Purpose: This study aimed to evaluate the ability of bacteriocinogenic isolates obtained from raw milk cheese to control Listeria monocytogenesin co-cultures in skim milk.
Methods: Overnight cultures of bacteriocinogenic Enterococcus hirae ST57ACC was inoculated at concentration of 2% in flasks containing 10 % of reconstituted skim milk. An overnight culture of L. monocytogenes 422 was also inoculated in the flask, at concentration of 0.1% to mimic conditions normally expected in food contamination scenario. L. monocytogenes 422 was also inoculated as a single culture and in the same concentration in skim milk as control. The flasks were incubated at 37 °C for 48 h and at 3 h intervals aliquots were taken to determine changes in cell numbers of L. monocytogenes 422 and to monitor bacteriocin production, by using agar spot method.
Results: E. hirae ST57ACC was capable of reducing cell numbers of L. monocytogenes 422 from 4 log CFU/ml (time 0) to undetectable levels after 48 h. Production of bacteriocin was observed during all periods evaluated, reaching a stable level of production after 12 hours (3,200 AU/mL), remaining until the end of the experiment. In the control flask, Listeria monocytogenes 422 counts varied from 5 log CFU/mL (time 0 h) to 8 log UCF/mL (time 48 h).
Significance: The obtained results indicated that E. hirae ST57ACC was able to eliminate L. monocytogenes in milk after 48 h of inoculation, demonstrating the potential for biocontrol of this pathogen in milk.