The effect of temperature and citric acid, alone, and in combination with nisin, on the growth of Arcobacter butzleri in culture

Elevated temperature and citric acid have been shown to enhance the susceptibility of gram-negative bacteria to nisin both in culture and in those foods routinely contaminated with Arcobacter butzleri. This study investigated the sensitivity of A. butzleri cells to elevated temperature and varying concentrations of citric acid, alone and in the presence of nisin. The effect of a combination of short-term exposure to citric acid and low-temperature (modeling a chill-wash procedure) followed by continuous exposure to nisin, was also carried out in order to assess the effects to A. butzleri from a multiple hurdle approach to control. When incubated at sub-optimal temperatures (i.e. for aerobic growth, lower than 30 °C) A. butzleri cells show less sensitivity to 500 IU ml−1 nisin than at 30 °C. Elevating the temperature to 60 °C for 10 min, followed by 24 h incubation at 30 °C resulted in no viable cells being detected. However, elevating the temperature to 50 °C resulted in some viable cells with the presence of nisin during the heat treatment significantly reducing number of survivors. A 30-min treatment with 1, 20, 50 or 100 mM citric acid, in the absence and presence of 500 IU ml−1 nisin, reduced survival of A. butzleri cells. Stationary phase cells appear significantly more resistant to both citric acid alone, and citric acid in combination with nisin, than log phase cells. 10-min treatment with 20 mM or 100 mM citric acid, at 30 or 4 °C followed by incubation in the presence of 500 IU ml−1 nisin, completely inhibited growth of A. buzleri cells over five hours. Over 24 h the most effective treatment was with 100 mM citric acid at 4 °C followed by incubation in the presence of 500 IU ml−1 nisin suggesting that nisin prevents the recovery of sublethally damaged cells.