Abstract
In the oral cavity Candida albicans interacts with many oral bacteria, including Porphyromonas gingivalis, both physically and metabolically. The aim of this in vitro study was to characterize these interactions and study their effects on the survival of P. gingivalis. First, metabolic interactions were evaluated by counting the colony forming units (CFU) after co-culturing. The results indicated that the anaerobic bacterium P. gingivalis survives under aerobic conditions when co-cultured with C. albicans. This is due to the oxygen consumption by C. albicans as determined by a reduction in survival upon the addition of Antimycin A. By measuring the protease activity, it was found that the presence of C. albicans induced gingipain activity by P. gingivalis, which is an important virulence factor. Adherence of P. gingivalis to hyphae of C. albicans was observed with a dynamic flow system. Using various C. albicans mutants, it was shown that the mechanism of adhesion was mediated by the cell wall adhesins, members of the agglutinin-like sequence (Als) family: Als3 and Als1. Furthermore, the two microorganisms could be co-cultured into forming a biofilm in which P. gingivalis can survive under aerobic culturing conditions, which was imaged using scanning electron microscopy. This study has further elucidated mechanisms of interaction, virulence acquisition and survival of P. gingivalis when co-cultured with C. albicans. Such survival could be essential for the pathogenicity of P. gingivalis in the oxygen-rich niches of the oral cavity. This study has emphasized the importance of interaction between different microbes in promoting survival, virulence and attachment of pathogens, which could be essential in facilitating penetration into the environment of the host.