The antibacterial activity of the new fluoroquinolone rufloxacin (MF 934) was evaluated against 1095 clinical isolates and compared with that of other quinolones and various commonly used antibiotics. Rufloxacin was highly effective against members of the Enterobacteriaceae, inhibiting 98% of the isolates at a concentration of 1 mg/l. Ninety-two percent of Aeromonas hydrophila and 65% Acinetobacter strains tested were inhibited by 1 mg/l of rufloxacin, whereas 98% of methicillin-susceptible and 87% of methicillin-resistant Staphylococcus aureus strains and 76% of coagulase-negative staphylococci strains required 4 mg/l for growth inhibition. The MIC values of rufloxacin for most bacteria were 4-16 times higher than those of ciprofloxacin and norfloxacin. Rufloxacin had little activity against xanthomonads, pseudomonads and enterococci. Approximately 95-96% of isolates of Pseudomonas aeruginosa were inhibited by 2 mg/l of ciprofloxacin and norfloxacin as compared to 29% inhibited by rufloxacin at this concentration.

The in vitro activity of azithromycin, an orally active azalide, was compared with that of erythromycin and oral beta-lactams against 893 clinical isolates of staphylococci, streptococci, enterococci, Haemophilus influenzae and Salmonella typhi. MIC 90 of azithromycin for streptococci was 0.12 mg/L, 0. Azithromycin is an orally active azalide antibiotic with a chemical structure of 9-deoxo-9a-aza-9a-methyl-9a-homoerythromycin A, molecular formula of C 38 H 72 O 12 N 2 , 2H 2 O and molecular weight of 785.01 Kd.1 It contains an aza-methyl substitution at position 9a of the 15-member aglycone ring as compared to 14-member erythromycin.24 Insertion of nitrogen into the lactone ring has been reported to increase its antibacterial activity against gram negative bacteria.1,2 We compared the in vitro activity of this compound with erythromycin and other oral beta-lactam drugs against clinical isolates of staphylococci, streptococci, enterococci, Haemophilus influenzae and Salmonella typhi. Material and MethodsClinical isolates from 893 patients at the King Faisal Specialist Hospital and Research Centre (KFSH&RC) were used for comparative in vitro evaluation of azithromycin. KFSH&RC is a 500-bed tertiary care referral facility in Riyadh, Saudi Arabia. Bacterial isolates were identified by standard routine laboratory procedures.5 Antimicrobial susceptibility testing was performed by the agar dilution method as recommended by the National Committee for Clinical Laboratory Standards.6 Mueller-Hinton agar with or without 5% sheep blood (Difco Laboratories, Detroit, MI, USA) with a pH between 7.2 and 7.4, was used throughout the study except for H. influenzae, where chocolate agar was used. The bacterial suspensions were adjusted to 10 7 CFU/ml and inoculated onto the agarsurface with a multipoint inoculator to contain 10 4 CFU/spot. All incubations were at 35°C for 18 to 24 hours. Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 were used as quality control (QC) organisms. The QC results were found to be within the normal expected range during the period of this study. ResultsA total of 893 isolates, consisting of 393 staphylococci, 228 streptococci, 210 H. influenzae and 62 strains of S. typhi were used to evaluate the in vitro activity of azithromycin and the results were compared with erythromycin, ampicillin, augmentin and cephalexin (Table). MIC 90 of azithromycin for members of the genus Streptococcus was 0.12 mg/L, which was comparable to that of erythromycin. Erythromycin-resistant enterococci had an MIC of >32 mg/L for azithromycin. MIC 50 and MIC 90 of azithromycin for methicillin-susceptible S. aureus were four to eight times higher than erythromycin; like erythromycin, azithromycin had virtually no activity against methicillinresistant S. aureus. All the 210 isolates of H. influenzae were inhibited by <0.5 mg/L of azithromycin, its activity being superior to erythromycin and the beta-lactams tested. A single concentration of 8.0 mg/L of this drug inhibited 97% i...

The in vitro activity of GR 69153, a new catechol-containing cephalosporin, was compared with other commonly used antibacterial agents against 651 isolates of Enterobacteriaceae, 204 isolates of other Gram-negative bacilli, and 435 isolates of Gram-positive cocci. The minimum inhibitory concentrations of GR 69153 against 90% of tested strains (MIC90S) of Enterobacteriaceae, including the notoriously resistant Serratia marcescens, were between < 0.03 and 1.0 mg/L. It was the most effective of the drugs tested against Pseudomonas aeruginosa. All 170 isolates of methicillin-susceptible Staphylococcus aureus were inhibited at a GR 69153 concentration of 1.0 mg/L. Like other members of its class, it had little or no activity against Xanthomonas, methicillin-resistant S. au reus and enterococci.