The aim of this experiment was to study the persistence in time of bacterial and methanogenic archaeal communities that establish in the rumen of lambs fed two different diets at weaning. Twenty ewes with single lambs were used in two phases. In phase I, 10 lambs had access only to grass hay (H group). The other 10 lambs had free access to concentrate and grass hay (C group). After 20 weeks, five lambs from each group were slaughtered and rumen samples were kept for analysis. In phase II, the remaining lambs were grouped together and fed grass plus concentrate for 4 months and then slaughtered, and rumen samples were collected for analysis. Terminal restriction fragment length polymorphism analysis showed a different bacterial and methanogen population established in the rumen of H and C lambs in phase I. These differences disappeared for methanogens after both groups were fed the same diet for 4 months; however, the total bacterial community remained different for the H and C samples. Our results suggest that some of the differences in the microbial populations that establish in animals fed different diets at weaning persist in the long term, which provides the possibility of programming the microbial populations in the adult animal.

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.