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

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MOLECULAR STUDY OF RECURRENT TUBERCULOSIS CASES
Alves, Adriana; Miranda, Anabela; Tuberculosis Reference Laboratory Group
Tuberculosis Reference Laboratory, Department of Infectious Diseases, National Institute of Health, Porto, Portugal
Tuberculosis recurrence is frequently attributed to reactivation of the isolate responsible for the first episode of the
disease. Nevertheless, this can also be due to an infection with another isolate, or to mixed infections. Clarification of
the cause of recurrence is very important and can be achieved by molecular typing of serial isolates of M. tuberculosis. The
most appropriate methods to do so are IS6110 RFLP and MIRU-VNTR.
In this work, 39 clinical isolates of M. tuberculosis belonging to nine individuals with recurrent disease were studied
throughout time. Seven of these patients were resistant to isoniazid and rifampicin as well as to most other 1 st and 2 nd
line drugs. Another patient was resistant to isoniazid and streptomycin, and the last one was resistant to rifampicin only.
For some of these individuals, resistance to drugs worsened during the cause of the disease, which in some cases has
lasted for more than a decade. All 39 strains were analyzed by IS6110 RFLP. MIRU-VNTR was used to type: (i) the first
strain of each patient when serial isolates showed no change in the IS6110 RFLP profile; or (ii) each strain with a pattern
change in relation to the previous one.
RFLP results showed that only one out of nine patients displayed a change in the pattern of serial isolates with gain of
one IS6110 element. Analysis of the results using Bionumerics grouped these patients in nine clusters, being that: (i) strains
from two patients belong to the same cluster; and (ii) strains of one patient are divided in two clusters. Results of 15
MIRU-VNTR loci typing corroborate the IS6110 RFLP findings. In other words, the serial isolate that gained one IS6110
element also shows a change in MIRU-VNTR results. In this case, we observed a reduction of one repeat in loci Mtub21
and QUB11b. Finally, 40% of these strains belong to the LAM family, 10% to the Haarlem family, and the remaining 50%
did not find a match in the database.
This work shows that the cause of recurrent tuberculosis of the nine patients included in this study is due to persistence
of initial M. tuberculosis strain or to reactivation when there is more than one episode of disease. Antibiotic resistance is
the most important cause of chronic tuberculosis in these patients, since all analyzed strains are resistant to the majority
of the 1 st and 2 nd line drugs.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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