Urine culture transport tubes: effect of sample volume on bacterial toxicity of the preservative

Abstract

Stable bacterial counts in urine specimens before culture are necessary to assure the accurate diagnosis of urinary tract infections. Preservative-containing tubes are commercially available for urine transport. As these tube containers are not always filled to the manufacturer's specifications, we studied the effects of stabilizer formation with low urine volumes. The Sage Urine Culture Tube and the Becton-Dickinson Urine Culture Kit were evaluated by using 30 cultures diluted in urine to 10(5) colony-forming units per ml. Both tube types were injected with 1, 2, 3, and 4 to 5 ml (tube capacity) of urine containing each culture. Specimens were held at 22 degrees C and cultured at 0, 4, and 24 h. Colony counts were corrected for the dilution due to the preservative. The Becton-Dickinson Urine Culture Kits were toxic to Escherichia coli and Klebsiella pneumoniae in specimens containing up to 2 ml of urine, and the minimum usable amount of urine for reliable results was 3 ml. The Sage Urine Culture Tube maintained the number of bacteria in 1 to 4.5 ml of urine in 83% of the specimens. However, the Sage tube was toxic to E. coli when held for 24 h. Quantitative counts of enterococci tended to significantly increase in specimens that contained 2 ml or more of urine with either system. The limitation of preservative-containing tubes for urine transport need to be recognized in order to avoid false-positive and false-negative results.