The purpose of this study was to examine the effectiveness of selected essential oils for the control of growth and survival of pathogenic microorganisms of significant importance in food hygiene and to determine whether the antimicrobial effect was due to the major compounds of the oils. MIC and MBC were determined by the tube dilution method. Essential oils from Thymus vulgaris from Spain and France, Salvia sclarea, Salvia officinalis, Salvia lavandulifolia, Lavandula latifolia, Lavandula angustifolia, three hybrids of Lavandula latifolia x Lavandula angustifolia (Lavandin 'Super', Lavandin 'Abrialis', and Lavandin 'Grosso'), Rosmarinus officinalis, Hissopus officinalis, and Satureja montana were evaluated. Inhibition ranged from the strong activity of Satureja montana and Thymus vulgaris (France) to no inhibition with Salvia sclarea and Hissopus officinalis for each of the test strains: Salmonella Enteritidis, Salmonella Typhimurium, Escherichia coli O157:H7, Yersinia enterocolitica, Shigella flexneri, Listeria monocytogenes serovar 4b, and Staphylococcus aureus. Because some of the essential oils were highly inhibitory in small quantities to selected pathogenic microorganisms, they may provide alternatives to conventional antimicrobial additives in foods.

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The aim of this work was to study the occurrence of Listeria monocytogenes in several types of ready-to-eat (RTE) meat products and in the environment of meat processing plants. A total of 129 samples of RTE meat products and 110 samples from work surfaces and equipment were analyzed. L. monocytogenes was detected in 6 out of 35 cooked products (17.14%), 21 out of 57 raw-cured products (36.84%), and 9 out of 37 dry-cured, salted products (24.32%). The number of sample units that exceeded the food safety limit of 100 cfu/g decreased from the manufacture date to half shelf life, and then it was further reduced at the end of shelf life. L. monocytogenes was detected in 25 out of 110 (22.72%) food contact surfaces. The number of positive and negative results from both food and environmental samples were cross-tabulated and the calculated Cohen’s kappa coefficient (κ) was 0.3233, indicating a fair agreement in terms of Listeria contamination. L. monocytogenes was recovered after cleaning and disinfection procedures in four plants, highlighting the importance of thorough cleaning and disinfection.

The resistance to 12 commonly used antimicrobial agents of 144 foodborne isolates belonging to the genus Listeria (23 L. monocytogenes, 54 L. innocua, 66 L. seeligeri, and 1 L. welshimeri) was tested by using the agar disc-diffusion assay. The Listeria strains were isolated from dairy products (different varieties of unripened fresh and bacteria-ripened hard cheeses made from ewe's, cow's, and goat's milk) and meat products (longaniza, a type of pork sausage). A total of 84 (93%) and 54 (100%) Listeria strains isolated from cheese and pork sausage, respectively, were resistant to multiple antimicrobial agents. More than 80% of the Listeria strains of both food origins were found to be susceptible to penicillin G and ampicillin, whereas the proportion of isolates resistant to the cephalosporins cefotaxime and cefoxitin was nearly 100%. The prevalence of resistance was much higher for isolates from pork sausage (73.8% on average) than for isolates from cheese (20.9%). This marked difference was statistically significant (P < 0.05; chi-square test) for all antibiotics except ampicillin, cefotaxime, and cefoxitin. The strains of the foodborne pathogen L. monocytogenes isolated from cheese were all susceptible to 9 of the 12 antimicrobial agents evaluated. In contrast, more than 80% of the L. monocytogenes strains isolated from pork sausage exhibited resistance to cefotaxime, cefoxitin, tobramycin, amikacin, chloramphenicol, tetracycline, and erythromycin. The appearance of substantial resistance to antibiotics in foodborne Listeria isolates suggests the need for more prudent use of antibiotics by farmers, veterinarians, and physicians.