Bactericidal effects of norfloxacin towards bacteria in urine.

Norfloxacin produced a reliably bactericidal effect at concentrations from 3 to 90 mg/l against urine pathogens suspended in human urine. These included Enterobacteriaceae, Pseudomonas aeruginosa, Streptococcus faecalis and Staphylococci. Resistant mutants of Staphylococcus aureus were isolated on two occasions (out of 33 experiments). At high concentrations (c. 90 mg/l) the activity was less but this was probably due to the need for a low pH to dissolve the antibiotic. The pH for optimum activity of norfloxacin in urine was 7.5 to 8.0. Human blood had little effect on the bactericidal activity. Compared to other antibiotics, the rate of killing of cultures in urine was second only to gentamicin.

In-vitro evaluation of miokamycin: bactericidal activity against streptococci.

Miokamycin is a diacetyl derivative of the macrolide antibiotic, midecamycin. In vitro, it has an unusual spectrum, inhibiting the growth of Gram-positive cocci and anaerobes, but few Haemophilus spp; enterobacteria are highly resistant. Most erythromycin-resistant Staphylococcus aureus were sensitive (MIC approximately 0.8 mg/l). Resistance to miokamycin in Staph. aureus and streptococci was difficult to select, unless the staphylococci were already resistant to erythromycin. Both miokamycin and erythromycin were bactericidal towards groups A,B,C and G streptococci. Clinical trials of the drug in pelvic, upper respiratory, skin and soft tissue and other staphylococcal infections may be worthwhile.

Double-blind study to compare the selection of antibiotic resistance by amoxycillin or cephradine in the commensal flora.

Elderly patients with acute urinary infections were treated in a double-blind study with either amoxycillin or cephradine. In 52 patients who had received amoxycillin for one week about a third of all intestinal Escherichia coli were highly resistant to amoxycillin, and many were resistant to tetracycline, trimethoprim, or chloramphenicol. Cephradine selected less resistance. At a week after completion of chemotherapy, cephradine-resistant E coli were replaced by sensitive cultures at a greater frequency than were amoxycillin-resistant E coli. Neither antibiotic altered the skin flora. Amoxycillin, but not cephradine, selected for Enterobacteriaceae in the saliva. The propensity of amoxycillin to select resistance in E coli will limit its usefulness in treating urinary infections.

Bactericidal effects of cefotetan and other antibiotics in human fluids.

Antibiotics were added at final concentrations of 0.5 to 10 mg/l to either human blood, serum, urine, bile or ascitic fluid inoculated with sensitive cultures. Bactericidal effects were monitored by estimation of viable counts over 24 h at 37 degrees C. Cefotetan was reliably bactericidal to bacteria suspended in human urine over a wide range of conditions. Gentamicin, cefotaxime, cefotetan and azthreonam were predominantly bactericidal against Enterobacteriaceae in serum and blood; gentamicin, cefotetan and cefotaxime were bactericidal in bile, and cefotetan bactericidal in ascitic fluid. The above antibiotics all also produced a bactericidal effect against Haemophilus influenzae in serum, and the macrolides erythromycin and rosaramicin destroyed haemophilus in serum more rapidly than did ampicillin or amoxycillin. In most of these fluids, destruction (reduction in viable counts by greater than 10-fold) of the inoculum occurred within 2 to 4 h for gentamicin and 4 to 6 h for similar concentrations of beta-lactam agents.