REPRODUCTIVE FITNESS OF DRUG-RESISTANT MYCOBACTERIUM TUBERCULOSIS TRANSMITTED AMONG MEMBERS OF DIFFERENT FAMILIES

MORCILLO N; B IMPERIALE

Bled

Congreso; 31 Congreso Anual de la Sociedad Europea de Micobacteriologia; 2010

ESM

Physiological fitness has been defined as the ability of a microorganism to survive, reproduce and be transmitted. Mutations in M. tuberculosis genome leading to a drug-resistant profile compatible with resistance to isoniazid and rifampicin (MDR) may influence the fitness of mycobacteria and are associated to tuberculosis (TB) treatment failure. In vitro growth can be used as a measure of fitness. Variations in fitness can be also used as indicators to study the transmission capability of MDR-TB among close contacts. The aims of this study were to determine the difference in growth velocity of several clinical isolates transmitted among members of different families; to establish the relationship between mutations related to drug-resistance and genetic patterns with the in vitro fitness of these strains and with elements given by conventional epidemiology. A total of 101 clinical isolates from 68 members of 24 different families were included in the study. TB episodes occurred in a 12 years long period. For these cases, clinical and epidemiological data as well as drug-susceptibility and genetic patterns of the isolates were obtained. MDR was also analyzed by molecular methods. For fitness experiments, previously stored strains were cultured on fresh Middlebrook 7H9 media enriched by OADC (M7H9). A volume of 0.5 ml of a dilution 1:500 from N°1 McFarland suspension, was added to a tube of the BACTEC MGIT 960 system (BD, Argentina), incubated and continuously monitored for increasing of fluorescence. The software Epicenter with modifications was used to detect the changes in fluorescence registered as growth units (GU). The length of lag phase (t0), the exponential growth time, and the relative fitness (RF) compared to H37Rv reference strain were calculated. MDR was found in 27 patients from 15 families; 17 patients generated 32 secondary cases (range 1-4) with identical genetic patterns. Generally, t0 was longer in MDR isolates; RF was decreasing as secondary cases appeared. Mutations in positions 531 and 526 of the rpoB gene were found in 6 and 16 patients, 2 and 8 of the secondary cases generated respectively from the index cases. Drug-resistant strains had diminished RF compared to their ancestors. Mutations in katG 315 leading to isoniazid resistance were not associated to cost-fitness.