The activity of azlocillin, a new semisynthetic penicillin, was determined against 582 clinical isolates of gram-negative bacilli and gram-positive cocci. Over 75% of the isolates ofPseudomonas aeruginosa were inhibited at a concentration of 12.5 ug or less per ml. Azlocillin is also active against indole-negative and -positive Proteus spp., inhibiting 98 and 71%, respectively, at a concentration of 12.5 ug or less per ml. Isolates of Klebsiella spp. and Enterobacter spp. showed less susceptibility than isolates of Escherichia coli and Serratia spp. Gram-positive cocci except penicillin G-resistant Staphylococcus aureus were susceptible to azlocillin. Azlocillin failed to inhibit the growth of gram-negative bacilli when large inocula were used. It was more active in alkaline pH, but the type of medium used had little effect on its activity. Azlocillin was more active than mezlocillin, ticarcillin, and carbenicillin and as active as BLP-1654 against isolates ofP. aeruginosa. It was not as active as mezlocillin against the majority of the other gram-negative bacilli.Gram-negative bacilli, especially Klebsiella spp. and Pseudomonas aeruginosa, continue to be a major cause of infection among patients with malignant diseases and patients receiving immunosuppressive therapy (6, 7). Some of these patients fail to improve even when an appropriate antibiotic is administered on the basis of in vitro susceptibility testing (2). In general, penicillins have been more effective than other antibiotics against susceptible organisms in the compromised host (1). Since penicillins have been more effective than other classes of antimicrobial agents for the treatment of such infections, new penicillin derivatives with broad-spectrum activity, particularly against gram-negative bacilli, are of special interest. Azlocillin, a new semisynthetic penicillin, is of interest because of its activity against these organisms and especially P. aeruginosa. Figure 1 shows the chemical structure of azlocillin (6[u-2-(2-oxoimidazolidine-1-carboxamido) -2 -phenylacetamido] -penicillanic acid, sodium salt). This report presents an in vitro evaluation of azlocillin and compares its activity with other semisynthetic penicillins, including another new derivative, mezlocillin.MATERIALS AND METHODS Susceptibility tests were conducted on 479 clinical isolates of gram-negative bacilli and 99 clinical isolates of gram-positive cocci, using a dilution technique with an automatic microtiter system (Canalco, Autotiter Instruction Manual). All gram-negative bacilli and Staphylococcus aureus isolates to be tested were incubated in Mueller-Hinton broth (pH 7.4) for 18 h at 37°C. Streptococcus pyogenes and S. pneumoniae were incubated in tryptose phosphate broth. Approximately 105 colony-forming units (CFU) per ml was used as the inoculum for gramnegative bacilli and S. aureus. For the remaining gram-positive cocci, an inoculum of 106 CFU/ml was used for the in vitro susceptibility testing.All gram-negative bacilli used in this study were cultured from blood spec...

BB-K8, an aminoglycoside antibiotic which is a derivative of kanamycin, was tested in vitro against 466 clinical bacterial isolates. Over 90% of gram-negative bacilli, except Proteus spp., were inhibited by 3.12 μg of BB-K8 per ml. This antibiotic was consistently more active than kanamycin but less active than tobramycin or gentamicin. Unlike kanamycin, BB-K8 was active against Pseudomonas aeruginosa . Eleven of 19 isolates resistant to either gentamicin or tobramycin, or both, were susceptible to BB-K8.

The in vitro activity of tobramycin was

No abstract