Optimized molecular resolution of cross-contamination alerts in clinical mycobacteriology laboratories

BACKGROUND. The phenomenon of misdiagnosing tuberculosis (TB) by laboratory cross-contamination when culturing Mycobacterium tuberculosis (MTB) has been widely reported and it has an obvious clinical, therapeutic and social impact. The final confirmation of a cross-contamination event requires the molecular identification of the same MTB strain cultured from both the potential source of the contamination and from the false-positive candidate. The molecular tool usually applied in this context is IS6110-RFLP which takes a long time to provide an answer, usually longer than is acceptable for microbiologists and clinicians to make decisions. Our purpose in this study is to evaluate a novel PCR-based method, MIRU-VNTR as an alternative to assure a rapid and optimized analysis of cross-contamination alerts. RESULTS. MIRU-VNTR was prospectively compared with IS6110-RFLP for clarifying 19 alerts of false positivity from other laboratories. MIRU-VNTR highly correlated with IS6110-RFLP, reduced the response time by 27 days and clarified six alerts unresolved by RFLP. Additionally, MIRU-VNTR revealed complex situations such as contamination events involving polyclonal isolates and a false-positive case due to the simultaneous cross-contamination from two independent sources. CONCLUSION. Unlike standard RFLP-based genotyping, MIRU-VNTR i) could help reduce the impact of a false positive diagnosis of TB, ii) increased the number of events that could be solved and iii) revealed the complexity of some cross-contamination events that could not be dissected by IS6110-RFLP.

INDAL-TB group: MI Sánchez, MC Rogado, T Cabezas, W SánchezYebra, J Martínez, MA Lucerna, P Barroso, I Cabeza- Barrera, LF Díez, M Rodríguez, M Escámez, P Marín, A Lazo, J Gamir, J Vázquez, C Gutiérrez, A Reyes and T Peñafiel. Journal Article; Research Support, Non-U.S. Gov't;

This study was partially financed by Fondo de Investigaciones Sanitarias (FIS030654; FIS030986; FIS060882; FIS061467; 06/90490; 06/90357), Junta de Andalucía (0453/06, 151/05) and by the Instituto de Salud Carlos III (CIBER Enfermedades Respiratorias CB06/06/0058). A.M is receptor of a grant from Comunidad de Madrid cofinanced by the European Social Fund (Order no 5297/2006).