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A total of 334 clinical anaerobic isolates were tested in an anaerobic glove box by the agar dilution technique for susceptibility to clinically achievable levels of ticarcillin, carbenicillin, and penicillin. Thirty-two micrograms or less of penicillin per milliliter inhibited 91% of all strains, whereas 100 ug of carbenicillin and ticarcillin per ml inhibited 95 and 98%, respectively. A total of 82% (85 strains) of Bacteroides were inhibited by penicillin, and 93 and 96% were inhibited by carbenicillin and ticarcillin, respectively. Thirteen (24%) of 55 strains of Bacteroides fragilis tested were resistant to 32 ,ug of penicillin per ml, and 6 (11%) and 3 (5%) were resistant to 100 ug of carbenicillin and ticarcillin per ml, respectively. Within the therapeutic range, ticarcillin was the most effective of the three penicillins tested against B. fragilis subsp. fragilis.Ticarcillin, a new semisynthetic penicillin, resembles carbenicillin in structure and in in vitro antimicrobial activity against aerobic bacteria including Pseudomonas species. Its effect against anaerobic bacteria is not established. We examined the efficacy of ticarcillin against 334 clinical anaerobic isolates (234 ofthem were derived from the female genital tract) in comparison with the effect ofpenicillin and carbenicillin in vitro.(This work was presented in part at the 76th Annual Meeting of the American Society for Microbiology, Atlantic City, N.J., 2-7 May 1976.) MATERIALS AND METHODS Identification of all isolates was done as described in the anaerobic laboratory manual of the Virginia Polytechnic Institute (1). All 334 were human isolates identified in our laboratory between August 1975 and July 1976. Two-thirds of these (i.e., 234)were isolated from healthy cervices or from female genital tract infections, and the remaining were from infections of the lung or abdomen. The inocula were overnight brain heart infusion broth cultures diluted to McFarland standard I delivered with a Steers replicator to deposit 105 colony-forming units. Solutions containing concentrations of drug were prepared by dissolving the standard powders of penicillin G (Eli Lilly & Co., Indianapolis, Ind.), sodium carbenicillin (Roerig), and disodium ticarcillin (Beecham Products Inc., Clifton, N.J.) in distilled water. The antibiotic solutions were freshly prepared and added to brain heart infusion agar (Clinical Standard, Torrance, Calif.) and supplemented with defibrinated sheep blood (5%), 10 ug of vitamin K per ml, and hemin (Scott Laboratories, Fiskeville, R. I.). The inocula were planted with a Steers replicator (6), and the plates were incubated in an anaerobic glove box filled with a gas mixture of 85% nitrogen, 5% carbon dioxide, and 10% hydrogen and incubated at 37°C for 48 h. The minimal inhibitory concentration (MIC) was read as the least amount of antibiotic that permitted no growth. A set of aerobic and anaerobic plates without antibiotics was included as a control with each set of tests. Tables 1, 2, and 3 depict the MIC of penicillin, carbenicilli...

A total of 900 clinical isolates of aerobic (462 isolates) and anaerobic (438 isolates) bacteria were tested against mezlocillin in comparison with other penicillins, and the aerobes were also tested against cephalothin, cefoxitin, and cefamandole. Among penicillins, mezlocillin was the most effective against Escherichia coli, Klebsiella pneumoniae, Salmonella species, Pseudomonas aeruginosa, and Bacteroides fragilis. Mezlocillin was more effective than cephalothin against Klebsiella pneumoniae.Bodey and Pan reported that mezlocillin was more active than ampicillin, carbenicillin, and cephalothin against certain gram-negative bacilli and that it inhibited 95% of isolates of Pseudomonas aeruginosa at 100 ,g/ml (1). Their preliminary clinical trials with mezlocillin demonstrated that it was effective in the treatment of respiratory and urinary tract infections caused by Escherichia coli, Klebsiella, Enterobacter, and Pseudomonas. Mezlocillin, like carbenicillin and ticarcillin, is known to be ineffective against penicillin-resistant strains ofStaphylococcus aureus. We have examined the in vitro efficacy of mezlocillin against aerobic bacteria in comparison with ampicillin, carbenicillin, piperacillin, cephalothin, cefoxitin, and cefamandole. Against anaerobic bacteria, mezlocillin was tested in comparison with penicillin, carbenicillin, ticarcillin, piperacillin, and cephalothin.The aerobic bacteria were clinical isolates from our laboratory and from the laboratories of Los Angeles County General Hospital. The anaerobic bacteria were clinical isolates exclusively derived from our laboratory. All isolates were reidentified before actual in vitro antibiotic susceptibility testing.The standard antibiotic powders were obtained from the following sources: penicillin G, cephalothin sodium, and cefamandole, Eli Lilly & Co., Indianapolis, Ind.; ampicillin, Bristol Laboratories, The minimal inhibitory concentrations were determined by an agar dilution method, and the inoculum was adjusted to match McFarland no.