European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-36
FITNESS COST OF Mycobacterium tuberculosis CLINICAL
ISOLATES RESISTANT TO FLUOROQUINOLONES
VON GROLL, Andrea 1 ; MARTIN, Anandi 1 ; JUREEN, Pontus 2 ; HOFFNER, Sven 2 ; PORTAELS, Françoise 1 ; PALOMINO,
Juan Carlos 1 ; ALMEIDA DA SILVA, Pedro 3
1 - Institute of Tropical Medicine, Antwerp, Belgium
2 - Swedish Institute for Infectious Disease Control, Solna, Sweden
3 - Universidade Federal do Rio Grande, Rio Grande, Brazil
Fluoroquinolones (FQs) have been used as effective second-line drugs in the treatment of the tuberculosis. However, the
emergence of M. tuberculosis resistant to FQs has contributed for the occurrence of XDR-TB. This study investigated the
fitness cost related to the mechanism of resistance to FQs in M. tuberculosis clinical isolates. A total of 37 isolates had
the ofloxacin, moxifloxacin and gatifloxacin susceptibility determined by the proportion method and were sequenced
to look for mutations in gyrA and gyrB. The role of efflux pumps was evaluated by determining the minimal inhibitory
concentration of the FQs in the presence and absence of verapamil by resazurin microtiter assay. Growth curves of the
isolates were obtained using the MGIT960 automated system and the lag phase time and rate of growth were established
to compare the fitness. On the 25 FQ resistant isolates (FQ R ), the most frequent mutation was at Ala-90→Val, followed
by mutations at Asp-94 to Gly, Tyr, Ala and Asn. Some unusual mutations were identified at Asp-89→Asn, Asn-533→Thr
(gyrB) and deletion of the codon 678 and 679 in gyrB. The isolate with mutation at Asn-533→Thr was the only case of
no whole cross resistance among the three FQs tested. One FQ R isolate was wild type for the region investigated. The
efflux mechanism was indentified in 36% of the FQ R isolates, being more frequently found in moxifloxacin and gatifloxacin.
In regard to the fitness parameters, the mutation at Asp-94 showed a longer lag phase while the mutation at Asn-90 had
not any significant difference related to the wild type FQ S . The establishment of FQ R isolates without fitness cost warns
for the possibility of a continue emergence of XDR-TB and highlights for a more rational use of FQs, not only for the
treatment of TB, but also, for other bacteria.
108 ESM 2009