Changes in growth of artificially inoculated refampicin-resistant Listeria monocytogenes in refrigerated lightly pickled cucumber induced by addition of antimicrobial food additives
2008
Ito, Y.(Tokyo-to. Agriculture and Forestry Research Center (Japan). Food Technology Research Center) | Hosoi, T. | Miyao, S.
Listeria monocytogenes is a bacterium with wide distribution in natural environments that causes contamination of various food ingredients. L. monocytogenes contamination in ready-to-eat foods such as lightly pickled vegetables creates a risk of foodborne listeriosis outbreaks. To estimate the L. monocytogenes levels in foods, Listeria-selective media such as PALCAM and MOX supplemented with specified antibiotics are usually used. However, when estimating the growth of L. monocytogenes artificially inoculated to lightly pickled cucumber using these media, the high levels of bacteria associated with the cucumbers inhibit the formation of L. monocytogenes colonies and certain bacteria other than L. monocytogenes form colonies with morphology similar to that of L. monocytogenes. In this study, we therefore established a new method to estimate the growth of L. monocytogenes in lightly pickled cucumber by artificially inoculating rifampicin-resistant L. monocytogenes and using PALCAM-Listeria-Selective-Agar-Base supplemented with rifampicin (50 micro g/ml) and 1/100 of a specified concentration of PALCAM-Listeria-Selective-Supplement. Analyses using this method showed that initial artificial inoculation levels of live L. monocytogenes were maintained during storage for 10 days at 4 deg C and for 2 days at 10 deg C, respectively. The addition of 0.05 and 0.1% chitosan significantly decreased the levels of live L. monocytogenes.
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