SUMMARY: Screening tests indicated that Gram positive bacteria are inhibited by long chain fatty acids. No inhibition was demonstrated with Gram negative bacteria. The minimum inhibitory concentrations (MIC) for a series of the fatty acids are presented. Growth curves in the presence of linolenic acid showed increases in lag phase duration and calcium addition reversed this effect, thus indicating the arbitrary nature of the MIC values. Bactericidal studies showed lauric acid to be the most active saturated fatty acid but the activity was less than that of the C18 unsaturated fatty acids. Oleic acid was more effective than elaidic acid. Calcium ions, cholesterol and ergocalciferol reversed the activities of lauric and linoleic acids but magnesium ions effectively counteracted lauric acid only. A physicochemical explanation for the relative activities has been attempted.

1. The potential for improving the nutritive value of commercial solvent-extracted, heat-treated soya-bean meal (SBM) by protease treatment was measured using growing broiler chicks and tube-fed broiler cockerels. 2. SBM was pre-treated (50 degrees C for 2 h) with water alone; at alkaline pH (initial pH 8.25) with and without protease P1 (isolated from a Bacillus species) or at acid pH (initial pH 4.5) with and without protease P2 (isolated from an Aspergillus species) and incorporated into diets (290 g SBM/kg diet) for broiler chicks (20 chicks/treatment). Only protease P2 treatment improved chick performance; from 7 to 28 d of age, chicks fed on treated SBM had greater feed intakes and gained more weight than chicks fed on untreated SBM. Both proteases P1 and P2 significantly reduced chick serum anti-soya antibodies while protease P2 treatment increased apparent ileal nitrogen (N) digestibility and apparent N retention across the whole digestive tract. 3. Two tube-feeding experiments established that, of the treated SBMs used in experiment 1, only protease P2 treatment improved apparent N digestibility and true metabolisable energy. Also it was shown that increasing the temperature at which treated SBM was dried to 60 degrees C, compared with freeze-drying or drying at 50 degrees C reduced apparent N digestibility and true metabolisable energy of SBM with no significant interactions between enzyme treatment and drying temperature for both apparent N digestibility and TME. 4. It is concluded that, overall, the nutritional value of SBM assayed in a growth trial and by tube feeding was improved by treatment with protease P2 and not by treatment with protease P1.

1. A study was undertaken to examine the effect of supplementation of diets with fats of different chain length and degree of unsaturation on the performance, carcase characteristics and tissue fatty acid composition of broilers. 2. Three hundred and sixty 19-day-old female broilers were fed on diets containing supplemental fat/oil (50 g/kg) in the form of beef tallow (BT) (diet T-T), soyabean oil (SBO) (diet S-S), rapeseed oil (RSO) (diet R-R), marine oil (MO) (diet M-M) or binary mixtures (0.5:0.5 w/w) of these lipids (diets T-S, T-R, T-M, S-R, S-M, and R-M) to 54 d of age. Food intake, live weight, plucked weight and the lipid concentration and fatty acid composition of abdominal fat pad, liver and breast muscle were measured. 3. Food intake, plucked weight and live weight were greatest for diet T-T and lowest for diet R-R. Food conversion ratio was poorest for birds fed on diets containing BT. Lipid concentration in abdominal fat pad was significantly higher in birds fed on diets containing SBO. Liver lipid concentration was significantly reduced by diets containing RSO. 4. Abdominal fat pad fatty acid profile was most readily altered by dietary fatty acids. There was a strong correlation between dietary fatty acid composition and tissue fatty acid composition for all fatty acids except C14:0, C20:0, C20: 2n-6 and C20: 4n-6. The tissue P/S ratio ranged from 0.40 for diet T-T to 1.40 for diet S-S. The n-6/n-3 ratio was significantly increased by the inclusion of SBO and decreased by the inclusion of MO. 5. Liver fatty acid profile was least modified by dietary fatty acids. There was an inverse relationship between liver and dietary C20:4n-6 concentration. Tissue C18:2n-6 and C20:4n-6 were highly correlated, suggesting significant interconversion by delta-6 desaturase in this tissue. The n-6/n-3 ratio was significantly increased by inclusion of SBO and significantly decreased by the inclusion of MO. 6. In breast muscle MO-based diets increased the proportion of n-3 PUFA at the expense of n-6 PUFA. The tissue concentrations of C18:1n-9, C18:2n-6, C20:1n-9, C20:5n-3, C22:5n-3 and C22:6n-3 were strongly correlated with dietary fatty acid composition. Muscle and diet P/S and n-6/n-3 ratios were highly correlated.

SUM-Y.Long chain fatty acids stimulated oxygen uptake by Gram positive bacteria a t bactericidal and protoplast lytic concentrations and produced inhibition at higher levels. The order of activity between individual acids and effects of reversal agents on respiratory activity corresponded to those which produced bactericidal activity. Protoplasts were more susceptible to inhibition than whole cells. Gram negative bacteria were inhibited to a limited extent at high fatty acid concentrations, but spheroplasts were highly sensitive. Fatty acids inhibited amino acid uptake both aerobically and anaerobically a t sub-bactericidd levels. The effects were reversed by metal cations, and reflected the activity of dinitrophenol and sodium azide. The susceptibility of organisms to inhibition was of the same order as the sensitivity to other antibacterial effects. The probable mode of action of the fatty acids is discussed in terms of the interference with energy metabolism within the bacterial cell.

Fatty acids of chain length > C,, induced lysis of protoplasts at pH 7.4 when the concentration was nearly bactericidd. At p H 6, lauric and linoleic acids produced lysis above bactericidal concentrations but, at pH 8, lysk was produced by the same acids below bactericidal concentrations. The lysis was immediate a t p H 8, but at pH 6 the effect was preceded by contraction of protoplasts. At pH 7.4 the order of lytic activity between individual fatty acids was similar to that of bactericidal activity and the response of protoplasts of Bacillwr megaterium relative to those of 2Mimcoccus lyeodeikticus reflected differences in bactericidal sensitivity though whole cells were much less sensitive to fatty acid-induced leakage effects then protoplasts. Reversal agents antagonized the lysis of protoplasts by fatty acids. A physicochemical basis for the action of fatty acids and reversal agents on protoplasts and whole cells is discussed.ANTIBACTERIAL EIWECTS of long chain fatty acids have already been discussed in relation to bactericidal activity and physicochemical properties in solution (Galbraith, Miller, Paton & Thompson, 1971 ;Galbraith & Miller, 1973a).Several workers have produced evidence which suggests that antibacterial compounds with lipophilic and hydrophilic properties act on the cytoplasmic membrane (Hugo, 1967; Salton, 1968). The most convenient method of investigating the interaction between these antibacterial compounds and the bacterial membrane involves the use of protoplasts and spheroplasts. Gilby & Few (1957, 1960) have demonstrated the lysis of protoplasts by surface active agents and correlated the lytic activity with antibacterial activity on whole bacterial cells. In previous work with long chain fatty acids (Galbraith & Miller, 1973a) the reversible uptake of 14C labelled fatty acids by bacterial cells and protoplasts also indicated that the probable site of action of the fatty acids was the cytoplasmic membrane and so in the present work the lysis of protoplasts has been studied in order to investigate the relationship between antibacterial action and phyaicochemical activity on the membrane. The studies have included the effects of pH, aliphatic chain length, reversal agents and the sensitivity of the individual bacterial species which were used to determine bactericidal activity and uptake. An attempt was also made to investigate the physicochemical effects of fatty acids on whole cells in order to determine whether the overall response is similar to that found with protoplasts in the absence of the cell wall. Materials and MethodsCultures and media The organisms used were Bacillus megaterium NCIB 9521 and Micrococcus lysodeiktieus NCIB 9278. Bacterial suspensions and protoplasts of B. megaterium were prepared [6471