Potential effect of monolaurin and nisin on the growth of three aerobic spore-forming bacteria isolated from Tunisian milk

Antibacterial capacities of monolaurin and nisin on the growth of vegetative cells of three sporeforming bacteria isolated from cow milk collected from Tunisia (Terribacillus aidingensis, Bacillus sporothermodurans and Paenibacillus sp and) were evaluated. Nisin or monolaurin, at different concentrations, can inhibit the growth of three Bacillus. 500 IU/mL and 25 μg/mL corresponded to the minimum inhibitory concentrations of nisin and monolaurin, respectively. The growth of the tested species in the presence of sub-lethal concentrations of monolaurin and nisin was monitored in UHT milk for 7 days at three different temperatures (4°C, 37°C and 25°C). Nisin (250 IU/mL) was able to induce an immediate reduction (after 3 h of incubation at 4°C) of Bacillus species growth (5 log for B. sporothermodurans, 4 log for Paenibacillus sp and 3.2 log for T. aidingensis). Also, monolaurin (25 µg/mL) reduce the growth, at 4°C of B. sporothermodurans by 5 log, Paenibacillus sp by 3 log and T. aidingensis by 4 log, after 3 h of incubation. In the presence of nisin or monolaurin, it can be observed a low reduction in cell growth followed by a rapid regrowth which can attenuate 10 log, at 37°C and 25°C. The obtained data elucidate the potency of nisin and monolaurin, and the application of these antimicrobial agents at low temperatures (4°C) to decontaminate any product from these spoilage bacteria.