Effect of γ-immunoglobulin on the asaccharolytic growth of Porphyromonas gingivalis

Background and Objectives: A minimal medium is indispensable for examining the growth properties of the asaccharolytic bacterium, Porphyromonas gingivalis. The purpose of the present study was to improve the widely used KGB medium to support good growth of P. gingivalis. Material and Methods: Growth of P. gingivalis (W50, W83, and ATCC33277) in a minimal medium was monitored by measuring the optical density of the culture during incubation. Results: W50, W83, and ATCC33277 grew poorly with bovine serum albumin as the sole carbon and nitrogen source, and α‐ketoglutarate had little or no effect on this poor growth. In contrast, FeCl3 improved the growth of W83 and ATCC33277; however, the use of a high concentration of FeCl3 elicited black pigmentation of the cells. Bovine γ‐immunoglobulin greatly recovered the growth defect. None of α‐ketoglutarate, citrate, or trace metal ions, when used to supplement KGB medium, was required for growth. We determined the optimal conditions for growth, and developed a new simple minimal medium for P. gingivalis (GA medium). Growth of ATCC33277 in GA medium was dependent on gingipains; Arg‐gingipains and Lys‐gingipain contributed comparably to proliferation of the bacterium. Conclusion: These data indicate that GA medium is currently the most reliable minimal medium for examining the growth properties of P. gingivalis.