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1.
The growth and toxin production of Clostridium botulinum type E in various types of vacuum packed fish products was tested, with particular reference to the time/temperature relationship of storage. Toxin production was most rapid in herring although smoking retarded its development. With as small an inoculum as 102 spores/pack, fresh herring became toxic after storage for 15 days at 5°. Irradiation of three species of fish after inoculation with Cl. botulinum type E showed that spores surviving radiation germinated and produced toxin more rapidly than an equivalent concentration of spores in nonirradiated fish.  相似文献   

2.
ABSTRACT. Various doses of a microsporan parasite, Nosema sp., were fed to third and fourth instar larvae of Lesioderma sericorne that infested different types of stored grains. A spore dose of 3 × 103 spores/individual resulted in a 39% infection rate, reduction in larval and adult weights, and mean spore concentrations of 1.28 ± 0.2 × 108 spores/larva and 1.1 ± 0.2 × 108 spores/adult. At the above dose, mortality was not well marked (about 35% in larvae and 25% in adults). At 3 × 104 spores/individual, the rate of mortality increases to 80% in larvae and 60% in adults. However, more of the pest population (88% of larvae and 73% of adults) died at a dose of 3 × 105 spores/individual. This dose produced mean spore concentrations of 3.91 ± 0.2 × 108 spores/larva and 2.89 ± 0.2 × 108 spores/adult. Insect death was caused by heavy damage to gut epithelia and fat bodies.  相似文献   

3.
Inactivation of spores of Bacillus subtilis (ATCC 6633) on two different grades of cellulose filter paper (Whatman Grades 2 and 6), by ultraviolet light (u.v.), at an intensity of approximately 4·5 Wm−2 and at fluences of up to 2 × 103 Jm−2, and u.v. in the presence of hydrogen peroxide, is described in terms of multi-target and single hit–single target kinetic expressions. Wet spores were inactivated at rates ranging from 6·7 to 10·6 higher than that of dry spores on both grades of filter paper. In addition, spore inactivation was up to 5·6 times more rapid on Grade 2 filter paper. Synergistic inactivation was seen to occur when spores were irradiated in the presence of 1% (w/v) hydrogen peroxide with rates up to 5·3 times higher than with treatment solely by u.v. The results obtained are discussed in general terms with particular reference to surface characteristics which might provide shielding to micro-organisms from incident u.v. light.  相似文献   

4.
Abstract An examination of samples obtained from a commercial fish smoker, using seawater agar with incubation at 4°, 15° and 37°C for up to 28 days, revealed the presence of large bacterial populations in smoked fish. However, initially only low bacterial numbers, i.e., 2 × 103/g, were present in the muscle of fresh, whole haddock ( Melanogrammus aeglefinus ). With filleting, there was a sudden increase in numbers to 9.2 × 105/g. Yet immediately after smoking, the bacterial populations decreased (5 × 105/g), followed by a gradual increase with storage (e.g., 2 × 106/g after 24 h). Representative colonies were presumptively identified as Acinetobacter, Alcaligenes , coryneforms, Pseudomonas and Vibrio spp.  相似文献   

5.
SUMMARY: Experiments are described in which minced chicken meat, packed anaerobically, was irradiated at room temperature and in the frozen state with a wide range of doses of 4 MeV cathode rays. Sterility was achieved in 14 out of 15 samples which had received 2 × 106 rads or more. Doses of 0·5 and 1·0 × 106 rads allowed survival of a few bacteria/g, usually spore formers. Bacterial counts indicated an approximately logarithmic decrease in numbers at lower doses, while freezing reduced the bactericidal effect.
The storage life at 5° was prolonged only slightly by doses of 5 × 104 and 10 × 104 rads, and highly variable results were obtained with 17·5 × 104 rads. A dose of 25 × 104 rads, however, increased the storage life very considerably. The types of bacteria present initially, and after irradiation with low doses and storage at 5°, were studied. After storage for 12 days or more various types of nonsporing Gram-positive rods were predominant in almost all samples, both control and irradiated. Streptococci were also important where irradiation with 17·5 × 104 and 25 × 104 rads was followed by long storage.  相似文献   

6.
The heat treatment necessary to inactivate spores of non-proteolytic Clostridium botulinum in refrigerated, processed foods may be influenced by the occurrence of lysozyme in these foods. Spores of six strains of non-proteolytic Cl. botulinum were inoculated into tubes of an anaerobic meat medium, to give 106 spores per tube. Hen egg white lysozyme (0–50 μg ml-1) was added, and the tubes were given a heat treatment equivalent to 19·8 min at 90°C, cooled, and incubated at 8°, 12°, 16° and 25°C for up to 93 d. In the absence of added lysozyme, neither growth nor toxin formation were observed. A 6–D inactivation was therefore achieved. In tubes to which lysozyme (5–50 μg ml-1) had been added prior to heating, growth and toxin formation were observed. With lysozyme added at 50 μg ml-1, growth was first observed after 68 d at 8°C, 31 d at 12°C, 24 d at 16°C, and 9 d at 25°C. Thus, in these circumstances, a heat treatment equivalent to 19·8 min at 90°C was not sufficient, on its own, to give a 6–D inactivation. A combination of the heat treatment, maintenance at less than 12°C, and a shelf-life not more than 4 weeks reduced the risk of growth of non-proteolytic Cl. botulinum by a factor of 106.  相似文献   

7.
Larval haddock and cod spawned on northeastern Georges Bank during spring have continuous recruitment to the shoal central part of the bank (< 55 m) as they develop and are advected along the southern flank in a sheared flow field. Larval age distribution data from an intensive grid of sampling stations across the flank in spring of 1981 and 1983 show a consistent cross-shelf age gradient, with older larvae found nearer the shoals. The estimated average shoalward movement of larvae is 0.65 cm s−1, which is consistent with both estimated dispersion rates and observed and predicted near bottom cross-isobath currents of < 1-2 cm s−1. The retention of larvae on the shoals of Georges Bank appears to be enhanced by their residing nearer to the bottom in waters shallower than 70 m, but the degree to which their swimming behaviour interacts with currents remains uncertain.  相似文献   

8.
Spores of psychrotrophic (able to grow at 5°C) aerobic sporeformers occurred in soil in high numbers (2 × 103-5 × 106/g), whereas psychrophilic (able to grow at 0°C) spores were present at significantly lower levels (500–105/g). Psychrotrophic spores were absent in herbs and spices: in pasteurized meals prepared industrially their numbers varied from <10 to 1000/g. For spores harvested from Trypticase Soy Agar (TSA), the heat resistance of the cold-tolerant sporeformers was low with D 90°C-values from 1–11 min. The recovery of heated psychrophilic spores on this medium at 5°C was equal to their recovery at 20°C. However, the recovery of heated psychrotrophic spores was lower at 5°C than at 20°C, whereas unheated spores gave the same counts at both temperatures. The heat resistance of naturally occurring spores of cold-tolerant sporeformers washed from soil was comparable with the resistance of spores formed on TSA.  相似文献   

9.
SUMMARY: Sodium benzylpenicillin, contaminated with Bacillus subtilis spores by freeze-drying a suspension of spores in an aqueous penicillin solution ( c . 50% w/v), was exposed to gamma radiation and a 70-tube dilution method was used to determine the surviving spores after various doses. The correlation coefficient between log10 percentage survival and dose was −0.9523. The regression of the former on the latter was calculated and the decimal reduction dose found to be 20.2 × 104 rads. The regression and the decimal reduction dose were similar to those obtained when suspensions of spores in distilled water were irradiated.  相似文献   

10.
Abstract— 45Ca2+ uptake by cerebral cortex synaptosomes was determined by gel filtration, glass fibre disc filtration under suction and by centrifugation with EGTA present. The filtration methods gave comparable results which were higher than values obtained by the centrifugation method. Uptake was increased by 25mM-K+ at all times investigated. The accumulated 45Ca2+ was bound within the synaptosome. 45Ca2+-ionophore A23187 stimulated uptake only during the first min; levels of intra-synaptosomal 45Ca2+ then returned to control values. A23187 also increased intra-synaptosomal Na+ and Cl contents. Botulinum toxin inhibits the K.+-stimulated release of [14C]ACh from synaptosomes but the ionophore released [14C]ACh from both normal and botulinum-treated preparations in a Ca2+-dependent manner. However, it also elicited Ca2+-dependent release of [choline. Increased extracellular Ca2+ (10 mM and 20 mM) released [14C]ACh (but not [14C]choline) from both normal and botulinum-treated synaptosomes. It is concluded that botulinum toxin interferes with the provision of Ca2+ essential for the mechanism of ACh release.  相似文献   

11.
ABSTRACT. Spores of Nosema bombycis Y9101, isolated from the beet armyworm, Spodoptera exigua , were primed with an alkaline solution and inoculated into Antheraea eucalypti cell cultures. Infected cells were subcultured every five days at three cell densities (2.5 × 103, 5.0 × 103, and 1.0 × 104 cells/cm2). A difference was observed in the spread of N. bombycis Y9101 infection between low-density and higher-density cultures of host cells. The host cell density did not affect the productivity of secondary infective forms of the parasite. The principal factor determining the rate of microsporidian infection in vitro was the number of host cells existing within the reach of extruded short-coiled polar tubes from spores germinated intracellularly.  相似文献   

12.
The number of aerobic bacteria in a blanket peat decreased with depth from 26 times 106/g dry peat in the surface layers to 0.5 times 106/g dry peat at 30–40 cm down the profile, thereafter remaining roughly constant. Obligate psychrophiles comprised <2.5% of this population. Anaerobes were most numerous, 9 times 106/g dry peat at 6–10 cm depth, decreasing to 0.5 times 106/g at 20–30 cm. Calculations indicated that these counts, 103–104-fold lower than the direct counts, substantially underestimated the active microbial population. Gram negative rods, the predominant aerobes in the surface layers, were replaced by unidentified Bacillus strains at 10–20 cm depth but became increasingly more numerous further down the profile. The Gram negative rods were the most numerous organisms/m2 but the Bacillus strains, one third of which were present as spores, made the largest contribution to the biomass/m2. Gram positive cocci, Arthrobacter and, infrequently, Nocardia were also isolated. Actinomyces -like forms were the predominant obligate anaerobes and were approximately three times more numerous than clostridia and a curved Gram negative rod.  相似文献   

13.
One laboratory and three greenhouse experiments were conducted to study the pathogenicity and efficacy of Finnish isolates of entomopathogenic hyphemycetous fungi against cabbage root flies. In Petri dishes, exposure to 1.5 × 1010 spores of Metarhizium anisopliae per dish caused 40–50% mortality of undifferentiated second- and third-stage larvae of Delia floralis , and 1 × 107 spores per dish caused 40–50% mortality of Delia radicum larvae. In one greenhouse test, 1 × 108 and 1 × 109 spores of M. anisopliae and Paecilomyces fumosoroseus reduced the root damage of head cabbage by 20–70% compared with untreated controls, although this was not accompanied by significant reductions in the number of pupae. Only M. anisopliae consistently grew out of larvae and pupae of D. floralis during incubation that followed their recovery from the soil at the end of an experiment testing different formulations of M. anisopliae and Beauveria bassiana , but the frequency of the latent infections of the pest by M. anisopliae was not associated with reduced severity of damage to seedlings of head cabbage.  相似文献   

14.
Endurance and swimming speed were measured in mackerel, herring and saithe when they were induced by the optomotor response to swim at prolonged speeds along a 28-m circular track through still water in a 10-m diameter gantry tank. The maximum sustained swimming speed ( U ms was measured as body lengths per second ( b.l.s −1) for each species and for saithe of different size groups. Herring with U ms of 4.06 b.l.s −1 (25.3 cm, 13.5°C) were the fastest, mackerel U ms was 3.5 b.l.s 1 (33 cm, 11.7°C) and saithe (14.4°C) showed a size effect where U ms at 25 cm was 3.5 b.l.s 1 and at 50 cm 2.2 b.l.s 1. When swimming at speeds higher that U ms, all three species showed reduced endurance as speed increased. How the curved track reduces the swimming speed is discussed.  相似文献   

15.
Reproductive characteristics of the male herring in the northern Baltic Sea   总被引:1,自引:0,他引:1  
The gonad weight and gonadosomatic index of the male Baltic herring Clupea harengus membras L., were highest at the beginning of the reproductive season (April/May), the values decreasing towards the end of it (July/August) during 1988–1991. The decline could not be explained by fish size but may have been due to fish condition. A high individual variation was typical for both gonad weights and gonadosomatic indices in fish of the same size and maturity stage. The mean density of sperm cells was significantly higher in June (34·9 × 109 ml−1) than in July (19·2 × 109 ml−1, Mann-Whitney U= 17; P<0·05), the variation among the males being high in both groups. Electron microscope analysis showed a severe disruption of the mitochondrial elements in males spawning at 22°C.  相似文献   

16.
S ummary : Strains of Salmonella senftenberg isolated from Norwegian herring meal and strain 775W were exposed to gamma radiation from a 60Co source. When they were irradiated in phosphate buffered saline solution, the average D10 values for all the strains was 19·3 krad. On irradiating strains 56 and 775W in herring meal the D10 values were 192·1 and 188·5 krad, respectively, thus indicating that the suspending medium had a great effect on the radiation resistance of the organisms. Radiation doses of the order of 0·8–1·3 Mrad are recommended for the decontamination of herring meal.  相似文献   

17.
Survival and growth of Bacillus cereus in bread   总被引:1,自引:1,他引:0  
Bread doughs were artificially inoculated with spores of six Bacillus cereus strains at different inoculum levels and counts of survivors in bread determined during storage at 27·5°C. No B. cereus were isolated from the centre crumb of 400 g loaves when the dough contained less than 104 spores/g whereas with 800 g loaves survival occurred with doughs containing 5·0 times 103 spores/g. With all strains there was a period of at least 24 h before multiplication took place in the bread. The inclusion in dough of 0·2% of calcium propionate, based on flour, effectively delayed germination and subsequent multiplication of B. cereus spores. It is concluded that the risk of food poisoning due to the presence of B. cereus in bread is minimal.  相似文献   

18.
Weekly estimates of numbers of Pseudocercosporella herpotrichoides conidia on naturally infected wheat straw, made from February to July 1982, showed there were most conidia (8.1 × 106 per straw) in February and least (1.9 × 104 per straw) at the end of June. The viability of these spores remained high throughout this period, with an average of 85 % germination after 24 h.
After removal of spores produced in the field, straws were incubated at 5, 10, 15, 20 or 25°C and subsequent sporulation assessed after 3 or 5 weeks. The optimum temperature for spore production was 5°C and very few spores were produced at 25°C. There was no difference in viability between spores produced at different temperatures.
Wheat seedlings placed amongst infected straw collected and retained spores on the upper and lower surfaces of all leaf blades and on outer leaf sheaths. Both naturally dispersed spores and spores sprayed on to plants were not removed by subsequent rainfall.
When wheat seedlings were inoculated between the coleoptile and outer leaf sheath with different numbers of P. herpotrichoides spores, lesion development was most rapid in seedlings inoculated with the greatest numbers of spores. However, after incubation for 12 weeks visible lesions were present on all plants inoculated with > c. 10 spores.  相似文献   

19.
Refrigerated processed foods of extended durability rely on a mild heat treatment combined with refrigerated storage to ensure microbiological safety and quality. The principal microbiological safety risk in foods of this type is non-proteolytic Clostridium botulinum. In this article the combined effect of mild heat treatment and refrigerated storage on the time to growth and probability of growth from spores of non-proteolytic Cl. botulinum is described. Spores of non-proteolytic Cl. botulinum (two strains each of type B, E and F) were heated at 90°C for between 0 and 60 min and subsequently incubated at 5°, 10° or 30°C in PYGS broth in the presence or absence of lysozyme. The number of spores that resulted in turbidity depended on the combination of heat treatment, incubation time and incubation temperature they received. Heating at 90°C for 1 or more min ensured a 106 reduction when spores were subsequently incubated at 5°C for up to 23 weeks. Heating at 90°C for 60 min ensured a 106 reduction over 23 weeks when subsequent incubation was at 10°C in the presence of added lysozyme. The same treatment did not reduce the spore population by 106 when subsequent incubation was at 30°C.  相似文献   

20.
Aims:  Concentration of pathogens diluted in large volumes of water is necessary for their detection. An automated concentration system placed online in drinking water distribution systems would facilitate detection and mitigate the risk to public health.
Methods and Results:  A prototype concentrator based on dead-end hollow fibre ultrafiltration was used to concentrate Bacillus atrophaeus spores directly from tap water. Backflush was used to recover accumulated particulates for analysis. In field tests conducted on a water utility distribution system, 3·2 × 104–1·4 × 106 CFU ml−1 (6·1 × 106–3·0 × 108 CFU) were recovered from the filter when 2·9 × 107–1·0 × 109 CFU were spiked into the system. Per cent recovery ranged from 21% to 68% for flow volumes of 15–21 l. Tests using spore influent levels <10 CFU l−1 (spike < 1000 CFU) yielded 23–40% recovery for volumes >100 l.
Conclusions:  B. atrophaeus spores at levels <10 CFU l−1 were concentrated directly from tap water using an automated dead-end hollow-fibre ultrafiltration system.
Significance and Impact of the Study:  The prototype concentrator represents a critical step towards an autonomous system that could be installed in drinking water distribution lines or other critical water lines to facilitate monitoring. Recovered samples can be analysed using standard or rapid biosensor methods.  相似文献   

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