Kazuaki Saheki

Studies on the destruction of Salmonella in fish meals produced in the coastal areas of Japan - II. Decontamination of Salmonella from the coastal fish meals by 60Co .GAMMA. ray irradiation.

The decontamination of salmonellae from fish meal samples by irradiation which 60Coγ ray was examined. Sixteen strains of Salmonella were used. A composite fish meal sample was prepared by mixing with different coastal meals, and after radiation sterilization at a dose of 20 kGy 60Coγ ray, which was employed as the salmonella-free meal sample. D10 values of test strains determined in buffered saline were found to range from 0.08 to 0.36 kGy, and inactivation factors at a dose of 1 kGy ranged from 102.8 to 1013. D10 values of test strains determined in the salmonella-free meal sample ranged from 0.59 to 1.64 kGy, and the inactivation factors at a dose of 10 kGy were found to range from 106.1 to 1017. Interestingly the D10 values of salmonellae determined in fish meal samples were 10 times as much compared with those determined in buffered saline. From the commercial aspects of coastal fish meal production, destruction of salmonellae in fish meals by 60Coγ ray irradiation was found to be much more practical than other methods such as dry heating and ethylene oxide fumigation.

Salmonella contamination of fish meals prepared in the coastal areas of Japan.

A survey was conducted on the contamination of fish meals with Salmonella in Japan. Samples belonging to the so-called coastal fish meals were collected mostly at three fish meal factories located in Choshi, Chiba Prefecture. Samplings were conducted on once a month bases from October, 1981 to December, 1982. The results obtained can be summarized as follows: 1) Twenty six samples out of 112 were positive qualitatively, and MPN of Salmonella in 17 samples except 9 samples ranged from 2 to 170 cells/100g, 2) Total viable counts in these Salmonella posi-tive samples ranged from 1.3×103 to 1.4×108 cells/g, those of coli forms, from 0 to 6.7×105 cells/g, and those of fungi, from 0 to 2.7×105 cells/g, respectively. 3) Out of the 416 Salmonella isolates, 354 isolates were identified as 10 serovars, including S. cerro (21%), S. senftenberg (H2S negative) (15%) S. anatum (15%) and S. havana (12%) etc., however, 62 isolates were not identified. 4) It was found that the contamination of Salmonella in fish meals; mainly, occurred after the preparation, especially during and after cooling step of the production. The results mentioned above strongly indicate the necessity for promoting appropriate sanitary control in the production of coastal fish meals in Japan.

Comparative studies on the pre-enrichment media for the isolation of Salmonella in fish meal samples.

Comparative studies were carried out on the pre-enrichment media for the isolation of salmonellae from fish meal samples. In Experiment I, the following three media: buffered saline solution (BS), buffered peptone water (BPT) and Enterobacteriaceae enrichment mannitol broth (EEM) were compared with their selectivities for qualitative pre-enrichment media. In Experiment II, seven pre-enrichment media, including the directly employed selenite broth for the quantitative estimation of salmonellae were evaluated for their effectiveness, using S. typhimurium suspension and the fish meal sample inoculated with the same organism. Results obtained can be summarized as follows: In Exp. I, 39 commercial fish meal samples were examined to compare selectivities of 3 pre-enrichment media, and BS exhibited the highest positive rates being 24.9%, followed by BPT (23.0%), while the positive rates of EEM were as low as 11.1%. In Exp. II, it was found that 0.1% meat extract containing BS (BSM), 0.1% peptone water (0.1% PW) and nutrieut broth gave high recoveries, followed by a half concentration of BPT. However, BPT, EEM and the directly employed selenite broth gave rather poor recoveries as compared with the former four media. As a selective culture medium of salmonellae, Hajinas tetrathionate broth was found to give higher recoveries than the selenite broth. Based on the aforementioned results, the author wishes to propose the following procedures for the isolation and estimation of salmonellae from fish meal samples; BS will be employed as a pre-enrichment culture medium at 37°C, and for the qualitative test, Hajinas tetrathionate broth will be used as a selective enrichment medium at 43°C, in addition, for the quantitative estimation, BSM is recommended as the pre-enrichment medium.

A SELECTIVE LIQUID MEDIUM FOR DETECTION OF THE TAKIKAWA'S GROUP OF HALOPHILIC BACTERIA

It was revealed by recent investigations in our country that numerous cases of food poisoning from eating of marine products are presumed to be caused by a certain species of halophilic organisms, so-called Takikawas pathogenic halophilic bacteria. In general the causative organisms can be easily isolated from the stool of patients affected by this disease. Although the bacteria has been suspected to be of marine origin, it is very difficult to isolate them from marine products or sea water which is generally connected with causative foods. In investigating the distribution of the organisms in natural environment, use of an excellent selective medium is considered to be necessary. The authors devised, for the selective cultivation of pathogenic halophilic bacteria, a liquid medium, 5% NaCl mannitol ethyl violet broth. This medium can be prepared as follows: 5g. peptone, 3g. meat extract, 5g. mannitol, 50g. NaCl, 0.03g. bromothymol blue and 0.001g. ethyl violet are dissolved in 1, 000ml. of distilled water and the reaction of mixture is adjusted with an NaOH solution before autoclaving to pH 9.5.