Quantitation of Bacterial Interactions Using the Spiral Plater and Membrane Filters

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Abstract
The spiral plater was used to evaluate bacterial interactions by plating one organism on the surface of a dried agar medium in a petri plate, placing a 0.45-.mu.m membrane filter over the 1st organism and plating the 2nd organism on top of the membrane. Most bacteria above the membrane produced smaller colonies when another organism was growing below the membrane. Reduction in numbers of colonies above the membrane was evidence of inhibition by organisms below the membrane. Increase in colony numbers was evidence of stimulation. Different interactions were observed between lactics and nonlactics. Lactics wer emore inhibitory to and less inhibited by Staphylococcus aureus and Streptococcus agalactiae than when challenged with coliform organisms. Interactions between lactic strains were not consistent with previous work. The technique does not appear useful for studying interactions between lactic strains or between lactic strains with various proteolytic activities.