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

PP-27
Mutational analysis of genes associated with
resistance to injectable second-line drugs in Mycobacterium
tuberculosis clinical isolates from Lisbon, Portugal
João Perdigão 1 , Ana Ferreira 1 , Ana Malaquias 1 , Rita Macedo 2 , Laura Brum 2 and Isabel Portugal. 1,2
1 - Centro de Patogénese Molecular, URIA, Faculdade de Farmácia da Universidade de Lisboa
2 - Laboratório de Micobactérias, Centro de Bacteriologia, Instituto Nacional de Saúde Dr. Ricardo Jorge
Objectives
Multidrug resistance (MDR) constitutes a serious problem to tuberculosis (TB) control program in Portugal. An even
more serious threat is the one posed by the high rate of extensive drug-resistant TB (XDR-TB). Our laboratory has
already shown that high rates of this form of TB exist in Lisbon. Given the fact that MDR-TB and XDR-TB are currently
associated with a limited number of genetic clusters, mainly Lisboa family clusters, the diversity of genetic polymorphisms
conferring resistance to second-line drugs is also probably limited. In this study we intended to characterize the genetic
polymorphisms associated with resistanace to second-line injectable drugs and to assess the clinical isolates clonality.
Methods
We have analyzed 19 MDR-TB strains resistant to one or more second-line injectable drugs, collected from several hospital
units across Lisbon Health Region during the year of 2005. All isolates were typed by Mycobacterial Interspersed
Repetitive Units (MIRU-VNTR) and, screened for mutations in tlyA and rrs genes.
Results
Three different mutations were identified on tlyA gene and another three at rrs gene. Overall, 9 isolates had mutations in
tlyA gene and 8 isolates had mutations in rrs gene; two isolates didn’t have any mutation in either gene. The most frequent
mutations found were A1401G in rrs gene (6/19) and 755InsGT in tlyA gene (6/19). We also verified that there was no
overlapping of mutations from different genes. The genotyping analysis revealed that the isolates could be distributed
through two different MIRU-VNTR genetic clusters: Lisboa3 and Q1. Cluster Q1 contained all clinical isolates bearing the
A1401G mutation in rrs gene, while Lisboa 3 cluster contained all isolates that had the 755InsGT mutation in tlyA gene.
Conclusion
We have identified several mutations that might be associated with resistance to different but related second-line drugs:
kanamycin, amikacin and capreomycin. The two most prevalent mutations were associated with different genetic clusters,
which suggests recent transmission and, ultimately, that XDR-TB transmission is taking place. The most prevalent
mutations associated with injectable second-line drugs have therefore been defined, which opens the way for molecular
detection of resistance to second-line drugs in the region.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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