Clinical isolates of Staphylococcus aureus carry various antiseptic and disinfectant resistance determinants (qac genes) on a variety of plasmids. The biochemistry and specificity of these resistance genes in S. aureus is the subject of this report. The qac genes were separated into two families on the basis of resistance profiles and DNA homology. Isotopic and fluorimetric assays demonstrated that the qac genes encode efflux systems that rely on proton motive force.

An alcohol dehydrogenase was shown to be induced in Aspergillus nidulans by periods of anaerobic stress. This alcohol dehydrogenase was shown to correspond to the previously described cryptic enzyme, alcohol dehydrogenase III (McKnight et al. 1985), by analysis of a mutation in the structural gene of alcohol dehydrogenase III, alcC, created by gene disruption. Survival tests on agar plates showed that this enzyme is required for long-term survival under anaerobic conditions. Northern blot analysis and gene fusion studies showed that the expression of the alcC gene is regulated at both the transcriptional and translational levels. Thus there are mechanisms in this filamentous fungus allowing survival under anaerobic stress that are similar to those described in higher plants.

Clinical isolates of Staphylococcus aureus carry various antiseptic and disinfectant resistance determinants (qac genes) on a variety of plasmids. The biochemistry and specificity of these resistance genes in S. aureus is the subject of this report. The qac genes were separated into two families on the basis of resistance profiles and DNA homology. Isotopic and fluorimetric assays demonstrated that the qac genes code efflux systems that rely on proton motive force.

1. Mitochondrial DNA from Tetrahymena pyriformis strain T has a buoyant density (ρ) of 1.685 compared with ρ1.688 for whole cell DNA. Mitochondrial preparations from T. pyriformis strain W show an enrichment of a light satellite (ρ1.686), although this is not obtained free from nuclear DNA (ρ1.692). 2. T. pyriformis mitochondrial DNA renatures rapidly and the kinetics of this process indicate a complexity of approx. 3×107 daltons. 3. The base-pairing in the renaturation product is of a precise nature, since the ‘melting’ temperature (80.5°C) is indistinguishable from that of the native DNA (80.5°C). 4. Centrifugation of mitochondrial DNA in an alkaline caesium chloride density gradient gives two bands, implying the separation of the complementary strands.

The gene specifying the ethidium efflux system of Escherichia coli has been cloned on a 3.2 kbp HindIII fragment and located on a 1.2 kbp fragment within this. Cross-resistance studies indicate that the system has a broad specificity for monovalent cations and the gene shows no hybridisation with similar genes found in Staphylococci.