Rapid Differentiation of Mycobacterium tuberculosis and Mycobacterium bovis Using Glycerol Susceptibility and Quantitative Polymerase Chain Reaction

Abstract

Background

The differentiation between Mycobacterium tuberculosis (MTB) and Mycobacterium bovis has significant epidemiological and therapeutic implications, such as their susceptibility to different drugs and the need for different approaches to patient isolation. However, currently this differentiation is based on laboratory methods that take 8 to 16 weeks. Simple qualitative polymerase chain reaction (PCR) can not differentiate between MTB and M bovis because of their genetic similarities.

Methods

We evaluated the use of quantitative PCR (QPCR) and glycerol susceptibility to differentiate MTB from M bovis. Three patient isolates of M bovis and 5 patient isolates of MTB were suspended in 7H9 broth containing 0.0%, 0.2%, or 0.6% glycerol. These suspensions were inoculated on 7H11 plates and incubated at 37°C and 5% CO₂. QPCR was performed after 0, 3, and 6 days of incubation.

Results

After 6 days of incubation for M bovis isolates, the mean DNA concentration decreased by one log in the presence of 0.6% glycerol while for MTB isolates, the mean DNA concentration increased by one log regardless of the glycerol concentration.

Conclusion

These data suggest that QPCR and glycerol susceptibility may be used to differentiate between MTB and M bovis within 1 week.