Comparison of conventional and miniaturized biochemical techniques for identification of animal streptococcal isolates

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Abstract
Human clinical streptococcal isolates can be identified rapidly by means of commercially available miniaturized biochemical systems, in contrast to animal and environmental isolates which may require extensive characterization using conventional methods. Streptococcal isolates (n=548) from fresh animal feces of cattle, swine, and broiler chickens were tested by means of conventional biochemical and physiological techniques, and also with a miniaturized technique in which conventional formulations were dispensed in 0.1 ml volume into microtiter plates. Agreement of the positive feature frequencies of the two methods were compared. Results from the tolerance tests in the two methods were generally in good agreement. However, the miniaturized method tended to give false negative results in some carbohydrate fermentation tests. Agreement between the 2 methods ranged from 100% for bile esculin tests to 71% for raffinose fermentation. Cluster analysis of the conventional method data indicated that there were 11 biochemically related groups of isolates, 2 of which were identified asStreptococcus faecalis, andS. morbillorum. Half of the isolates biochemically resembledS. faecium. Errors of miniaturized tests occurred mainly in certain tests and in certain biochemically related clusters of isolates. The data indicate that further investigation of experimental conditions such as medium formulation and inoculum size could lead to a successful miniaturized technique for testing animal streptococcal isolates.