Bactericidal activity of antimicrobial drugs in simulated urine specimens at various temperatures of incubation.

A total of 23 antimicrobial drugs were examined for bactericidal activity in midstream-urine against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, or Streptococcus faecalis ATCC 29212 at incubation temperatures of 35, 22, and 7 degrees C, respectively. The majority of chemotherapeutic agents significantly reduced bacterial inocula within 2 h at 35 degrees C. At room temperature, most drugs required 4 h for significant killing activity to ensue. At 7 degrees C only nitrofurantoin, polymyxin B, and rifampin were significantly active within 2 to 4 h following exposure. Following prolonged (overnight) incubation at 7 degrees C, however, 10 of 23 drugs (amikacin, cefotaxime, chloramphenicol, gentamicin, nalidixic acid, netilmicin, nitrofurantoin, polymyxin B, rifampin, and vancomycin) effected reduction of bacterial colony counts of greater than or equal to 50%. On the basis of these data it is recommended that urine specimens from patients with known antibacterial chemotherapy should not be refrigerated for longer than 2 to 4 h following collection.