Susceptibility of clostridia from farm animals to 21 antimicrobial agents including some used for growth promotion.

The minimal inhibitory concentrations of 21 antimicrobial agents were determined by an agar dilution method against 68 strains of 18 Clostridium species isolated from caeca of pigs, cattle and poultry. Of the therapeutically used antibiotics, chloramphenicol was most active in vitro followed by penicillin G, the lincosamides and tetracycline. Penicillin-resistant Cl. butyricum strains produced a beta-lactamase. Avoparcin, carbadox, monensin, nitrovin and virginiamycin were the most effective of the growth promoting antimicrobial agents. Many clostridial species were naturally resistant to flavomycin and Cl. sporogenes was naturally resistant additionally to bacitracin, tiamulin, the lincosamides and virginiamycin component M. The macrolide, lincosamide and streptogramin resistant strains showed four different patterns of resistance to the antibiotics. One of these resistance patterns was the natural resistance of Cl. sporogenes to the lincosamides and virginiamycin component M which is a streptogramin group A antibiotic.

Differentiation of Bacteroides fragilis species by gas chromatographic detection of phenylacetic acid.

Of 382 strains tested, 261 strains of the species Bacteroides fragilis, B. thetaiotaomicron, B. ovatus, and B. distasonis produced phenylacetic acid; the remaining strains, belonging exclusively to the species B. vulgatus, failed to do so. This differentiation characteristic may be useful in routine clinical bacteriology.

Occurrence of megasphaera elsdenii in faecal samples of young pigs.

Important numbers of Megasphaera elsdenii, known as a normal inhabitant of the rumen of cattle and sheep were recently cultured from intestinal contents of man and pigs. Studying the occurrence of this organism in faecal contents of pigs, we paid attention to the use of a strict anaerobic isolating and counting technique. It was demonstrated that Megasphaera elsdenii is a strict anaerobic organism. Exposure to air during 15 minutes caused an important decrease of the colony count. Comparison of the biochemical properties of some isolates with the data of other investigators is given. Pigs isolates were nearly similar to rumen strains.

In vitro study of the influence of virginiamycin and spiramycin on the composition and biochemical activities of the gastrointestinal flora of piglets. I. influence on the composition of the flora.

In vitro fermentations with the gastro-intestinal flora of 18 treated piglets (Control, Virginiamycin, Spiramycin) were carried out to study the influence of Nutritional doses of Virginiamycin and Spiramycin on the composition of the microflora. Each total flora was used for three different incubations: Control, 50 ppm Virginiamycin, 50 ppm Spiramycin. To obtain comparable results with experiments in vivo, an artificial fermentation medium was made on the basis of several chemical analyses of intestinal contents. The treatments with nutritional doses in vivo had little influence on the different in vitro fermentations. Addition of Spiramycin during incubation was of little influence on the growth and the composition of the flora. Virginiamycin on the other hand caused marked changes in the gastro-intestinal microflora, such as a decrease of the total growth and a decrease in the number of Lactobacilli and Enterococci, combined with a slight increase of the Gram negative aerobic population.

In vitro study of the influence of virginiamycin and spiramycin on the composition and biochemical activities of the gastrointestinal flora of piglets. II. Influence on the biochemical activities of the microflora.

Chemical analysis was carried out on 54 in vitro fermentations to study the influence of nutritional doses of Virginiamycin and Spiramycin on the metabolic activity of the gastro-intestinal flora of 18 in vivo treated piglets. Changes in the decomposition of glucose and the production of NH3, volatile acids and lactic acid are recorded in function of time. These results are in good accordance with changes noted in the composition of the bacterial flora, such as a marked decrease in the production of lactic acid, caused by Virginiamycin, combined with a decrease in the number of Lactobacilli and Enterococci. Virginiamycin caused marked changes in the metabolic activity of certain groups of bacteria, while there was only a slight effect noted for Spiramycin, although in vivo treatments with this antibiotic still show up in the results of the in vitro incubations. The overall results indicate that both antibiotics have marked influences on the intestinal flora of the pig, either by selective inhibiting of the flora resulting in a change of the metabolities formed, either by a change in the metabolic activity of some bacterial groups.