In March 1999, food poisoning from the ingestion of dried squid contaminated with S. Oranienburg and S. Chester spread throughout Japan. To determine the causes leading to the outbreak of S. Oranienburg and S. Chester infections in Ehime prefecture, we screened Salmonella germs isolated for S. Oranienburg and S. Chester from seven hospitals and one clinical laboratory in Ehime prefecture between November 1998 and May 1999. Since June 1999, 18 strains of S. Oranienburg and 6 strains of S. Chester have been isolated in stool specimens from patients with diarrhea, mostly aged 12 years or younger. These strains were also isolated from blood and urine samples. Isolates from patients and dried squid samples were compared by pulsed-field gel electrophoresis (PFGE) and other epidemiological markers. Biochemical characterization data, drug susceptibility and PFGE patterns of the isolates from the patients and the dried squid samples matched closely. The results of epidemiological and bacteriological studies suggest that the diffuse outbreak of S. Oranienburg and S. Chester infections in Ehime prefecture were caused by the ingestion of contaminated dried squid.
A rapid and readily-available DNA probe kit “KAKUSAN Test Staphylococcus aureus” was developed for the detection of Staphylococcus aureus. This kit utilized the colorimetric DNA/rRNA sandwich hybridization method in microplate wells. In this paper, we evaluated and compared this kit with conventional culture methods. The detection limits of the kits were 7.0×105 cfu/ml in pure culture and 3.2×106cfu/ml in 10% homogenate of commercial foods. The detectability of the kit for 10% homogenate which was sterilized by heating or stored frozen after heating was equal to untreated 10% homogenate. The ECDP method combined enriched culture with assay by the DNA probe kit. The examination period was shorter than the enriched culture method by two days, but the detectability of these methods were equal. A total of 273 naturally contaminated samples (commercial lunches, frozen foods and other foods) were tested by direct plate culture method, enriched culture method and the ECDP method. Of these 52 were positive by the ECDP method and enriched culture method. The method agreement rate of the ECDP method and enriched culture method was 100%. All 273 were negative by direct plate culture method. Those results show that the DNA probe kit and the ECDP method are useful tool to examine various foods for contamination by S. aureus.
The Shigatoxin genes and toxin production of 498 clinically pathogenic Escherichia coli were studied by polymerase-chain reaction (PCR) and reverse passive latex agglutination (RPLA). Of these isolates tested, 39 isolates were positive in both PCR and RPLA, 459 isolates were negative in PCR and RPLA. Moreover, feces from 521 diarrheal patients and 765 food handlers, which were collected between July of 1999 and July 2000, were tested for detection of Shigatoxin-producing Escherichia coli (STEC). Although STEC was not isolated from any of the feces by direct plating method, the Shigatoxin gene was detected in 3 (0.6%) and 2 (0.3%) of the fecal specimens from patients with diarrhea and food handler, respectively by the PCR after enrichment culture of the feces. However, STEC was not isolated from these PCR positive fecal specimens.
In our laboratory, a simple method is used for adding agar to thioglycolate medium (Eiken) as a culture medium for the detection of the Clostridium and the spore number assay. However, the method appears to be inconsistent, resulting in inaccurate spore counts. The clostridia assay (the official method) and a substitution method are described in the manual, “Microorganism Test Methods in Food” (K. MISE and F. INOUE, ed.). In the official method, the anaerobic pouch is impractical for examining a lot of tested samples at one time. In the substitution method, it is necessary to add 15 ml of culture medium after pouring 10ml of well emulsified sample solution in petri dish. In this method, however, there is a hazard that the culture media will rapidly cool and partially solidify before mixing. Therefore, we changed the mixing ratio of the sample solution and the culture media in the official method, and examined the effectiveness of this modified method . We found that this modified method gave satisfactory results, and report our results herein.