A novel serum-based medium for drug susceptibility testing of Mycobacterium tuberculosis

Sheep serum agar (SSA) is a new serum-based medium developed as an alternative to Middlebrook 7H10 agar for the isolation of Mycobacterium tuberculosis from clinical samples and for use in antimicrobial susceptibility testing. This study aimed to evaluate the performance of SSA in primary anti-tuberculosis drug susceptibility testing. A total of 107 M. tuberculosis isolates with different susceptibility profiles were tested simultaneously against primary anti-tuberculosis agents on SSA and Middlebrook 7H10 agar using the proportion method. The findings were compared with those obtained using the BACTEC MGIT 960 (M960) method. The agreement between the M960 and 7H10 agar proportion method was determined as 93.45% for isoniazid (INH) and ethambutol (EMB), 96.26% for rifampicin (RIF), and 79.43% for streptomycin (STR), respectively. The agreement between the M960 and SSA proportion method was determined as 95.32% for INH, 97.19% for RIF, 92.52% for STR, and 86.91% for EMB, respectively. The agreement between the 7H10 agar proportion method and the SSA proportion method was determined as 98.13% for INH, 99.06% for RIF, 86.91% for STR, and 93.45% for EMB, respectively. SSA medium was more effective at detecting INH, RIF and STR resistance than 7H10 agar. The results demonstrate the potential of SSA as an alternative medium to 7H10 agar. Further research is needed to confirm its reliability and evaluate its performance.