The antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli was evaluated at concentrations from 50 to 10 000 mu g ml(-1) and pH levels from 5.5 to 8.0. The minimum inhibitory concentrations...
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The antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli was evaluated at concentrations from 50 to 10 000 mu g ml(-1) and pH levels from 5.5 to 8.0. The minimum inhibitory concentrations decreased with increasing pH. Protamine inhibited E. coli at all pH values while L. monocytogenes was inhibited at pH 6.5 and above. The antimicrobial efficacy of protamine decreased in the presence of negatively charged gelatine B but remained almost unchanged with addition of the positively charged gelatine A. Binding studies showed that the amount of protamine adsorbed to culture media components in tryptic soy broth and bacterial cells increased with increasing pH values. The increased efficacy of protamine at alkaline pH may be explained on the basis of an increase in electrostatic affinity for the cell surface of target cells. E. coli produced a protamine-degrading enzyme, however, was still susceptible to protamine.
The effect of a high hydrostatic pressure treatment on the Gram-positive Listeria monocytogenes strain Scott A and the Gram-negative Salmonella typhimurium strain Mutton (ATCC13 311) has been determined in stationary ...
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The effect of a high hydrostatic pressure treatment on the Gram-positive Listeria monocytogenes strain Scott A and the Gram-negative Salmonella typhimurium strain Mutton (ATCC13 311) has been determined in stationary phase cell suspensions. Pressure treatments were done at room temperature for 10 min in sodium citrate (pH 5.6) and sodium phosphate (pH 7.0) suspension buffers. Increasing pressure treatments resulted in an exponential decrease of cell counts. Salmonella typhimurium suspended at low pH was more sensitive to pressure treatments. Progressive morphological changes were evident with the pressure increase. Cell lysis only appeared with the highest pressure treatments. Cell volume was not affected by pressure treatment. A progressive decrease of delta pH (pH(in) - pH(out)), intracellular potassium and ATP contents was demonstrated with the pressure increase. A parallel lowering of membrane potentials was measured.
Establishment and maintenance of an intracellular niche are critical to the success of an intracellular pathogen, Here, the pore-forming protein listeriolysin O (LLO), secreted by Listeria monocytogenes, was shown to ...
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Establishment and maintenance of an intracellular niche are critical to the success of an intracellular pathogen, Here, the pore-forming protein listeriolysin O (LLO), secreted by Listeria monocytogenes, was shown to contain a PEST-like sequence (P, Pro;E, Glu;S, Ser;T, Thr) that is essential for the virulence and intracellular compartmentalization of this pathogen. Mutants lacking the PEST-like sequence entered the host cytosol but subsequently permeabilized and killed the host cell. LLO lacking the PEST-like sequence accumulated in the host-cell cytosol, suggesting that this sequence targets LLO for degradation. Transfer of the sequence to perfringolysin O transformed this toxic cytolysin into a nontoxic derivative that facilitated intracellular growth.
Listeria monocytogenes 19112, Scott A, and 10403S were grown in tryptic soy broth (TSB) and TSB supplemented with 25 to 100 mu g/ml of iron (Fe) and 0.5 to 2.5 mu g/ml selenium (Se) to examine the effects on catalase ...
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Listeria monocytogenes 19112, Scott A, and 10403S were grown in tryptic soy broth (TSB) and TSB supplemented with 25 to 100 mu g/ml of iron (Fe) and 0.5 to 2.5 mu g/ml selenium (Se) to examine the effects on catalase (CA), superoxide dismutase (SOD), and listeriolysin O (LLO) activities. Growth in TSB supplemented with Fe resulted in significant increases in CA, SOD, and LLO activities in all three strains when compared to growth in TSB. The addition of 0.5 mu g/ml Se to TSB resulted in significantly higher CA and LLO activities in L. monocytogenes 19112 but showed no effect on Scott A or 10403S. These results suggest that Fe plays a role in increasing the activities of CA, SOD, and LLO.
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