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1.
We investigated the combined effects of pressure, temperature, pH, initial spore concentration and the presence of nisin on the survival of spores of Bacillus coagulans. Spores were more sensitive to pressure both at lower pH and at higher treatment temperatures. An additional 1.5-log10 reduction in cfu ml-1 was observed when pH was lowered from 7.0 to 4.0 during pressurization at 400 Mpa and 45°C. A 4-log10 cfu ml-1 reduction was observed when the temperature was increased from 25°C to 70°C during pressurization at 400 Mpa. The spores were sensitive to nisin at concentrations as low as 0.2 IU ml-1. At least a 6-log10 reduction was generally achieved with pressurization at 400 Mpa in pH 4.0 buffer at 70°C for 30 min when plated in nutrient agar containing 0.8 IU ml-1 nisin.  相似文献   

2.
The microbiological quality and heterotrophic bacterial populations of 26 thermal mineral water springs in Spain were studied. In most of the springs the number of viable aerobes was less than 103 cfu ml-1 and the number of sporulated bacteria less than 102 cfu ml-1. No significant differences were foundin the counts obtained with Plate Count Agar (PCA) and PCA diluted 1 : 10 and incubated at 22°, 37° and 45°C. Total coliforms were found in 14 springs, faecal streptococci in three, spores of sulphite-reducing Clostridium and Pseudomonas aeruginosa in seven. Neither Escherichia coli nor Staphylococcus aureus were found. A total of 665 strains were isolated and 85·4% of these identified; 329 were Gram-positive and 239 were Gram-negative. The genera most prevalent present in the springs were Pseudomonas (in 92.3%), Bacillus (65.4%), Enterobacter, Micrococcus and Staphylococcus (50%), Acinetobacter (42.3%), Arthrobacter (38.4%), Clostridium (27%) and Xanthomonas (23%). Gram-negative bacteria predominated in the mesothermal springs and Gram-positive bacteria in the hyper- and hypothermal springs. The most common Gram-negative rod species isolated were Ps. fluorescens, Ps. aeruginosa, Ps. putida, Ent. agglomerans, Ent. sakazakii, Ac. calcoaceticus and Ent. amnigenus.  相似文献   

3.
Cow's milk was inoculated with ca 103 and 107 cfu ml−1 Escherichia coli O157 : H7. After fermentation at 42°C for 0–5 h, the yoghurt was stored at 4°C. Two kinds of yoghurt were used : traditional yoghurt (TY), made with Streptococcus thermophilus and Lactobacillus bulgaricus starter cultures, and 'bifido' yoghurt (BY), made with the two starter cultures plus Bifidobacterium bifidum . After 7 d E. coli O157 : H7 decreased from 3·52 to 2·72 log10 cfu ml−1 and from 7·08 to 5·32 log10 cfu ml−1 in TY, and from 3·49 to 2·73 log10 cfu ml−1 and from 7·38 to 5·41 log10 cfu ml−1 in BY. The pH values of yoghurt dropped from 6·6 to 4·5 and 4·4 in TY (for low and high pathogen inocula, respectively), and from 6·6 to 4·6 and 4·5 in BY (for low and high pathogen inocula, respectively).  相似文献   

4.
This study examined the attachment kinetics of Yersinia enterocolitica serotype O:3 to determine the optimum conditions for its isolation from meat enrichment systems using a novel surface adhesion technique. Minced beef was inoculated with Y. enterocolitica at an initial level of 10 cfu g−1 and incubated at 25 °C in an enrichment broth. Yersinia was recovered from enriched samples on polycarbonate membranes by surface adhesion and enumerated using immunofluorescence microscopy. The surface adhesion immunofluorescence technique (SAIF) had a minimum detection limit of approximately 4·0–4·5 log10 cfu ml−1 and provided good correlation between the estimation of the numbers of Yersinia in the enrichment broth derived from plate counts on Yersinia Selective agar (CIN) and those determined by SAIF ( r 2 = 0·94; rsd = ± 0·21). A derived regression equation of the SAIF count vs plate counts was used to predict Y. enterocolitica numbers in spiked meat samples stored at 0 °C for up to 20 d. The numbers as predicted by the SAIF method showed good correlation with counts derived by plating techniques ( r 2 = 0·78; rsd = ± 0·42). The application of the SAIF technique for the rapid detection of Y. enterocolitica serotype O:3 from meat is discussed.  相似文献   

5.
Four media were tested for their ability to detect the soft rot potato pathogens Erwinia chrysanthemi (Ech) and Erwinia carotovora ssp. atroseptica (Eca) in potato tubers by means of automated conductance measurements. The specificity of the conductimetric assays was determined by testing a set of different Erwinia spp. and potato-associated saprophytes, including the genera Pseudomonas, Bacillus, Enterobacter and Flavobacterium. All bacteria tested produced conductance responses in Special Peptone Yeast Extract, whereas in minimal medium with L-asparagine only Erwinia spp. and Pseudomonas spp. were able to generate large conductance responses. In minimal medium supplemented with glucose and trimethylamine- N -oxide only Enterobacteriaceae, Erwinia spp. included, generated conductance responses, while with pectate as sole carbon source only Erwinia spp. produced distinct conductance responses. The pectate medium proved to be particularly useful for specific automated conductimetric detection of Erwinia spp. in potato peel extracts. Within 48 h, the detection threshold of the conductimetric assay for Eca varied between 102 and 103 cfu per ml peel extract at both incubation temperatures of 20° and 26°C. Ech was detected at concentrations of 104–105 or 103–104 cfu ml-1 at 20° and 26°C, respectively. To eliminate 'false'-positive reactions in conductimetry caused by Erwinia carotovora ssp. carotovora , results of the conductance measurements have to be confirmed by other techniques, like serology or DNA assays.  相似文献   

6.
Skimmed milk powders were spiked with one of three Salmonella serovars and incubated in buffered peptone water for 24 h. No false-negative results were obtained by immunomagnetic separation (IMS), compared to seven for selenite cysteine, one for Müller-Kauffmann tetrathionate and two for Rappaport-Vassiliadis enrichment broths. Salmonella virchow was detected and enumerated during the pre-enrichment incubation by IMS and indirect conductance techniques. The Salm. virchow cell number did not increase after 12 h incubation and remained at 3 times 106 cfu ml-1. IMS was able to capture Salm. virchow cells at cell numbers ca 50 ml-1 in the presence of a 1000 greater number of non-salmonella cells.  相似文献   

7.
Test protocols for detecting Pseudomonas syringae pv. pisi , the causal agent of bacterial blight, in pea seeds are generally based on dilution-plating assays. These assays are usually very specific and reliable, but are time-consuming and laborious. Tests suited for large scale screening of seed lots are therefore needed. Conductimetric assays, immunofluorescence microscopy (IF) and an enzyme-linked immunosorbent assay (ELISA) for detecting Ps. syr. pv. pisi in pea seed extracts were compared with dilution-plating by two extraction methods, viz. 6 h soaking of seeds and 2 h soaking of flour of ground pea seeds in water. In general, the detection of Ps. syr. pv. pisi with conductimetric, IF and dilution-plating assays in the suspension water of the ground and 2 h-soaked pea samples was less sensitive than detection in suspension water of the 6 h-soaked pea seeds. The detection threshold of these assays varied per seed lot between 0 and 4.08 log cfu ml-1 for the 6 h soaking procedure. The detection threshold of ELISA varied for both extraction methods generally between 4.08 and 6.08 log cfu ml-1. Detection times recorded in conductimetric assays correlated well (— 0.89 < r < —0.98) with the log colony-forming units of Ps. syr. pv. pisi added to seed extracts at 27 as well as 17°. However, confirmation of results by isolation on semi-selective media after conductimetry was more successful at 17° than at 27°, because of the relatively lower activity of saprophytic Pseudomonas spp. at this temperature.  相似文献   

8.
Sheep milk, compared with cow and goat milk, had a protective effect on Gram-negative bacteria and Listeria spp. heated at 65°C in a test-tube method. This effect was not solely due to fat content as cow milk artificially reconstituted to 10% homologous fat was not as protective. Listeria monocytogenes in whole sheep, cow and goat milks at an inoculum level of 1 times 106 cfu ml-1 was heated at 68°C for 15 s in the plate pasteurizer and survival was only detected in whole sheep milk after heating. Whole sheep, cow and goat milks containing high levels of L. monocytogenes (1 times 106 cfu ml-1) could not survive the current HTST plate pasteurization protocol.  相似文献   

9.
Extracts of black and green tea inhibited in-vitro growth of six clinical isolates of Helicobacter pylori in an agar diffusion assay. Tea extracts killed H. pylori (106 cfu ml-1) within 5 h. Heat treatment of extracts did not affect the inhibitory or bactericidal activity.  相似文献   

10.
Recovery of Rhizobium leguminosarum cells by centrifugation after growth in an industrial fermenter was 100-fold higher when cells were grown on yeast extract (5 g/1) as sole source of carbon and nitrogen when compared with the yields recovered when cells were grown in standard mannitol-yeast extract medium. Methods of storing concentrated suspensions of R. leguminosarum were investigated. Freeze-drying caused a marked decrease in viable cell numbers. Viable cell numbers of bacterial concentrates stored in peat decreased steadily from 1011-1012 cfu/g to 109 cfu/g or less during 26 weeks storage at room temperature or at 4°C. Cell concentrates stored in 40% glycerol at — 20°C maintained viable numbers higher than 1011 cfu/ml during a 76 week storage period.  相似文献   

11.
The current improvements in nucleic acid hybridization technology provide new techniques for the identification of micro-organisms. One such technique is the Gene-trak® DNA hybridization system (Framingham, MA, USA), which was introduced in 1983. The objective for this study was to evaluate the new Gene-trak® Yersinia enterocolitica kit in comparison with the API 20E and Vitek systems. A total of 101 strains including 18 reference non- Yersinia strains from the authors' stock culture collection and 83 suspected positive isolates from CIN agar were tested. Of these 83 isolates, 40 were identified as Y. enterocolitica after incubation at 37°C for 24 with the API 20E system; 37 strains were identified at 30°C for 48 h. The Gene-trak® method gave positive results with 39 strains. The Vitek system gave positive results with 27 strains.
With the Gene-trak® method, Y. enterocolitica was detectable in mixed cultures provided that the numbers of cfu ml-1 were equal to or above 106 Y. enterocolitica ml-1. Although enrichment procedures are still needed, the system provides a quick detection of these food-borne pathogens.  相似文献   

12.
Slurry storage tanks on Lancashire farms were sampled in May, June, October and November. There was a seasonal pattern in the number of thermophilic campylobacters. The average log10 MPN per gram fresh weight (log10 MPN gfw−1) in stored samples in May and June was 0·78 ( S.D. 0·71) compared to 2·07 ( S.D. 0·70) in November and December. Campylobacters were readily detected in samples of mature slurry and composted bedding that farmers were about to put to land. The survival of campylobacters in slurry sprayed on land was studied in two seasons. In June, on farm A, stored slurry was mechanically aerated for 48 h and very low numbers of campylobacters (0·9 log10 MPN gfw−1) remained in the slurry before it was sprayed onto land. They became undetectable within 24 h once sprayed on land. In contrast, campylobacters in matured but unaerated slurry that was sprayed onto land on farm B in February were still detectable in samples taken 5 d after application to land, dropping from 2·11 log10 MPN gfw−1–1·37, a decline of only 0·74 log10 MPN gfw−1 in the first 5 d after application.  相似文献   

13.
W.G. VAN DOORN AND K. D'HONT. 1994. Flowering stems of four rose cultivars (Sonia, Madelon, Jacaranda and Frisco) were placed in aqueous suspensions of bacteria at 104 and 108 colony-forming units (cfu) ml-1 for 24 h at 5C, then stored dry or held in water for 24 h at 8C and subsequently placed in vase-water at 20C. The effects of these treatments on vase-water uptake were similar to the effects on flower opening. In Sonia and Madelon roses flower opening was negatively affected both by 108 cfu ml-1 of bacteria and by dry storage. No effect was found at 104 cfu ml-1, but this concentration had a detrimental effect on flower opening when combined with dry storage. Although flower development in Jacaranda roses was not affected by the bacteria treatments it was inhibited by dry storage. This inhibition was progressively greater when the stems had previously been pulse-treated with a larger number of bacteria. Flower opening in Frisco roses was not affected by even the highest concentration of bacteria, nor by the period of dry storage. It is concluded that placing flowers in water containing bacteria (up to 108 cfu ml-1) may not always have a negative effect on flower development in cut rose flowers but, together with the effects of dry storage, the presence of even a low number of exogenous bacteria (104 cfu ml-1) inhibits the development in several cultivars. Such bacterial counts are nearly always found in samples of water used for standing roses during distribution to the consumers.  相似文献   

14.
A steam-vacuum sanitizer reduced aerobic plate counts associated with bovine faecal contamination from 5.5 log10 cfu cm−2 to 3.0 ± 0.21 log10 cfu cm−2 on beef carcass short plates. The same beef carcass short plates inoculated wiht 7.6 ± 0.09 log10 cfu cm−2 Escherichia coli O157: H7 in faeces, yielded an average residual level of E. coli O157: H7 of 2.1 ± 0.21 log10 cfu cm−2 after steam-vacuum treatments. This study demonstrates the effectiveness of a steam-vacuum sanitizer for removing E. coli O157: H7 from beef carcasses.  相似文献   

15.
Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O2 increased with temperature and decreased with body weight. However, Q O2 decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log10 Q O2 (mg O2 g−1 h−1) = 0.129 loglo salinity (%0) + 1.604 log10 temperature (°C)-0.1401og10(g)-2.767.  相似文献   

16.
The solubility of carbon dioxide (CO2) in microbiological media at different pH values, water activities ( aw ), temperatures, buffering capacities and ratios of headspace to media volumes was determined by using a coulometer. Buffering capacity and ratio of headspace to media volume were shown to be the major factors influencing the solubility of CO2 in modified atmosphere model systems. The growth inhibitory effects of different dissolved CO2 concentrations (0–50 μmol ml-1) were determined for Pseudomonas fragi at 8°C and 22 C. Pseudomonas fragi was shown to be strongly affected by the CO2 concentration in the media. A carbon dioxide concentration of 40 μmol ml-1 was needed to inhibit Ps. fragi at 8°C. The importance of measuring dissolved CO2 concentrations in modified atmosphere packaging applications was shown and the coulometer proved to be an excellent tool for this purpose.  相似文献   

17.
Abstract A method was developed for direct extraction, purification and amplification of DNA from forest soil. Eighty-two % of the DNA in Pseudomonas aeruginosa UG2Lr introduced into soil was recovered. The detection limit for the strain was approximately 800 cfu g−1 of dry soil based on the polymerase chain reaction (PCR). Survival of κ-carrageenan-encapsulated and unencapsulated UG2Lr was monitored by antibiotic selective and bioluminescence-based nonselective plating and PCR-amplification of a tnsA fragment. After freeze-thaw treatment of soil samples, the unencapsulated UG2Lr declined from an initial population density of 1 × 109 cfu g−1 of dry soil to below the detection threshold of both selective (14 cfu g−1 of dry soil) and nonselective (1 × 103 cfu g−1 of dry soil) plating. However, presence of nonculturable UG2Lr cells in the soil was revealed by PCR and resuscitation of the bacteria. Population density of the encapsulated UG2Lr increased from 2.7 × 106 to 2.9 × 108 cfu g−1 of dry soil after a 3-week incubation at 22°C and declined to 6.3 × 106 cfu g−1 of dry soil after the freeze-thaw treatment.  相似文献   

18.
Bavaricin MN, a bacteriocin produced by Lactobacillus bavaricus MN, reached titres of 2000 AU ml-1 in APT broth maintained at pH 6.0, 30°C in a batch fermenter. Levels of bavaricin MN at pH 5.5 and 6.5 were lower despite comparable levels of producer cells. The addition of 3.0 g l-1 beef extract to APT broth resulted in increases in both the growth rate of the culture and the production of bavaracin MN. The titre of bavaricin MN in batch fermenters controlled at pH 6.0 in APT broth plus 3 g l-1 beef extract reached 3200 AU ml-1 at 30°C. This level was reduced to 800 AU ml-1 by 76 h. Glucose-limited continuous culture of Lact. bavaricus MN under the same conditions resulted in an increase in the titre of bavaricin MN to 6400 AU ml-1. This level was maintained, independent of growth rate, for 345 h. Growth rates of 0.205, 0.118, 0.169 and 0.058 h-1 were examined.  相似文献   

19.
Combined analysis of three experiments showed that when lamb carcases with initial bacterial numbers of between logi103.29 and 4.22/cm2 were spray washed, statistically significant reductions in bacterial numbers of log10O.5 were obtained when the spray wash water temperature was > 57°C, and reductions of log101.0 were obtained when the temperature was ≥ 80°C. Reductions at all temperatures were enhanced by log100.66 when the water contained 30 µg/ml chlorine, but increasing the concentration to 450 µg/ml reduced bacterial numbers only by a further log100–29. At highly contaminated sites increasing the duration of spraying from 30 to 120 s significantly increased the reductions obtained when water containing added chlorine was used. Reductions in bacterial numbers after spray washing with pressures of 3.5, 5.6. 7.7 kg/cm2 were not significantly different.  相似文献   

20.
SUMMARY. Growth of Lemna minor fronds in the River Frome during summer was found to be logarithmic with time and the growth rate (log10) was 0.066 day−1. This is equivalent to a doubling time of 4.5 days. The life expectancy of the fronds was 34 days.
The net change in the density of bacteria epiphytic on the lower surface of Lemna fronds in the R. Frome was monitored using a direct microscopic technique. The observed increase in bacterial numbers has been partitioned into the components of attachment and growth, assuming that attachment occurred at a constant rate and that the bacterial population grew logarithmically. The line which fitted the data best gave an attachment rate of 5.7 × 105 bacteria cm−2 day−1 and a growth rate (log10) for the bacteria of 0.044 day−1 which is equivalent to a doubling time of 164 h.
Estimates of the rate of detachment of bacteria from Lemna plants were obtained from a laboratory experiment which assumed negligible growth of bacteria in 1 h. The number of bacteria which detached per hour and the sizes of the bacterial populations on the plants before and after detachment were estimated using a plating technique. Different detachment rates were monitored. The detachment rate (analogous to growth rate) which is judged to be most similar to an in situ value was 0.0031 h−1 (0.074 day−1). This rate added to the specific growth rate given above resulted in a corrected growth rate of 0.118 day−1 equivalent to a doubling time of 61 h.  相似文献   

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