Evaluation of diacetyl antimicrobial activity against Escherichia coli, Listeria monocytogenes and Staphylococcus aureus

The antimicrobial activity of diacetyl was evaluated against Escherichia coli, Listeria monocytogenes and Staphylococcus aureus. The molecule was added to broth culture media, supplemented or not with NaCl, or introduced in the head space of closed systems containing solid media. The results obtained in liquid media showed that E coli was the most sensitive, while L. monocytogenes the most resistant organism. In fact, the addition of 300 ppm of diacetyl determined, with respect to the control, increases the lag phase length of 4.23, 2.48 and 1.52 times in E coli, S. aureus and L. monocytogenes, respectively. One hundred ppm of diacetyl, directly introduced in the head space, had a bactericidal effect against E coli and S. aureus. Only L. monocytogenes exhibited growth in the presence of 100 ppm of diacetyl. Higher concentrations was bactericide also for this Gram-positive species. The higher antimicrobial efficacy of diacetyl when added directly in the head space was probably due to its initial higher partition in the vapor phase. The addition of NaCl increased the antimicrobial activity of diacetyl against E coli in liquid growth media, due to the "salting out" effect played by solutes which enhances its vapor pressure. (C) 2003 Elsevier Ltd. All rights reserved.