The in vitro activity of BAY 12-8039, a new fluoroquinolone, was studied in comparison with those of ciprofloxacin, trovafloxacin (CP 99,219), cefpodoxime, and amoxicillin-clavulanate against gram-negative, grampositive, and anaerobic bacteria. Its activity against mycobacteria and chlamydia was also investigated. BAY 12-8039 was active against members of the family Enterobacteriaceae (MIC at which 90% of strains tested were inhibited [MIC 90 s] <1 g/ml, except for Serratia spp. MIC 90 2 g/ml), Neisseria spp. (MIC 90 s, 0.015 g/ml), Haemophilus influenzae (MIC 90 , 0.03 g/ml), and Moraxella catarrhalis (MIC 90 , 0.12 g/ml), and these results were comparable to those obtained for ciprofloxacin and trovafloxacin. Against Pseudomonas aeruginosa, the quinolones were more active than the ␤-lactam agents but BAY-12-8039 was less active than ciprofloxacin. Strains of Stenotrophomonas maltophilia were fourfold more susceptible to BAY 12-8039 and trovafloxacin (MIC 90 s, 2 g/ml) than to ciprofloxacin. BAY 12-8039 was as active as trovafloxacin but more active than ciprofloxacin against Streptococcus pneumoniae (MIC 90 , 0.25 g/ml) and methicillin-susceptible Staphylococcus aureus (MIC 90 s, 0.12 g/ml). The activity of BAY 12-8039 against methicillin-resistant S. aureus (MIC 90 , 2 g/ ml) was lower than that against methicillin-susceptible strains. BAY 12-8039 was active against anaerobes (MIC 90 s < 2 g/ml), being three-to fourfold more active against Bacteroides fragilis, Prevotella spp., and Clostridium difficile than was ciprofloxacin. Against Mycobacterium tuberculosis, BAY 12-8039 exhibited activity comparable to that of rifampin (MICs < 0.5 g/ml). Against Chlamydia trachomatis and Chlamydia pneumoniae BAY 12-8039 was more active (MICs < 0.12 g/ml) than either ciprofloxacin or erythromycin and exhibited a greater lethal effect than either of these two agents. The protein binding of BAY 12-8039 was determined at 1 and 5 g/ml as 30 and 26.4%, respectively. The presence of human serum (at 20 or 70%) had no marked effect on the in vitro activity of BAY 12-8039.

We evaluated toxigenic Clostridium difficile detection by a lateral flow assay for antigen and toxin, an enzyme immunoassay, and two commercial PCR methods. Compared to the cell cytotoxicity neutralization assay and toxigenic culture, both toxin detection methods lacked sensitivity. PCR following combined antigen and toxin detection provided the most useful diagnostic information.

The in-vitro activity of colistin sulphomethate sodium was compared with that of other commonly used antimicrobial agents against 377 recent clinical isolates of Gram-negative bacteria (including 94 strains of Pseudomonas aeruginosa from patients with cystic fibrosis) and 16 organisms with defined resistance patterns. Colistin was active against most strains of P. aeruginosa (MIC90 4 mg/L), Shigella spp. (MIC90 0.5 mg/L), Salmonella spp. (MIC90 1 mg/L), Acinetobacter spp. (MIC90 2 mg/L), Citrobacter spp. (MIC90 1 mg/L), Escherichia coli (MIC90 1 mg/L), Klebsiella spp. (MIC90 8 mg/L) and Enterobacter spp. (MIC50 1 mg/L). No useful activity was demonstrated against Providentia spp. or Serratia spp. The results show that colistin remains a useful antimicrobial agent against Gram-negative bacteria, particularly those strains which are resistant to more commonly used antibiotics.

An open reading frame (ORF) homologous to norA was insertionally inactivated with cat in a fluoroquinolone-resistant pneumococcus with an efflux phenotype; this inactivation caused reversion to drug sensitivity. The ORF product has 24% amino acid sequence identity each to NorA and Bmr, which suggests that it is a major facilitator system pump of the 12-transmembrane-segment class.

Twenty-three norfloxacin-selected first-step mutants ofStreptococcus pneumoniae showed low-level fluoroquinolone resistance. Their susceptibility to norfloxacin in the presence or absence of reserpine and known efflux pump substrates was determined by an agar dilution method. Five mutants showed four- to eightfold increases in their susceptibility to norfloxacin in the presence of reserpine and four- to eightfold decreases in their susceptibility to acriflavine and ethidium bromide. This phenotype is suggestive of an efflux mechanism of resistance. A representative of these mutants, 1N27, accumulated significantly less ethidium bromide than the parent strain; reserpine abolished these differences. No changes in the quinolone resistance-determining regions of parC,parE, gyrA, or gyrB were found in this mutant. By our validated agar dilution method, the efflux phenotype was sought in clinical isolates of S. pneumoniae. Of 1,037 clinical isolates examined from the United Kingdom, 273 showed reduced susceptibility to norfloxacin or ciprofloxacin. Of these, 45.4% showed the efflux phenotype. Our findings suggest that an efflux mechanism may be a frequent cause of clinically significant fluoroquinolone resistance in pneumococci.