Qualitative and quantitative methods of studying the effect of lipids on bacteria grown on the surface of solid...

New qualitative and quantitative methods are described for the investigation of the antibacterial activity of lipids on solid media by the application of lipid-impregnated filter paper over a lawn of the organisms. The methods have been used to investigate the antibacterial activity of unsaturated fatty acids that are important in skin defence. Oleic and linoleic acids inhibited Streptococcus pyogenes markedly, Staphylococcus aureus and Staph epidermidis to a lesser extent and had no effect on Escherichia coli and Pseudomonas aeruginosa. The inhibition of growth of a strain of Str. pyogenes from a sore throat was greater than that of a strain from an outbreak of impetigo. Linoleic acid was a more potent inhibitor of bacterial growth than oleic acid, and with both acids inhibition was more pronounced under aerobic than under anaerobic conditions of incubation. The methods described could be applied in other fields such as pharmacology, horticulture and industry.