The prevalence of histamine-producing bacteria was examined in 100 commercially available processed seafood products and the histamine productivity of the isolated bacteria was evaluated. Aerobic plate count of the processed seafood samples ranged from below the detection limit to 10⁸ CFU/g and mostly ranged between 10³ to 10⁵ CFU/g. Histamine-producing bacteria were detected in 44 out of the 100 samples: 24 out of the 50 dried products and 20 out of the 50 pickled products. The contamination level of histamine-producing bacteria was generally low (<10² MPN/100 g), although a wide range of processed seafood products might be contaminated. Of the 163 histamine-producing bacterial isolates, 124 were identified as Raoultella ornithinolytica, 25 were as Morganella morganii, and 6 were as Enterobacter aerogenes. R. ornithinolytica/planticola isolated in this study showed high histamine-productivity almost comparable to the notable histamine-producer M. morganii. Our findings indicate that R. ornithinolytica/planticola might be as important histamine-producing bacteria as M. morganii in Enterobacteriaceae.

In recent years, the consumption of cooked rice produced in rice cooking factory has been increasing. To clarify the risk of food poisoning associated with cooked rice, we investigated the bacterial contamination in rice cooking factories, bacterial proliferation in cooked rice during storage tests, and the growth and enterotoxin production of Staphylococcus aureus spiked into cooked rice. Cooked rice was less contaminated during production, but the viable cell count increased remarkable with the storage test at 35℃. In the S. aureus spiked tests, high growth of S. aureus was observed and a sufficient amount of enterotoxin was produced after 24 to 48 hr at 35℃ storage. It suggests that staphylococcal food poisoning can be caused by improperly contaminated or stored cooked rice. The pH adjusters added to the cooked rice were shown to be insufficient bacteriostatic activity under the conditions of storage tests and S. aureus spiked tests in this study. These results indicate that mishandling of cooked rice can lead to a major food poisoning outbreak with or without pH adjusters.

This article was withdrawn.

Exports of oysters from Japan have increased in recent years. However, the current domestic norovirus testing method for oysters prior to export has some technical challenges, mainly in terms of sensitivity. In this study, to examine the performance of testing methods expected to have higher sensitivity than the current domestic method, we compared the sensitivity of the “Standard method,” a newly developed method in Japan, and the ISO 15216 method by quantifying the norovirus genogroup I (GI) and GII. The limit of detection 95 and the limit of quantification were statistically determined using serial dilutions of oyster digestive glands artificially contaminated with norovirus according to the guidance note of the European Union reference laboratory. The ISO method was more sensitive for the detection and quantification of GII than the Standard method. No significant differences were observed between the two methods in the values obtained from quantifying norovirus GI and GII at three different concentrations. These results indicate that the ISO method is more suitable for pre-export testing in Japan.