The continuing rise of antibiotic resistance among human and animalpathogens supports the growing need for the development of noveland efficient antimicrobial approaches in a time- and cost-effectivemanner. Antimicrobial peptides (AMPs), short proteins with antibioticproperties, have shown efficacy against pathogens in the laboratorysetting. Traditional AMP discovery strategies have been target-centric(“top-down”), addressing one candidate at a time, thus making theprocess resource intensive and time consuming. As a result the currentnumber of characterized AMPs remains small (∼1130) (Fjell et al., 2007).AMPs are known to interfere with intracellular functions and topenetrate and disrupt microbial membranes. Upon expression of someDNA sequences in bacterial hosts the bacterial membranes get damagedeven to the extent of lethality. Vital dyes can be used to identify thesebacterial colonies with compromised membranes. Trypan blue (M.W.=960.81) exclusion assay has been the most widely accepted method fordiscriminating between living and dead cells in a cell culture. Usingtrypan blue exclusion, dead cells are stained blue, while live cells excludetrypan blue and, hence, are unstained. The bacterial colony, a collection ofmany bacterial cells, can be envisaged as a kind of “cell” consisting ofconsensus membranes with analogous dye-exclusion ability. Forexample, vital staining using chlorazol black E and efficient rescuing ofcolonies has been described for Mycoplasma (Berliner et al.,1969). To ourknowledge, themembrane integrity of entire colonies growing on a solidsupport medium (e.g.filter, agar,membrane) for the purpose of screeningDNA libraries has not been probed, assessed or utilized extensively forvitality studies. Induction of cloned genes in such libraries thereforepresents a unique opportunity to screen for membrane disruption.The sequences identified through vital dye inclusion assaysprovide a great resource for potentially novel AMPs. The problemwith expressing potential AMPs in bacterial host cells arises at theidentification step. If the expressed insert is lethal to the host, thebacteria are killed early on, and the insert cannot be recovered. Toovercome this problem, bacterial colonies can be grown beforeinducing the expression of the peptide, and upon induction thedying colonies can be identified using vital dye inclusion.In this report we propose a “bottom-up” screening tactic to identifynovel and useful AMPs through simultaneous testing of thousands ofexpressed DNA sequences. In the method presented, all cloned insertswhich express any form of an antagonizing molecule are identifieddirectly from the initial screen through a simple trypan blue dyeinclusion step to test membrane integrity. We tested this approachusing a whole-colony screening assay to discover novel bactericidalmolecules from the synthetic combinatorial library. This inexpensiveand technically simple screen enables genomes, transcriptomes, orsynthetic DNA libraries to be evaluated and may well address thecurrent need for more suitable AMPs.