Evaluation of Gram-stain screen and Micro-ID methods for direct identification ofEnterobacteriaceae from urines
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A rapid method of urine screening and enterobacterial identification was evaluated. Results indicated that an average of 13.5 bacteria/oil immersion field (threshold value ⩾ 1) was observed in unsedimented urine of patients with significant bacteriuria, with an average of < 1 bacterium/field in urines of patients without significant bacteriuria. In centrifuged urines, numbers of bacteria divided by amount of urine sedimented yielded similar results. Of 1758 urines studied, 136 yielded ⩾ 105 bacteria/ml, and 58 > 104 but < 105 bacteria/ml, by conventional techniques. Gram-screening of unsedimented specimens gave sensitivity rates of 94.1%, specificity of 97.7%, and predictive positive and negative values of 78.5%, 99.5%, respectively; similar values were obtained with sedimented urines. Sensitivity rates of both screening methods for the 58 urines with > 104 but < 105 bacteria/ml were 9.0%, 10.0%, respectively. Total correct enteric identification in 113 urines with positive screens and significant bacteriuria (⩾ 105/ml) was 82.3% and 90.3% with direct saline and broth Micro-ID methods, respectively. In 99 urines yielding pure or predominantly pure growth of 1 species ofEnterobacteriaceae identification by direct saline and broth Micro-ID corresponded with isolated colony identification in 85.9%, 94.9% of cases, respectively. Gram-stain screening (together with back-up conventional plating in certain patient categories) and enterobacterial identification by direct broth Micro-ID, of urines with pure stains suggestive of ⩾ 105 Gram-negative rods/ml has been shown to be useful in laboratories without automated equipment for urine screening.
KeywordsSensitivity Rate Conventional Technique Rapid Method Bacteriuria Screen Method
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