Periodontal diseases are infectious. Gram-positive bacteria from saliva express adhesions that selectively bind to pellicle and mediate colonization and growth of supragingival plaque. In a matter of days, Gram-negative species colonize through specific receptors binding to the Gram-positive bacteria. If left unhindered a few days later tightly adherent microbial plaque becomes visible on the tooth surface at the gingival margin and an acute inflammatory response manifested as gingivitis develops. Biofilms are "Matrix enclosed bacterial populations adherent to each other and surfaces or interfaces". The biofilm concept is important in understanding the patho-microbiology of periodontitis and its relation to systemic diseases. As in the case of biofilms in general, subgingival plaques are difficult to eliminate. Gram-negative bacteria in the biofilms shed vesicles that are rich in LPs. The biofilms serve as a constantly renewing source of LPs which once pocket epithelium forms, have ready access to the connective tissue and circulation. Physical disruption and removal are effective ways of dealing with biofilms.