A novel, inhibitor-potentiated disc-diffusion test for detecting extended-spectrum beta-lactamases (ESBLs) in bacteria was evaluated. This test uses the principle of augmentation (by > or = 10 mm) of inhibition zones produced by ceftazidime, cefotaxime, ceftriaxone or aztreonam discs on Mueller-Hinton agar supplemented with clavulanate (4 mg/L). The test was initially compared with the double-disc synergy test, Kirby-Bauer disc-diffusion test and Etest ESBL screen with a panel of 45 reference strains with known resistance profiles. This panel consisted of 27 ESBL-positive Escherichia coli strains expressing 14 Bush group 2be enzymes and 18 other E. coli and Klebsiella pneumoniae strains (14 non-ESBL beta-lactamase producers and four non-beta-lactamase producers). The Kirby-Bauer disc-diffusion test was the least sensitive method: 11-44% of the ESBL-positive control strains were misclassified as susceptible to ceftazidime, cefotaxime, ceftriaxone or aztreonam when interpreted by National Committee for Clinical Laboratory Standards (NCCLS) criteria. The sensitivities of the inhibitor-potentiated disc-diffusion test, the double-disc synergy test (when discs were 25 or 30 mm apart) and the Etest ESBL screen (with a breakpoint of > 4-fold reduction in ceftazidime MIC in the presence of clavulanate) were 100%, 96% and 89-96%, respectively. The inhibitor-potentiated disc-diffusion test was further evaluated with 81 E. coli and K. pneumoniae clinical isolates, which were identified as putative ESBL-producers by the double-disc synergy test. For these isolates, the sensitivity of both the inhibitor-potentiated disc-diffusion test and the Etest ESBL screen was 100%. In conclusion, the inhibitor-potentiated disc-diffusion test is a sensitive, convenient and inexpensive method of screening for ESBLs in E. coli and K. pneumoniae isolates, with potential for incorporation into routine clinical laboratory service.

Fifty-five Neisseria gonorrhoeae strains isolated in Hong Kong over a period of 6 months were tested for their in vitro susceptibility to 13 antimicrobial agents by the agar dilution method. Six strains were ,8-lactamase producing. In addition, five fB-lactamase strains from Singapore were tested. Among the non-fl-lactamaseproducing strains, 34 sulfamethoxazole-trimethoprim (ratio, 19:1). Among the cephalosporins, the order of effectiveness was cefuroxime, cefamandole, and cefoxitin. The older generation of cephalosporins, cephradine and cephalexin, was the least effective: 45 and 37% of the strains, respectively, required for inhibition MICs of -8 jig/ml. Cefotaxime, a new parenteral cephalosporin, was the most active; the median MIC was at least 10-fold lower than that of cefuroxime.The antibiotic susceptibility of Neisseria gonorrhoeae, and more recently of f8-lactamase-producing strains of N. gonorrhoeae isolated from many parts of the world, has been well documented (15,22,23

The in vitro susceptibility of 363 strains of Salmonella isolated in Honk Kong to various antimicrobial drugs was tested, and the minimum inhibitory concentrations of ampicillin, mecillinam, and six cephalosporins (cephalexin, cephradine, cefamandole, cefoxitin, cefuroxime, and Ro 13-9904) for these strains were determined by an agar dilution method. Although strains of the typhoid and paratyphoid group remained susceptible to most antibiotics tested, many strains of the gastroenteric group of salmonellae were found to be resistant to multiple antibiotics, including ampicillin, chloramphenicol, and, occasionally, trimethoprim. Mecillinam and cefamandole, although active against most of the Salmonella strains tested, were shown to be less active against ampicillin-resistant strains. By contrast, Ro 13-9904 exhibited remarkably uniform and high activity against all the Salmonella strains tested, irrespective of their ampicillin resistance.

Ro 13-9904 has high in vitro activity, as does cefotaxime, against 57 Haemophilus influenzae and 60 Neisseria gonorrhoeae strains, including 5 and 11 filactamase-producing strains in each group, respectively.The appearance of 8i-lactamase-producing Haemophilus influenzae (2, 9) and Neisseria gonorrhoeae strains (1, 7) resistant to ampicillin and penicillin has prompted the search for alternative safe and effective drugs which are not affected by the enzyme. The second-and thirdgeneration cephalosporins, including cefamandole, cefuroxime, cefoxitin, and cefotaxime, have shown promising results in this respect. Recently, a new semisynthetic cephalosporin, Ro 13-9904 (W.H.O. approved generic name, ceftriaxone), has also been shown to have high in vitro activities against many gram-negative bacteria (8, 10). We therefore determined, by the agar dilution technique, the in vitro susceptibility of 57 H. influenzae and 60 N. gonorrhoeae strains to Ro 13-9904, and the results were compared with those of penicillin, ampicillin, and six other cephalosporins.H. influenzae strains were identified by their morphology, growth characteristics, and X-and V-factor requirements. All strains except two were isolated from sputum specimens of patients with respiratory tract infections, mostly exacerbation of chronic bronchitis. A total of five ,Blactamase-producing Haemophilus strains, identified by the filter-paper chromogenic cephalosporin test (6), were found among the sputum isolates, and two type B H. influenzae strains isolated from cerebrospinal fluid were non-,B-lactamase producers. The strains were kept at -20°C in tryptic soy broth (Difco) containing 0.5% yeast extract, 0.5% soluble hemoglobin (Oxoid), and 20% glycerol (vol/vol) until ready for susceptibility testing. The 60 N. gonorrhoeae strains, including 11 ,B-lactamase-producing strains, the sources of the antibiotics, and the agar dilution technique have been described in a previous report (5). Ro 13-9904 was supplied by F. Hoffmann-La Roche Co. A standardized inoculum of 103 colony-forming units per ml was used for all bacterial strains throughout this study. The test medium was Mueller-Hinton agar (Difco) supplemented with 1% hemoglobin (Oxoid) and 1% supplement B (Difco) for both Haemophilus and gonococcal strains.The activity of Ro 13-9904 and eight other ,Blactam antibiotics against H. influenzae and N. gonorrhoeae strains is shown in Table 1. Ro 13-9904 and cefotaxime were the most active compounds tested. Both drugs showed extremely high in vitro activities (minimal inhibitory concentration, -0.125,g/ml) against all Haemophilus and gonococcal strains, including the 5 and 11 /8-lactamase-producing strains of each group, respectively. All of the H. influenzae and N. gonorrhoeae strains were susceptible to the second-generation cephalosporins cefuroxime, cefamandole, and cefoxitin, and none of the strains required minimal inhibitory concentrations of >4 ,ug/ml. In contrast, a great proportion of H. influenzae strains were resistant to the firstgeneration cephalosp...

Ro 15-8074, a new cephalosporin the pivaloyloxymethylester of which (Ro 15-8015) is orally absorbable, showed greater in vitro activity than cefaclor ngainst 48 Neisseria gonorrhoeae strains, including 25 penicillinase-producing strains. Unlike cefaclor, Ro 15-8074 was unaffected by increase in ihoculum size, and it exhibited a remarkable stability against gonococcal P-lactamase hydrolysis.The emergence of penicillinase-producing Neisseria gonorrhoeae (PPNG) strains showing high resistance to penicillin has prompted the search for effective alternative drugs against these isolates. Although a number of new P-lactam antibiotics have been reported to show promising in vitro and in vivo activities (2,3,6,8,9), few can be administered orally. Of these drugs, cefaclor and amoxicillin-clavulanic acid (Augmentin) have been reported to be active against PPNG strains both in vitro and in vivo (4, 10). In this study, therefore, we evaluated the in vitro activity of Ro 15-8074 in comnparison with those of cefaclor and amoxicillin-clavulanic acid against N. gonorrhoeae strains and also tested their hydrolytic stability to gonococcal P-lactamase. Ro 15-8074 is an aminothiazolyl-2-methoxyiminoacetamido-3-desacetoxy cephalosporanic acid, and its pivaloyloxymethylester, Ro 15-8075, is orally absorbable. After absorptioh, the ester group of Ro 15-8075 is enzymatically split off the cephalosporin ring, giving rise to the active cephalosporanic acid Ro 15-8074 (Fig. 1).The 48 N. gonorrhoeae strains tested were clinical isolates NH2