Persistent infection by a Mycobacterium tuberculosis advantageous strain responsible for a massive outbreak. Beijing Gran Canaria M. tuberculosis strain

The strains involved in tuberculosis outbreaks are considered to be highly virulent and transmissible. We analyzed the case of a patient in Madrid, Spain, who was persistently infected over an 8-year period by the same Beijing Mycobacterium tuberculosis (MTB) strain which was responsible for a severe outbreak on Gran Canaria Island. The case provides us with a unique opportunity to challenge our assumptions about MTB Beijing strains. No clinical/radiological findings consistent with a virulent strain were documented, and the in vitro growth rate of the strain in macrophages was only moderate. No secondary cases stemming from this prolonged active case were detected in the host population. The strain did not acquire resistance mutations, despite constant treatment interruptions, and remained extremely stable, as demonstrated by the lack of SNP-based differences between the sequential isolates. Our data suggest that the general assumptions about MTB Beijing strains considered to be advantageous, regarding virulence, transmissibility and tendency to acquire mutations and even resistance, are not always fulfilled.