Vascular occlusion in stems of cut rose flowers exposed to air: Role of xylem anatomy and rates of transpiration

Stems of cut rose flowers were exposed to air at 20°C and 60% relative humidity and then placed in water. The rate of water uptake in Frisco, Sonia, Madelon, and Cara Mia roses was maximally inhibited after 72, 36, 24, and 3 h of exposure to air. respectively. Anatomical observations showed no tyloses, gums, or deposition of hydrophobic material in the xylem conduits (tracheids and vessels) of any of the investigated cultivars. Frisco, Sonia, Madelon, and Cara Mia roses showed no difference in the number, the length, the wall thickness, or the diameter of the lumina of either the tracheids or the vessels. This indicates that differences in recovery are not related to capillary diameter or length.
During exposure to air the decrease in transpiration rate, fresh weight, and water potential was the same in Sonia, Madelon, and Cara Mia roses. Upon exposure to air Frisco roses lost less water than the other cultivars studied In Frisco roses stomatal conductance was similar to that of other cultivars, but the rate of cuticular transpiration was lower.
It is concluded that conservation of water through low cuticular transpiration is one of the reasons for the relatively slow development of the vascular occlusion in Frisco roses, but the differences between Sonia. Madelon and Cara Mia roses were not related to their rates of transpiration.     

Effect of heat treatment on Listeria monocytogenes and Gram-negative bacteria in sheep, cow and goat milks

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.     

Survival of κ-carrageenan-encapsulated and unencapsulated Pseudomonas aeruginosa UG2Lr cells in forest soil monitored by polymerase chain reaction and spread plating

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.     

Efflux of ions and ATP depletion induced by pediocin PA-1 are concomitant with cell death in Listeria monocytogenes Scott A

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.     

Heterotrophic bacterial populations in the mineral waters of thermal springs in Spain

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.     

Quantification of pathogenic micro-organisms in the sludge from treated hospital wastewater

The sludge from hospital waste treatment facilities is a potential source of infectious organisms. The average numbers of micro-organisms in the sludge of hospital wastewater in Taiwan were as follows: total count 8·1 × 10⁷ cfu g⁻¹ (dry weight of sludge), and 1·4 × 10⁶, 3·6 × 10⁵, 1·6 × 10⁵, 2·2 × 10⁵ and 5·5 × 10⁴ cfu g⁻¹ (dry weight of sludge) for total coliforms, faecal coliforms, faecal streptococci, Pseudomonas aeruginosa and Salmonella spp., respectively . Salmonella spp. were detected in 37% (10 of 27) of the sludges from hospital wastewaters. Therefore, the treatment of such sludge to reduce pathogenic micro-organisms should be considered.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

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.     

The bactericidal activity of tea against Helicobacter pylori

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.     

The development of a conductimetric assay for automated detection of metabolically active soft rot Erwinia spp. in potato tuber peel extracts

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.     

Sensitivity of Bacillus coagulans spores to combinations of high hydrostatic pressure, heat, acidity and nisin

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.     

Effect of high-temperature, short-time (HTST) pasteurization on milk containing low numbers of Mycobacterium paratuberculosis

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.     

Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

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.     

The detection of Salmonella in skimmed milk powder enrichments using conventional methods and immunomagnetic separation

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.     

Behaviour of Staphylococcus aureus strains, producers of enterotoxins C1 or C2, during the manufacture and storage of Burgos cheese

Burgos cheese was manufactured from pasteurized ewes milk inoculated with Staphylococcus aureus strains FRI 137 and FRI 361, at levels of ca 10³ and 10⁵ cfu/ml and stored at 4°, 10° and 15°C and at room temperature (10°-15°C). Populations of Staph. aureus and mesophilic aerobes, pH, and production of thermonuclease and enterotoxins C₁ and C₂ were investigated. Aerobic counts increased during cheese-making and storage. With both test strains, important growth was observed only during the storage period, the larger levels corresponding to the higher temperatures. Although Staph. aureus strains attained populations of over 10⁸ cfu/g, no enterotoxin was detected. Strain FRI 361 reached 10⁷ cfu/g without production of a detectable amount of thermonuclease. With strain FRI 137, the minimal population associated with enzyme activity was influenced by the inoculum size. Staphylococcus aureus counts are better indicators of staphylococcal growth in Burgos cheese than the thermonuclease test.     

Association of bacteria with the fungal fermentation of soybean tempe

Bacteria grew to viable populations of 10⁸–10⁹ cfu/g during the fermentation of soybeans into tempe with the fungus, Rhizopus oligosporus. Bacillus pumilus and B. brevis were the predominant bacterial species, reaching populations of approximately 10⁸ cfu/g during the 48 h fermentation. Species of Streptococcus faecium, Lactobacillus casei, Klebsiella pneumoniae and Enterobacter cloacae also contributed to the fermentation and achieved populations of 10⁶–10⁷ cfu/g. and accepted 25 May 1989     

Monitoring the fate of genetically engineered bacteria sprayed on the phylloplane of bush beans and grass

Abstract The fate of a Bacillus amyloliquefaciens with the recombinant plasmid pSB20 sprayed on the phyllosphere of grass, and of a Tn 5 marked Pseudomonas syringae sprayed on the phyllosphere of bush beans was studied in planted soil microcosms. B. amyloliquefaciens showed a decline from 1.5×10⁸ to 3.1×10² cfu g⁻¹ on the phylloplane of grass in the course of the experiment. B. amyloliquefaciens was easy to follow by selective cultivation due to the complete absence of bacterial background growth. Southern blot hybridization of Hin dIII digested genomic DNA showed plasmid restriction patterns identical with pSB20 indicating high plasmid stability. In total DNA extracts from phyllosphere bacteria the recombinant plasmid was detectable by Southern blot hybridization up to 6×10⁴ cfu g⁻¹ (wet weight). Counts of hybridizing colonies showed that P. syringae established on the phyllosphere of bush beans at between 5×10³ and 4×10⁶ cfu g⁻¹ fresh weight. During senescence of the bean plants the strain was no longer detectable by selective cultivation and subsequent colony hybridization. In contrast, Tn5 marked DNA was detected after PCR amplification over the whole period of the experiment.     

Effect of chill and freezing temperatures on survival of Vibrio parahaemolyticus inoculated in homogenates of oyster meat

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.     

Effect of some factors on determination of viable microbial cells by peroxyoxalate chemiluminescence method

The effects of physical and chemical factors on the production of H₂O₂ 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 H₂O₂ 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 Na₂SO₄ in inorganic salts significantly reduced the ETS activity above 70%. In addition, the optimum temperature for the production of H₂O₂ 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.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

Inhibition and inactivation of pathogenic serogroups of Yersinia enterocolitica by a bacteriocin produced by Yersinia kristensenii

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.