Mode of action of nalidixic acid

In vitro activity of ciprofloxacin, norfloxacin and nalidixic acid

The in vitro antibacterial activity of the new quinoline derivative ciprofloxacin (BAY 0 9867) was evaluated in comparison to norfloxacin and nalidixic acid using 495 clinical strains of gram-negative and gram-positive bacteria. The compound was highly active against Enterobacteriaceae, with MICs ranging from 0.008 mg/l to 4 mg/l, whereas the MICs of norfloxacin ranged from 0.03 mg/l to 16 mg/l. All strains of Pseudomonas aeruginosa and Acinetobacter calcoaceticus were inhibited with a concentration of 2 mg/l ciprofloxacin and 32 mg/l norfloxacin. Ciprofloxacin was also active against gram-positive cocci. The MICs for Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus faecalis ranged from 0.008 to 2.0 mg/l. The activity of ciprofloxacin was only slightly influenced by inoculum size, whereas an acid environment caused a noticeable decrease in the activity. Ciprofloxacin would seem to be a promising antibacterial agent for the treatment of urinary tract infection.

Sublethal heat stress of Vibrio parahaemolyticus

When Vibrio parahaemolyticsu ATCC 17802 was heated at 41 degrees C for 30 min in 100 mM phosphate-3% NaCl buffer (pH 7.0), the plate counts obtained when using Trypticase soy agar containing 0.25% added NaCl (0.25 TSAS) were nearly 99.9% higher than plate counts using Trypticase soy agar containing 5.5% added NaCl (5.5 TSAS). A similar result was obtained when cells of V. parahaemolyticus were grown in a glucose salts medium (GSM) and heated at 45 degrees C. The injured cells recovered salt tolerance within 3 h when placed in either 2.5 TSBS or GSM at 30 degrees C. The addition of chloramphenicol, actinomycin D, or nalidixic acid to 2.5 TSBS during recovery of cells grown in 2.5 TSBS indicated that recovery was dependent upon protein, ribonucleic acid (RNA, and deoxyribonucleic acid (DNA) synthesis. Penicillin did not inhibit the recovery process. Heat-injured, GSM-grown cells required RNA synthesis but not DNA synthesis during recovery in GSM. Chemical analyses showed that total cellular RNA decreased and total cellular DNA remained constant during heat injury. The addition of [6-3H]uracil, L-[U-14C]leucine, and [methyl-3H]thymidine to the recovery media confirmed the results of the antibiotic experiments.

Bactericidal effect of combinations of nalidixic acid and various antibiotics on Enterobacteriaceae

The activity of nalidixic acid combined with each of 10 other antimicrobial agents on 95 strains of Enterobacteriaceae was studied. Synergism was found less often than antagonism, and the commonest outcome was indifference. Combinations of nalidixic acid with kanamycin, gentamicin, or colistin were more often synergistic than antagonistic, whereas with the other antibiotics the combination was more often antagonistic than synergistic. Synergistic effects were more common with Shigella than with other genera. In vitro examination for synergism or antagonism appears to be advisable before nalidixic acid is used therapeutically in combination with other antimicrobial agents.