Differentiation of Lactobacilli Strains by Electrophoretic Protein Profiles

Lactic acid bacteria (LAB) comprise a diverse group of Gram-positive, non-spore-forming microorganisms (
1
). Fermentable carbohydrates are used as energy sources and are degraded to lactate (homofermentatives) or to lactate and additional products such as acetate, ethanol, carbon dioxide, formate, or succinate (heterofermentatives). Lactobacilli species are widely used in food technology. The manufacture of high-quality products requieres close attention to characterization, differentiation, and maintenance of lactobacilli starter culture strains. The species identification of LAB depends mainly on physiological and biochemical criteria. These conventional methods are time-comsuming and difficult and the results are often ambiguous. Therefore, for microbiological quality control, it is necessary to develop more reliable and quicker identification methods. The electrophoretic separation of cellular proteins is a sensitive technique, applied in bacterial systematics, that mainly provides information on the similarity of strains within the same species or subspecies. The present chapter deals with the most common technique of polyacrylamide gel electrophoresis (PAGE) in the presence of denaturing agents (sodium dodecyl sulfate [
SDS
]) of whole and wall-cell-associated proteins extracts for strain typing of lactobacilli. These methods will be useful for culture maintenance by giving each particular strain a fingerprint.