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1.
Effect of heat treatment on Listeria monocytogenes and Gram-negative bacteria in sheep, cow and goat milks 总被引:1,自引:0,他引:1
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
2.
Antibacterial effect of protamine assayed by impedimetry 总被引:5,自引:0,他引:5
Impedimetric measurements were used to assay the antibacterial effect of protamine. A good linear correlation between the impedance detection time and the initial cell counts was obtained ( r = 0.99, n = 2). As basic peptides may cause clumping of cells, this correlation curve was used when estimating the cell number after protamine treatment, rather than colony counts.
Protamine from salmon killed growing Gram-positive bacteria and significantly inhibited growth of Gram-negative bacteria in Tryptone Soy Broth (TSB) at 25°C. In general Gram-positive bacteria were more sensitive to protamine than Gram-negative bacteria; the minimum inhibitory concentrations (MIC) determined for Gram-positive strains varied from 20 to 1000 μ ml-1 and for Gram-negative strains from 500 μ ml-1 to more than 4000 μ ml-1 .
The effect of protamine on non-growing Listeria monocytogenes Scott A suspended in buffer was not lethal as was the effect on growing cells; however, protamine (50–500 μg ml-1 ) killed the Gram-negative fish spoilage bacteria Shewanella putrefaciens when the live cells were suspended in buffer. 相似文献
Protamine from salmon killed growing Gram-positive bacteria and significantly inhibited growth of Gram-negative bacteria in Tryptone Soy Broth (TSB) at 25°C. In general Gram-positive bacteria were more sensitive to protamine than Gram-negative bacteria; the minimum inhibitory concentrations (MIC) determined for Gram-positive strains varied from 20 to 1000 μ ml
The effect of protamine on non-growing Listeria monocytogenes Scott A suspended in buffer was not lethal as was the effect on growing cells; however, protamine (50–500 μg ml
3.
Interaction between the effects of bacteria and dry storage on the opening and water relations of cut rose flowers 总被引:1,自引:0,他引:1
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
4.
Basil essential oils, including basil sweet linalool (BSL) and basil methyl chavicol (BMC), were screened for antimicrobial activity against a range of Gram-positive and Gram-negative bacteria, yeasts and moulds using an agar well diffusion method. Both essential oils showed antimicrobial activity against most of the micro-organisms examined except Clostridium sporogenes , Flavimonas oryzihabitans , and three species of Pseudomonas . The minimum inhibitory concentration (MIC) of BMC against Aeromonas hydrophila and Pseudomonas fluorescens in TSYE broth (as determined using an indirect impedance method) was 0·125 and 2% (v/v), respectively; the former was not greatly affected by the increase of challenge inoculum from 103 to 106 cfu ml−1 . Results with resting cells demonstrated that BMC was bactericidal to both Aer. hydrophila and Ps. fluorescens . The growth of Aer. hydrophila in filter-sterilized lettuce extract was completely inhibited by 0·1% (v/v) BMC whereas that of Ps. fluorescens was not significantly affected by 1% (v/v) BMC. In addition, the effectiveness of washing fresh lettuce with 0·1 or 1% (v/v) BMC on survival of natural microbial flora was comparable with that effected by 125 ppm chlorine. 相似文献
5.
B. A. Fraaije Y. Birnbaum A. A. J. M. Franken R.W. Van den Bulk 《Journal of applied microbiology》1996,81(4):375-382
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.
Kamtin Leung Michael B. Cassidy Steve B. Holmes Hung Lee Jack T. Trevors 《FEMS microbiology ecology》1995,16(1):71-82
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
7.
Sensitivity of Bacillus coagulans spores to combinations of high hydrostatic pressure, heat, acidity and nisin 总被引:2,自引:1,他引: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
8.
Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices 总被引:1,自引:1,他引:0
Frozen fruit juice concentrates containing an average microbial population of log10 1.54 cfu ml-1 were examined by traditional plating techniques and direct and indirect conductimetry. The initial populations in diluted (1:4) concentrates increased to an average of log10 3.82 cfu ml-1 during incubation at 25°C for 24 h. Incubation before plating and subjecting to conductimetric tests also facilitated the resuscitation of cells that may have been freeze-injured. Yeasts were recovered in equal numbers on acidified (pH 3.5) potato dextrose agar and dichloran rose bengal chloramphenicol agar (pH 5.6). Yeasts and bacteria were recovered on orange serum agar. Detection times determined by indirect conductimetry correlated fairly well ( r = -0.73) with populations (cfu ml-1 ) detected on traditional plating media. Populations in diluted concentrates which were not incubated before examination were detected conductimetrically in an average of 48.9 h, whereas detection times for diluted concentrates incubated for 24 h at 25°C before testing were reduced to an average of 14.1 h. Examination by conventional (direct) conductimetry required an additional 10–20 h to reach changes in conductance of 5 μS h-1 . 相似文献
9.
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
10.
The Microflora of Milking Equipment Cleansed by Chemical Methods 总被引:1,自引:1,他引:0
S ummary : The incidence of the main types of bacteria among 2,856 isolated on Yeastrel-milk agar incubated at 30° from 121 rinses of dairy equipment cleansed by chemical methods, showed that micrococci were dominant in low colony count (<104 /ft2 ) rinses of equipment treated by immersion cleaning in caustic soda or cleansed in detergent-hypochlorite solutions, whereas nonpigmented Gram-negative rods were dominant in low count rinses of equipment cleansed with detergent-sterilizers containing quaternary ammonium compounds. Gram-negative rods were dominant and streptococci frequent in high count (<2·5 × 105 /ft2 ) rinses irrespective of the chemical used. A high proportion of the streptococci and coli-aerogenes organisms gave acid reactions in litmus milk after 72 h at 22°, many of the anaerogenic Gram-negative rods and several of the aerobic sporeformers gave proteolytic reactions, whereas the majority of the micrococci, corynebacteria and other asporogenous Gram-positive rods showed no change. Bacteria isolated from high count rinses were more active in producing milk spoilage reactions at 22° than those isolated from low count rinses. 相似文献
11.
Birgit Janning P.H. in't Veld S. Notermans J. Krämer 《Journal of applied microbiology》1994,77(3):319-324
The Viability of 18 bacterial strains desiccated on anhydrous silica gel and stored at a temperature of 22°C for at least 3 months was determined. According to their stability in the dried state, these strains could be classified into three typical groups. Group 1, containing Gram-positive strains and Salmonella serotypes, was marked by a very slow decrease of the concentration of culturable cells from day 14 on (respectively day 21 for Salmonella thompson . The rate of decrease expressed as regression coefficient (b) ranged from —0.000389 to —0.00521 log (cfp ml-1 ) per d. The Group 2 strains Enterobacter cloacae and Escherichia coli did not reach a comparable slow decrease in the dry material within the indicated time period. Regression coefficients were respectively —0.04406 and —0.03412 log (cfp ml-1 ) per d. The reciprocal values —(1/b) were respectively 23 d per log (cfp ml-1 ) and 29 d per log (cfp ml-1 ), indicating the time periods in which a reduction of 1 log unit of culturable cells occurred. Group 3 strains Pseudomonas aeruginosa, Aeromonas hydrophila and Aer. sobria were marked by a significant susceptibility to cell damage caused during desiccation and reconstitution. A high initial decrease (ID) of the concentration of culturable organisms seems to be a characteristic property of these bacterial strains: culturable organisms could not be detected after storage for 1 d ( Aer. hydrophila, Aer. sobria ) or 7 d ( Ps. aeruginosa ). The wide range of resistance of the different bacterial strains tested indicated that the silica gel model system is a suitable tool for microbiological challenge tests to investigate the survival of micro-organisms exposed to desiccation and their stability in dry materials. 相似文献
12.
Jorge Briozzo Lidia Núncez Jorge Chirife León Herszage Miguel D'aquino 《Journal of applied microbiology》1989,66(1):69-75
Essential oil of clove, dispersed (0.4%v/v) in a concentrated sugar solution, had a marked germicidal effect against various bacteria and Candida albicans. Staphyloccus aureus (five strains), Klebsiella pneumoniae, Pseudomonas aeruginosa, Clostridium perfringens , and Escherichia coli inoculated at a level of 107 cfu/ml, and C. albicans (inoculum 4.0×105 cfu/ml) were killed (< 99.999%) after 2–7 min in a laboratory broth supplemented with 63% (v/w) of sugar, and containing 0.4% (v/w) of essential oil of clove. Added organic matter (i.e. human or bovine serum) did not impair its antimicrobial activity.
Sugar was not necessary for the antimicrobial activity of clove oil, but the concentrated sugar solution provided a good vehicle for obtaining an oil dispersion that is relatively stable for certain practical applications. 相似文献
Sugar was not necessary for the antimicrobial activity of clove oil, but the concentrated sugar solution provided a good vehicle for obtaining an oil dispersion that is relatively stable for certain practical applications. 相似文献
13.
Efflux of ions and ATP depletion induced by pediocin PA-1 are concomitant with cell death in Listeria monocytogenes Scott A 总被引:2,自引:1,他引:1
Domination of Carnobacterium divergens LV13 by a bacteriocin-producing (bac+ ) organism Carnobacterium piscicola LV17 was dependent on the level of inoculum of the producer strain and its bacteriocin production. When C. piscicola LV17 was grown in APT broth from an initial inoculum of α-104 cfu ml-1 , bacteriocin was not produced (bac- ) although maximum population was reached. The culture remained bac- during subsequent inoculation at 102 -107 cfu ml-1 unless it was first grown on solid medium or if heat-treated supernatant fluids from a bac+ culture of C. piscicola LV17, LV17A or LV17B were added to the culture prior to the stationary phase of growth. Use of purified carnobacteriocins from C. piscicola LV17A and LV17B confirmed their role in regulation of the bac+ phenotype. The need for induction might account in part for differences in bacteriocin production by cultures in liquid and on solid growth media. 相似文献
14.
J. M. Muntada-Garriga J. J. Rodriguez-Jerez E. I. Lopez-Sabater M. Teresa Mora-Ventura 《Letters in applied microbiology》1995,20(4):225-227
Survival of Vibrio parahaemolyticus was determined in oyster meat homogenates at various temperatures. (4°C, 0°C, -18°C and -24°C) and bacterial levels (102 , 104 , 105 and 107 ml-1 ). In all cases, the numbers of V. parahaemolyticus were a logarithmic function of log time. This study indicates that high numbers of V. parahaemolyticus can be inactivated at low temperatures. The time of total inactivation depends on the initial number of micro-organisms and incubation temperature. It is possible to use this information to determine the storage time necessary to reduce V. parahaemolyticus hazards in fish. 相似文献
15.
Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 102 to 8.0 × 104 cfu/g. Fungal counts ranged from 1.0 × 102 to 1.5 × 104 cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 104 cfu/g dry sample. 相似文献
16.
The effects of physical and chemical factors on the production of H2 O2 from Escherichia coli cells were studied. When 20 mmol 1-1 Tris-HCl buffer was used for this purpose the electron transport system (ETS) showed the highest activity at pH 7.6-8.2. KCN promoted the production of H2 O2 from E. coli cells, and the optimum concentration was changed in different reaction times and pH values. Glucose, 5 mg ml-1 , increased the ETS activity about twofold. The other substrates and surfactants did not increase the chemiluminescence intensity. NaNO2 and Na2 SO4 in inorganic salts significantly reduced the ETS activity above 70%. In addition, the optimum temperature for the production of H2 O2 was 30°C in this study. When glucose (5 mg ml-1 ) and KCN (0.2 mmol 1-1 ) were added to the reaction buffer containing 0.5 mmol 1-1 menadione, the detectable minimum cell densities (averages of triplicate assay) of E. coli, Enterobacter cloacae and Serratia marcescens were 5 times 103 cells ml-1 , 104 cells ml-1 and 104 cells ml-1 respectively. 相似文献
17.
Effect of high-temperature, short-time (HTST) pasteurization on milk containing low numbers of Mycobacterium paratuberculosis 总被引:2,自引:1,他引:2
The efficacy of high-temperature, short-time (HTST) pasteurization (72 °C/15 s) when low numbers (≤ 103 cfu ml −1 ) of Mycobacterium paratuberculosis are present in milk was investigated. Raw cows' milk spiked with Myco. paratuberculosis (103 cfu ml−1 , 102 cfu ml−1 , 10 cfu ml−1 , and 10 cfu 50 ml−1 ) was subjected to HTST pasteurization using laboratory pasteurizing units. Ten bovine strains of Myco. paratuberculosis were tested in triplicate. Culture in BACTEC Middlebrook 12B radiometric medium detected acid-fast survivors in 14·8% and 10% of HTST-pasteurized milk samples at the 103 and 102 cfu ml−1 inoculum levels, respectively, whereas conventional culture on Herrold's egg yolk medium containing mycobactin J detected acid-fast survivors in only 3·7% and 6·7% of the same milk samples. IS900-based PCR confirmed that these acid-fast survivors were Myco. paratuberculosis . No viable Myco. paratuberculosis were isolated from HTST-pasteurized milk initially containing either 10 cfu ml−1 or 10 cfu 50 ml−1 . 相似文献
18.
Bacteriological stability of water bottled in plastic containers and the growth kinetics of Pseudomonas aeruginosa were determined. Samples of water from the source, water to be bottled, finished product and sterile water bottled in non-returnable and returnable containers were analysed for aerobic colony count, coliforms, Escherichia coli and Ps. aeruginosa. The samples were examined for up to 30 d storage. Aerobic colony count increased 6 d after bottling to between 103 and 105 cfu ml−1 . Coliforms and E. coli were not found in any sample. Pseudomonas aeruginosa was isolated from commercial products bottled in returnable plastic containers due to the contamination from the containers and the subsequent multiplication utilizing trace nutrients. The predominant Ps. aeruginosa strains showed high doubling time (26 h) due to competition from the accompanying flora. In the absence of competing flora Ps. aeruginosa reached higher density than the maximum reached by aerobic flora, with a doubling time of only 3·6 h. After 30 d storage, this micro-organism was predominant. 相似文献
19.
B.A. Fraaije A.A.J.M. Franken P.S. van der Zouwen R.J. Bino C.J. Langerak 《Journal of applied microbiology》1993,75(5):409-415
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
20.
Inhibition and inactivation of pathogenic serogroups of Yersinia enterocolitica by a bacteriocin produced by Yersinia kristensenii 总被引:1,自引:1,他引:0
Growth of Yersinia enterocolitica strains representing serogroups O: 3, O: 5, 27, O:6, 30, O:8, O:9 (human isolates) and O:6, 31 (food isolate) were inhibited in the presence of a bacteriocin produced by Yersinia kristensenii at high initial cell count of 106 ml-1 . Complete (100%) inactivation of most Y. enterocolitica cells of different serotypes was observed within 24 h at low initial cell counts of 104 ml-1. Complete injury of the cells was observed within 4–8 h, with all the serotypes at 10°C and 28°C. The degree of susceptibility to the injury and the recovery of cells from the injury varied from serogroup to serogroup. 相似文献