Fig. 2

Colony morphology, size, and acid-fast staining results of WT, SCVs, and RVT MAC phenotypes from patients with MAC-pulmonary disease. (A) Colony morphology of wild type (WT), small colony variants (SCVs), and revertant (RVT) strains phenotypes. Two distinct colony morphotypes were observed on 7H10 agar after 4 weeks incubation at 37 °C. WT showed large, yellow-pigmented, and opaque colony morphology, while SCV demonstrated small and translucent colony in primary cultures. RVT phenotype was observed after the subculture of SCV to new 7H10 agar. RVT showed large, irregular, and opaque colony morphology. WT, SCVs, and RVT were marked with red, black, and blue arrowhead, respectively. (B) Colony size of WT, SCVs, and RVT strains was measured after 4 weeks of incubation at 37℃. SCVs showed a significantly smaller colony size than WT and RVT strains. During the incubation, the size of the SCVs colony was increased but did not exceed 1 mm in all MAC species. Error bars represent the standard deviation, and statistical significance was analyzed with the ANOVA (*, p < 0.05; **, p < 0.01; ***, p < 0.001). (C) Microscopic observation through the acid-fast staining of WT, SCV, and RVT strains. All WT, RVT, and SCT strains of MAC showed similar acid-fastness and bacterial cell morphology