The antimicrobial activity of fatty acids, monolaurin, citric, succinic, fumaric, malic and lactic acid was determined in cultures of two strains of Escherichia coli, three strains of Salmonella sp. and two strains of Clostridium perfringens. Antimicrobial activity was expressed as minimum inhibitory concentration (MIC) that prevented growth and glucose utilization in treated cultures. Caprylic acid was the only acid inhibiting glucose utilization in all cultures. Its MIC varied from 1 to 3 mg/ml. Strains CCM 3954 and CCM 4225 of E. coli were inhibited also by capric acid at 5 mg/ml. Strains CCM 4435^Tand CNCTC 5459 of Cl. perfringens were inhibited by medium-chain fatty acids (C₈ to C₁₄), oleic acid and one strain also by linoleic acid. The minimum MICs were those of lauric and myristic acid (between 0.1 and 0.2 mg/ml). Growth of Cl. perfringens, but not other bacteria, was inhibited also by monoglyceride of lauric acid (MIC = 3 mg/ml), and by citric acid (MIC = 4 mg/ml). Inhibitory effects of other acids were not observed at 5 mg/ml. Caprylic and lauric acid did not influence the K⁺permeability of the cytoplasmic membrane in cells of E. coli CCM 4225 and Cl. perfringens CCM 4435^T, respectively. In cultures of both strains of E. coli treated with caprylic acid at 5 mg/ml, and in those of Cl. perfringens CCM 4435^Ttreated with lauric acid at 1 mg/ml, or with its monoglyceride at 5 mg/ml, the transmission electron microscopy revealed damage of cytoplasmatic structures. In cells of Cl. perfringens the separation of inner and outer membranes was apparent, the integrity of the outer membrane, however, was maintained. It can be concluded that medium-chain fatty acids are more efficient antimicrobials than other, more polar organic acids tested.

Aims: To determine susceptibility of Clostridium perfringens strains CCM 4435 T and CNCTC 5459 to C 2 -C 18 fatty acids, and evaluate influence of pH in cultures grown on glucose. Straw particles were added to cultures to simulate the presence of solid phase of the digestive tract milieu. Methods and Results: Antimicrobial activity of fatty acids was expressed as a concentration at which only 50% of the initial glucose was utilized. Lauric acid showed the highest antimicrobial activity, followed by myristic, capric, oleic and caprylic acid. Only strain CNCTC 5459 was susceptible to linoleic acid. Neither caproic acid and acids with a shorter carbon chain nor palmitic and stearic acid influenced substrate utilization. The antimicrobial activity of myristic, oleic and linoleic acid decreased when clostridia were grown in the presence of straw particles. In cultures of both strains treated with capric and lauric acid at pH 5AE0-5AE3, the number of viable cells was <10 2 ml )1 . Only lauric acid reduced number of viable cells of both strains below 10 2 ml )1 at pH > 6. Transmission electron microscopy revealed separation of inner and outer membranes and cytoplasma disorganization in cells treated with lauric acid. Conclusions: Lauric acid had the highest activity towards C. perfringens among fatty acid tested. Its activity was not influenced by the presence of solid particles and did not cease at pH > 6. Significance and Impact of the Study: Lauric acid might be a means for control of clostridial infections in farm animals.

The antimicrobial activity of C2-C18 fatty acids was determined in vitro in cultures of two strains of Escherichia coli grown on glucose. Antimicrobial activity was expressed as IC50 (a concentration at which only 50% of the initial glucose in the cultures was utilized). Utilization of glucose was inhibited by caprylic acid (IC50 0.30-0.85 g/L) and capric acid (IC50 1.25-2.03 g/L). Neither short-chain fatty acids (C2-C6) nor fatty acids with longer chain (C12-C18) influenced substrate utilization. Caproic acid, however, decreased cell yield in cultures of E. coli in a dose-dependent manner. No inhibition of glucose utilization was produced with unsaturated fatty acids, oleic and linoleic. Calcium ions added in excess reversed the antimicrobial effect of capric acid, but not that of caprylic acid. Antimicrobial activity of caprylic and capric acid decreased when the bacteria were grown in the presence of straw particles, or repeatedly subcultured in a medium containing these compounds at low concentrations. Counts of viable bacteria determined by plating decreased after incubation with caprylic and capric acid (30 min; 1 g/L) at pH 5.2 from > 10(9) to approximately 10(2)/mL. A reduction of a mere 0.94-1.96 log10 CFU was observed at pH 6.5-6.6. It can be concluded that caprylic acid, and to a lesser extent also capric acid, has a significant antimicrobial activity toward E. coli. Effects of other fatty acids were not significant or absent.

The aim was to assess the effects of intact dried Ascophyllum nodosum seaweed on piglet performances, gut bacteria and function and plasma oxidative status. A total of 160 weaned piglets (21 days, 6.59 ± 0.91 kg) were allocated to four dietary treatments with eight pen replicates of five animals each for 28 days: a control diet; based on cereals, soybean meal and milk products, and three basal diets supplemented with either 2.5, 5.0 or 10.0 g dried seaweed per kg. At day 12/13 one piglet from each pen was sacrificed. Plasma samples were taken to determine parameters of oxidative status. Digesta were sampled for microbiological plate countings onto selective media and molecular analysis using PCR-DGGE. Small intestinal tissue was taken for morphological and electro-physiological determinations. Data were analysed by a linear model with treatment as fixed effect. A. nodosum supplementation had no effect on daily weight gain, nor did it alter feed conversion ratio. Plate countings failed to reveal differences among treatments. Dendograms prepared using PCR-DGGE banding patterns did not indicate clustering of microbial profiles based on diet supplement. Plasma oxidative status and outcome of morphology and of electro-physiological measurements from gut tissues were similar for all treatments. Thus, the addition of A. nodosum seaweed to well digestible diets did not enhance performances of piglets nor some gut health parameters and plasma oxidative status.

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Organic acids can be used as feed supplements or for treatment of poultry carcasses in processing plants. The antimicrobial activity of nineteen organic acids and two monoacylglycerols in cultures of Campylobacter jejuni CCM 6214(T) (ATCC 33560) was determined using a SYBR Green-based real-time PCR assay. The IC(50) was a concentration at which only 50 % of a bacteria specific DNA sequence was amplified. Caprylic, capric and lauric acids were the most efficient antimicrobials among the compounds tested (IC(50) < or = 0.1 mg/mL). In a weakly acidic environment (pH 5.5), the antimicrobial activity was more pronounced than at pH 6.5. At pH 5.5, oleic and fumaric acid also had clear antimicrobial activity, as did monocaprylin. The antimicrobial activity of acetic, butyric, stearic and succinic acid was low. In cells treated with fumaric acid, the potential of potassium and tetraphenylphosphonium ion-selective electrodes changed, indicating an increase in cytoplasmic and outer membrane permeability, respectively. No changes in membrane permeability were observed in cells treated with capric acid or monocaprin. Transmission electron microscopy revealed separation of the inner and outer membrane in cells treated with capric and fumaric acid, as well as cytoplasmic disorganization in cells exposed to capric acid.

Hovorková P., Laloučková K., Skřivanová E. (2018): Determination of in vitro antibacterial activity of plant oils containing medium-chain fatty acids against Gram-positive pathogenic and gut commensal bacteria. Czech J. Anim. Sci., 63, 119-125.Increasing antibiotic resistance has led to a ban on antibiotic use in feed additives in the EU. Therefore, new non-antibiotic, pathogen-inhibiting agents are urgently needed. Inhibitory effects of eight plant oils containing medium-chain fatty acids (MCFAs) were evaluated against Gram-positive pathogenic and beneficial bacteria. The oils tested were palm, red palm, palm kernel (Elaeis guineensis), coconut (Cocos nucifera), babassu (Attalea speciosa), murumuru (Astrocaryum murumuru), tucuma (Astrocaryum vulgare), and Cuphea oil (Cuphea ignea); the method used was broth microdilution, and the findings were expressed as minimum inhibitory concentration (80%). Both hydrolyzed and unhydrolyzed forms of the oils were tested. MCFA hydrolysis was catalyzed by porcine pancreas lipase. The selective effect of the hydrolyzed forms of tested oils was highly evident. While the hydrolyzed oils were active against all tested bacteria (Clostridium perfringens, Enterococcus cecorum, Listeria monocytogenes, and Staphylococcus aureus), at 0.14-4.5 mg/ml, the same oils did not show any effect on commensal bacteria (Bifidobacterium spp. and Lactobacillus spp.). Tucuma and Cuphea seed oils showed the strongest antibacterial activity. Unhydrolyzed forms of all tested oils exerted no antibacterial effect against any test bacteria. This study, thus, forms a basis for the development of selective inhibitors in animal husbandry.