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Biomedical subjects

A Hurst

Publications and source records attributed to A Hurst.

At least 55 records · Page 3Linked to original sources
PubMed1973

Pysiological studies on the recovery of salt tolerance by Staphylococcus aureus after sublethal heating.

Cultures of S. aureus in 100 mM potassium phosphate buffer heated at 52 C for 15 min lost their tolerance to 7.5% NaCl. After incubation in a complex growth medium or in a diluted dialyzed medium in which unheated cells were unable to grow, salt tolerance was regained. Heat injury caused 30% loss of lipid. During recovery, the concentration of C(15) and C(17) fatty acids returned to normal, and there appeared to be an oversynthesis of C(16) and C(18) unsaturated acids. Penicillin abolished the latter reaction without affecting recovery; chloramphenicol did not affect fatty acid oversynthesis but reduced recovery. The K/Na ratio was 12.6 in control cells and 3.4 in injured cells, where it remained during the recovery of salt tolerance. Aspartate uptake was about 10% of the control level after injury and about 35% at recovery. Control cells grew without a lag on subculture, but injured cells which had regained their salt tolerance needed about 2 more h of incubation. Cells recovering with penicillin needed 6 more h, and cells recovering with chloramphenicol did not grow without a prolonged lag. Cells of S. aureus, therefore, may recover their salt tolerance while various membrane functions are still damaged.

Aspartic Acid↗
PubMed1972

Effect of secondary metabolites on the organisms producing them: effect of nisin on Streptococcus lactis and enterotoxin B on Staphylococcus aureus.

The effect of secondary metabolites added to cultures of the organisms producing them was investigated. Nisin was added to growing cultures of a nisin-producing strain of Streptococcus lactis (354/07) and enterotoxin B to strains of Staphylococcus aureus (S6 and 243) producing enterotoxin B. One quarter (12 mug/ml) of the amount of nisin formed by the culture of S. lactis inhibited lag-phase cells and lysed log-phase cells. The same amount of nisin added before inoculation or at a time when nisin synthesis had started (in late log phase), caused only transient delay in growth. Inhibition of growth of the two enterotoxin B-producing strains of S. aureus could not be demonstrated at any stage of their growth cycle with as much as 1 mg of enterotoxin B per ml of medium.

Anti-Bacterial Agents↗
PubMed1969

Change in the absorbancy of bacterial suspensions before initiation of growth.

The apparent absorbancy of suspensions of stationary-phase cells of Streptococcus lactis strain 354/07 decreased immediately after being placed in fresh media. This optical effect also occurred in defined mixtures of buffer glucose and KCl. CaCl(2) caused the absorbancy to increase. CaCl(2) and KCl together had about the same effect as KCl alone. SrCl(2) could replace CaCl(2), but it was less effective by a factor of 10(2). MnCl(2), MgCl(2), and NaCl were without effect. The absorbancy did not change when cells were first killed by p-chloromercuribenzoate or when the reaction was carried out at 0 C. The rate of the reaction was dependent on temperature and concentration of glucose and salts. Gradient centrifugation suggests that this optical effect was caused by change in the refractive index of the test organism rather than by change in volume. Nine other organisms representing four additional genera gave the same optical effect as S. lactis 354/07. Two other organisms reacted feebly whereas another strain of S. lactis reacted in the opposite way, the absorbancy of the suspension increasing instead of decreasing. Spores of Bacillus cereus did not respond.

Anti-Bacterial Agents↗
PubMed1969

Electron microscopic study of membranes and walls of bacteria and changes occurring during growth initiation.

Thin sections of stationary-phase Streptococcus lactis cells showed that the wall and membrane are 20 and 7 nm thick, respectively. Whole cells were examined by negative staining with ammonium molybdate and by shadowing. On air-drying of whole cells, the membrane pulled away from the wall revealing adhesions between these organelles. Adhesions could not be seen after subculture of the stationary-phase cells into complex media or into solutions containing glucose, KCl, and CaCl(2) in tris(hydroxymethyl)aminomethane buffer. The adhesions were also observed in stationary-phase cells of other gram-positive bacteria. Fractured freeze-etched cells of S. lactis had a smooth outside surface, but the inside of the wall (or outside of the membrane) had a regular structure, repeating at 10 nm, which could correspond to the adhesions observed in the negatively stained air-dried cells. Freeze-etching also revealed holes in the outside wall which had the shape of inverted truncated cones. The outside diameter of the cone was 60 nm, and the diameter on the inside surface of the wall was 20 nm. The membrane had upstanding plugs, 20 nm in diameter, which could fill the holes in the wall.

Bacillus cereus↗