Ethambutol resistance testing by mutation detection.

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Tuberculosis (TB) remains a significant global health challenge.
• Drug resistance in Mycobacterium tuberculosis complicates treatment regimens.
• Ethambutol (EMB) is a crucial first-line drug for TB treatment.

Purpose of the Study:

• To identify specific chromosomal mutations conferring ethambutol resistance in Mycobacterium tuberculosis.
• To evaluate the diagnostic accuracy of genotypic methods for EMB resistance detection.

Main Methods:

• Analysis of embB gene mutations in 235 drug-resistant and 117 drug-susceptible M. tuberculosis isolates.
• Comparison of genotypic findings with phenotypic EMB susceptibility testing (agar diffusion and BACTEC).
• Utilized a novel one-step amplification refractory mutation system polymerase chain reaction (ARMS-PCR) for genotype detection.

Main Results:

• Mutations at embB codon 306 were identified in 20% of resistant isolates, significantly higher than in susceptible ones.
• Phenotypic testing revealed that 91.4% of EMB resistance cases were missed by routine laboratory procedures.
• EMB resistance was strongly associated with multidrug resistance (MDR), co-occurring with isoniazid and rifampicin resistance in 87.2% of cases.
• The ARMS-PCR method demonstrated effectiveness in detecting EMB-resistant genotypes.

Conclusions:

• Current diagnostic methods for EMB resistance in M. tuberculosis may miss a substantial number of resistant cases.
• Improved diagnostic strategies, including genotypic analysis, are essential for accurate patient management.
• Accurate EMB resistance testing is critical for guiding standardized treatment of multidrug-resistant TB (MDR-TB).