A microdilution technique using commercially available media and materials was developed and used to determine the minimal inhibitory concentrations (MICs) of clindamycin, chloramphenicol, tetracycline, minocycline, ampicillin, carbenicillin, cephalothin, and gentamicin for 101

Chemical and cellular characteristics of fluid within subcutaneously implanted polyethylene chambers in rabbits were studied over a 3-month period. The fluid attained a relatively stable protein and cellular composition which was consistent with a mononuclear exudate. After a single dose of intramuscular penicillin G, the antibacterial activity of chamber fluid was found to be dynamic and similar to the serum antibacterial activity. This animal model may be useful for in vivo studies of the interaction of microorganisms with antimicrobial agents.

The minimal inhibitory concentrations of clindamycin and gentamicin alone and in combinations were determined by a microdilution method for 163 aerobic, facultative, and anaerobic clinical isolates. All 77 strains of Staphylococcus aureus, Diplococcus pneumoniae, Streptococcus pyogenes, and anaerobic bacteria (except for three strains of Clostridium) were inhibited by 1.6,ug or less of clindamycin per ml. Gentamicin did not interfere with the activity of clindamycin within the range of concentrations tested (0.1 to 100 Mg/ml); for some strains combinations were synergistic. Sixty-two (94%) of 66 strains of Enterobacteriaceae and Pseudomonas aeruginosa were inhibited by 6.2 ,g or less of gentamicin per ml. Combinations of clindamycin and gentamicin were indifferent for 29 strains and synergistic for 33 strains. All 20 strains of enterococcus, three strains of Clostridium, three strains of Escherichia coli, and one stiain of Proteus rettgeri were resistant to both clindamycin (minimal inhibitory concentration greater than 3.1 ,g/ml) and gentamicin (minimal inhibitory concentration greater than 6.2 ,g/ml). Combinations of clindamycin and gentamicin were indifferent for 16 and synergistic for 11 of the resistant strains. Except for clindamycin-sensitive isolates, synergy was usually observed only at concentrations of one or both drugs which are not readily obtainable in vivo. Antagonism was never observed.

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