Chemical studies of some gram-negative bacteria and their interaction with antibacterial agents

Abstract

The growth of cells of Klebsiella aerogenes and Pseudomonas aeruginosa in the presence and absence of antibacterial agents was studied using microcalorimetry, with the concurrent measurement of such parameters as oxygen tension, pH, biomass and glucose concentration.

Cells of K. aeroqenes growing in chemically-defined synthetic medium exhibited a characteristic thermogram (heat output time curve). Oxygen depletion in the growing culture led to increasing fermentation, and growth ceased when the glucose was used up. Subsequently, acidic fermentation products were used as energy sources.

Sub-lethal concentrations of penicillin G, carbenicillin, methicillin, nalidixic acid, gentamicin, proflavine and sulphanilamide all decreased the rate of growth of cells of K. aerogenes; the greater the concentration, the greater the effect. The pattern of the heat evolution of the growing cells was also altered by growth in the presence of the antibacterials, as compared with drug-free growth. Very pronounced changes in the heat output were observed at high drug concentrations. The results are discussed in terms of changes in metabolic pathways brought about by the presence of the drug. The effects of any given antibacterial was largely reduced when used against cells which had been trained to grow in the presence of that agent.

Cells of an R-factor mediated gentamicin-resistant strain of P. aeruginosa growing in synthetic medium exhibited a thermogram which was quite different from those of cells of three other strains of differing sensitivity to gentamicin. Sub-lethal concentrations of gentamicin decreased the rate of growth of cells of P. aeruginosa strains and altered the pattern of heat output.

Small exothermic heat changes accompanied bacterial surface/gentamicin interactions.

Chemical analysis of whole cells of P. aeruginosa strains revealed differences in lipid, protein, amino acid and polysaccharide content between a very highly gentamicin-resistant strain and other resistant and sensitive strains.