A xerophilic fungi (KIH CO214), isolated from a spoilage outbreak involving importedAustrian chocolate from Austria, was identified asChrysosporium farinicola(Deuteromycota).This was the first time this fungus isolated in Japan. This fungus grew well and produced large numbers of conidia on MY5OG agar (Aw0.897), and the colony formed on common media was white and powdery. The teleomorph of this fungus was not seen on 5 selected media including natural substrates. The optimal growth of this fungus was obtained at 30°C, the minimum accorded at 15°C and the maximum at nearly 37°C . The fungus could grow at a pH range of 3-9.As a result of heat inactivation treatment, the lethal thermal point for this fungus was shown as 5 min at 65°C. Thus, an inactivation temperature of more than 70°C proved to be most practical. As an inoculation test on sterilized chocolate samples which were adjusted to water activity conditions from Aw 0.901 to Aw 0.752, mycelial growth of this fungus was found on all substrates after 1month at 25°C. For a comparison, 9 xerophilic fungi were also used in the above physiological experiments.
In Hiroshima city, when medical facilities report the occurrence of a sporadic food poisoning case to the public health center, the center collects the bacterial isolate and the isolate is tested for serotype, antibiotics susceptibility and other attributes at the institute of public health to monitor trends in food poisoning. This surveillance system has noted the gradually increasing tendency toward Salmonella serogroup O7 isolates since the end of 1998 that were almost all serotyped as Salmonella Oranienburg, suggesting an epidemiological relation between these isolates. Therefore, we evaluated the availability of random amplified polymorphic DNA (RAPD) method as a molecular-epidemiological technique for comparison of them and investigated food poisoning cases by applying RAPD and other techniques, including pulsed-field gel electrophoresis (PFGE), to the isolates. Most Salmonella isolates showed the same RAPD and PFGE patterns. Consequently, the investigation by these techniques and field-epidemiological data revealed that the sporadic food poisoning cases in Hiroshima city were a diffuse outbreak due to cuttlefish chips contaminated by not only S. Oranienburg but also S. Chester. The RAPD method was a rapid and useful tool for molecular-epidemiological approach to this outbreak.
Orange mold isolated from spoiled white bread was morphologically and physiologically identified as Moniliella suaverolens. When the M. suaverolens was inoculated on white bread, and incubated at 25°C for 2 weeks, the white bread formed an orange spot during storage. The assimilation of ethanol by this isolated mold and its growth in a 2% yeast extract and 1% malt extract with 15% sucrose (15% SY) broth contaning 0.5-10% ethanol was investigated. This isolated mold assimilated ethanol and grew better in the 15% SY broth containing 0.5-2.0% ethanol than in medium without ethanol and grew even in 15% SY broth containing 10% ethanol at 25°C. The predominant strains of airborne molds detected in the white bread manufacturing process were Cladosporium, M. suaverolens, Aspergillus, Penicillium, Aureobacidium. M. suaverolens was detected in all manufacturing processes. The survival ratio of M. suaverolens was found to decrease with increasing dissolved ozone concentration ranging from 1 to 15mg/l and all mold cells (2.7×105/ml) were completely killed with ozonated water containing 15mg/l dissolved ozone at 25°C for 5 min.
Immunomagnetic separation technique was used for the isolation of Salmonella from 87 raw chicken meat specimens. Two kinds of immunomagnetic beads are available in Japan. Both of them were covered with Salmonella antibodies, but one was for O-antigens and the other was for H-antigens. In this study, two kinds of immunomagnetic beads were mixed and added to the broth for isolation testing. Findings were compared with those obtained by the single use of immunomagnetic beads and the conventional method. The mixed immunomagnetic beads isolated 15 of 17 positive samples, 13 by beads for Oantigens, 11 by conventional method, and 10 by beads for H-antigens. The isolation rate was increased by using both types of immunomagnetic beads because their targets were different. The mixed immunomagnetic beads enhanced the likelihood of isolating Salmonella.
Histamine-producing bacteria (HPB) were isolated from 21 of 36 seafood samples (58.3%) consisting mainly of scombroid fish and by products. All HPB isolates devoloped purple colonies with a purple halo on Niven's agar containing 0.1% glucose and produced 3, 090-11, 790 ppm of histamine in tuna fish infusion broth . Bacterial isolates were identified as 8 species of Morganella morganii, Klebsiella oxytoca, Pantoea spp., and Klebsiella ornithinolytica. Although 58.3% of seafood samples were contaminated by HPB, histaminelevel exceeded 50μg/g in only one sample.
It is known that vegetables can serve as vehicles of food-borne illness when they are grown from seeds contaminated with pathogens. In this study, we investigated the fate of enterohemorrhagic Escherichia coli O157: H7 in experimentally contaminated radish and komatsuna seeds, after long-term storage at 4°C. The bacteria survived for 36 weeks in radish seeds initially contaminated at 103 cfu/ml, and 20 weeks survival . observed at as low as 102 cfu/ml. On komatsuna seeds, the bacterial count decreased more rapidly . Using scanning immunoelectron microscopy, the bacteria were detected on the surface of sprouts grown from contaminated seeds, and the bacteria were also present inside the stomata . However, heat treatmentat 100°C for 5 sec effectively eliminated the bacteria from the sprouts . These results underscore the possible health risk from contaminated vegetable seeds even after long-term storage at a low temperature, and also the importance of heat treating of harvested vegetables.
Salmonella contamination of raw meat from domestic chickens in Tama, Tokyo between 1992 and 1999, investigated. Salmonella was detected in 197 (25.2%) of 783 samples, raning from 9.4% to 40.8% per year. On serological typing test, 202 strains isolated were classified into 20 serovars including a strain of untypable O7 and O8. The most predominant serovar was Salmonella serovar Infantis (S. Infantis) (45.0%), following S. Hadar (6.9%), S. Typhimurium (4.5%), S. Schwarzengrund and S. Vichow (2.0%). Especially, the increases in S. Infantis in the past 3 years is notable, accounting for 77 strains (84.6%). On drug-resistance test using 9 drugs (CP, TC, SM, KM, ABPC, ST, NA, FOM and NFLX), 90% of strains tested were resistant to some of the drugs. S. Infantis isolated was resistant to all, and the main resistance patterns were TC/SM/KM/ST (28 strains), TC/SM/KM (26 strains), and TC/SM (20 strains). Almost all strains of S. Hadar and S. Typhimurium also were resistant to 2 to 5 drugs.