The effects of the riminophenazine antimicrobial agents clofazimine and B669 as well as those of lysophosphatidylcholine (LPC), on microbial K(+)-transporting systems were investigated in a range of Gram-positive and Gram-negative bacteria using 42K and 86Rubidium (86Rb) as tracers. Exposing the Gram-positive bacteria to 0.1-10 mg/L of the drugs resulted in a dose-related inhibition of uptake of both radiolabelled cations due primarily to the inhibition of their influx which was prevented by pretreating the microorganisms with 25 mg/L alpha-tocopherol (vitamin E) which forms a complex with lysophospholipids. In contrast, Gram-negative bacteria were resistant to riminophenazine-mediated inhibition of K(+)-transport, with only one of four well-characterised K(+)-transport system mutants of Escherichia coli, namely Kup, being affected by the antimicrobial agents. The selective antimicrobial activity of riminophenazines against Gram-positive bacteria is probably achieved by lysophospholipid-mediated inactivation of K(+)-transport, while Gram-negative microorganisms possess several K(+)-transport systems which are either inaccessible and/or insensitive to lysophospholipids. Thus, K(+)-transport systems may represent novel targets for antimicrobial agents.
The importance of sulfate-reducing bacteria (SRB) in nature has been widely recognized for many years. However, little is known about the ecology of SRB. The problem has been detecting, classifying, and quantifying these organisms. There are many shortcomings in the use of culture media for this purpose. As an alternative, fluorescent antibody (FA) techniques were considered as a method for the detection and identification of SRB. Antisera were prepared against whole cells of different species of SRB and evaluated for detection and identification of these organisms. Surface antigens of SRB were species specific. In addition, culture conditions influenced the expression of surface antigens, causing the antisera to be extremely specific. These results were confirmed by the sodium dodecyl sulfate-polyacrylamide-gel electrophoresis (SDS-PAGE) profiles of membrane proteins. On the basis of this specificity, the application of FA produced against culture collection strains would have limited application for detecting, identifying, and enumerating these organisms in nature.
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