INJURY AND SURVIVAL OF AEROMONAS HYDROPHILA 7965 AND YERSINIA ENTEROCOLITICA 9610 FROM HIGH HYDROSTATIC PRESSURE

Responses of Aeromonas hydrophila 7965 and Yersinia enterocolitica 9610 to high hydrostatic pressure were investigated in microbiological media and meat. Cultures were pressurized from 51 to 304 megaPascals (MPa) for 15 min in 200 mM sodium phosphate buffer (pH 7.0), tryptic soy broth and radiation-sterilized ground pork. Trends in pressure response were similar in all three pressure menstrua. A 7-log₁₀ CFU/g reduction of A. hydrophila in pork resulted from treatment of 253 MPa for 15 min. A 7-log₁₀ CFU/g reduction of Y. enterocolitica in pork resulted from treatment of 304 MPa for 15 min. Pressure-induced injury of both pathogens was detected in all pressure menstrua at most pressure levels. No growth of either pathogen occurred in irradiated pork after pressurization of 128–203 MPa for 15 min and storage at 4C for 14 days; however, an upshift to 30C of cold-stored A. hydrophila in pork resulted in growth after a lag time of approximately 10 h, and an upshift to 30C of cold-stored Y. enterocolitica in pork resulted in recovery of injured cells within 2 h, and growth after a lag time of 4–6 h. This suggests that temperature abuse (30C) of pressure-processed pork for greater than 6 h would allow growth and possibly repair of A. hydrophila and Y. enterocolitica which survive following pressure treatment. Although neither the processor nor the consumer would likely abuse the product to such an extent, the results suggest that A. hydrophila and Y. enterocolitica have the ability to repair or grow following pressure treatment in pork.     

TOXICOLOGY AND HISTOPATHOLOGY OF THE HEAT-STABLE ENTEROTOXIN OF YERSINIA ENTEROCOLITICA IN INFANT AND ADULT MICE

Yersinia enterocolitica heat-stable enterotoxin (YST) was partially purified by ion exchange, gel filtration and Fast Protein Liquid chromatography. Infant mice given YST orally (p.o.) exhibited diarrhea 4 h after administration; a few infants died by 6.5 h. Pups dosed intraperitoneally (i.p.) and adults dosed p.o., i.p. and intravenously showed no symptoms during the 7 days of observations. Tissues of adult mice orally challenged with YST showed no pathological changes by light microscopy. Livers of infant mice orally dosed with YST showed evidence of severe glycogen depletion. The intestinal tracts of YST-dosed (p.o.) infant mice exhibited severe pathological changes including: epithelial cell and villous tip necrosis, villous edema, and capillary and lacteal engorgement. Kidneys of YST-dosed (p.o.) infant mice exhibited devacuolization of the proximal convoluted tubule cells which indicates metabolic inactivity and a probable decrease in the resorption of glomerular filtrate (protein, carbohydrate, electrolytes and water).     

EFFECT OF PACKAGING METHODS ON THE DEVELOPMENT OF YERSINIA ENTEROCOLITICA ON BEEF STEAKS

Top and bottom round steaks inoculated with Yersinia enterocolitica were stored vacuum packaged and in polyvinyl chloride (PVC) films at 1, 2.5 and 5°C for 21–35 days. Y. enterocolitica and total aerobic plate counts of steaks were consistently higher in the more oxygen permeable film (PVC) than in the vacuum packages. The microbial flora of the vacuum packaged steaks at the end of the storage period (21–35 days) consisted, in addition to Y. enterocolitica, primarily of Lactobacillus spp., that of the steaks stored in PVC of Pseudomonas spp.     

葡萄及葡萄酒中的有机酸及降酸研究

为了探索降低葡萄酒中过量有机酸的有效方法,综述了葡萄和葡萄酒中有机酸的形成及变化,较系统地论述了国内外葡萄酒降酸研究的进展,着重介绍了本研究室以粟酒裂殖酵母与葡萄酒酵母为亲株,采用原生质体融合技术进行生物降酸的研究。     

LACK OF CORRELATION BETWEEN PLASMID-ASSOCIATED PHENOTYPES OF YERSINIA ENTEROCOLITICA AND PATHOGENICITY IN THE MOUSE1

Various phenotypic characteristics have been correlated with the pathogenicity of plasmid-bearing virulent strains of Yersinia enterocolitica. Two transposon Tn801-insertion derivatives (JD193 and JD217) of the virulence plasmid from serotype 0:3 were used to determine the correlation between pathogenicity and plasmid-associated properties of this organism. Both Tn801-inserted derivatives expressed five plasmid-associated phenotypic characteristics at 37C: (1) colony morphology, (2) calcium-dependent growth or low-calcium response, (3) crystal violet binding, (4) autoagglutination, and (5) hydrophobicity. However, for mouse pathogenicity only JD193 was positive whereas, JD217 was avirulent for mice. Thus, it is possible to have a lack of correlation between plasmid-mediated traits and the actual pathogenicity of the organism in the mouse; however, these plasmid-mediated phenotypic characteristics provide simple and efficient techniques to evaluate the virulence potential of wild-type strains isolated from food poisoning outbreaks and clinical cases.     

THERMAL RESISTANCE OF YERSINIA ENTEROCOLITICA AND LISTERIA MONOCYTOGENES IN MEAT AND POTATO SUBSTRATES

The heat resistance of a wild type and nalidixic acid resistant strain of Yersinia enterocolitica, and Listeria monocytogenes, was measured in meat (minced beef and minced beef homogenate) and potato substrates over the temperature range 50–60C. Comparisons of heat resistance were determined using D-values calculated using a linear survival model. The results showed that the wild-type strain of Y. enterocolitica was more heat resistant than the mutant (p<0.05). Under most conditions, the use of a nonselective/overlay recovery medium resulted in higher D-values compared to a selective recovery medium (p<0.05). Analysis of the data using a nonlinear survival model (D₁ and D₂ -values) suggested the presence of heat resistant subpopulations and was particularly evident for the mutant strain, and in potatoes compared to minced beef.     

酸乳中有机酸检测方法的研究进展

有机酸是酸乳中的重要指标.对有机酸的研究,不仅可以了解发酵的代谢背景,调控有机酸的产生,同时也对评价酸乳的营养价值、口感风味和研究其生理功能有重要作用.简要介绍酸乳中有机酸分离与定量的毛细管电泳法、离子色谱法、气相色谱法以及高效液相色谱法的步骤及其优缺点.     

原料乳中嗜冷菌的分离鉴定及Nisin,EDTA对其抑制作用

嗜冷菌是引起低温食品多种致害的主要原因之一.选用LA培养基从低温贮藏原料乳中分离出14株具有典型特性的嗜冷菌,并时的嗜冷菌进行了分离鉴定.通过形态学及生理生化特性的研究,对筛选的14株嗜冷菌进行了鉴定.一共得到9种嗜冷菌的菌种,分别是:气单胞菌属(Aeromonas)3株、黄杆菌属(Flavobacterium)1株、巴斯德氏菌属(Pasteurella)2株、节杆菌属(Arthrobacter)3株、短杆菌属(Brevibacterium)1株、片球菌属(Pediococcus)1株、乳球菌属(Lactococcus)1株,明串珠菌属(Trichococcus)1株,微球菌属(Micrococcus)1株.同时研究了不同浓度的Nisin,EDTA协同对牛乳中嗜冷菌的抑制作用,结果表明在牛乳中加入40ms/ks～100mg/kg的Nisin和等量的EDTA,对嗜冷菌有较好的抑制作用.     

果品中有机酸提取方法比较研究

以新疆地产四种特色果品为试验材料，采用蒸馏水水浴、蒸馏水超声、80％乙醇匀浆、80％乙醇超声等分别提取有机酸，并通过反相高效液相色谱法同时测定。结果表明，不同的提取溶剂和提取工艺对4种干鲜果品中各种有机酸的提取效果有一定影响，其提取的种类和含量有一些差异。综合考虑试验步骤和结果等各方面因素发现，80％乙醇匀浆提取方法既能有效保证有机酸的提取种类和提取数量，又能大大简化试验步骤。     

THE CONTENT OF SOME ORGANIC ACIDS IN BEER AND OTHER FERMENTED MEDIA

The acid content of a range of ales and lagers has been measured for some organic acids related to the Krebs cycle, and found to vary widely. Acetate, pyruvate, lactate, succinate, pyroglutamate, malate and citrate were present in all cases and α-ketoglutarate was usually detected. α-Hydroxyglutarate was recognized in a number of beers. The effect of the acids on the pH of beer is assessed. The strain of yeast which is used markedly influences the levels of all acids except pyroglutamate and the conditions of yeast propagation have a substantial influence on the extent of acid accumulation. During the fermentation of wort and synthetic media the extent of organic acid excretion is proportional to the extent of fermentation, but the nature of the acids which are excreted varies during the fermentation period. In synthetic media, nitrogen source is shown to have a substantial effect on the accumulation of organic acid. Pyruvate and acetate levels vary inversely towards the end of fermentation, suggesting that yeast converts pyruvate to acetate.     

EFFECT OF ATTACHMENT TIME FOLLOWED BY CHLORINE WASHING ON THE SURVIVAL OF INOCULATED LISTERIA MONOCYTOGENES ON TOMATOES AND SPINACH

ABSTRACT

The effect of attachment time (30 min, 24, 48 and 72 h) followed by chlorine washing (200 ppm) on the survival of inoculated Listeria monocytogenes on the surface and subsurface of tomatoes and spinach were studied. The work was done to determine the efficacy of chlorine to decontaminate surface and subsurface pathogens that may have come into contact with produce during preharvest. Tomatoes and spinach leaves were inoculated with a 6 log cfu/mL 18 h culture of L. monocytogenes ATCC 7644 (LM) on the surface and subsurface and incubated at 20C for either, 30 min, 24, 48 or 72 h. LM attached and survived on the surface and subsurface structures of both control and chlorine‐washed vegetables after each attachment time, up to 72 h. Higher levels of LM attachment and survival was however noticed on the subsurface structures. Chlorine had a greater effect on the LM on the surface structures compared to those in the subsurface structures, possibly because chlorine was not able to access the subsurface structures where the pathogens were located. Chlorine was not effective in totally inactivating the surface LM on spinach and tomato. This research indicated that LM could attach to both surface and subsurface structures of both tomatoes and spinach within 30 min and that even after 72 h, it still remained viable.

PRACTICAL APPLICATIONS

This study will inform the produce industry on the ability of L. monocytogenes ATCC 7644 to attach and grow on the surface and subsurface structures of tomato and spinach during post harvest. More attention should be given to this phenomenon because the use of fresh or minimally processed fruits and vegetables are recommended as part of a healthy diet. It also indicates that minimal processors should avoid using vegetables with wounds since L. monocytogenes attached more to the subsurfaces structures of the produce. Moreover, the use of sanitizers such as chlorine is less effective under these conditions. It has also brought to light the inability of chlorine to effectively decontaminate pathogens making it imperative for the produce industry to implement Hazard Analysis Critical Control Point, Good Agricultural Practice and Good Hygiene Practice.     

GROWTH OF LISTERIA MONOCYTOGENES, AEROMONAS HYDROPHILA AND YERSINIA ENTEROCOLITICA ON COOKED MUSSEL TISSUE UNDER REFRIGERATION AND MILD TEMPERATURE ABUSE

Strains of the psychrotrophic bacteria Listeria monocytogenes, Aeromonas hydrophila and Yersinia enterocolitica were inoculated onto samples of cooked mussel tissue and incubated at 5 and 10C under both aerobic and anaerobic conditions. These organisms were enumerated over a time course and data were analyzed to give values for the lag and generation times. All species grew under all conditions, and the rate of growth was similar under aerobic and anaerobic incubation. Predicted growth kinetic values from response surface models and measured growth rates for L. monocytogenes and A. hydrophila were in reasonable agreement, but similar comparisons for Y. enterocolitica gave shorter predicted lag and generation times than were measured. A combination of models from different sources would have given more accurate predictions than any one individual model.     

GROWTH OF STAPHYLOCOCCUS AUREUS S-6 AND YERSINIA ENTEROCOLITICA CDC A2635 IN COW, SOY AND WINGED BEAN MILKS

The two common foodborne pathogens, Staphylococcus aureus S-6 and Yersinia enterocolitica CDC A2635 were inoculated into whole cow, soy and winged bean milks and incubated at three different temperatures (10°, 25°, 37°C) to evaluate the potential for their growth. The legume milks were prepared by a hot grind method from either whole soybeans (Essex variety) or whole winged beans (Chimbu variety). In general, both foodborne pathogens grew well in all test media. However, S. aureus incubated at 10°C for 120 h, and Y. enterocolitica incubated at 37°C for 48 h were the only two conditions in which less than 10⁸ cells/mL were obtained.     

红提葡萄中有机酸成分的GC-MS分析

为研究葡萄中的有机酸成分，将葡萄有机酸提取、酯化后，采用GC—MS分析葡萄中的有机酸，研究表明，葡萄中含有17种有机酸，其中多元酸7种，饱和脂肪酸5种，不饱和脂肪酸4种，此外，还包括1种氧代有机酸。     

INFLUENCE OF WASHING TREATMENT ON NATIVE MICROFLORA AND ESCHERICHIA COLI POPULATION OF INOCULATED CANTALOUPES

The influence of chlorine or hydrogen peroxide treatment on populations of Escherichia coli 25922 on the external surface of inoculated cantaloupe was investigated. Surface treatment with 70% EtOH, followed by immersion in 10⁸ CFU/mL E. coli inoculum deposited an average of 4.4 log₁₀CFU/cm² cell population on the cantaloupe surface. The efficncy of washing inoculated cantaloupe was dependent on storage interval between inoculation and treatment. Dipping the cantaloupes in solutions containing 1000 mg/L chlorine or 5% peroxide for 5 min, within 24 h of inoculation, caused a 2 log₁₀ CFU/cm² reduction of the indigenous surface microflora and a 3–4.0 log₁₀ CFU/cm² reduction in E. coli. The efficacy was less when the interval between inoculation and treatment exceeded 24 h. Chlorine appeared in be a better antimicrobial agent than hydrogen peroxide against F. coli ATCC 25922 inoculated on cantaloupe surfaces while hydrogen peroxide was better in reducing surface microflora of cantaloupe.