Open Access Research article

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

Ana Martín1, Marta Herranz1, Miguel Martínez Lirola2, Rosa Fernández Fernández3, INDAL-TB group, Emilio Bouza1 and Darío García de Viedma1*

Author Affiliations

1 Servicio de Microbiología Clínica y Enfermedades Infecciosas. Hospital Gregorio Marañón, Universidad Complutense, Madrid, CIBER-Enfermedades Respiratorias CIBERES, Spain

2 Servicio de Microbiología, Complejo Hospitalario Torrecárdenas, Almería, Spain

3 Unidad de Tuberculosis del Distrito Poniente, Almería, Spain

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BMC Microbiology 2008, 8:30  doi:10.1186/1471-2180-8-30

Published: 14 February 2008



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.


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.


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.