Figure 2.

Formation of non-haemolytic mutants on exposure to erythromycin. The graphs depict the percentage of non-haemolytic colonies detected over time in triplicate cultures of B. bronchiseptica RB50 grown at 37°C (200 rpm) in SS medium with 0, 1, 2 and 3 mg/L erythromycin. The numbers of non-haemolytic and haemolytic colonies were separately noted to calculate the percentage of non-haemolytic colonies detected. As the graphs show, the percentage of non-haemolytic colonies increased incrementally in response to the antibiotic concentrations. Student’s t-test significance values were determined by comparing the percentage of non-haemolytic colonies observed with antibiotics on each day with corresponding percentage values observed without antibiotics. *P < 0.05; ***P < 0.0001 (P values of <0.05 were considered statistically significant).