"The oregano oil exhibited significant inhibitory activity against Citrobacter spp., (24.0 mm ± 0.5 SD), Salmonella typhi (22.4 mm ± 1.5 SD) and Escherichia coli (19.0 mm ± 2.2 SD) (Table 1). It has long been acknowledged that oregano oil is among the most active against strains of E. coli and also presents antimicrobial activity against pathogenic microorganisms like Salmonella. choleraesuis, S. typhi, S. typhimurium and many others related GNB strains of Enterobacteriaceae family (Penalver et al., 2005) and H. pylori (Stamatis et al., 2003). Similarly, the results of present study are in accordance with the reports on oregano oil against GNB viz., Proteus vulgaris, Aeromonas hydrophila, Klebsiella pneumoniae and Escherichia coli (Baydar et al., 2004). "

The growth of Salmonella typhimurium in liquid culture and in a gel matrix system at two pH values (5.0 and 7.0) with (0.03% w/v) or without oregano essential oil was studied. It was shown that the type of growth media (liquid or gel) influenced significantly both the type of end-product formation and growth of bacteria as well as the inhibitory efficacy of the essential oil. The oil inhibited S. typhimurium more strongly in the liquid medium than in the gelatin matrix. In particular, the addition of essential oil in gelatin matrix delayed the initiation of growth and caused a slight suppression of the maximum population level, while in liquid culture, growth was prevented completely in identical conditions. Structure also was found to affect the rate of consumption of glucose and the rate of production of end products. Formic and acetic acids were produced in both systems, while an unidentified peak was formed only in broth samples.

The effect of oregano essential oil and film permeability on the behaviour of Salmonella typhimurium in sterile and naturally contaminated beef fillets stored under aerobic, modified atmosphere consisting of 40% CO2 /30% O2 /30% N2 (MAP) and a vacuum packaged (VP) environment was studied during storage at 5°C. In samples without oregano essential oil, the pathogen survived under all storage conditions. Addition of oregano essential oil at a concentration of 0·8% v/w resulted in an initial reduction of 1–2 log10 cfu g−1 of the majority of the microbial population of meat with lactic acid bacteria and S. typhimurium showing the greatest reductions in all gaseous environments regardless of film permeability. The use of VP/MAP at chill temperatures in conjunction with oregano essential oil as a means of controlling spoilage and safety of meat is discussed.

The antimicrobial efficacy of sumac (Rhus coriaria L.) water extracts (1%, 3% and 4%) and oregano (Oreganum onites) oil suspensions (25 ppm, 75 ppm and 100 ppm) was tested against the nalidixic acid resistant strain of Salmonella Typhimurium ATCC 13311 inoculated to tomatoes. The inoculated tomatoes (2.71–4.35 log cfu/tomato) were subjected to treatment for 5, 10, 15 and 20 min by washing with sterile distilled water (control), sumac extracts or oregano oil suspensions with or without rinsing in sterile distilled water. Treatment of tomatoes with sumac and oregano caused significant reductions in S. Typhimurium population compared to the control (P < 0.05). However, there was no significant difference between washing times in the reduction of S. Typhimurium (P > 0.05). The maximum logarithmic reductions of S. Typhimurium were obtained at levels of 2.38 and 2.78 logarithmic units on tomatoes treated with 4% sumac extract and 100 ppm oregano, respectively. No statistical difference was obtained in the number of S. Typhimurium recovered in different concentrations of treatment solutions in four different treatment times (P > 0.05). The results suggest that the use of sumac water extract or oregano oil suspensions can be used to enhance microbial safety of tomatoes without loss in quality attributes.