Although many investigators have demonstrated that the dip-slide method is reliable in the diagnosis of significant bacteriuria, the reliability in the diagnosis of low grade bacteriuria, which is necessary for evaluating the efficacies of antimicrobial agents on urinary tract infections, is still nuclear. Therefore, we attempted to estimate whether the dip-slide method is also available in the diagnosis of low grade bacteriuria.
Firstly, Bacterial counts of low grade bacteriuria determined by six kinds of commercially available dip-slides were compared with those determined by the standard flood plate method. Low grade bacteriuria were experimentally prepared by inoculating the strains of urinary isolated E. coli or S. epidermidis in normal urine obtained from healthy volunteer. As far as bacterial counts were determined by the criteria indicated in the standard pictures of each dip-slides, correlation between the bacterial counts determined by the two methods was not so high. Bacterial counts were overestimated in four kinds of dip-slides and underestimated in two. However, if colonies on the dip-slides were counted, the correlation coefficients were 0.9 or higher and a significant correlation was observed between the bacterial counts detemined by the two methods, even though the absolute colony counts on dip-slides were approximately 100-1000 fold smaller than those determined by flood plate method.
Secondly, bacterial counts in the clinical urine specimens which contain single organism with bacterial counts of less than 105CFU/ml were compared by the dip-slide and standard flood plate method. The correlation of bacterial counts determined by both methods was also not so good and similar to the results observed in the experimental bacteriuria.
According to the Criteria proposed by the UTI Committee in Japan, differentiation of four grades of bacteriuria, 104CFU/ml, 103CFU/ml, < 103CFU/ml and negative, is necessary for the assessment of clinical efficacies of antimicrobila agents. Nevertheless, of the six kinds of dip-slides, five could differentiate these three degree of bacteriuria in less than 60% of the urine specimens tested. Furthermore, the detection of negative urine culture was impossible as mentioned before.
These results suggest that the differentiation of low grade bacteriuria with dip-slide method is inadequate in several points. Improvement and some device of dip-slide method should be attempted in the future.
