Effect of ozone pretreatment on fish storage life at low temperatures.

The purpose of the present study was to determine the effect of ozone pretreatment of live fish on their shelf life and storage characteristics during storage at 0 and 5 degrees C. The evaluation included sensory, chemical, physical, and bacteriological tests at set intervals throughout a storage period of 30 days under two temperature regimes (0 and 5 degrees C). The results of the sensory tests showed that ozone pretreatment of live tilapia prolonged their shelf life by 12 days and improved their quality characteristics during storage at 0 degrees C for 30 days. These results were corroborated by the bacteriological tests. The sensory qualities of ozone-treated tilapia stored at 5 degrees C became unacceptable 3 days later than those of control fish. Although the most important factor affecting the fish shelf life is storage temperature, the combination of ozone pretreatment with storage at 0 degrees C appears to be a promising means of prolonging the shelf life.

Temperature dependent characteristics of intestinal glycyl-L-leucine dipeptidase in boreal zone fish.

Three kinds of boreal zone fish were investigated for gastrointestinal glycyl-L-leucine (GL) dipeptide cleaving activity as a function of feeding stage and seasonal changes. The enzyme activity tested in the perch (Perca fluviatilis L.) intestine increased steadily during digestion and rapidly disappeared after completion. The temperature characteristics and the seasonal changes in dipeptide cleaving activity in pike perch (Stizostedion lucioperca L.) and bream (Abramis brama L.) were studied. In summer, the maximal activities in the pike perch and the bream were found at temperatures of 40 and 30 degrees C, respectively. In winter, the temperature of maximal activity in pike perch fell to only 30 degrees C, whereas no changes were observed in bream. The activation energies in bream and pike perch were several times lower in winter than in summer. Seasonal changes in the dipeptide cleaving activity at low temperature relative to that at the temperature of maximal activity were found. At high temperatures, the stability of the enzyme decreases in winter and increases in summer, but in the presence of a substrate the thermal stability of the enzyme increases both in winter and in summer. In our experiments, we found that in these fish, GL dipeptidase was unstable at 0 and -10 degrees C.

Effects of herbal essential oils used to extend the shelf life of freshwater-reared Asian sea bass fish (Lates calcarifer).

Sensory and microbiological characteristics of Asian sea bass (Lates calcarifer) fish raised in a freshwater pond were evaluated during cold storage for 33 days. Whole fish (averaging 400 g each) were stored in a cold storage room at 0 to 2 degrees C. Essential oils of herbs--thyme (Thymus vulgaris) and oregano (Origanum vulgare)--added at 0.05% (vol/vol) were used as preservatives. On the basis of the sensory test results as well as the bacteriological tests, the addition of oregano and thyme essential oils can considerably slow the process of spoilage. The fish treated with these oils were still fit for human consumption after 33 days of storage. The results obtained through sensory tests are corroborated to a great extent by the chemical (hypoxanthine) tests and to a lesser extent by the physical (Cosmos units) tests. The initial total bacteriological counts were 1.7 x 10(3) CFU/cm2 on the fish surface and <10(2) CFU/g in the fish flesh, and in the control treatment (without preservatives), these counts rose continuously, reaching around 10(7) CFU/cm2 on the fish surface and 10(3) CFU/g in the flesh after 33 days of storage at 0 to 2 degrees C. The use of herbal essential oils as preservatives, on the other hand, resulted in a maximal count of 10(5) CFU/cm2 on the fish surface, while the bacterial count in the flesh remained <10(2) CFU/g by the end of the 33-day storage period at 0 to 2 degrees C.

Amylolytic activity in fish intestinal mucosa: temperature effects.

The activity, temperature characteristics and energy of activation of amylolytic enzymes in the intestinal mucosa were studied in six species of fish living in a boreal zone [burbot (Lota lota L.), northern pike (Exos lucius L.), perch (Perca fluviatilis L.), bream (Abramis brama L.), roach (Rutilis rutilis L.), and carp (Cyprinus carpio L.)] and in three species from tropical and subtropical areas [pilchard (Sardina pilchardus W.), jack mackerel (Trachurus trecae C.) and round sardinella (Sardinella aurita V.)]. The amylolytic activity correlated with the feeding habits: it was essentially lower in predators. The enzyme activity at low temperature, relative to the maximal activity, was correlated with the natural environmental temperature where the species lived. At low temperature the relative activity was higher in boreal fish than in tropical and subtropical fish. We found a breakpoint in the Arrhenius plots in all fish species, except for jack mackerel. The energy of activation in predators decreased below the breakpoint in the low-temperature region. The energy of activation in benthophages of the Aral-Ponto-Caspian area was lower at higher temperatures above the breakpoint. A reduction in activation energy in the range of physiological temperatures might indicate adaptation to the environmental temperature.

Effects of storage temperature and preservative treatment on shelf life of the pond-raised freshwater fish, silver perch (Bidyanus bidyanus).

Sensory and microbiological characteristics of pond-raised freshwater silver perch (Bidyanus bidyanus) fish, during cold storage over a period of 25 days were evaluated. Whole fish (averaging 400 g each) were stored in cold storage rooms at either 0 to 2 degrees C, 5 degrees C, or 5 degrees C + potassium sorbate as a preservative. The organoleptic and hypoxanthine test results show that the treatment of potassium sorbate can slow the process of spoilage by about 5 days. Yet, the most important factor affecting the shelf life of these fish is the storage temperature. Keeping the fish at 0 to 2 degrees C can prolong the storage prior to spoilage by 10 days compared with those kept at 5 degrees C. These results obtained through organoleptic tests are corroborated by both the chemical (hypoxanthine and total volatile basic nitrogen) and to some extent by the physical (cosmos) tests. The initial total bacteriological counts were 5 x 10(2) CFU/cm2 for fish surface and <10(2) CFU/g for fish flesh, and these counts rose continuously, reaching about 106 CFU/g (0 to 2 degrees C) and 10(7) CFU/g (5 degrees C) in flesh and 10(7) to 10(8) CFU/cm2 on the surface by the end of the storage period. The addition of potassium sorbate led to a smaller increase in bacterial numbers, especially during the first 15 days. Bacterial composition fluctuated during storage. The initial load on the fish surface was predominantly mesophilic and gram positive and consisted mostly (80%) of Micrococci, Bacillus, and Corynebacterium. During the next 10 days, these bacteria were practically replaced by gram-negative flora comprised mostly of Pseudomonas fluorescens that rapidly increased with storage time and accounted for 95% after 15 days.

Genetic and molecular R-plasmid analysis of Enterobacteriaceae hospital strains at Children's Hospitals of the former USSR.

R-plasmids from Enterobacteriaceae clinical strains, mainly Klebsiella and Serratia, isolated at different neonatal and children's hospitals of different cities of the former USSR for 10 years, were studied for their possible influence on the bacterial host phenotype. Hospital R-plasmids of stable inheritance persisted in hospitals from 2 to 7 years and were disseminated among strains of different genera (Klebsiella, Serratia, Enterobacter) and among different units. The data showed a possibility of long-term molecular rearrangements of R-plasmids in the hospital settings and an acquisition of genetic determinants encoding enterotoxin production. A novel R-plasmid encoding cytotoxicity to HEp-2 cells involved in two nosocomial outbreaks due to K. pneumoniae strains was reported. K. pneumoniae population heterogeneity was evaluated by using the plasmid parameters of strains. Their heterogeneity of a bacterial population was significantly lower during nosocomial outbreaks than in interepidemic periods.

The cleavage sites and localization of genes encoding the restriction endonucleases Eco1831I and EcoHI.

The restriction endonucleases Eco1831I and EcoHI cleave before the first 5'-cytosine in the recognition sequence 5'-decreases CCSGG--3'/3'--GGSCC increases-5' (where S = G or C), generate 5-base 5' cohesive ends, and are encoded by homologous plasmids that are restricted in McrA+ hosts. Thus, they differ in their cleavage specificity from that of the BcnI isoschizomer, which cleaves after the second 5' cytosine.

[The resistance plasmid of Klebsiella pneumoniae that controls its cytotoxic activity]. / Plazmida rezistentnosti Klebsiella pneumoniae, kontroliruiushchaia tsitotoksicheskuiu aktivnost'.

R-plasmid (40 MD) isolated from K. pneumoniae hospital strain makes Escherichia coli strain J62 capable of inducing a cytotoxic effect which can be detected in Hep-2 cell culture. In contrast to the initial E. coli strain J62 producing no changes in the monolayer, E. coli J62 cells containing P-plasmid induced pronounced cytotoxic changes and a sharp increase in the number of nonviable Hep-2 cells by hour 24 of interaction.

[A new site-specific endodeoxyribonuclease EcoHI]. / Novaia saitspetsificheskaia éndodezoksiribonukleaza EcoHI.

A new sitespecific endonuclease of the II class EcoHI has been isolated from Escherichia coli strain and characterized. Restriction endonuclease EcoHI recognises the nucleotide sequence C C (C/G) G G with the cleavage site between the fourth and fifth nucleotide. It is an isoshizomer of the restriction endonuclease CauII. The yield of enzyme is 2500 units of activity per 1 g of biomass. The producing strain Escherichia coli HI is nonpathogenic, easily grown with the antibiotic resistance markers permitting to cultivate the strain under selective conditions.

[Cloning and regulation of gene expression of EcoRV restriction- modification system]. / Klonirovanie i reguliatsiia ékspressii genov sistemy restriktsii i modifikatsii EcoRV.

A number of recombinant plasmids, containing EcoRV restriction-modification genes have been constructed. Individual genes of this system were introduced into plasmids of various incompatibility groups. Promoter regions of genes encoding methylase and restrictase have been cloned and studied. With the use of specialized vector pVE8 it was shown that the efficiency of the endonuclease gene promoter is comparable with early lambda phage promoters and produced about 70% of PL efficiency. The efficiency of the methylase gene promoter region was twice less than the efficiency of the restriction endonuclease gene promoter. Plasmid with restriction endonuclease gene promoter located downstream in relation to the additional regulatable phage lambda promoter PL has been obtained. It enabled us to construct strains 30-40 fold overproducing this enzyme under conditions of inactivation of the temperature sensitive phage repressor c1857. This construction directs the production of a high level (10%) of the total cellular soluble proteins) of the EcoRV restriction enzyme. The factors that influenced the level of enzyme synthesis under induction are discussed.

[Isolation and primary characteristics of elastase from a clinical strain of Pseudomonas aeruginosa]. / Poluchenie i pervichnaia kharakteristika élastazy iz klinicheskogo shtamma Pseudomonas aeruginosa.

The homogeneous preparation of elastase has been obtained from P. aeruginosa clinical strain. The molecular weight of the isolated enzyme is 33,000 daltons, and its isoelectric point is 6.8. Two media manufactured in this country (dialyzed bovine heart hydrolysate and a dried semisynthetic medium) ensuring good production of the enzyme have been proposed. The optimum time for the cultivation of the producer strain (30-40 hours) has been established. Elastase has been shown to be widely spread among P. aeruginosa clinical strains.

[Physico-chemical and biological characteristics of Pseudomonas aeruginosa elastase]. / Nekotorye fiziko-khimicheskie i biologicheskie kharakteristiki élastazy Pseudomonas aeruginosa.

Elastase isolated from P. aeruginosa clinical strain hydrolyzes elastin, casein, hemoglobin, ovalbumin, gelatin, fibrin, collagen. The optimum pH ensuring the activity of the enzyme is 7.8-8.0. Elastase shows maximum stability at pH 6.6-9.0. Heating at 80 degrees C for 10 minutes results in its practically complete inactivation. Elastase is a highly radiosensitive enzyme. Chelating agents and zinc, cobalt, mercury ions suppress its activity. Sodium and ammonium chlorides selectively inhibit the elastolytic, but not proteolytic activity of the enzyme. Elastase shows pronounced dermonecrotic and keratolytic action.

[The role of R plasmids in the resistance of bacteria in air]. / Rol' R-plazmid v rezistentnosti bakterii v vozdukhe.

The study of Escherichia coli J 53, used as a model, has revealed that some R plasmids isolated from Serratia marcescens and Klebsiella pneumoniae, found to be the cause of the outbreak of hospital infection, ensure, besides multiple drug resistance, also their viability in the air.

[Possible use of plasmids for studying the effect of space flight factors on biological objects]. / Vozmozhnost' ispol'zovaniia plazmid dlia izucheniia vliianiia faktorov kosmicheskogo poleta na biologicheskie ob"ekty.

The action of space flight factors on the phenotype and certain molecular and genetic parameters of E. coli plasmids (R, Col, Hly and others) was studied. The E. coli strains were grown and multiplied in the "Cytos" apparatus during the orbital flight of "Salyut-7" in June 1982. A synchronous experiment in the "Cytos" apparatus was performed under the Earth conditions. It was shown that space flight factors had no effect on the properties of the test strains and plasmids (antibiotic resistance, capacity for production of colicin, hemolysin, restriction endonuclease, conjugative capacity, frequency of conjugative transfers and molecular weight).

[Biological characteristics of bacteria during the Cytos-2 Soviet-French space experiment]. / Izuchenie nekotorykh biologicheskikh kharakteristik bakterii v usloviiakh provedeniia sovetsko-frantsuzskogo kosmicheskogo éksperimenta "Tsitos-2".

The experiment "Cytos-2" made it possible to reveal a certain increase in the antibiotic resistance of bacteria constituting the opportunistic pathogenic microflora of man (Staphylococcus, Escherichia coli and Pseudomonas aeruginosa) to oxacillin, erythromycin, colistin and kanamycin under the conditions of space flight. The electron-microscopic study of the postflight staphylococcal cultures revealed the thickening of the cell membrane in staphylococci. The conditions of the experiment did not affect the stability of the biochemical characteristics of P. aeruginosa cultures, as well as their virulence, immunogenic properties and type specificity.

[Use of genetic and molecular characteristics of R plasmids as an epidemiological marker in an outbreak of hospital infection]. / Ispol'zovanie geneticheskoi i molekuliarnoi l kharakteristiki R-plazmid v kachestve épidemiologicheskogo markera pri vspyshke vnutribol'nichnoi infektsii.

Antibiotic sensitivity of 38 strains of enteric bacteria, such as Serratia marcescens Klebsiella pneumoniae and others and Ps. aeruginosa isolated during an outbreak of meningitis in a premature infant resuscitation department was studied. It was shown that all the isolates were multiple resistant, most frequently to 7 antibiotics. All the resistance markers were transferred on conjugation, segregation of some markers being observed. Investigation of the plasmid composition of the clinical strains and transconjugants of E. coli revaled the presence of 2 plasmids with the molecular weights of 40 and 60 Md or one of them. The restriction analysis demonstrated that the plasmids with the same molecular weights isolated from different strains were identical. It was suggested that such plasmids originated from the same source and were distributed by conjugation. The possible part of R plasmids in epidemiological analysis of hospital infections is discussed: the possible part as an additional marker in determination of the infection source and the possible part through its ability to change the host cell phenotype, including the phage and bacteriocin types.

[Possible dependence of the results of phage typing Ps. aeruginosa strains on the presence of R plasmids]. / Vozmozhnaia zavisimost' rezul'tatov fagotipirovaniia shtammov Ps. aeruginosa ot nalichiia R-plazmid.

The plasmid composition of 209 strains of Ps. aeruginosa was determined. The strains were isolated from patients, animals and environment in different geographical areas. The number of the plasmid-containing strains averaged 26.8 per cent. The molecular weights of the plasmids varied from less than 10 to more than 150 MD. 41 conjugative plasmids were transmitted to the recipients of Ps. aeruginosa RAO 303. 66 per cent of them had a restrictive effect on the development of phages used in genetic studies, epidemiological phage typing (Lindberg Collection), and medical practice. This resulted in the changing of the phage type of the host strain. Similar results were obtained in the studies with 10 standard R plasmids representing different incompatibility groups. No relation between the spectrum of the phage restriction, group specificity and the other properties of the plasmids was observed. About 50 per cent of the plasmids markedly lowered the sensitivity level of Ps. aeruginosa RAO 303 to the therapeutic pyocyanic phage. The systems of restriction and modification of DNA coded with plasmids were not detected. A possible changing of the phage type of Ps. aeruginosa strains under the effect of R plasmids should be considered in epidemiological assays and respective treatment measures.