Factors affecting iron sulfide-enhanced bacteriophage plaque assays in Salmonella

Reaction of ferric ions with hydrogen sulfide (H2S) enhances contrast of phage plaques in H2S+ Salmonella, but contrast diminishes in weak H2S+ strains. H2S was affected by concentrations of peptones, glucose, ferric ammonium citrate (FAC) and sodium thiosulfate (ST), and by FAC:ST ratio, temperature, pH, air, and host strain. Increasing peptone levels was most important for improving contrast in weak H2S+ strains.