Sensitivity of Paucilactobacillus wasatchensis strains to nisin

Paucilactobacillus wasatchensis is a nonstarter lactic acid bacterium that has been isolated throughout the United States and is associated with late blowing gas defect (LBD), a continuing problem in the cheese industry, which results in downgraded product and economic loss. Although the route of Pa. wasatchensis contamination in milk destined for cheesemaking remains inconclusive, the addition of nisin or the application of nisin-producing starter cultures in Cheddar production may mitigate LBD by inhibiting Pa. wasatchensis. Nisin sensitivity has not yet been evaluated for Pa. wasatchensis strains. The goal of the current study was to evaluate 8 strains of Pa. wasatchensis for nisin sensitivity using the agar well diffusion method. Nisin inhibition was evaluated across a range from 5 to 100 IU/mL. To compare strain sensitivity, the lowest nisin concentration that displayed inhibition for all strains was selected (30 IU/mL), and the corresponding inhibition zones were statistically analyzed by ANOVA with a Tukey-Kramer post hoc test. The MIC for each strain were also estimated. Each Pa. wasatchensis strain showed inhibition within the tested range of nisin concentration. Results from the Tukey-Kramer post hoc test showed some strain differences in nisin sensitivity, but these were not correlated with region of isolation. All strains showed inhibition at 30 IU/mL nisin, which indicates that Pa. wasatchensis is highly sensitive to nisin. This supports addition of nisin, or the application of nisin protective cultures, as a potential effective strategy in mitigating LBD caused by Pa. wasatchensis.