Dados do Trabalho

Título

Rifampicin resistance in Mycobacterium tuberculosis with rpoB gene borderline mutations from patients in Sao Paulo state is still missed by the new proposed critical concentration in MGIT

Introdução

In the state of São Paulo, the frequency of tuberculosis (TB) caused by Mycobacterium tuberculosis strains genotypically resistant to rifampicin (gRIF-R) but phenotypically susceptible to RIF (pRIF-S) by MGIT is high (~ 51%), according to a previous study using 1.0 µg/mL of RIF as the critical concentration (CC). Current data from our laboratory, in which GenoType MTBDRplus 2 assay is performed since 2019, corroborate our previous data in the sense that most of these isolates are mono-RIFR and present the rpoB mutation H445(526)N (70%) followed by L430(511)P (9%), both borderline mutations with minimal association to pRIF-R.

Objetivo (s)

To re-evaluate RIF susceptibility at the current CC of 0.5 µg/mL on MGIT of M. tuberculosis isolates gRIF-R by Xpert version 4 and whose RIF resistance-determining region of rpoB gene has been sequenced by the Sanger method.

Material e Métodos

Eighty-five isolates with the following rpoB mutations H445(526)N (n=61); L430(511)P (n=8); D435(516)Y (n=4); P439(520)L (n=3); H445(526)C and L452(533)P (n=2); T427(508)G, L430(511)R, D435(516)F, H445(526)L, and L452(533)Q (n=1) were examined for susceptibility to 0.25 and 0.5 ug/mL of RIF. The tests were performed in BACTEC MGIT 960 using the TB eXiST software because it allows the test not to be over when the RIF-free control tube (GC) becomes positive. If growth was observed first in the presence of RIF, the strain was considered RIF-R, but if it occurred first in GC, the strain was considered RIF-S. The period of time between the positivity in GC and RIF test was calculated.

Resultados e Conclusão

None of the isolates was pRIF-R at 0.5 µg/mL. Growth in 0.5 µg/mL of RIF during the first week after GC became positive was observed only for isolates with mutations highly associated with RIF-R [D435(516)F, H445(526)C, H445(526L], suggesting that MGIT failure was probably due to heteroresistance. Strains with these three mutations were also the only ones RIF-R at 0.25 µg/mL. Strains from patients in São Paulo, 88% of which present borderline mutations, remained RIF-S at the current RIF CC on MGIT. Since most of them are mono-RIF-R, clinical studies are needed to confirm whether MDR-TB treatment, as recommended by the WHO, is the most appropriate in these cases. This study suggests that increasing the MGIT incubation period may help to elucidate RIF heteroresistance.


Note: Escherichia coli numbering of rpoB gene is in parenthesis right after the M. tuberculosis codon numbering

Palavras-chave

rifampicin, rpoB mutation, drug-resistant tuberculosis