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.

The effect of caprylic acid (CA) on Campylobacter jejuni in chickens was evaluated using two approaches: dietary supplementation or surface treatment of chilled chicken carcasses. To analyze the dietary effect of CA, individually housed broiler chickens (n = 48) were artificially infected with C. jejuni VFU612 (10(6) colony-forming units [CFU]/bird) on the 21st and 35th days of life. Dietary CA (2.5 and 5 g/kg of feed, fed throughout the entire experiment) significantly decreased C. jejuni shedding (p<0.05). However, the effect only lasted for 3-7 days after infection. The numbers of Campylobacter shed by the positive control birds reached its maximum on the 37th day of life, while on that same day, both Treatment I and Treatment II groups shed significantly lower (p<0.05) numbers of Campylobacter (by 0.8 and 1.8 log10 CFU/g, respectively). Also, peak shedding was delayed by 1 day in both treated groups. After euthanasia of each chicken on the 42nd day of life, no differences in Campylobacter counts in the crop, gizzard, ileum, and cecum were found between the positive control and the treated groups (p>0.05). Surface contamination of the chilled chicken halves was performed with C. jejuni VFU612 (clinical isolate) and CCM6214 (collection strain). Surface treatment with CA at 1.25 and 2.5 mg/mL for 1 min significantly reduced C. jejuni VFU612 contamination of chicken skin (p<0.05) by 0.29-0.53 and 1.14-1.58 log10 CFU/g of skin, respectively. Counts of C. jejuni CCM6214 were reduced by 0.68-1.65 log10 CFU/g of skin). In conclusion, dietary CA affected numbers of C. jejuni in the gastrointestinal contents of chickens, whereas surface treatment reduced C. jejuni contamination in processed chicken carcasses.

ABSTRACT:The sucrose monoesters of capric and lauric acid were tested for their antibacterial activity towards two foodborne enteropathogenic bacteria -Escherichia coli (CCM 3954 -serotype O6 and E22 -serotype O103) and Clostridium perfringens (CNCTC 5459 and CIP 105178). Antibacterial activity was evaluated by the plating technique. Sucrose monocaprate significantly decreased the number of viable cells of E. coli at all tested concentrations (0.1-5 mg/ml). The overnight incubation of C. perfringens with the sucrose ester of lauric acid at 0.1-5 mg/ml reduced the number of viable cells below the detection limit (2 log 10 CFU/ml). Incubating E. coli CCM 3954 and C. perfringens CNCTC 5459 with monoesters (0.1 and 2 mg/ml) did not influence the K + permeability of the cytoplasmic membrane in cells during a 2.5-minute treatment. A 30-minute incubation of E. coli CCM 3954 and C. perfringens CNCTC 5459 with esters (0.1 and 2 mg/ml) revealed damage to cytoplasmic structures, as observed by transmission electron microscopy.

Clostridium perfringens-induced necrotic enteritis is generally controlled by antibiotics. However, because of increasing antibiotic resistance, other antibacterial agents are required, preferably ones that do not affect the beneficial intestinal microbiota of the host. This study evaluated the in vitro selective growth-inhibitory effect of 8-hydroxyquinoline (8HQ) on C. perfringens vs. bifidobacteria in a medium containing chicken ileal digesta. Prior to the experiments, the minimum inhibitory concentrations of 8HQ and penicillin G were determined by broth microdilution assay. The minimum inhibitory concentration values of 8HQ for C. perfringens were 16–32 times lower than the values for bifidobacteria. Treatment of autoclaved and non-autoclaved chicken ileal digesta with 8HQ showed a selective anticlostridial effect. After incubation of C. perfringens with autoclaved ileal digesta for 3 h, all 8HQ concentrations tested (32–2048 μg/mL) significantly reduced C. perfringens bacterial count. In contrast, the same treatment had no or only a slight effect on bifidobacteria counts. Unlike 8HQ, penicillin G did not exhibit any selectivity. Similar results were obtained after incubation for 24 h. In non-autoclaved ileal digesta, all 8HQ concentrations tested significantly reduced C. perfringens bacterial counts after incubation for 30 min and 3 h, while no effect was observed on bifidobacteria. These results suggest that 8HQ may serve as a prospective veterinary compound for use against necrotic enteritis in poultry.