Quantitative Determination of Anti-bacterial Activity During Bacterial Co-culture

Anti-bacterial activity assays are an important tool in the assessment of the ability of one bacterium to kill or inhibit the growth of another, for example during the study of the Type VI secretion system (T6SS) and the anti-bacterial toxins it secretes. The method we describe here can detect the ability of a bacterial strain to kill or inhibit other bacterial cells in a contact-dependent manner when co-cultured on an agar surface. It is particularly useful since it enumerates the recovery of viable target cells and thus enables quantification of the anti-bacterial activity. We provide a detailed description of how to measure the T6SS-dependent anti-bacterial activity of a bacterium such as Serratia marcescens against a competitor prokaryotic organism, Escherichia coli, and also describe possible variations in the method to allow adaptation to other attacker and target organisms.