European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-104
USE OF NICOTINAMIDE IN COLORIMETRIC METHODS FOR RAPID
DETECTION OF PYRAZINAMIDE RESISTANCE IN
MYCOBACTERIUM TUBERCULOSIS
Montoro, Ernesto 1 , Lemus, Dihadenys 1 , Madruga, Mariela 1 , Mirabal, Niuris 1 , Milián Yoslaine 1 , Yzquierdo, Sergio 1 ,
Echemendía, Miguel 1 , Martín, Anandi 2 , Van der Stuyft, Patrick 2 , Palomino, Juan Carlos 2
1 - Institute of Tropical Medicine Pedro Kourí (IPK), Havana, Cuba
2 - Institute of Tropical Medicine, Antwerp, Belgium
Pyrazinamide (PZA) is one of the most effective anti-tuberculosis drugs. It is also bactericidal to semidormant
Mycobacterium tuberculosis and it reduces the total treatment time. The current susceptibility testing methods for this
drug are difficult due to the poor growth of the bacteria in acid medium which is required for drug activity. One alternative
has been the use of nicotinamide (NIC), an analogue of PZA that can be converted by PZAase into active form in
a physiological pH that does not hinder bacterial growth. Recently, the NIC has been applied successfully in inexpensive
susceptibility testing such as nitrate reductase assay (NRA) for rapid detection of PZA resistance. The purpose of this
study was to develop the NRA and malachite green indicator (MGI), both with NIC, as rapid susceptibility testing to PZA
in M. tuberculosis. The NRA and MGI were carried out on 120 M. tuberculosis strains from the collection at Tuberculosis
National Reference Laboratory. The concentration of NIC applied in both methods was 1 000 µg/mL and all results
were compared with Wayne method which was used as gold standard, employing 100 µg/mL of PZA. The Wayne method
results were obtained in 4-7 days whereas MGI and NRA results required 7-14 days. A total of 17 and 85 strains were
reported as resistant and susceptible respectively by the three methods but MGI had 16 discordant results and NRA only
4 discrepancies. The MGM showed a sensitivity and specificity of 80,95% and 87,88% respectively whereas NRA provided
a sensitivity of 90,48% and specificity of 97,98%. In general, the concordance of MGI and NRA were 86,67% and 96,67%
respectively. The MGI employing NIC showed a low sensitivity to detect resistance to PZA. In contrast, the NRA showed
a high concordance with Wayne method. This assay is rapid, accurate and could be an attractive option for rapid detection
of PZA resistance, especially in limited-resource countries with high levels of resistance.
176 ESM 2009