Further Studies on the Antibotulinal Effectiveness of Nisin in Acidic Media

The antibotulinal effectiveness of nisin in TPYG broth was increased somewhat by lowering the pH to pH 5.5. The ability of nisin to inhibit the outgrowth of strain 56A spores was markedly increase at pH 5.5 by comparison to its effectiveness at higher pHs observed in previous studies. The increased effectiveness of nisin at pH 5.5 was less notable for the strain 69A, 113B, and 213B spores. The nisin sensitivity of the type E spores was essentially unchanged from that observed in earlier studies at higher pHs. At pH 6, nisin levels of 5000 I.U./ml were insufficient to prevent spore outgrowth by C. botulinum in cooked meat medium. Comparatively, much lower levels of nisin were effective in preventing botulinal outgrowth in TPYG broth at pH 6. The decreased effectiveness of nisin in cooked meat medium may be due to the binding of nisin to meat particles, and this binding is apparently not affected by lowering the pH to pH 6.0.