Comparative in vitro activities of two glycylcyclines against gram-positive bacterial isolates. Abstr. 33rd Intersci

minocycline and 6-demethyl-6-deoxytetracycline, respectively. In vitro activities of these two antimicrobial agents were compared with those of tetracycline, minocycline, and seven other antimicrobial agents against 412 gram-positive organisms. Both new drugs were significantly more active than minocycline against methicillin-resistant Staphylococcus aureus (MICs for 90%o of isolates tested, 0.25 and 0.5,ug/ml versus 4 pg/ml). CL 329,998 inhibited all streptococci, lactobacilli, and Leuconostoc spp. at concentrations of <0.5,ug/ml, with CL 331,002 slightly less active against some species. All enterococci, including minocycline-resistant and multidrug-resistant isolates, were inhibited at 50.5- and l1.0-,ug/ml concentrations of the new drugs, respectively. Only bacteriostatic activity was evident by time-kill curves. The two glycylcyclines demonstrated activities in vitro that were superior to those of minocycline against several gram-positive bacterial species, and at relatively low concentrations, they inhibited isolates resistant to both tetracycline and minocycline. Although the tetracyclines remain valuable agents for the treatment of a variety of infectious diseases, resistance to this class of antibiotics limits their use against a number of impor-tant gram-positive bacterial pathogens. The reported rates of resistance to tetracycline among coagulase-positive and-neg