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Objective: Our aim was to study the influence of efflux pump systems in the resistance of Mycobacterium tuberculosis to fluoroquinolones and linezolid. Methods: We studied the mutations in gyrA and gyrB genes and the influence of efflux pump systems with 2 inhibitors (reserpine and MC 207.110). Results: The effect of the active efflux system on the decrease in sensitivity to ciprofloxacin, moxifloxacin, levofloxacin, ofloxacin, gatifloxacin and linezolid was studied by investigating the variation in the in vitro activity of these compounds when assayed in association with reserpine and MC 207.110. These inhibitors exhibit activity both in strains that are resistant and in strains that are susceptible to these antibiotics. However, they are seen to be most active in resistant strains, since the minimum inhibitory concentration of the antibiotics studied in these strains was reduced between 2- and 6-fold. Conclusions: Therefore, these mechanisms are involved in the resistance to both compounds. It would be of interest to carry out further studies to determine to what extent these active efflux systems influence resistance to the different groups of drugs used in the treatment of tuberculosis, with a view to the possibility of using the inhibitors of these systems in future therapeutic applications.

When we compare this parameter with the drug levels in serum and tissue, it can be seen that ciprofloxacin is the least useful of the fluoroquinolones studied, whereas moxifloxacin appears to be the most active. Linezolid exhibits excellent activity against this microorganism (MPC(90) 1.2 mg/L and AUC 140.3 mg.h/L) and this makes us consider that its usefulness in the treatment of this pathology should be thoroughly evaluated.