Search PubMed⌕ Search

Biomedical subjects

A Hurst

Publications and source records attributed to A Hurst.

At least 37 records · Page 2Linked to original sources
PubMed1983

Survival in foods of Staphylococcus aureus grown under optimal and stressed conditions and the effect of some food preservatives.

Staphylococcus aureus was grown in a rich peptone medium which became alkaline with continued incubation. Cells were grown at 37 degrees C and in the same medium containing 1 M NaCl at 46 degrees C, a temperature at which this organism can grow only when protected by NaCl. Cells of these cultures are hereafter called 37 degrees C-cells and 46 degrees C-cells, respectively. The 37 degrees C-cells harvested when the pH was 7.1 to 7.7 had decimal reduction times (D60-value) of 1.8 to 3.1 min in 50 mM pH 7.2 Tris buffer. The D60 value of 46 degrees C-cells tested in the same way, harvested from cultures at pH 6.6 to 7.6, ranged from 5.3 to a maximum of 12.8 min. In milk, green beans, peas, or beef slurry, the D60-value of 46 degrees C-cells was about four times higher than that of 37 degrees C-cells. Length of survival after freeze-drying in skim-milk powder exposed to air was longest for the cells with the highest D-value. In freeze-dried peas and media acidified with acetic and lactic acids, 46 degrees C-cells survived longer than 37 degrees C-cells. However, the sensitivity of the two kinds of cells to potassium sorbate, sodium benzoate, and sodium propionate was essentially the same, but the 46 degrees C-cells were more resistant to butylated hydroxyanisole and sodium nitrite.

Acetates↗
PubMed1982

N-Acetylprocainamide kinetics and clinical response during repeated dosing.

Kinetics of and clinical responses to N-acetylprocainamide (NAPA) were evaluated in 10 patients with chronic ventricular arrhythmias who had not responded to usual doses of currently available antiarrhythmic drugs. Kinetic data analysis was by measured NAPA concentrations (n = 149) collected during repeated dosing. Response was evaluated with serial 24-hr ambulatory ECGs. An a priori kinetic model based on earlier studies predicted NAPA concentrations well (r = 0.94, SEE = 3.6 mg/l). The capability for defining patient-specific estimates for drug disposition with six or seven serum concentrations measured at the outset of therapy was subsequently confirmed with larger data sets from the same patients. Mean values for elimination rate (0.082 hr -1 +/- 0.017) and volume of distribution (1.25 l/kg +/- 0.28) were of the same order as in earlier single-dose studies. A substantial degree of interpatient and intrapatient variability in the absorption rate for NAPA was observed. NAPA was not found to be clinically effective in any of the 10 patients, although two patients demonstrated a greater than 70% reduction in frequency of premature ventricular contractions. There were adverse effects in all patients, which frequently required dose reduction or cessation of therapy. In this group of patients with resistant arrhythmias, NAPA was no more effective than baseline therapy, and adverse effects often limited complete evaluation. The kinetic analysis demonstrated the feasibility of a strategy for developing patient-specific kinetic models that may have applications to other antiarrhythmic drugs.

Acecainide↗
PubMed1981

Nisin: a possible alternative or adjunct to nitrite in the preservation of meats.

Nisin at 75 ppm (75 microgram/g) was superior to 150 ppm of nitrite in inhibiting outgrowth of Clostridium sporogenes PA3679 spores in meat slurries, which had been heated to simulate the process used for cooked ham. The inhibitory activity of nisin decreased as the spore load or pH of the slurries increased. Unlike nitrite, inhibition by nisin was unaffected by high levels of iron either as a constituent of meats or when added as an iron salt. In slurries treated with 75 ppm of nisin, refrigerated storage for 56 days resulted in depletion of nisin to a level low enough to allow outgrowth within 3 to 10 days if the slurries were subsequently abused at 35 degrees C. In contrast, a combination of 40 ppm of nitrite and either 75 or 100 ppm of nisin almost completely inhibited outgrowth in these slurries. The nisin-nitrite combination appeared to have a synergistic effect, and the low concentration of nitrite was sufficient to preserve the color in meats similar to that of products cured with 150 ppm of nitrite.

Animals↗
PubMed1981

Repair of salt tolerance and recovery of lost D-alanine and magnesium following sublethal heating of Staphylococcus aureus are independent events.

Sublethal heating of Staphylococcus aureus S6 in potassium phosphate buffer caused loss of salt tolerance, D-alanine, and magnesium. During incubation in rich complex media all three of the damaged sites were repaired. Repair occurred more slowly but went to completion in a dilute synthetic medium (DSM), free of D-ala. DSM plus penicillin or D-cycloserine allowed repair of salt tolerance but recovery of normal levels of D-ala or Mg was prevented. When DSM-repaired cells were cultured into fresh rich medium they grew rapidly after a short lag. Cells which had acquired their salt tolerance in DSM plus cycloserine and were D-ala and Mg deficient grew slowly and had a lag of 3 h. We suggest that heat damage has two separate primary targets in S. aureus cells: the membrane, which is manifested by loss of salt tolerance, and a second site, possibly teichoic acids, manifested by loss of D-ala and Mg.

Alanine↗
PubMed1981

Salt extends the upper temperature limit for growth of food-poisoning bacteria.

Inclusion of NaCl into the growth medium raised the upper temperature limit of growth of the following organisms: Staphylococcus aureus (two strains), Salmonella senftenberg, S. typhimurium, Escherichia coli, Streptococcus faecalis, Bacillus cereus, Clostridium sporogenes, C. perfringens (two strains). The magnitude of the response varied with the culture, the largest being 3.5 degrees with B. cereus cells. The spores of B. cereus were not protected by salt but clostridial spores behaved as the vegetative cells (response of 2.5 degrees). The optimal salt concentration for the protective effect varied with the organism ranging from 0.2 M for the Gram-negative organisms to 1.0 M for S. aureus.

Bacillaceae↗
PubMed1980

The effect of NaCl on the upper temperature limit for growth of and enterotoxin synthesis by Staphylococcus aureus.

The upper temperature limit for growth of an enterotoxin A producing strain (MF31) and of an enterotoxin B producing strain (S6) was about 44-45 degrees C in either a peptone-based medium or heart infusion broth. In the presence of NaCl, growth and production of enterotoxin, coagulase, and thermostable nuclease occurred up to 2 degrees C higher. The optimal concentration of NaCl for the temperature elevation effect was 1 M.

Bacterial Toxins↗
PubMed1980

Mechanism of the temperature protective effect of salts on Staphylococcus aureus.

In the previous paper we reported that the maximum temperature for growth of Staphylococcus aureus was about 2 degrees C higher in media supplemented with NaCl. We now show that MgCl2 was the most effective protectant at 0.4 M. NaCl and KCl were as effective as MgCl2 when tested at 1 M. NH4Cl was less effective at all concentrations and LiCl was not protective. Sucrose and glucose (1M) gave about half the biomass of 1M NaCl. Glycerol, Na2SO4, NaNO2, NaNO3, and CH3COONA were not protective. Protection is probably due to the nonpenetrating solute (sucrose) or the nonpenetrating Cl- anion. Mg2+ had an effect additional to that attributable to Cl- because MgSO4 and to a slight extent (CH3COO)2Mg were protective. The morphology of the cells grown at 45 degrees C in 1 M NaCl was abnormal: septation became irregular, cell walls were thickened, and the cells occurred in irregularly sized clumps surrounded by capsular material.

Ammonium Chloride↗
PubMed1978

Stability of ribosomes of Staphylococcus aureus S6 sublethally heated in different buffers.

Cells of Staphylococcus aureus heated at 52 degrees C in magnesium-chelating buffers [pH 7.2, 50 mM potassium phosphate or 50 mM tris(hydroxymethyl)-aminomethane containing 1 mM ethylenediaminetetraacetic acid] leaked 260-nm absorbing material, shown to be RNA, and suffered destruction of their ribosomes. These cells did not regain their salt tolerance when repair was carried out in the presence of actinomycin D (5 microgram/ml). Cells similarly heated in magnesium-conserving buffers [pH 7.2, 50 mM tris(hydroxymethyl)aminomethane containing 10 mM MgCl2 or piperazine buffer] did not leak RNA, suffered no ribosomal damage when heated for 15 min, and recovered, at least partially, in the presence of actinomycin D. Ribosomal damage, is therefore, a consequence of Mg2+ loss and is not an effect of heat per se. Cells suspended in either Mg2+-chelating or Mg2+-conserving buffers lost salt tolerance to about the same extent during heating at 52 degrees C. Therefore, sublethal heat injury can not be attributed to ribosomal damage.

Buffers↗
PubMed1976

Enumeration of sublethally heated staphylococci in some dried foods.

The effect of 45 substances to restore the salt tolerance of sublethally heat-injured Staphylococcus aureus was tested. Sodium pyruvate, yeast extract, L-histine, casitone (Difco), adenosine triphosphate, and acetylphosphate were effective. For enumeration a repair medium was first used, containing sodium pyruvate and penicillin in 1% skim milk. This step was followed by counting on Baird-Parker agar with penicillinase. This method was selective; fewer than 100 staphylococci/g food could be enumerated and it gave counts about 8 times higher than the method of Giolitti and Cantoni used as a five-tube most probable number technique. Heat injury sensitized S. aureus to polymyxin.

Adenosine Triphosphate↗
PubMed1976

Magnesium requirement of Staphylococcus aureus for repair from sublethal heat injury.

Heating in potassium phosphate buffer causes Staphylococcus aureus to lose its salt tolerance and 30-40% of its cellular Mg2+. Repair from injury (regain of salt tolerance) occurred when injured cells were incubated under optimal conditions in synthetic media containing penicillin to prevent growth. Cells died when phosphates or amin acids were omitted from the medium. Omission of vitamins, glucose, Na+, and K+ had no effect. Omission of Mg2+ diminished repair. In a minimal repair medium (MRM) which contained only 3 X 10(-6) M Mg (as an impurity), injured cells rapidly regained their original Mg content. About 20-50% of the cells also regained their salt tolerance provided that less than 10(9) cells/ml were used. With 10(10) cells/ml there was no repair and cellular Mg content was half that of the control. Addition of 10(-3) M ethylenediamine-tetraacetic acid (EDTA) to MRM also prevented repair. Addition of 10(-2) M Mg to MRM EDTA permitted complete repair.

Amino Acids↗
PubMed1975

Loss of D-alanine during sublethal heating of Staphylococcus aureus S6 and magnesium binding during repair.

Staphylococcus aureus S6 sublethally heated at 52 degrees C for 15 min to 0-1 M-potassium phosphate buffer pH 7-2, lost neither the ribitol teichoic acid of the wall nor the glycerol teichoic acid of the membrane. Hurst et al. (1974) showed that this heating caused 40% loss of the cellular Mg, and we now report the loss of 65% of the ester-bound D-alanine of teichoic acid. Repair from sublethal heat injury, measured by the return of salt tolerance, occurs in a simple no-growth medium provided that the cell concentration is less than 5 x 10(8)/ml. During repair, D-alanine is rapidly synthesized. Fully-repaired cells contain four times more D-alanine than do freshly-injured cells. Magnesium is present in the medium at only 3 x 10(-6) M, yet the cellular Mg concentration returns to normal within 1 h of incubation, even in the presence of EDTA. The results suggest that repair occurs in two stages. Soon after injury, in the absence of the competitive effect of D-alanine, Mg is strongly bound to teichoic acid. In repaired or uninjured cells Mg is less strongly bound. The implications of these findings are discussed in relation to the cation-binding function of teichoic acid.

Alanine↗
PubMed1975

A technique for obtaining linear heat-survivor curves with Staphylococcus aureus and its application to the assay of sublethal heat injury.

Staphylococcus aureus was grown in a complex (HK) medium either by a batch technique or by a modified batch technique after growth in a chemostat. These cultures were heat-treated at 52 degrees C, and counted on trypticase soy agar (TSA) or trypticase soy agar containing 7.5% NaCl (TSAS). When linear heat-survivor curves were obtained decimal reduction times (D52 degrees C) could be calculated from the TSA counts and pseudodecimal reduction times (D' 52 degrees C) from the TSAS counts. The D or D' values of batch-grown cells varied from 22 to 133 min and from 3 to 12 min, respectively. With cells grown by the modified technique the values were less variable (D was 22-51 min and D' was 3-7 min). D and D' values could be calculated from the same heat treatment in two of the six estimations with cells grown by the modified technique.

Bacteriological Techniques↗