The role of quorum sensing (QS) is well known for bacterial virulence, antibiotic resistance and biofilm production. Consequently, inhibition of QS may reduce the risk of microbial pathogenicity in systemic and local infections. Hence, in the present study, the marine sediment bacterial isolate Bacillus spp. SS4 (GenBank accession number GU471751) isolated from the Point Calimere coastal region was assessed for its anti-quorum-sensing (anti-QS) activity against acyl homoserine lactone (AHL)-dependent prodigiosin, protease production and biofilm formation in Serratia marcescens (FJ584421). The ethyl acetate extract obtained from SS4 exhibited a concentration-dependent (50–200 μg/ml) reduction in prodigiosin production in S. marcescens to a level of 40–87%. The azocasein-degrading proteolytic activity of S. marcescens was also reduced by up to 60%, when treated with the SS4 extract at a final concentration of 200 μg/ml. Light- and confocal laser scanning-microscopic (CLSM) analysis further confirmed the reduction in the biofilm-forming ability of S. marcescens when treated with this extract. In an antibiotic susceptibility assay, cells of S. marcescens showed increased susceptibility towards antibiotics in the presence of SS4 extract. In addition, SS4 extract by itself showed no growth inhibitory effect on S. marcescens. Thus, the results of present study reveal the anti-QS potential of Bacillus spp. SS4 by notably reducing AHL-dependent behaviors in S. marcescens.