Abstract
Listeriosis is a foodborne disease caused by the pathogenic Listeria monocytogenes and is considered as a serious health problem due to the severity of symptoms and its high mortality rate. Listeria genus is divided into six species and especially L. monocytogenes is an important foodborne pathogen in humans and livestock. Recently, other Listeria species are reported as pathogenic strains in decayed foods and environments as well. High mortality rate of listeriosis demands for rapid methods to detect the potential presence of the food pathogens in the food industry. We have developed a multiplex PCR for rapid and simultaneous detection of six Listeria species including Listeria grayi, Listeria innocua, Listeria ivanovii, L. monocytogenes, Listeria seeligeri and Listeria welshimeri to identify specific Listeria species in processed foods. The optimized multiplex PCR in this study utilized one Listeria genus specific and each Listeria species-specific primer pairs. Each primer pair yields the products of 370-bp for Listeria genus-specific, 201-bp for L. grayi-specific, 749-bp for L. innocua-specific, 463-bp for L. ivanovii-specific, 509-bp for L. monocytogenes-specific, 673-bp for L. seeligeri-specific and 281-bp for L. welshimeri-specific. We have successfully applied multiplex PCR strategy to 93 Listeria isolates from processed meat products to determine specific Listeria species and out of which 81 strains of L. monocytogenes, 10 strains of L. innocua and 2 strains of L. welshimeri were identified. This established multiplex PCR provides rapid and reliable results and will be useful for the detection of Listeria species in contaminated food products and clinical samples.
Abstract
The aim of this study was to investigate the efficacy of natural antimicrobial substances for inhibiting vegetable spoilage bacteria. Natural antimicrobial compounds (carvacrol, thymol, eugenol, cinnamic acid, nisin, and chitosan), organic acids (acetic acid and lactic acid), and chemical sanitizers (sodium hypochlorite and chlorine dioxide) were evaluated for their antibacterial activities, as single and combination treatments, against 15 spoilage bacteria isolated from vegetables, using the agar disc diffusion and broth dilution methods. Carvacrol, thymol, and eugenol showed strong inhibitory effects compared to those of the other antimicrobial substances, and their average minimum inhibitory concentration (MIC) values against 15 spoilage bacteria were 167, 648, and 168 μg/ml, respectively. When they were combined, four kinds (carvacrol + thymol, carvacrol + eugenol, thymol + eugenol, and carvarol + thymol + eugenol) of the combination formulas showed higher antibacterial effect than others against spoilage bacteria, with average MIC values of 47, 43, 59, and 42 μg/ml, respectively. However, two combinations (carvacrol + thymol, and carvacrol + thymol + eugenol) showed the strongest inhibitory effects against bacteria in fresh vegetables among all treatments. These results could be used for the development of new sanitation or preservation methods to improve freshness and to extend the shelf-life of fresh produce.
