Microbiological Quality of Ready-to-eat Foods

The objective of this study was to investigate the microbiological quality of ready-toeat food in the Municipality of Khon Kaen, Thailand. Four categories of 186 food samples were collected: 1) high heat food; 2) low heat food; 3) no heat food; and, 4) on-site prepared fruit juices and beverages. Of the food samples, 145 (78%) failed to meet acceptable microbiological standards, including fruit juice and beverages (100%), no heat food (91.7%), low heat food (81.7%) and high heat food (57.9%). The most frequent bacterial indexes indicating unacceptability were the most probable number (MPN) of coliforms (78%), the bacterial colony count (58%), and the MPN of E. coli (46%). Pathogenic bacteria were found in 6.5% of food samples. Salmonella, Vibrio cholerae non O1 and Aeromonas hydrophila were found in 4.3, 1.6 and 0.5% of the total food samples, respectively. The serovars of Salmonella found in food were S. Derby, S. Give, S. Krefield, S. Paratyphi B, S. Verchow, S. Lexington and S. Senftenberg. Staphylococcus aureus concentrations of >102 CFU/g and >105 CFU/g were found in 10.8% and 1.1% of the food samples. Enterotoxin types AB and A of S. aureus were found in 2.7% of the food samples. These results indicate that more than half of the ready-to-eat foods tested in Khon Kaen municipality did not meet microbiological national standards and many kinds of enteropathogenic bacteria were found, suggesting food stalls may be a source of foodborne disease. are reported in Thailand each year (Bureau of Epidemiology, 2004). Food is considered the main source of microorganisms causing diarrheal diseases (Rabbani and Greenough, 1999; Jay, 2000; Fang et al, 2003). Foodborne disease outbreaks from enteropathogenic bacteria, such as Salmonella, Vibrio cholerae, V. parahaemolyticus and Staphylococcus aureus, are common causes of foodborne infection throughout the world, including Thailand (Chomvarin et al, 1993; Mosupye and von Holy, 1999; Adams and Moss, 2000; Bangtrakulnonth et al, 2004; Meldrum et al, 2006). Salmonella caused diseases ranging from diarrhea to septicemia. Salmonellosis from contaminated food genSOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 984 Vol 37 No. 5 September 2006 erally causes diarrhea. V. cholerae and V. parahaemolyticus are the important Vibrio species causing watery-diarrhea and gastroenteritis (Jay, 2000; Murray, 2002; Montville and Matthews, 2005). S. aureus can also cause food poisoning even with very small amounts (100-200 ng) of its heat-stable enterotoxin (Evenson et al, 1988; Jay, 2000). Aeromonas spp are an emerging important pathogen causing diarrhea, and can be found in food and water (Kirov, 1993). Microbiological criteria are used to distinguish between acceptable and unacceptable foods. They assess: 1) the safety of food for consumers, 2) adherence to good manufacturing practices, 3) the keeping quality (shelf life) of perishable foods, and 4) the suitability of a food or ingredient for a particular purpose (Montville and Matthews, 2005). Food is considered safe for consumers if there is : 1) an absence of pathogenic microorganisms and toxins, and 2) the types and numbers of microorganisms are within acceptable ranges (Montville and Matthews, 2005). Therefore, isolation of relevant bacterial pathogens and indicator organisms is used to evaluate microbiological safety and quality of food. Microbiological standards for ready-to-eat food in Thailand are determined by the guidelines of microbiological standards in food (1993) of the Department of Medical Sciences, Ministry of Public Health, Thailand. The following bacterial colony counts have been specified as maximum acceptable levels: bacterial colony count (BCC) (≤ 106 CFU/g), MPN of coliforms (≤500 CFU/g), MPN of Escherichia coli (≤ 3 CFU/g), and S. aureus (≤102 CFU/g), and the absence of pathogenic bacteria. Ready-to-eat foods are processed (peeled, squeezed, cut up and/or cooked) and readily available for purchase and consumption. This type of food is popular among Thai consumers. However, ready-to-eat foods have been impl icated in the transmission of foodborne disease (Chomvarin et al, 1993; Gillespie et al, 2000; Fang et al, 2003). Readyto-eat foods at venders in Khon Kaen municipality were frequently left on the shelf too long, thus exposing them to bacterial contamination from the environment or food handing. S. aureus frequently causes food poisoning in Thailand, however, the types of staphylococcal enterotoxin in ready-to-eat foods have not been well studied (Chomvarin et al, 1993). Therefore, to investigate the types of staphylococcal enterotoxin and to establish the microbiological quality of ready-to-eat foods in Khon Kaen municipality, we investigated bacterial colony counts (BCC), two types of indicator organisms (ie, MPN coliform, MPN Escherichia coli), and selected foodborne pathogens, such as Salmonella, Shigella, Vibrio, and S. aureus (especially S. aureus producing enterotoxin) in ready-to-eat foods in Khon Kaen. MATERIALS AND METHODS