rpoB, katG and inhA mutations in multi-drug resistant strains of Mycobacterium tuberculosis clinical isolates from southeast Mexico

Phenotypic and Genotypic Drug Resistance of Mycobacterium tuberculosis Strains Isolated from HIV-Infected Patients from a Third-Level Public Hospital in Mexico

BACKGROUND

Drug-resistant tuberculosis (TB) is associated with higher mortality rates in patients with human immunodeficiency virus (HIV). In Mexico, the number of deaths due to TB among the HIV-positive population has tripled in recent years.

METHODS

Ninety-three Mycobacterium tuberculosis strains isolated from the same number of HIV-infected patients treated in a public hospital in Mexico City were studied to determine the drug resistance to first- and second-line anti-TB drugs and to identify the mutations associated with the resistance.

RESULTS

Of the 93 patients, 82.7% were new TB cases, 86% were male, and 73% had extrapulmonary TB. Most patients (94%) with a CD4 T-lymphocyte count <350 cells/mm3 were associated with extrapulmonary TB (p <0.0001), whilst most patients (78%) with a CD4 T-lymphocyte count >350 cells/mm3 were associated with pulmonary TB (p = 0.0011). Eighty-two strains were pan-susceptible, four mono-resistant, four poly-resistant, two multidrug-resistant, and one was extensively drug-resistant. In the rifampicin-resistant strains, rpoB S531L was the mutation most frequently identified, whereas the inhA C15T and katG S315T1 mutations were present in isoniazid-resistant strains. The extensively drug-resistant strain also contained the mutation gyrA D94A.

CONCLUSIONS

These data highlight the need to promptly diagnose the drug resistance of M. tuberculosis among all HIV-infected patients by systematically offering access to first- and second-line drug susceptibility testing and to tailor the treatment regimen based on the resistance patterns to reduce the number of deaths in HIV-infected patients.

Prediction of Mycobacterium tuberculosis drug resistance by nucleotide MALDI-TOF-MS

OBJECTIVES

To evaluate the performance of nucleotide matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) in predicting the drug resistance of Mycobacterium tuberculosis.

METHODS

A total of 115 rifampin-resistant and 53 rifampin-susceptible tuberculosis (TB) clinical isolates were randomly selected from TB strains stored at -80℃ in the clinical laboratory of Shanghai Pulmonary Hospital. Nucleotide MALDI-TOF-MS was performed to predict the drug resistance using phenotypic susceptibility as the gold standard.

RESULTS

The overall assay sensitivities and specificities of nucleotide MALDI-TOF-MS were 92.2% and 100.0% for rifampin, 90.9% and 98.6% for isoniazid, 71.4% and 81.2% for ethambutol, 85.1% and 93.1% for streptomycin, 94.0% and 100.0% for amikacin, 77.8% and 99.3% for kanamycin, 75.0% and 93.3% for ofloxacin, and 75.0% and 93.3% for moxifloxacin. The concordances between nucleotide MALDI-TOF-MS antimicrobial susceptibility testing (AST) and phenotypic AST were 94.6% (rifampin), 90.1% (isoniazid), 79.2% (ethambutol), 89.9% (streptomycin), 99.4% (amikacin), 97.0% (kanamycin), 88.1% (ofloxacin), and 88.0% (moxifloxacin).

CONCLUSION

Nucleotide MALDI-TOF-MS could be a promising tool for rapid detection of Mycobacterium tuberculosis drug sensitivity to rifampin, isoniazid, ethambutol, streptomycin, amikacin, kanamycin, ofloxacin, and moxifloxacin.

Two Novel katG Mutations Conferring Isoniazid Resistance in Mycobacterium tuberculosis

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis, is among the top 10 leading causes of death worldwide. The treatment course for TB is challenging; it requires antibiotic administration for at least 6 months, and bacterial drug resistance makes treatment even more difficult. Understanding the mechanisms of resistance is important for improving treatment. To investigate new mechanisms of isoniazid (INH) resistance, we obtained three INH-resistant (INH-R) M. tuberculosis clinical isolates collected by the Taiwan Centers for Disease Control (TCDC) and sequenced genes known to harbor INH resistance-conferring mutations. Then, the relationship between the mutations and INH resistance of these three INH-R isolates was investigated. Sequencing of the INH-R isolates identified three novel katG mutations resulting in R146P, W341R, and L398P KatG proteins, respectively. To investigate the correlation between the observed INH-R phenotypes of the clinical isolates and these katG mutations, wild-type katG from H37Rv was expressed on a plasmid (pMN437-katG) in the isolates, and their susceptibilities to INH were determined. The plasmid expressing H37Rv katG restored INH susceptibility in the two INH-R isolates encoding the W341R KatG and L398P KatG proteins. In contrast, no phenotypic change was observed in the KatG R146P isolate harboring pMN437-katG. H37Rv isogenic mutant with W341R KatG or L398P KatG was further generated. Both showed resistant to INH. In conclusion, W341R KatG and L398P KatG conferred resistance to INH in M. tuberculosis, whereas R146P KatG did not affect the INH susceptibility of M. tuberculosis.