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[A study of INH 0.1 microgram/ml resistant M. tuberculosis strains assessed by BrothMIC MTB-1 method]
Hiroko Yoshida1, Hiromi Ano, Chieko Ishida
1Department of Clinical Pathology Laboratory, Osaka Prefectural Habikino Hospital, 3-7-1, Habikino, Habikino-shi, Osaka 583-8588, Japan. ZUM11464@nifty.ne.jp
Abstract:
In the antimycobacterial susceptibility test for INH using the egg-based Ogawa media, 3 concentrations (0.1, 1, or 5 micrograms/ml) of INH were used, and 1 microgram/ml was used as a critical concentration for INH resistance. However, it was controversial whether INH 0.1 microgram/ml resistant M. tuberculosis was clinically significant or not. We investigated the MIC values of INH 0.1 microgram/ml resistant strains by using BrothMIC MTB-1 method, and 115 strains of M. tuberculosis confirmed by DNA-prove test were used. The distribution of MIC values of 115 strains determined by Ogawa INH susceptibility test was shown in figure. By BrothMIC MTB-1 method, they were classified into 3 groups; susceptible, low resistant and high resistant groups. The mean MIC value of INH 0.1 microgram/ml resistant M. tuberculosis was estimated to be 4.53 micrograms/ml with its 95% confidence interval 3.21-5.85 micrograms/ml, and they were determined as "resistant" in BrothMIC MTB-1 method. These results supported the idea that patients with INH 0.1 microgram/ml resistant M. tuberculosis strains should be regarded as clinically "resistant".
Insights
Tuberculosis strains resistant to 0.1 microgram/ml of isoniazid (INH) are clinically significant. These INH-resistant Mycobacterium tuberculosis strains demonstrate higher minimum inhibitory concentrations, confirming resistance and impacting patient treatment strategies.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Context:
- The Ogawa egg-based medium uses 0.1, 1, or 5 micrograms/ml of isoniazid (INH) for antimycobacterial susceptibility testing.
- A critical concentration of 1 microgram/ml is used to define INH resistance.
- Clinical significance of INH resistance at 0.1 microgram/ml remains controversial.
Purpose:
- To investigate the minimum inhibitory concentration (MIC) values of INH 0.1 microgram/ml resistant Mycobacterium tuberculosis strains.
- To determine the clinical significance of INH resistance at lower concentrations using the BrothMIC MTB-1 method.
Summary:
- 115 DNA-proven Mycobacterium tuberculosis strains were tested.
- The BrothMIC MTB-1 method classified strains into susceptible, low resistant, and high resistant groups.
- INH 0.1 microgram/ml resistant strains had a mean MIC of 4.53 micrograms/ml, classifying them as resistant by the BrothMIC MTB-1 method.
Impact:
- Results support classifying patients with INH 0.1 microgram/ml resistant M. tuberculosis strains as clinically resistant.
- This finding aids in refining treatment guidelines for tuberculosis.
- Improved management of drug-resistant tuberculosis cases.