Some observations on the use of the ‘API STREP’ bacterial identification system to classify strains of lactococci (lactic streptococci) from commercial starter cultures

Abstract

Strains of Lactococcus sp. isolated from a commercial mixed strain starter culture were classified according to their cultural characteristics, as determined using the API STREP bacterial identification system. A correlation between the API STREP profile and plasmid profile of strains was observed. However, certain key tests for lactococci gave frequent anomalous or variable results, notably for failure to hydrolyse esculin, although most strains were able to acidify a medium containing esculin as sole carbohydrate source. This led to some unsatisfactory classifications. Correct storage of API STREP test reagents was important and the inclusion of controls is recommended. There is tentative evidence that the ability to ferment ribose rapidly is a plasmid encoded function in these bacteria.