title: In vitro antibiotic susceptibility of enteric bacteria isolated from commercial broiler chickens.
abstract: The in vitro activity of six different antimicrobial agents was evaluated by an agar dilution method against enteric bacteria isolated from broilers. Of 923 isolates, 796 were gram-positive bacteria and 127 were Escherichia coli (E. coli). Thiopeptin at 25 microgram/ml inhibited 75% of lactobacilli. This antibiotic at .78 microgram/ml inhibited 82% of staphylococci and more than 92% of other gram-positive organisms. Bacitracin at 100 microgram or less per ml was active against 42% of staphylococci and 30% of streptococci. At 6.25 microgram or less per ml, 70% of clostridia and 78% of lactobacilli were inhibited. The minimum inhibitory concentrations (MIC) of penicillin G and ampicillin shown as cumulative distribution curves for all isolates were very similar. Both antibiotics showed a wide range of MIC distribution. Streptomycin at 50 microgram or less per ml was active against 87% of lactobacilli and 50% of E. coli. Only 32% of staphylococci were inhibited at these concentrations. At 100 microgram or less per ml, 30% of streptococci and 12% of clostridia were inhibited. Tetracycline at 100 microgram or less per ml inhibited 63% of clostridia. Lactobacilli and E. coli were not inhibited by this antibiotic at 100 microgram or less per ml.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D001414:Bacitracin / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects*; D002645:Chickens / Q000382:microbiology*; D003013:Clostridium / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D007421:Intestine, Small / Q000382:microbiology*; D007778:Lactobacillus / Q000187:drug effects; D010400:Penicillin G / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D013210:Staphylococcus / Q000187:drug effects; D013291:Streptococcus / Q000187:drug effects; D013307:Streptomycin / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D010455:Peptides; C022076:thiopeptin; D001414:Bacitracin; D000667:Ampicillin; D013752:Tetracycline; D010400:Penicillin G; D013307:Streptomycin