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Antimicrobial Agents and Chemotherapy, Aug 1997, 1697-1703, Vol 41, No. 8
P Domenico, RJ Salo, SG Novick, PE Schoch, K Van Horn and BA Cunha
The antibacterial properties of bismuth are greatly enhanced when bismuth
is combined with certain lipophilic thiol compounds. Antibacterial activity
was enhanced from 25- to 300-fold by the following seven different thiols,
in order of decreasing synergy: 1,3- propanedithiol, dimercaprol (BAL),
dithiothreitol, 3-mercapto-2- butanol, beta-mercaptoethanol,
1-monothioglycerol, and mercaptoethylamine. The dithiols produced the
greatest synergy with bismuth at optimum bismuth-thiol molar ratios of from
3:1 to 1:1. The monothiols were generally not as synergistic and required
molar ratios of from 1:1 to 1:4 for optimum antibacterial activity. The
most-active mono- or dithiols were also the most soluble in butanol. The
intensity of the yellow formed by bismuth-thiol complexes reflected the
degree of chelation and correlated with antibacterial potency at high molar
ratios. The bismuth-BAL compound (BisBAL) was active against most bacteria,
as assessed by broth dilution, agar diffusion, and agar dilution analyses.
Staphylococci (MIC, 5 to 7 microM Bi3+) and Helicobacter pylori (MIC, 2.2
microM) were among the most sensitive bacteria. Gram-negative bacteria were
sensitive (MIC, < 17 microM). Enterococci were relatively resistant
(MIC, 63 microM Bi3+). The MIC range for anaerobes was 15 to 100 microM
Bi3+, except for Clostridium difficile (MIC, 7.5 microM). Bactericidal
activity averaged 29% above the MIC. Bactericidal activity increased with
increasing pH and/or increasing temperature. Bismuth-thiol solubility,
stability, and antibacterial activity depended on pH and the bismuth-thiol
molar ratio. BisBAL was stable but ineffective against Escherichia coli at
pH 4. Activity and instability (reactivity) increased with increasing
alkalinity. BisBAL was acid soluble at a molar ratio of greater than 3:2
and alkaline soluble at a molar ratio of less than 2:3. In conclusion,
certain lipophilic thiol compounds enhanced bismuth antibacterial activity
against a broad spectrum of bacteria. The activity, solubility, and
stability of BisBAL were strongly dependent on the pH, temperature, and
molar ratio. Chelation of bismuth with certain thiol agents enhanced the
solubility and lipophilicity of this cationic heavy metal, thereby
significantly enhancing its potency and versatility as an antibacterial
agent.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Enhancement of bismuth antibacterial activity with lipophilic thiol chelators
Infectious Disease Division, Winthrop-Unversity Hospital, Mineola, New York 11501, USA.
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