Determining the Minimum Inhibitory Concentration of Bacteriophages: Potential Advantages *

The minimum inhibitory concentration (MIC) is the concentration at which an antibacterial agent experiences the complete inhibition of organism growth. Bacteriophages represent a rich and unique resource of anti-infectives to counter the growing world-wide problem of antibiotic resistance. In this study, we compared the host range of lytic bacteriophages and temperate phagesbelonging to various genera, namely Staphylococcus, E. coli and Salmonella, with a range of clinical isolates using two methods: the classical agar overlay method and a newly developed MIC method. MIC was only observed with isolates that were susceptible to phage infection, which correlated with the agar overlay assay, whereas no MIC was detected with isolates that were resistant to phage infection. The simple MIC method was useful in determining phage adsorption and host range, and detecting possible prophage contamination in phage preparations. Interestingly, this method was also applicable to strain differentiation through phage susceptibility testing using a 96-well, high throughput format that proved to be easy, cost-effective, fast and reliable.