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Open Access Research article

Characterization of Mycobacterium tuberculosis Beijing isolates from the Mediterranean area

M Alonso123, N Alonso Rodriguez1, C Garzelli4, M Martínez Lirola5, M Herranz13, S Samper36, MJ Ruiz Serrano13, E Bouza13 and D García de Viedma123*

Author Affiliations

1 Servicio de Microbiología Clínica y Enfermedades Infecciosas, Hospital Gregorio Marañón, Madrid, Spain

2 Unidad Central de Análisis Molecular (UCAM), Hospital Gregorio Marañón, Madrid, Spain

3 CIBER Enfermedades Respiratorias (CIBERES), Spain

4 Dipartimento de Patologia Sperimentale, Biotecnologie Mediche, Infettivologia ed Epidemiologia, Università de Pisa, Pisa, Italy

5 Complejo Hospitalario Torrecárdenas, Almería, Spain

6 Instituto Aragonés de Ciencias de la Salud, Zaragoza

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BMC Microbiology 2010, 10:151  doi:10.1186/1471-2180-10-151

Published: 25 May 2010

Abstract

Background

The Beijing lineage of Mycobacterium tuberculosis is causing concern due to its global distribution and its involvement in severe outbreaks. Studies focused on this lineage are mainly restricted to geographical settings where its prevalence is high, whereas those in other areas are scarce. In this study, we analyze Beijing isolates in the Mediterranean area, where this lineage is not prevalent and is mainly associated with immigrant cases.

Results

Only 1% (N = 26) of the isolates from two population-based studies in Spain corresponded to Beijing strains, most of which were pan-susceptible and from Peruvian and Ecuadorian patients. Restriction fragment length polymorphism typing with the insertion sequence IS6110 identified three small clusters (2-3 cases). Mycobacterial interspersed repetitive unit-variable number tandem repeat typing (MIRU-15) offered low discriminatory power, requiring the introduction of five additional loci. A selection of the Beijing isolates identified in the Spanish sample, together with a sample of Beijing strains from Italy, to broaden the analysis context in the Mediterranean area, were assayed in an infection model with THP-1 cells. A wide range of intracellular growth rates was observed with only two isolates showing an increased intracellular replication, in both cases associated with contained production of TNF-α. No correlation was observed between virulence and the Beijing phylogenetic group, clustered/orphan status, or resistance. The Beijing strain responsible for extensive spread on Gran Canaria Island was also identified in Madrid, but did not lead to secondary cases and did not show high infectivity in the infection model.

Conclusions

The Beijing lineage in our area is a non-homogeneous family, with only certain highly virulent representatives. The specific characterization of Beijing isolates in different settings could help us to accurately identify the virulent representatives before making general assumptions about this lineage.