Medicine, Seoul National University College of Medicine, Seoul, South Korea

Disclosures:

C. J. Kim, None

J. H. Hwang, None

P. G. Choe, None

K. H. Song, None

E. S. Kim, None

S. W. Park, None

H. B. Kim, None

N. J. Kim, None

W. B. Park, None

M. D. Oh, None

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