Coxiella burnetii from cell and axenic cultures has similar viability but varied vitality as measured by using a methylcellulose semi-solid medium

The invention of axenic media for culturing Coxiella burnetii has greatly promoted studies on this fastidious bacterium. In this study, we report a methylcellulose-supplemented ACCM-2 medium that allows the enumeration of C. burnetii colonies after growing for up to 15 days. Colony forming units (CFUs) of C. burnetii from both axenic and cell cultures were measured in this methylcellulose medium at various time points (8, 12, and 15 days post-plating). Increasing CFU numbers were observed for both cultures at these time points. The ratios of genome equivalents to CFUs at 15 days post-plating and the ratios of CFUs at 15 days to 8 days post-plating were employed to evaluate the viability and vitality of C. burnetii, respectively. We discovered that C. burnetii from cell and axenic cultures exhibit similar viability (7.72 vs 7.11), but that cell culture-derived C. burnetii demonstrates greater vitality than axenic cultures (1.63 vs 5.2). This work sheds light on the normal viability but low vitality of ACCM-2-derived C. burnetii.