Over the last few years, periodontal disease has become a serious oral health problem worldwide. P. gingivalis has long been implicated as a major etiological agent in the onset & progression of periodontitis. The fimbriae, an important virulence factor of P. gingivalis, have been classified into six genotypes (I-V, and Ib), based on the genomic diversity of the fimA gene. This book is based on research work that suggests a close association between periodontal disease activity and P. gingivalis type II fimA genotype. On the basis of this association, detection of type II fimA genotype can be recommended as a marker for periodontal disease diagnosis as well as its disease activity. This book will be of interest to researchers, under- and post-graduate students in microbiology, immunology, as well as molecular medicine and dentistry.