Laboratory assessment of physical and chemical methods of preserving urine specimens

Abstract

Three methods of preserving simulated specimens of urine were studied with six test strains of bacteria. Viable counts were measured by a surface viable count and by the filter-paper-strip method during a holding period of 72 hours. Refrigeration at approximately 4°C was effective and reliable. Boric acid (1.8%) at room temperature was toxic for the strain of Escherichia coli at a density of 107 cfu/ml but this may not be significant at the higher concentration of bacterial cells often found in clinical specimens. NaCl-polyvinylpyrrolidone (PVP) solutions containing PVP of mol. wt 44000 or 700000 were not effective; they were toxic for the Gram negative strains and did not retard the growth of Micrococcus subgroup 3. The two methods of measuring viable counts were compared for specimens held under different conditions; the specificity of the filter-paper-strip method was high but the sensitivity was low when many of the specimens contained approximately 105 cfu/ml.