Suphachai Nuanualsuwan has completed his Doctor of Veterinary Medicine from Chulalongkorn University. He has pursued his Master of Preventive Veterinary Medicine and PhD in Doctor of Philosophy in Food Science and Technology from University of California, USA. He is working as a Lecturer of Microbial Food Safety and Quantitative Risk Assessment at Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
Staphylococcus aureus (S. aureus) is Gram positive, facultative anaerobic, coccal bacterium that can be found on respiratory tract and skin of human as a normal flora and occasionally as an opportunistic pathogen. This bacterium causes foodborne disease. S. aureus is considered as world top three foodborne illnesses. S. aureus can proliferate in various types of food including milk, cheese, raw meat, cooked meat and pork. It can also contaminate environment during food preparation. Moreover, S. aureus can produce a variety of heat resistance Staphylococcal Enterotoxins (SE) e.g. SEA, SEB, SEC, SED and SEE. These enterotoxins remain in food after cooking process and attributable to typical foodborne intoxication symptoms such as abdominal pain, diarrhea and mainly vomiting. Although the foodborne illness symptoms are self-limited within 24 hours, their impacts range from economy, international trade to the reliability of exporting country. The objectives of this study were to evaluate the risk estimates upon consuming pork contaminated with S. aureus. Pork samples were obtained from 17 local markets across 6 Bangkok areas. All samples were stored on ice during the transportation to the laboratory. The pork samples were chopped and weighed 25 grams/sample. Pork samples were mixed with Buffered Peptone Water (BPW) 225 ml. Ten-fold serial dilution was performed three times with BPW. Then pipetting 0.1 ml of the suspension was spread onto Baird Parker agar supplemented with 10% egg yolk and 1% potassium tellurite. The plates were incubated in 37 oC for 48 hours. Selecting up to 5 colonies with metallic sheen was transferred to Mannitol salt agar and incubated at 37 oC for 24 hours. The positive isolates on blood agar were indicated by beta hemolysis. The characteristic colonies were tested for catalase and coagulase activity with 3% hydrogen peroxide and rabbit serum, respectively. The prevalence and concentration of S. aureus were used for the Quantitative Microbial Risk Assessment (QMRA) consisting of 4 steps; hazard identification, exposure assessment, hazard characterization and risk characterization. Probability of exposure (PE) was calculated from Prevalence (P), Concentration (C) and pork consumption (M) as 1-e-CM. Probability of illness (PI) is calculated by dose-response model of S. aureus as 1-e-0.0000000764D. Risk characterization was integration of PE and PI. Monte Carlo simulation used simulación 4.0 software (José Ricardo Varela) for 20,000 iterations. Among total 378 pork samples, prevalence and mean concentration of S. aureus was 5.6×104 cfu/g. After simulated, PE and PI were 0.46 and 8.9×10-6, respectively. The risk estimation, product of PI and PE, was 4.12×10-6.
Thakiuku Richard Mutegi has completed his Bachelor’s degree in Food Science from University of Eldoret, Kenya. He has two years of working experience as Food Scientist under Ministry of Agriculture, Kenya. He is pursuing his Master’s degree in Food Safety and Quality Management at Khon Kaen University, Faculty of Technology.
Currently, marinated pork meats have become an imperative part of human diet. However, they are highly susceptible to microbial contamination, resulting to food safety risk and economic loss. This study was conducted to determine the antimicrobial effects of three commercial probiotic strains: Lactobacillus curvatus (TISTR 938), Lactobacillus sakei (TISTR 890) and Lactobacillus delbrueckii (TISTR 892) at concentrations of 8 logCFU/ml in comparison to nisin to extend shelf-life of marinated pork meat stored for 10 days at 4 ºC. Probiotic culture presenting strong antimicrobial performance on spoilage bacteria was used in subsequent part of study to inhibit L. monocytogenes and E. coli 0157:H7 pathogens at 4 logCFU/ml. The spoilage and pathogenic populations in the meat samples were determined on storage days 0, 3, 6 and 10. Obtained results revealed that L. sakei and nisin suppressed mesophilic and psychrotrophic microbes significantly (P>0.05) by 1.5 logCFU/g than control. L. sakei survived significantly higher than L. curvatus and L. delbrueckii at average of 6.2, 5.7 and 5.5 logCFU/g. No significant differences were detected on pH, color and aW parameters among the treatments and control. Nisin and L. sakei inhibited L. monocytogenes and E. coli 0157:H7 significantly by 2 and 1.2 logCFU/g. The results of the study indicated that addition of L. sakei probiotic culture in marinated pork meat may be an important intervention to extend shelf life and as protective culture to reduce the level of L. monocytogenes and to inhibit proliferation of E. coli 0157:H7. Further research on sensory evaluation is recommended on this study.