showed considerably increased susceptibility to amoxycillin in combination with clavulanic acid. Two beta-lactamase-producing strains of Pseudomonas aeruginosa remained resistant to carbenicillin in the presence of clavulanic acid.Clavulanic acid was isolated from Streptomyces clavuligerus, and the structure, which resembles the penicillin nucleus, has the formula pug/ml was incorporated into the agar both alone and in combination with clavulanic acid at concentrations of 10, 5, and 1.0 (or 0.5) ,ug/ml. Penicillin-free clavulanic acid control plates were included throughout.After inoculation, the plates were incubated at 370C for 24 h. Ten percent C02 was added to the environment for cultivation of H. influenzae and N. gonorrhoeae, and a GasPak system (BBL) was used for the anaerobes. The minimum inhibitory concentration (MIC) of penicillin alone and in combination with clavulanic acid was defined as the lowest amount of antibiotic giving a decrease in colony count of 99.9% compared with the initial inoculum. Any inhibitory effect of the clavulanic acid when acting alone was also noted.Beta-lactamase production by bacterial isolates was detected by the chromogenic cephalosporin method as described by O'Callaghan et al. (2). RESULTSAgainst the majority of organisms tested, clavulanic acid alone had no antibacterial activity at a concentration of 10, 5, 1.0, or 0.5 ,ug/ml. The exceptions were five strains of B. fragilis; two were inhibited by 10 ,ug of clavulanic acid per ml and three were inhibited by 5 ,ug/ml, both with an inoculum of 103 CFU/pl. These were not included in Fig. 2. Most strains of N. gonorrhoeae were inhibited by 1 ,ug or more of clavulanic acid per ml (Table 1).

HR 756, a new parenteral cephalosporin, was compared with cefazolin and carbenicillin for activity against a total of 264 strains ofPseudomonas aeruginosa, Escherichia coli, Klebsiella spp., Proteus mirabilis, Proteus spp. (indole positive), Enterobacter spp., Salmonella typhi, Serratia marcescens, Providencia stuartii, and Staphylococcus aureus. In every comparison, except that with the last organism, HR 756 was clearly more active than cefazolin and carbenicillin. All three compounds had similar activity against penicillin-susceptible staphylococci; against penicillin-resistant strains, HR 756 and cefazolin were equally active and superior to carbenicillin. HR 756 was compared with penicillin for activity against strains of Streptococcus pyogenes, Lancefield group D streptococci, and Neisseria gonorrhoeae; with ampicillin against Haemophilus influenzae; and with cefoxitin against Bacteroides fragilis. HR 756 was clearly more active than the respective reference compounds in all of these comparisons, except those involving the streptococci. HR 756 and penicillin were essentially equally active against S. pyogenes; against Lancefield group D, penicillin was 32 times as active as HR 756. HR 756 not only compared favorably with the reference compounds with respect to relative activity, but also effected growth inhibition of essentially all test organisms (P. aeruginosa and group D streptococci excepted) at remarkably low concentrations ranging from 0.015 to 2.0 ug/ml. A series of seven transfers of selected strains of E. coli, Klebsiella spp., S. aureus, and P. aeruginosa through medium containing HR 756 led to emergence of strains with significant levels of resistance to the agent. Resistance to HR 756 was retained for at least seven transfers through plain medium.Although a number of new cephalosporins have been studied in recent years and antibodies such as cefoxitin (3) and cefuroxime (6), which are stable to a wide range of B-lactamases, have been introduced, there is a need for agents with an enlarged spectrum of activity. We were therefore interested in evaluating the in vitro activity of a novel cephalosporin for parenteral administration, HR 756, developed by Roussel Laboratories (for structure, see Fig. 1 Methods. Sensitivity testing was performed by a routine agar plate dilution procedure using Isosensitest agar, pH 7.2 (Oxoid, Basingstoke, United Kingdom). The Enterobacteriaceae, P. aeruginosa, Staphylococcus aureus, streptococci, and Streptococcus pneumoniae were tested against HR 756, carbenicillin, and cefazolin. The Isosensitest agar was supplemented as follows: with 5% lysed human blood (to support the growth of Bacteroides fragilis), a Levinthal preparation (to support the growth of Haemophilus influenzae), and a chocolate agar preparation (to support the growth of N. gonorrhoeae).

The in vitro activity of GR 20263, a new cephalosporin, was compared primarily with the activities of moxalactam (LY 127935) GR 20263 is a new parenteral aminothiazolyl cephalosporin from Glaxo Group Research which combines stability to a wide range of,-lactamases, a broad antibacterial spectrum, and low toxicity (3). In this study a wide range of recent clinical isolates were tested gainst GR 20263 and other relevant fi-lactams, in particular cefotaxime (1, 7) and moxalactam, the novel oxa-

The desacetyl metabolite (DES) of cefotaxime (HR756) is formed in vivo to a significant extent. The in vitro activities of DES, the parent compound, and cefazolin, cefoxitin, and cefuroxime were compared against 70 (4) with two inocula (103 and 106 colony-forming units per I ,l of inoculum). Table 1 summarizes the results obtained from the five antimicrobial agents when tested at an inoculum of 103 colony-forming units.The high activity of CEF against the Enterobacteriaceae was confirmed. It is interesting to note that DES was consistently more active than cefoxitin, cefuroxime, or cefazolin against these strains but about 1/10th as active as the parent compound. In particular, DES was 10-to 20-fold more active than cefazolin, cefoxitin, and cefuroxime against Proteus mirabilis. The susceptibility of the indole-positive Proteus spp. to DES was more variable, the minimum inhibitory concentration for one strain of Proteus morganii being 128 pg/ml but that of another being 0.5 ,ug/ml. Two strains of Enterobacter spp. (minimum inhibitory concentrations of DES, 0.5 and 1 ug/ml), three strains Providencia stuartii (miniimum inhibitory concentration of DES 2, 0.06 and 0.06 ,ug/ml), and two strains of Serratia marcescens (minimum inhibitory concentration of DES, 0.5 and 1 pg/ml) were more susceptible to DES than cefoxitin, cefuroxime, and cefazolin. The 10 strains ofPseudomonas aeruginosa were uniformly resistant to DES yet were moderately susceptible to CEF.

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