It was recently proposed that bactericidal antibiotics, besides through specific drug-target interactions, kill bacteria by a common mechanism involving the production of reactive oxygen species (ROS). However, this mechanism involving the production of hydroxyl radicals has become the subject of a lot of debate. Since the contribution of ROS to antibiotic mediated killing most likely depends on the conditions, differences in experimental procedures are expected to be at the basis of the conflicting results. In the present study different methods (ROS specific stainings, gene-expression analyses, electron paramagnetic resonance, genetic and phenotypic experiments, detection of protein carbonylation and DNA oxidation) to measure the production of ROS upon antibiotic treatment in Burkholderia cepacia complex (Bcc) bacteria were compared. Different classes of antibiotics (tobramycin, ciprofloxacin, meropenem) were included, and both planktonic and biofilm cultures were studied. Our results indicate that some of the methods investigated were not sensitive enough to measure antibiotic induced production of ROS, including the spectrophotometric detection of protein carbonylation. Secondly, other methods were found to be useful only in specific conditions. For example, an increase in the expression of OxyR was measured in Burkholderia cenocepacia K56-2 after treatment with ciprofloxacin or meropenem (both in biofilms and planktonic cultures) but not after treatment with tobramycin. In addition results vary with the experimental conditions and the species tested. Nevertheless our data strongly suggest that ROS contribute to antibiotic mediated killing in Bcc species and that enhancing ROS production or interfering with the protection against ROS may form a novel strategy to improve antibiotic treatment.

Hydrogenation of ketones in presence of platinum oxide in alcoholic acid leads to ethers with good yields.THE reaction COR1R2 + R30H R1R2CH*OR3 seems generally to occur on hydrogenation in alcoholic acid in presence of platinum. A variety of ketones and also an aldehyde have been tested (see Table 1) and have given reasonable to excellent yields. As side products, the alkane and alcohol related to the carbonyl compound are also formed, in yields varying greatly according to the conditions. Possible intermediates are the hemiketal, R1R2C(OH)*OR3, the ketal, R1R2C(OR3),, and the enol ether R2*CH:CR1*OR3, the first seeming to be the most likely. TABLE 1. Yields of ethers obtained in presence of alcohols.*

A mechanism is proposed for the formation of ethers and alkanes by the alcoholic acidic reduction of ketones with Adam's catalyst. An enol precursor for the alcohol formation seems logical, while enol, enolether and a half hydrogenated carbonium ion (HHC) also play a role in the formation of ethers and alkanes, as depicted in chart 11. (*) Part of a thesis by M. Acke, University of Ghent 1964. Department of (1) M. VERZELE, M. ACKE and M. ANTEUNIS,

The methyl ketal formation is strongly exothermic (‐14,6 Kcal/mole) with cyclohexanone and moderately so with cyclopentanone (‐3,5 Kcal/mole) and with cyclobutanone (‐2,5 Kcal/mole). An exceptional low reaction entropy is noted for cyclohexanone (‐59 E.U.) and this is partly ascribed to the occurence of a high proportion of the twist conformation in cyclohexanone.