In vitro fitness of multidrug-resistant Mycobacterium tuberculosis strains prevailing in Argentina

LÓPEZ B; VON GROLL A; MARTIN A; BARRERA L; PALOMINO JC; RITACCO V

Bled

Congreso; 31st Annual Congress, European Society of Mycobacteriology; 2010

European Society for Micobacteriology

The burden of multidrug resistant (MDR) tuberculosis (TB) in Argentina is largely associated with transmission of four outbreak strains that in order of prevalence belong to lineages H2, LAM3, LAM5 and Tuscany. The aim of our study was to investigate whether these successful MDR strains differ in fitness from contemporaneous MDR strains of similar lineages that have been infrequent or disappeared in Argentina. To this end, we conducted in vitro fitness studies on 29 isolates obtained between 1998 and 2007, each from an individual patient. Fifteen isolates had the genotypes of those four outbreak MDR strains; five isolates had highly infrequent MDR variants of the same lineages; as control, we used eight fully susceptible isolates obtained in the study period that had genotypes closely related to those of the outbreak strains. Growth kinetic parameters were assessed in triplicate in MGIT 960™. Statistical analysis was performed using the t-test for independent samples (Welch-test). No significant difference was observed between prosperous and sporadic MDR strains in terms of mean growth rates, measured as doubling times during the exponential growth phase (p: 0.98). As expected, MDR strains had significantly slower growth rates than fully susceptible strains (p: 0.05). Compared with H2, LAM3 and LAM5 strains, the strains of the Tuscany lineage had a significantly slower growth rate, irrespective of drug resistance profile (30.4 hours vs 18.0, 20.1, and 21.0, respectively) and also reached significantly lower growth units in the stationary phase (16534 vs 25490, 23847 and 23517, respectively).Our data revealed certain differences in growth between lineages but failed to provide evidence of a relationship between in-vitro fitness of MDR strains and ability to disseminate in the community.