We also did this for the cultures in Exp. 7 and the various Bacillus isolates in Exp. Micrococcus and Pseudomonas are included in this table for comparison with Staphylococcus and the enterics, respectively. The last-named was included among the cultures in Experiment 7.1 and showed a bright purple pigmentation. Also included in the lactics are Leuconostoc, Aerococcus and Lactobacillus.
Sodium azide inhibits the activities of iron-porphyrin compounds such as catalase and cytochromes.
As the lactics do not possess these compounds, they are not affected by sodium azide. Click here for a graphic representation of what goes on in the medium for both types of organisms. Ingredients in enrichment and plating media which assist in the isolation of enteric bacteria include various selective agents which inhibit the growth of gram-positive bacteria . There is no medium which supports growth of enterics exclusively. To drive this fact home, we add Pseudomonas to our mixture of enteric unknowns in Experiment 14.1, and we find we can eliminate it sooner or later during the isolation process.