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Several studies have documented the association of blood and rectal-culture positivity for Streptococcus bovis with gastrointestinal neoplasia, especially colonic carcinoma. Conventional methods using bile-esculin hydrolysis, salt tolerance, and sugar fermentations to differentiate S. bovis from other streptococci are laborious, slow, and relatively expensive. Commercially available systems are costly and require at least 24 to 48 h of incubation. A rapid identification procedure for S. bovis and related bacteria was developed. The method uses a reagent containing two hydrolyzable substrates, p-nitrophenyl-alpha-D-galactopyranoside and 4-methylumbilliferyl-beta-D-glucoside, in the presence of 2.5% sodium deoxycholate. This combination test, performed with a rapid assay for L-pyrrolidonyl-aminopeptidase, could distinguish S. bovis, Streptococcus equinus, Enterococcus spp., Streptococcus pneumoniae, and the viridans group streptococci in culture within 30 min. Twelve species of the genera Streptococcus and Enterococcus were tested. The rapid method correlated well with conventional techniques. The reagents are readily available, inexpensive, and easy to make and can be stored in the refrigerator for at least 6 months.

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The detection of L-pyrrolidonyl peptidase activity is extremely useful for the differentiation of Enterococcus species and Streptococcus pyogenes from other members of the family Streptococaceae. This analysis has generally been performed utilizing the hydrolyzable substrate L-pyrrolidonyl beta-naphthylamine. After the substrate was hydrolyzed, free beta-naphthylamine has been detected utilizing the reagent para-dimethylaminocinnamaldehyde. The cinnamaldehyde and naphthylamine reagents combined to form an orange color, much like the indole reaction. The use of the cinnamaldehyde reagent had several drawbacks however: color development was not sharp, and the reagent was difficult to produce, and it was not stable. A new indicator system employing tetrazotized 0-dianisidine was developed. An extremely deep burgundy colored complex resulted from the reaction between the new indicator and B-Naphthylamine. This diazo reagent showed excellent correlation with results obtained with para-dimethylaminocinnamaldehyde and yielded more objective, distinct endpoints. This inexpensive reagent can be utilized either in a liquid form or dried on paper discs.

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In the family Streptococceae the ability to measure L-pyrrolidonyl-peptidase is limited to Lancefield group D Enterococcus and group A Streptococcus pyogenes. A number of methods exist to assay this enzyme. All measure pyrrolidonyl-peptidase by the ability of the bacterium to cleave L-pyrrolidonyl-beta-naphthylamide to form free beta-naphthylamine and L-pyrrolidone-carboxylic acid. Free beta-naphthylamine is then reacted with N,N-dimethylamino-cinnamaldehyde to form a red color complex. These methods are generally expensive and require a 2-4 h incubation period before results are available. A method, which employs the substrate dried on paper discs and can be easily made, is described herein. It is simple to perform, inexpensive, rapid, and has a long storage life. The results of this constitutive method are equivalent to those obtained using a commercial system.

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The coefficient of correlation (R) is one of the most commonly computed statistics in method-comparison studies. Usually, it is simply quoted without interpretation. In this paper, we show how R may be used to detect interference, nonlinearity, and misuse of the imprecision components. Specifically, one may precisely predict what R should be by considering the imprecisions of the two methods being compared, even before the comparison is performed. When the actual R disagrees with the predicted R, then one of the mentioned effects is present. We also describe a statistical test to detect these effects at the P = 0.05 level, then evaluate this test by using computer simulation and present two examples of its use. We also present the theory underlying the usage of R, including how R is affected by the distribution and range of the data, by the joint imprecisions of the methods being compared, by the sample size, and by the randomness of the specimen-selection process.

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Between-day variance is an ambiguous term representing either total variance or pure between-day variance. In either case, it is often incorrectly calculated even though analysis of variance (ANOVA) and other excellent methods of estimation are available. We used statistical theory to predict the magnitude of error expected from using several intuitive approaches to estimation of variance components. We also evaluated the impact of estimating the total population variance instead of pure between-day variance and the impact of using biased estimators. We found that estimates of variance components could be systematically biased by several hundred percent. On the basis of these results, we make recommendations to remove these biases and to standardize precision estimates.

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Two cases of unsuspected Strongyloides stercoralis infection were elucidated by the displacement of bacterial colonies on primary plating media. Observation of primary plates inoculated for the diagnosis of bacterial pneumonia or gastroenteritis revealed that normal flora colonies had been moved and were aligned in a pathway, or track. This unusual colony alignment prompted us to request a stool for the examination of parasites, and S. stercoralis was found. It was concluded that the parasite is capable of motility on agar surfaces, resulting in the displacement of bacterial colonies that make up the normal flora.

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