Sensitivity of Paucilactobacillus wasatchensis strains to nisin

<i>Paucilactobacillus wasatchensis</i> 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 <i>Pa. wasatchensis</i> 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 <i>Pa. wasatchensis.</i> Nisin sensitivity has not yet been evaluated for <i>Pa. wasatchensis</i> strains. The goal of the current study was to evaluate 8 strains of <i>Pa. wasatchensis</i> 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 <i>Pa. wasatchensis</i> 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 <i>Pa. wasatchensis</i> 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 <i>Pa. wasatchensis</i>.