Effect of electron beam and gamma radiation on drug-susceptible and drug-resistant Listeria monocytogenes strains in salmon under different temperature.

AIMS: To investigate the effect of gamma radiation and high energy electron beam doses on the inactivation of antibiotic-susceptible and antibiotic-resistant Listeria monocytogenes strains inoculated on the surface of raw salmon fillets stored at different temperature (-20, 4 and 25°C). METHODS AND RESULTS: The population of bacteria strains resistance to penicillin, ampicillin, meropenem, erythromycin and trimethoprim-sulfamethoxazole was generated. When using gamma irradiation, the theoretical lethal dose ranged from 1·44 to 5·68 kGy and for electron beam the values ranged from 2·99 to 6·83 kGy. The theoretical lethal dose for both radiation methods was higher for antibiotic-resistant strains. Gamma radiation proved to be a more effective method for extending salmon fillet shelf-life. The evaluation of pulsed-field gel electrophoresis electrophoregram revealed that the repair of radiation-caused DNA damage occurred faster in antibiotic-resistant L. monocytogenes strains. The number of live L. monocytogenes cells, 40 h after irradiation, also was higher in antibiotic-resistant strain suspension. CONCLUSIONS: The present study showed that gamma radiation was more effective in the elimination of the tested micro-organisms and food preservation, than a high energy electron beam. The antibiotic-resistant L. monocytogenes strains were more resistant to both radiation methods. SIGNIFICANCE AND IMPACT OF THE STUDY: There are a lot of research on the effect of radiation on the number of bacteria in food products. However, there is almost no information about the effect of strain properties, such as drug susceptibility, virulence, etc., on their resistance to ionizing radiation. An increasing number of drug resistant bacterial strains isolated from food, encourages to take up this research subject.

AMP-deaminase from human preterm placenta--kinetic regulatory properties of enzyme.

During pregnancy the isoform composition of human placental AMP-deaminase changes. This may reflect the adaptation of enzyme to changing metabolic requirements of the growing fetus. In this paper kinetic and regulatory properties of AMP-deaminase purified from human preterm (∼ 25 week of gestation) placenta were described and compared with these of the enzyme purified from term placenta. AMP-deaminase from preterm placenta was less sensitive to pH changes and in contrast to the enzyme from the term organ, at low range of substrate concentrations was not inhibited but activated by physiological concentrations of orthophosphate. This may significantly improve the catalytic efficiency of enzyme at early phase of the pregnancy.

AMP-deaminase from developing human placenta.

During pregnancy the activity of AMP-deaminase in developing human placenta gradually decreases, being in homogenates of mature, term placenta (approximately 40 week of gestation) one fourth to one third of that in homogenates of immature (approximately 25 week of gestation) organ. The gradual decrease of activity correlates inversely with the increasing presence of the form of enzyme predominating in homogenates of the mature placenta. The discrepancy observed indicate that isozymic pattern of AMP-deaminase in developing human placenta changes.

AMP-deaminase from human term placenta.

AMP-deaminase from human term placenta was chromatographed on a phosphocellulose column and physico-chemical and immunological properties of the purified enzyme were investigated. At physiological pH 7.0, in the absence of regulatory ligands (control conditions) studied AMP-deaminase manifested sigmoid-shaped substrate saturation kinetics, with half-saturation parameter (S0.5) value of about 7 mM. Addition of important allosteric effectors (ATP, ADP or orthophosphate) modified kinetic properties of studied AMP-deaminase, influencing mainly the value of S0.5, parameter. Micromolar concentrations of stearylo-CoA inhibited potently the enzyme making it no longer sensitive towards 1 mM ATP-induced activation. SDS-PAGE electrophoresis of the purified enzyme revealed presence of 68 kDa protein fragment, reacting with anti-(human) liver AMP-deaminase antibodies. Experimental results presented indicate that 'liver type' of AMP-deaminase is an enzyme form present in human term placenta.

Human liver AMP-deaminase--oligomeric forms of the enzyme.

AMP-deaminase (EC 3.5.4.6) is a key enzyme of nucleotide breakdown involved in regulation of adenine nucleotide pool in the liver. Mechanisms regulating activity of the enzyme are not completely elucidated, till now. In this paper experimental data indicating on the potential regulatory significance of changes in oligomeric structure of the enzyme are presented. SDS-PAG electrophoresis of human liver AMP-deaminase revealed the presence of three enzyme fragments. Only largest of them (the protein fragments weighing 68 kDa) reacted immunologically with anti- (human liver) AMP-deaminase antibodies. At physiological pH 7.0, in the absence of regulatory ligands, reaction catalysed by human liver AMP-deaminase was strongly dependent on enzyme concentration used, with half-saturation constant (S0.5) values increasing significantly with the degree of enzyme dilution. Preincubation with activated long-chain fatty acids--substances promoting dissociation of oligomeric enzymes, inhibited the activity of AMP-deaminase studied nearly completely. Gel filtration on Sepharose CL-6B column demonstrated existence of at least three active oligomeric forms of human liver AMP-deaminase. We postulate that oligomeric structure of the enzyme is a factor determining regulatory profile of AMP-deaminase studied.

Sulphur and oxygen isotopic composition of sulphates in springs feeding the Wieprz river and other springs of Lublin Upland and Roztocze.

Springs on Roztocze and Lublin Upland have been studied. Isotopic data are compared with data of chemical analyses. The results of studies allow us to distinguish five types of groundwaters. The differentiation is based upon different lithology; opokas, gaizes, sandy-silty-clay deposits, sands with shell sandstones, marly opokas, marly limestones and 'soft limestones of chalk type. A correlation can be observed between delta34S and the concentration of Ca or Mg ions also a correlation between HCO3- ion concentration and delta18O in sulphates. Probably these correlations are the result of some simultaneous processes, which occur in groundwater. The seasonal variations of the isotopic composition and sulphate concentration were observed in four springs feeding the upper Wieprz. The variations were simultaneous and often similar in these springs. Probably, these variations are caused by the admixture of sulphates coming from shallow water layers (or leached from soil); however the variations of the groundwater level may also change chemical and isotopic composition in groundwater.