Experimental Studies on the Formation of Volatile Nitrogen Compounds Induced by Pseudomonas Fragi in A Synthetic Medium with Amino Acids as Source of Nitrogen

The influence of the growth of Pseudomonas fragi strain F 111 was studied in a synthetic medium. It was shown that volatile nitrogen compounds were rapidly liberated as a result of the decomposition at 5°C of arginine and histidine. A later and slower increase of TVN was observed in media, which contained lysine or urea. From the other 7 amino acids which were included in the test, no increase of TVN was observed to be caused by the strain F 11. It was shown that within the range of 0.05 to 0.8 % histidine added to the basic salt solution the amount of TVN liberated was correlated to the amount of histidine included in the media. At the TVN maximum approx. 50 % of the amino acid nitrogen of the medium was recovered as TVN. It was further shown that the liberation of TVN was correlated to the added amount of arginine and histidine included in the growth medium. The presence of lysine also influenced on the TVN maximum which was reached. In the synthetic medium to which arginine or histidine was added the growth of strain F 111 was stimulated by the presence of glucose. The acids produced by the oxidative breakdown of glucose were neutralized partly by the volatile bases produced in the decomposition of amino acids. The ability of the Pseudomonas fragi to grow in anaerobic conditions and to produce enzymes which could decompose histidine was studied. It was concluded that the anaerobic breakdown of histidine was similar to the anaerobic breakdown of arginine reported by other authors.     

Antibacterial activity among Pseudomonas strains of meat origin

Almost 750 Pseudomonas strains from meat, fish, milk or plant were screened for inhibitory potential towards 10 selected Pseudomonas fragi isolated from meat. Only strains of fish origin and a reference Ps. putida strain produced an inhibitory substance which was either a siderophore or a bacteriocin-like substance. The two systems were efficient in meat extract medium suggesting potential use for controlling meat quality.     

GH–IGF system regulation of attenuated muscle growth and lipolysis in Atlantic salmon reared at elevated sea temperatures

Growth regulation in adult Atlantic salmon (1.6 kg) was investigated during 45 days in seawater at 13, 15, 17, and 19 °C. We focused on feed intake, nutrient uptake, nutrient utilization, and endocrine regulation through growth hormone (GH), insulin-like growth factors (IGF), and IGF-binding proteins (IGFBP). During prolonged thermal exposure, salmon reduced feed intake and growth. Feed utilization was reduced at 19 °C after 45 days compared with fish at lower temperatures, and body lipid storage was depleted with increasing water temperature. Although plasma IGF-1 concentrations did not change, 32-Da and 43-kDa IGFBP increased in fish reared at ≤17 °C, and dropped in fish reared at 19 °C. Muscle igf1 mRNA levels were reduced at 15 and 45 days in fish reared at 15, 17, and 19 °C. Muscle igf2 mRNA levels did not change after 15 days in response to increasing temperature, but were reduced after 45 days. Although liver igf2 mRNA levels were reduced with increasing temperatures after 15 and 45 days, temperature had no effect on igf1 mRNA levels. The liver igfbp2b mRNA level, which corresponds to circulating 43-kDa IGFBP, exhibited similar responses after 45 days. IGFBP of 23 kDa was only detected in plasma in fish reared at 17 °C, and up-regulation of the corresponding igfbp1b gene indicated a time-dependent catabolic response, which was not observed in fish reared at 19 °C. However, higher muscle ghr mRNA levels were detected in fish at 17 and 19 °C than in fish at lower temperatures, indicating lipolytic regulation in muscle. These results show that the reduction of muscle growth in large salmon is mediated by decreased igf1 and igf2 mRNA levels in addition to GH-associated lipolytic action to cope with prolonged thermal exposure. Accordingly, 13 °C appears to be a more optimal temperature for the growth of adult Atlantic salmon at sea.     

Campylobacter jejuni survival in chicken meat as a function of temperature.

Recognition of Campylobacter fetus subsp. jejuni (referred to hereafter as C. jejuni) as an important human pathogen and its isolation from meat products indicate the need for knowledge of its survival characteristics in meats. Thermal death times (D-values) for a single strain and a five-strain composite were determined in 1% peptone and autoclaved ground chicken meat at temperatures ranging from 49 to 57 degrees C. Survival was determined for these strains in chicken meat at 4, 23, 37, and 43 degrees C. Survival was also determined on raw chicken drumsticks stored at 4 degrees C in either an ambient or a CO2 atmosphere. D-values were greater in chicken meat than in peptone in all cases. D-values in peptone for strain H-840 at 49, 51, 53, 55, and 57 degrees C were 15.2, 4.90, 1.71, 0,64, and 0.25 min, respectively. The corresponding D-values in ground chicken meat were 20.5, 8.77, 4.85, 2.12, and 0.79 min, respectively. Similar results were obtained with a composite of five strains. When sterile ground chicken meat was inoculated with approximately 10(6) to 10(7) C. jejuni cells per g and stored at 37 degrees C in an ambient atmosphere, a 1-to 2-log count increase occurred during the first 4 days, followed by a gradual decline of about 1 log during the remainder of the 17-day storage period. No growth was observed among similarly inoculated samples that were stored at 4, 23, and 43 degrees C but counts declined by about 1 to 2 logs at 4 degrees C (17 day), by 2.5 to 5 logs at 23 degrees C (17 days), and to undetectable levels at 43 degrees C (between 10 and 16 days). Survival on raw chicken drumsticks stored at 4 degrees C in CO2 and in an ambient atmosphere declined by about 1.5 and 2.0 logs, respectively, during 21 days of storage. The effect of temperature on the survival of C. jejuni in chicken meat was similar to that reported in other natural and laboratory milieus. Ordinary cooking procedures that destroy salmonellae would be expected to destroy C. jejuni.     

Action of Pseudomonas fragi on the Proteins of Pig Muscle

Considerable salt-soluble protein degradation was observed in pork muscle inoculated with Pseudomonas fragi. During a 20-day incubation period at 10 C, the samples proceeded to rank spoilage or putrefaction. There was a large decrease in the salt-soluble protein fraction and a corresponding increase in nonprotein nitrogen. Disc gel electrophoretic patterns showed that breakdown of the salt-soluble proteins had occurred after incubation for 20 days. During incubation for 10 days at 10 C, P. fragi produced large amounts of extracellular proteolytic activity in ground pork. Most of the proteolytic activity appeared immediately after spoilage occurred. However, a significant increase in the ability to hydrolyze casein and a slight increase in the ability to hydrolyze denatured hemoglobin occurred prior to spoilage.     

Antimicrobial activity of Myrtus communis L. water-ethanol extract against meat spoilage strains of Brochothrix thermosphacta and Pseudomonas fragi in vitro and in meat

The antimicrobial activity of hydro-alcoholic extract of Myrtus communis L. was investigate in vitro and in situ against different meat spoilage biotypes of Pseudomonas fragi and Brochothrix thermosphacta. Water-ethanol myrtle extract (WEME) was prepared from myrtle leaves and used to study the antimicrobial activity, Minimum Inhibitory Concentration (MIC) and Minimum Lethal Concentration (MLC). Naturally contaminated ground beef was used to evaluate in situ antibacterial activity of freeze-dried myrtle extract at different concentrations. In vitro antimicrobial activity of WEME was significantly more effective against B. thermosphacta than P. fragi strains. MIC and MLC values were in the range of 12.5–50 and 25–100 mg DM/ml, respectively, for B. thermosphacta and P. fragi strains. In situ results showed that the microbial population, except for Pseudomonas spp., decreased significantly in ground meat with added 5 % of freeze-dried myrtle extract. In conclusion, the findings demonstrate the effectiveness of myrtle extract to control or prevent the proliferation of meat spoilage bacteria.     

Scanning electron microscope study of Pseudomonas fragi on intact and sarcoplasm-depleted bovine longissimus dorsi muscle.

Intact bovine longissimus dorsi muscle strips used 24 h postmortem were washed to remove sarcoplasmic fluid or left intact and were either left uninoculated or inoculated with Pseudomonas fragi ATCC 4973. The effects of decreased sarcoplasm concentration on growth of P. fragi and consequent microstructural changes of beef muscle during aerobic storage at 4 degrees C for 12 days were evaluated. P. fragi grew slower on washed muscle than on intact muscle. Scanning electron micrographs revealed surface degradation of both intact inoculated and washed inoculated muscle only in areas of localized colonization. Extracellular fibrils appeared to mediate adhesion of P fragi to the muscle surface as well as cell-to-cell attachment within microcolonies. P. fragi was also observed growing between muscle fibers.     

Investigation into the Potential of Bacteriocinogenic Lactobacillus plantarum BFE 5092 for Biopreservation of Raw Turkey Meat

The bacteriocin-producing Lactobacillus plantarum BFE 5092 was assessed for its potential as a protective culture in the biopreservation of aerobically stored turkey meat. This strain produces three bacteriocins, i.e. plantaricins EF, JK and N. The absolute expression of Lactobacillus plantarum BFE 5092 16S rRNA housekeeping gene, as well as l-ldh, plnEF and plnG genes as determined by quantitative, real-time-PCR, revealed that these genes were expressed to similar levels when the strain was grown at 8 and 30 °C in MRS broth. On turkey meat, Lactobacillus plantarum BFE 5092 did not grow but survived, as indicated by similar viable cell numbers during a 9-day storage period at 8 °C. When inoculated at 1 × 10⁷ CFU/g on the turkey meat and subsequently stored at 10 °C, the culture did again not show good growth. Lactobacillus plantarum BFE 5092 could not inhibit the growth of naturally occurring listeriae or Gram-negative bacteria on the turkey meat at 10 °C, or that of Listeria monocytogenes when it was co-inoculated at a level of 1 × 10⁵ CFU/g. Gene expression analyses showed that the bacteriocin genes were expressed on turkey meat stored at 10 °C. Moreover, the investigation into the absolute expression of the three plantaricin genes of Lactobacillus plantarum BFE 5092 in co-culture with Listeria monocytogenes on turkey meat by qRT-PCR showed that the plantaricin genes were indeed expressed during the low-temperature storage condition. The Lactobacillus plantarum BFE 5092 strain overall could not effectively inhibit L. monocytogenes and therefore it would not make a suitable protective culture for biopreservation of turkey meat stored aerobically at low temperature.     

Environmental remediation potential of Perinereis aibuhitensis (Polychaeta) based on the effects of temperature and feed types on its carbon and nitrogen budgets

The effects of three temperatures (15°C, 20°C and 25°C) and four feed types (artificial feed, AF; sediment, SM; fish faeces, FF; and fish meat, FM) on the growth, carbon budget and nitrogen budget of the polychaete Perinereis aibuhitensis were evaluated over a 35 day period. The final body weight and specific growth rate (SGR) of P. aibuhitensis were significantly affected by temperature and feed types (T, F?=?15.831, P?=?0.000; Feed, F?=?81.827, P?=?0.000), but the interaction between these factors was not significant (F?=?0.435, P?=?0.848). The worms achieved the highest SGR in the AF group at 20°C. However, the SGR in the SM group was only half that of the other groups. The food conversion efficiency (FCE) was significantly lower at 25°C than at 15°C and 20°C (P?P?=?0.000), with a mean of 39.83%. The apparent digestibility rate (ADR) at 25°C was significantly higher than at 15°C and 20°C (P?相似文献   

Effects of delaying fungicide treatment of wounded potatoes on the incidence of Fusarium dry rot in store

Potato tubers artificially inoculated with Fusarium solani var. coeruleum or F. sulphureum 3 months after harvest were uniformly wounded and held at 5, 10 or 15°C for up to 21 days before immersion in fungicide suspensions. Holding tubers for 14 days at 15°C (curing conditions) or at 5°C did not alter the incidence of dry rot subsequently developing on tubers stored at 10°C, and holding tubers for up to 21 days at 15°C slightly increased disease caused by both pathogens. Thiabendazole, imazalil and prochloraz applied to tubers immediately after wounding almost completely prevented dry rot. Treatment after 3 days was less effective and the amount of disease increased with further delay; fungicides were more effective on tubers held at 5°C than at 10 or 15°C before treatment and storage, and efficacy of the fungicide was decreased by increasing the amount of inoculum on tubers. Wounds became less susceptible to infection by F. solani var. coeruleum and F. sulphureum when tubers were held at 15°C before inoculation, and the incidence of rots was decreased by 70–80% by delaying inoculation for 7 days. Treating tubers with dichlorophen immediately after wounding slightly increased the disease. The effects of fungicide treatment, curing conditions and wound healing are discussed.     

Acclimation of Atlantic cod (Gadus morhua) to cold water: Sxtress response,osmoregulation, gill lipid composition and gill Na-K-ATPase activity

Atlantic cod (0.8–2.5 kg) were transferred froni 8°C to 1°C seawater for 17 days. No fish died. Exposure to 1°C water produced no changes in hematocrit, or in plasma concentrations of Cl⁻ or Mg²⁺. Cold water exposure caused a marked increase in plasma cortisol and glucose concentrations. Fish in 1°C seawater had higher gill Na-K-ATPase activity than fish in 8°C seawater, whereas there were no differences in gill lipid class or fatty acid composition.     

The Life Cycle of Trypanoplasma bullocki (Zoomastigophorea: Kinetoplastida)1

The leech Calliobdella vivida (Verrill) is the vector of Trypanoplasma bullocki. At 10°C, infective-stage flagellates were first present in the leech's proboscis sheath five days after feeding. At 5°C, infective-stage flagellates were not present in the leech's proboscis sheath until 10 days after feeding, but at 20°C, flagellates were located there as early as 24 h after feeding. Infected leeches retained flagellates through three subsequent feeds on uninfected fish. When flagellates were first observed in hogchoker, Trinectes maculatus (Bloch & Schneider), they were much larger than infective stages from the leech. Average flagellate length then decreased during early acute phase, but gradually increased thereafter. Peak parasitemia was greater in a hogchoker inoculated by only one leech but held at colder temperature than in a hogchoker inoculated by 45 leeches, suggesting that temperature may be more important than inoculum in determining peak parasitemia. Cell division in the fish host is described. SEM studies of fish blood flagellates revealed a pre-oral ridge and a cytostome.     

Temperature and state‐dependence of feeding and gastric evacuation in juvenile Pacific halibut

Relationships between nutritional state, behavioural response to prey and gastric evacuation rates were examined in juvenile Pacific halibut Hippoglossus stenolepis feeding on squid. Pacific halibut reared at 2, 6 and 10° C were fasted for 1 or 7 days to generate variation in energetic state. The 7 day fast resulted in measurable declines in condition indices at 10 and 6° C but not at 2° C. At 10° C, all Pacific halibut consumed the first meal offered, but fish previously fasted for 7 days took significantly longer to locate and consume the meal than fish fasted for only 1 day. At 2° C, Pacific halibut fasted for 7 days did not generally consume the first meal offered, but resumed feeding 2·1 days sooner, on average, than fish fasted for only 1 day. The gastric evacuation rate of the squid meal was best described by a power model with near‐exponential curvature ( a  = 1·011). The evacuation rate was strongly temperature‐dependent ( Q ₁₀ = 3·65) but displayed the same degree of variability at each temperature. The evacuation rate in Pacific halibut was not affected by feeding history, body size or energetic state. Furthermore, individual variation in gastric evacuation rate was not correlated with feeding responsiveness at any temperature. These results indicate a general plasticity in the behavioural but not physiological aspects of energy acquisition.     

Effects of temperature and photoperiod on ovarian recrudescence in the cyprinid fish Mirogrex terrae-sanctae

Mirogrex terrae-sanctae is a commercial, sardine-like cyprinid fish in the Sea of Galilee. The fish spawns from December to the end of March. Females collected at the quiescent phase of the cycle (June) were exposed to four combinations of photoperiod and temperature for 3 months. The highest GSI (2.44 ± 0.22) was found in females exposed to simulated winter conditions (16°C, 9L) while the lowest GSI (0.65 ± 0.04) was found in fish exposed to simulated summer conditions (27°C, 14L). The GSI of fish maintained at the unnatural combination of 16°C, 14L (1.30 ± 0.09) did not differ from that of fish maintained at the other unnatural combination of 27°C, 9L (1.07 ± 0.11). However, histological examinations revealed that vitellogenic oocytes were present only in fish maintained at low temperature regimes, which implies that the growth of the ovarian mass in the 27°C, 9L group was due mainly to oogonial proliferation and that vitellogenesis was inhibited in Mirogrex at a high temperature. Both protein and calcium concentrations increased in the serum of fish following injections of oestradiol-17β. The increase of calcium was evident only in the non-filtrable (bound) fraction, suggesting that the total serum calcium above 13 mg% could be used as an indirect parameter for circulating vitelloprotein. Fish collected at the quiescent phase were injected with oestradiol (50 μg/fish c. 15 g body weight) and subsequently transferred to tanks maintained at either 12°, 20° or 27°C. The total serum calcium increased to 23.0 ± 1.75 mg% in the fish maintained for 8 days at 20°C. This was significantly higher than the concentration of calcium in the serum of fish maintained at either 12°C (7.8 ± 0.52) or 27°C(l1.8 ± 0.77). This implies that the temperature may affect ovarian recrudescence by modulating the response of the liver to oestrogen, allowing the oestrogen-induced vitellogenesis to be relatively high in the cool environment during winter.     

Volatile compounds produced by meat pseudomonads and related reference strains during growth on beef stored in air at chill temperatures

Volatile compounds produced by 31 strains of pseudomonads and by reference strains of Pseudomonas fragi and Ps. fluorescens biotype 1 during growth on beef stored at 6°C in air were analysed by gas chromatography-mass spectrometry of headspace gases. Compounds of major sensory significance were ethyl and methyl esters of C₂–C₈ fatty acids and sulphur-containing compounds which included methane- and isopropanethiols and their related sulphides and thioesters but not hydrogen sulphide. Ester production was mainly associated with growth of some, but not all, Ps. fragi and related meat strains but sulphur-containing compounds were produced by all but a single meat strain. A minority of other meat strains produced greater amounts of methyl ketones, secondary alcohols and unsaturated hydrocarbons believed to be of lipid origin.     

Volatile compounds produced by meat pseudomonads and relate reference strains during growth on beef stored in air at chill temperatures

Volatile compounds produced by 31 strains of pseudomonads and by reference strains of Pseudomonas fragi and Ps. fluorescens biotype 1 during growth on beef stored at 6 degrees C in air were analysed by gas chromatography-mass spectrometry of headspace gases. Compounds of major sensory significance were ethyl and methyl esters of C2-C8 fatty acids and sulphur-containing compounds which included methane- and isopropanethiols and their related sulphides and thioesters but not hydrogen sulphide. Ester production was mainly associated with growth of some, but not all, Ps. fragi and related meat strains but sulphur-containing compounds were produced by all but a single meat strain. A minority of other meat strains produced greater amounts of methyl ketones, secondary alcohols and unsaturated hydrocarbons believed to be of lipid origin.     

Properties of some defective strains of tobacco mosaic virus and their behaviour as affected by inhibitors during storage in sap

From the type strain of tobacco mosaic virus, defective strains were isolated that produced chlorotic or ringspot type symptoms in tobacco and were difficult to transmit without carborundum in the inoculum. Their concentration was less than 0–1 μg/ml of sap instead of the usual 2 mg/ml with the type strain. Phenol extracts of infected leaves were a little more infective than extracts in buffer, whereas phenol extracts of leaves infected with type strain were very much less infective than extracts in buffer. Electron microscopy of infective sap rarely showed any virus particles, but preparations concentrated by ultracentrifugation contained virus particles, many of which were broken or seemed inadequately assembled. Changing the ambient temperature at which infected plants were kept from 20 to 35°C did not increase the amount or improve the appearance of the virus. Some of the strains were inactivated during heating for 10 min between 70 and 80 °C. Undiluted sap lost its infectivity in 3 days at 20 °C, as did the type strain when diluted to 0–1 μg/ml in sap from healthy leaves. This is because substances that inhibit infection were produced by microbes in the sap. The ability of sap from healthy leaves to inhibit infection increased by more than twenty-five times when left 3 days at 20 °C. Infectivity of appropriate mixtures of type strain and aged sap was restored by diluting them in buffer. Sodium azide at 0·02% in sap prevented formation of the inhibitor. The infectivity of the defective strains increased when inoculated together with the type strain.     

Suppression of Spoilage Rates of Bombay Duck (Harpodon nehereus) Homogenates by Gamma Radiation

The spoilage rates of unirradiated and irradiated (0.1 Mrad) Bombay duck (Harpodon nehereus) homogenates stored at 0°C, 10°C and 30°C in terms of organoleptic score (OS) total bacterial count (TBC), trimethylamine content (TMA), and total volatile basic nitrogen (TVBN) followed a linear response with increase in temperature. Unirradiated Bombay duck stored at 0°C were found to spoil faster than those irradiated at 0.1 Mrad; the spoilage rates derived for TBC, TMA, TVBN and OS were 0.42, 0.67, 1.93 and ?0.86 respectively for unirradiated samples as compared with corresponding values of 0.31, 0.55, 1.19 and ?0.19 for the irradiated samples. The spoilage rates of unirradiated Bombay duck stored at 10°C and 30°C measured as a function of OS, TMA and TVBN were consistently higher than their irradiated (0.1 Mrad) counterparts. In the case of irradiated samples, TBC was not a satisfactory index of spoilage.     

Glasshouse studies on the effect of low temperature on infection of perennial ryegrass seedlings by Fusarium nivale

In glasshouse experiments, isolates of Fusarium nivale, applied as mycelial macerates, caused marked reductions in the number and length of roots, and in the height and fresh weight of S. 321 perennial ryegrass seedlings. Spore inocula failed to cause infection. Damage by F. nivale was increased when inoculation was immediately followed by four alternate 12 h periods in a growth cabinet at 0°C and in a warm glasshouse at c. 17°C, succeeded by a further 11 days in the same glasshouse. Although inoculated seedlings receiving no cold treatments initially showed damage, regrowth of roots and some recovery of the shoots occurred in a fortnight. Exposure of the plants after that time to four intermittent 12 h periods at 0°C, however, arrested their recovery and caused further root damage. The implication of these results in the importance of low temperature in the winterkill syndrome is discussed.     

Characterisation of an Antilisterial Bacteriocin Produced by Lactobacillus sakei CWBI-B1365 Isolated from Raw Poultry Meat and Determination of Factors Controlling its Production

Amongst 101 lactic acid bacteria isolated from meat and fish samples, strain CWBI-B1365, identified as Lactobacillus sakei, was found to produce the subclass IIa bacteriocin sakacin G. Partial sequencing of the gene involved in the biosynthetic pathways revealed an unusual gene organisation in that the accessory gene associated with bacteriocin transport did not occur immediately downstream of the gene encoding an ABC transporter, but upstream of the putative immunity gene and encoded on the opposite DNA strand. Sakacin G production was strongly regulated by pH, temperature and the carbon sources used in the growth medium, as well as the concentration of carbon and nitrogen sources. The condition of pH 5.5 and the temperature of 25°C appeared to be optimal for bacteriocin production. The use of sucrose during culturing and the fed batch addition of sucrose and meat extract greatly enhanced bacteriocin production.