False-positive results for Mycobacterium celatum with the AccuProbe Mycobacterium tuberculosis complex assay

Abstract

Mycobacterium celatum type 1 was found to cross-react in the AccuProbe Mycobacterium tuberculosis complex assay. Subsequently, we found a statistically significant increase in the relative light units with lower temperatures, suggesting that it is necessary to perform this AccuProbe assay at between 60 and 61 degrees C. We also recommend the inclusion of M. celatum type 1 as a negative control.

FIG. 1

(A) Effect of selection time on RLU value in the AccuProbe M. tuberculosis complex assay with M. celatum. There were no statistically significant differences between the mean RLU values with solid or liquid medium for the different selection times. The RLU values from the solid medium suspension were significantly higher than those from the broth-grown suspension at all selection times (P < 0.05). Data are expressed as means plus SEM. The RLU cutoff is 30,000. (B) Effect of temperature on RLU value in the AccuProbe M. tuberculosis complex assay with M. celatum. The Mann-Whitney U test revealed significant differences between the mean RLU values with solid medium for 58°C versus 60 and 61°C, between 59°C versus 60 and 61°C, and 60°C versus 61°C (P < 0.05). The RLU values from the solid medium suspension were significantly higher than those from the broth-grown suspension at all selection temperatures (P < 0.05). Data are expressed as means plus SEM. The RLU cutoff is indicated by a horizontal line.