Eighty-eight specimens of raw hamburgers obtained at retail markets in Saitama Pref. were examined for the presence of Listeria monocytogenes and other Listeria spp. Listeria spp. were isolated from 66 (75.0%) of the specimens. Thirty-two (36.4%) specimens contained L. monocytogenes, 39 (44.3%) specimens contained L. innocua, 6 (6.8%) specimens contained L. weishimeri, and 3 (3.4%) specimens contained L. grayi. The serotypes of 32 isolated L. monocytogenes were 11 of both 1/2b and 1/2c, 4 of 1/2a, 3 of 4b and the rest were not determined. With the view of examining the bacteriological safety of raw hamburgers after cooking, 3 sizes of hamburgers (large 100 g, medium 75 g, small 50 g) innoculated with L. monocytogenes were examined for the change in central temperature during heating and viable bacterial count thereafter. Heating was done at 200°C and for 3 min (1.5 min each surface), and especially for large and medium-sized hamburgers, Heating was repeated for the same duration while covered. The change in central temperature with heating was represented by lower central temperature and greater time lag between heating duration and increase in central temperature for large size (average maximum temperature: large 69.7°C, medium 88.3°C, small 96.7°C). Viable inoculated L. monocytogenes were recognized in 2 of the 4 large hamburgers regardless of the inoculative concentration and 1 of 5 (inoculated at 103/g) and all 5 (inoculated o at 106/g) small hamburgers, compared with the medium-sized hamburgers having no viable inoculated L. monocytogenes at all. Similar tests performed 10, 10 and 5 min after the completion of heating for large, medium-sized and small hamburgers, respectively revealed no bacteriocidal effect of the remaining heat.
It was attempted to detect thermostable direct hemolysin (TDH) producing Vibrio parahaemolyticus in food by polymerase chain reaction (PCR) with VPD-1 and-2 primers (Shimadzu). This primer pair could amplify a 251-bp resion in tdh gene which encoded sequence to produce TDH. The KAP-RPLA “Seiken” (Denka Seiken) test showed that 35 (92%) of 38 strains from patients infected with V. parahaemolyticus produced TDH and 7 (100%) from food didn't. When these 45 strains were subjected to PCR, 251-bp products were demonstrated exclusively in TDH-positive strains. PCR deteced the strain producing TDH in minced prawn mixed experimentally with 103 cfu/g or more bacteria. PCR detected even fewer bacteria in prawn, if the supernatant of the enrichment culture incubation was tested. When a TDH-positive strain and more than hundred-fold negative one were inoculated together to prawn, it was recognized that the growth of positive one was inhibited by negative one during incubation. Then, PCR failed to detect the TDH-positive strain in prawn. It was indicated, however that this PCR was successfully applied to detect TDH producing V. parahaemolyticus in food incriminated for food poisoning due to these bacteria, because such food must contain a large number of pathogenic bacteria.
Anti B. thuringiensis H-sera were prepared with B. thuringiensis, Kurstaki (H-3a3b3c) and B. thuringiensis, Aizawai (H-7) which are used in the BT microbial pesiticide formulations, in addition to B. thuringiensis, Thuringiensis (H-1), B. thuringiensis, Sotto (H-4a4b) and B. thuringiensis, Israelensis (H-14). The prepared anti H-sera had relatively high specificity, and the titres of each anti H-sera ranged from 6, 400 to 12, 800. Eighty-four strains of B. thuringiensis isolated from various foodstuffs and farmland soil were identified with the 5 prepared anti H-sera. Consequently, 49 strains were identified by the anti H-sera, and included 38 of serovar H-3a3b3c, 7 of serovar H-7, 3 of serovar H-4a4b and 1 of serovar H-14. Particularly, strains presumed as serovar H-3a3b3c were frequently detected from imported corn and from native vegetables and soil. This suggested that BT formulations were applied to various crops as preharvest and/or postharvest pesticides, and that attention should be paid to the contamination of B. thuringiensis from the aspect of food hygiene.
From April, 1990 to March, 1992, a total of 107 raw meat specimens collected from slaughterhouses, supermarkets, and homes were examined for the presence of Listeria monocytogenes and other Listeria by using the modified FDA method. Listeria monocytogenes and other Listeria were isolated from chicken (34.5 and 44.8%), pork (26.7 and 33.3%) and beef (16.7 and 37.5%), respectively. The overall incidence of Listeria monocytogenes and other Listeria in the market distribution channel were 9.1% and 27.3% in the slaughterhouses, 31.5% and 22.2% in the supermarkets and 22.6% and 74.2% in the homes, respectively. Sixtyseven isolates were distributed into four species, 36 as L. innocua, 26 as L. monocytogenes, 3 as L. welshimeri and 2 as L. seeligeri. The L. monocytogenes isolates were identified as predominant serovars 1/2a, 1/2b, 1/2c and 4b (76.9%). The incidence of Listeria spp. contaminating raw meat gradually increased with longer storage. L. monocytogenes was also confirmed to be capable of growth in chicken meat at 4°C for 18 days.
A colourimetric DNA hybridization method (DNA probe method) was applied for detection of Campylobacter jejuni/coli in poultry specimens. A total of 32 specimens of chicken meats obtained at 6 retail stores (collection 1) was supplied for isolation of C. Jejuni/coli by conventional culture. The organism was isolated from 3 specimens by the direct smeared agar method (Skirrow's and Butzler's agars supplemented with the agents, Oxoid SR 69 and 85), and from 21 specimens with culture of 3 enrichment broths containing each supplement of Skirrow, Butzler, and Preston (Oxoid SR 69, 85, and 117). The surface of the direct smeared agar was covered with bacteria other than C. jejuni/coli after incubation. When the DNA probe method was applied for suspension of bacterial harvests from the agar surface, C. jejuni/coli was detected in 10 out of 32 specimens. However, the organism was not detected in any broths by the DNA probe method applied for the enrichment cultures. As a case of the specimens from which C. jejuni/coli was easy to be isolated because of low contamination with bacteria which disturb the isolation of C. Jejuni/coli, among 11 specimens from 2 stores (collection 2) and 5 specimens from 1 store (collection 3), C. jejuni/coli was isolated from the direct smeared agars of 7 and 4 specimens, and detected by the DNA probe method in 6 and 4 specimens, respectively. Furthemore, from the Preston enrichment broth, the isolation rate of the organism was 8/11 (collection 2) and 4/5 (collection 3), and the detection rate by the DNA probe method was 4/11 (collection 2) and 1/5 (collection 3). When the Preston broth including the specimens of collection 2 was inoculated with 104 colony forming units /ml of C. jejuni, the organism was detected from all the enrichment cultures by both the culture and the DNA probe metods.