Inhibition of Salmonella enteritidis and Staphylococcus aureus in nutrient broth by mint essential oil

The effect of different concentrations (0-1.2% v/v) of mint (Mentha piperita) essential oil on the growth/survival of Salmonella enteritidis and Staphylococcus aureus was studied in nutrient broth, using the viable count method and conductance measurements. In particular the addition of mint essential oil reduced the total viable counts of St. aureus about 6-7 logs while this of S. enteritidis only ca. 3 logs. The detection time measurements showed also that the inhibitory effect of mint essential oil was affected by the incubation temperature as well as by the concentration of essential oil added in the growth medium. At low concentration of essential oil (<0.1%), the addition of glucose in the growth medium prevented the formation of staphylococcal enterotoxin B, while the reduction of viable cells was only 2 logs. This glucose effect was not evident in Salmonella enteritidis samples. The percentage of glucose utilization in the growth medium of both pathogens, was reduced drastically with the addition of essential oil and as a consequence the assimilation or formation of different compounds, such as lactate, formate and acetate in the growth medium was also affected. (C) 2000 Elsevier Science Ltd. All rights reserved.