en Molecular & Cellolar Molecular & Cellolar Mini Review Mini Review <div style="text-align: justify;">Cell-to cell communication occurs via a signaling pathway referred to as quorum sensing. There are four main types of these systems according to the chemical nature of signal molecules used by microorganisms to elicit expression of target genes in response to environmental stimuli or need of microbial communities. Type I system acts by using acyl homoserine lactones as signals to trigger the expression of virulence genes in <em>Pseudomonas aeruginosa</em> and members of the Enterobacteriacae family. Other groups of bacteria possess a second system which uses certain furanones as a universal language among different species. Pathogenic <em>Shigella spp., Salmonella</em>, and <em>Escherichia</em> <em>coli</em> rely on catecholamines of the human host for inducing a third quorum sensing system in infection. Short cyclic peptides act mainly in <em>Staphylococcus</em> spp. and <em>Enteroccocus</em> <em>faecalis</em> to activate a forth system involved in their pathogenicity. Therefore, it is essential to analyze these systems for the design of antimicrobials that could eliminate pathogens or abolish their harmful activities.&nbsp;</div> Autoinducer, LuxI-LuxR homologues, LuxS, pathogenicity 126 135 http://ibbj.org/browse.php?a_code=A-10-304-1&slc_lang=en&sid=1 Mohammed Z. Al-Khayyat mzsaeed19@hotmail.com 10031947532846003404 10031947532846003404 Yes Biology Department, College of Education for Pure Sciences, University of Mosul, Mosul City, Iraq.