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Biomedical subjects

L D Sabath

Publications and source records attributed to L D Sabath.

At least 91 records · Page 5Linked to original sources
PubMed1968

Measurement of three antibiotics (penicillin, cephalothin, and chloramphenicol) when present together in mixtures.

Benzylpenicillin, cephalothin, and chloramphenicol were measured individually and quantitatively when present together in mixtures at concentrations found in patients. The assay depended on the selective inactivation of two of the antibiotics, permitting the third to be assayed as if present alone. Agar seeded with a chloramphenicol-resistant, penicillinase-negative Staphylococcus aureus was used for a cylinder-plate assay of appropriately diluted fluid to determine the activity of either benzylpenicillin or cephalothin after either beta-lactamase inactivation of the former or ultraviolet light inactivation of the latter. Chloramphenicol was assayed with Sarcina lutea after appropriate beta-lactamase inactivation of both cephalothin and benzylpenicillin. Fluids containing various amounts of the three antibiotics were assayed by this method with less than 8% error. Procedures that fail to measure each antibiotic individually may give larger errors.

Biological Assay↗
PubMed1968

Enhancing effect on alkalinization of the medium on the activity of erythromycin against gram-negative bacteria.

The antibacterial activity of erythromycin was markedly enhanced by alkalinization of the culture medium or urine within the clinical range (pH 6.0 to 8.2). This effect was demonstrated against recent isolates of Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., and Pseudomonas aeruginosa, as well as against Staphylococcus aureus and Streptococcus faecalis. The urine of normal volunteers was made alkaline by ingestion of sodium bicarbonate or acetazolamide (Diamox) during administration of 1.0 g of erythromycin every 8 hr; such urine was capable of inhibiting E. coli and K. pneumoniae even when diluted up to (in one instance) 128 times with broth of the same pH as the urine. Undiluted urine of the same subjects, without alkalinization, was seldom capable of inhibiting these organisms. The range of pH (6.6 to 8.6) over which the antibacterial effect was enhanced coincided with that over which there was decreasing ionization of a basic group.

Bacteria↗
PubMed1968

Thiol-group binding of zinc to a beta-lactamase of Bacillus cereus: differential effects on enzyme activity with penicillin and cephalosporins as substrates.

Zinc, which is required for the hydrolysis of cephalosporins by a crude enzyme from Bacillus cereus 569, also increased the stability of this activity during storage. A loss in activity of the zinc-activated enzyme which occurred on prolonged hydrolysis of cephalosporin C was not restored by further addition of zinc. The thiol reagents N-ethyl maleimide (NEM), iodoacetic acid (IAA), CdCl(2), and p-chloromercuribenzoate, all at 10(-3)m, and iodine at 1.6 x 10(-3)n prevent zinc activation of the "cephalosporinase" activity. However, NEM and IAA have minimal or no demonstrable inhibitory effect if the enzyme is first treated with zinc. This suggests that zinc is linked to the apoenzyme by a thiol group. Activation by zinc is only partially prevented by NEM if the crude enzyme is pretreated with nickel, which alone causes negligible activation of the apoenzyme. The order of affinities of these metals for the apparent thiol group is thus Hg(++), Cd(++) > Zn(++) > Ni(++). The "cephalosporinase" inhibition by Hg(++) was reversible with dithiothreitol. These metals and thiol reagents do not decrease the ability of the crude enzyme to hydrolyze benzylpenicillin, which is consistent with the report that purified "penicillinase" from B. cereus contains no cysteine residue. This suggests that the beta-lactamases of B. cereus that hydrolyze penicillin and cephalosporins differ from each other by at least one amino acid (cysteine).

Adsorption↗
PubMed1967

Independent measurement of ampicillin and cloxacillin in mixtures.

A simplified method of assaying mixtures of ampicillin and cloxacillin is presented. The method consists of cylinder-plate assays of appropriately diluted samples in three assay systems in which: (i) cloxacillin is measured, utilizing agar seeded with a penicillinase-producing Staphylococcus aureus; (ii) ampicillin is measured after the greatest dilution practicable, by use of agar seeded with Sarcina lutea; and (iii) the proportion of activity found in the second assay that remains after treatment with staphylococcal penicillinase is determined on agar seeded with S. lutea. The error was 4% or less when each system was run in quadruplicate, except when there was 10 or more times as much cloxacillin as ampicillin, in which case the greatest error was 12%. Mixtures of methicillin with benzylpenicillin or with ampicillin can also be quantitated by this method.

Ampicillin↗