Effect of temperature on synthesis of polyphosphates in Yersinia pseudotuberculosis and Listeria monocytogenes under starvation conditions

It was found that at low temperature (6-8 degrees C) in the absence of nitrogen supply and at the presence of phosphate ions in the medium, Yersinia pseudotuberculosis and Listeria monocytogenes are able to actively synthesize reserve substances as polyphosphates. Most of the bacterial polyphosphates are alkali-soluble, especially at the preliminary stage of cell growth (lag-phase). This is proved by electron microscopic studies of ultrastructure of model microorganisms. During a long starvation period under conditions of carbon and energy source deficit, L. monocytogenes and Y. pseudotuberculosis consume this biopolymer for biosynthetic and bioenergetic processes.     

Effect of volatile metabolites from germinating seeds on the reproduction of the bacteria Listeria monocytogenes and Yersinia pseudotuberculosis

The biological activity of volatile metabolites of germinating seeds of cabbage (Brassica oleacia), carrot (Daukus carota), salad (Zactuca sativa), and corn (Zea mays L.) against Listeria monocytogenes and Yersinia pseudotuberculosis was studied. It was shown that volatile metabolites are transfer factors and can be the sole carbon and energy source for these bacteria. Methanol is the main substance affecting their growth and reproduction.     

Effect of volatile metabolites from germinating seeds on the reproduction of the bacteria Listeria monocytogenes and Yersinia pseudotuberculosis

The biological activity of volatile metabolites of germinating seeds of cabbage (Brassica oleacia), carrot (Daukus carota), salad (Lactuca sativa), and corn (Zea mays L.) against Listeria monocytogenes and Yersinia pseudotuberculosis was studied. It was shown that volatile metabolites are transfer factors and can be the sole carbon and energy source for these bacteria. Methanol is the main substance affecting their growth and reproduction.     

Influence of gaseous metabolites of soil bacteria on the multiplication of Listeria monocytogenes and Yersinia pseudotuberculosis

The influence of gaseous metabolites of saprophytic soil bacteria on the growth and multiplication of L. monocytogenes and Y. pseudotuberculosis was studied. The study revealed that all cultures under study exhibited selectively both inhibiting and stimulating action on the multiplication of test cultures. Bacteria of the genera Pseudomonas and Acinetobacter showed the highest inhibiting activitywith respect to the test cultures. Volatile metabolites of bacteria of the genus Aeromonas showed the highest stimulating activity. Methanol, according to the data of chromatographic analysis, supposedly played the main role in this process and was contained in the volatile substances of Aeromonas bacteria in greater amounts than in the volatile substances of Pseudomonas bacteria.     

Use of poly-beta-oxybutyric acid by Yersinia pseudotuberculosis and Listeria monocytegenes bacteria at various temperatures

A comparative investigation of the intracellular content of poly-beta-hydroxybutyric acid showed that Yersinia pseudotuberculosis strains accumulated, on the average, lower amounts of this reserve substance than Listeria monocytogenes strains. The intracellular pool of poly-beta-hydroxybutyric acid was responsible for the growth of the bacteria at low temperatures (4-6 degrees C) in the absence of any exogenous carbon and energy source.     

The effect of the trophic and temperature conditions of cultivation on lipid synthesis by Yersinia pseudotuberculosis

The comparative study of the synthesis lipids in Y. pseudotuberculosis, depending on the conditions of their cultivation (at different temperatures in mineral media and in media, containing organic compounds), has been carried out. As demonstrated in this study, temperature in the main inducing factor, affecting the synthesis of lipids of definite classes and fatty acids, incorporated into these lipids. During the cultivation of Y. pseudotuberculosis in mineral and organic media under the conditions of low temperature their lipid composition remains unchanged, but at 6 degrees C the synthesis of unsaturated fatty acids prevails, while at 37 degrees C saturated fatty acids are mainly synthesized. On mineral media at 37 degrees C bacteria synthesize mostly nonpolar lipids in the form of reserve substances, represented by triglycerides and free fatty acids.     

Effect of acidin-pepsin on Yersinia pseudotuberculosis

The effect of acidin-pepsin solution at a concentration of 1 : 100 on newly isolated Yersinia cultures has been tested in three series of experiments. Acidin-pepsin has been found to exert a bactericidal effect on Yersinia and to induce the appearance of involutionary forms and large rod-shaped Yersinia cells with a better capacity for survival. The surviving Yersinia cells do not pass their resistance to acidin-pepsin on to their progeny and show low invasiveness and pathogenicity in white mice.     

Adaptive ultrastructural changes in soil-resident Yersinia pseudotuberculosis bacteria

After the prolonged residence (from 1 month to 2 years) in flow soil columns at 6 - 8 degrees C and 18 - 20 degrees C a complex of ultrastructural changes was detected in Y. pseudotuberculosis bacteria, depending on temperature, the duration of residence in the soil and, to a definite extent, on the strain. They were manifested in the form of cell-wall changes, the formation of the capsule and intercellular slime, changes in the ribosomal saturation of cytoplasm and the conformation state of DNA in the nucleoid zone. As the result of adaptation to nutritional deficit storage substances were accumulated in the form of electron-dense inclusions (polyphosphates) and pseudovacuoles (poly-beta-oxibutyric acid). Temperature influenced the process of mitotic division and the state of chromatin in bacteria. The described ultrastructural changes Y. pseudotuberculosis may be regarded as natural adaptive reaction to the altered conditions of their residence.     

The biochemical mechanisms of energy support in Yersinia pseudotuberculosis cells at a low cultivation temperature

The object of the study was the first stage of biological oxidation: the transfer of hydrogen electrons to the components of the respiratory chain of Y. pseudotuberculosis cells by NAD and NADF, coenzymes of pyridine-dependent dehydrogenases, having labile redox properties. The study revealed that in the low-temperature cultivation of Y. pseudotuberculosis an increase in the content of NAD and NADF was 1.5- to 2.0-fold greater than that observed at 37 degrees C, which was indicative of the fact that at low environmental temperature pyridine-dependent dehydrogenases played a more important role than at high temperature (37 degrees C). This, in combination with other mechanisms, made it possible for bacterial cells to maintain the level of energy metabolism, necessary for their survival, in the environment with low and constantly changing temperature.     

Fate of low temperature and acid-adapted Yersinia enterocolitica and Listeria monocytogenes that contaminate lactic acid decontaminated meat during chill storage

Pathogens found in the environment of abattoirs may become adapted to lactic acid used to decontaminate meat. Such organisms are more acid tolerant than non-adapted parents and can contaminate meat after lactic acid decontamination (LAD). The fate of acid-adapted Yersinia enterocolitica and Listeria monocytogenes, inoculated on skin surface of pork bellies 2 h after LAD, was examined during chilled storage. LAD included dipping in 1%, 2% or 5% lactic acid solutions at 55°C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at ≈1–1·5 pH units below that of water-treated controls. Growth permitting pH at 4·8–5·2 was reached after 1% LAD in less than 0·5 d (pH 4·8–5·0), 2% LAD within 1·5 d (pH 4·9–5·1) and after 5% LAD (pH 5·0–5·2) within 4 d. During the lag on 2% LAD meat Y. enterocolitica counts decreased by 0·9 log₁₀ cfu per cm² and on 5% LAD the reduction was more than 1·4 log₁₀ cfu per cm². The reductions in L. monocytogenes were about a third of those in Y. enterocolitica . On 1% LAD the counts of both pathogens did not decrease significantly. The generation times of Y. enterocolitica and L. monocytogenes on 2–5% LAD meats were by up to twofold longer than on water-treated controls and on 1% LAD-treated meat they were similar to those on water-treated controls. Low temperature and acid-adapted L. monocytogenes and Y. enterocolitica that contaminate skin surface after hot 2–5% LAD did not cause an increased health hazard, although the number of Gram-negative spoilage organisms were drastically reduced by hot 2–5% LAD and intrinsic (lactic acid content, pH) conditions were created that may benefit the survival and the growth of acid-adapted organisms.     

Effect of food processing-related stresses on acid tolerance of Listeria monocytogenes

Stationary-phase cells of Listeria monocytogenes grown in glucose-free or glucose-containing media were exposed for 90 min to various stresses, including acid stress (pH 4.0 to 7.0), osmotic stress (10.5 to 20.5% NaCl), and various temperatures (-5 to 50 degrees C), and were further exposed to pH 3.5. Exposure to a mildly acidic (pH 5.0 to 6.0) environment provided protection of the pathogen against acid upon subsequent exposure. This adaptive response, however, was found to be strongly dependent on other environmental conditions during the shock, such as temperature or the simultaneous presence of a second stress factor (NaCl). Growth of L. monocytogenes in the presence of glucose resulted in enhanced survival of the pathogen at pH 3.5. Sublethal stresses other than acidic stresses, i.e., osmotic, heat, and low-temperature stresses, did not affect the acid resistance of L. monocytogenes (P > 0.5). More-severe levels of these stresses, however, resulted in sensitization of the pathogen to acid.     

A nucleic acid sequence-based amplification system for detection of Listeria monocytogenes hlyA sequences.

A nucleic acid sequence-based amplification system primarily targeting mRNA from the Listeria monocytogenes hlyA gene was developed. This system enabled the detection of low numbers (< 10 CFU/g) of L. monocytogenes cells inoculated into a variety of dairy and egg products after 48 h of enrichment in modified listeria enrichment broth.     

Effect of rising temperature on the heat resistance of Listeria monocytogenes in meat emulsion

The heat resistance of a strain of L. monocytogenes was determined both in broth and in meat emulsion. The D -values for meat emulsion were approximately two to three times higher than those for broth and also the z -value increased significantly. The micro-organism proved to be more resistant when the cells were heated up slowly (0·5°C/min) to constant temperatures of 60, 63 and 66°C in meat emulsion. The D ₆₀, D ₆₃ and D ₆₆ were, respectively 12·95, 5·4 and 2·3 min. Results may have implications in the survival of Listeria monocytogenes in particular food preparations.     

Detection of Salmonella spp. and Listeria monocytogenes in suspended organic waste by nucleic acid extraction and PCR

A nucleic acid-based method for the detection of the bacterial pathogens Salmonella spp. and Listeria monocytogenes in biological waste was developed. The detection limits were less than 10 cells per ml of biological waste. The method does not include a phenol extraction step and can be easily performed in 1 to 2 days.