Cell surface charge of lactobacilli and enterococci isolated from pig small intestine as studied by free zone electrophoresis: a methodological study.

The net surface charge density, as revealed by electrophoretic mobility values, of fourteen strains of lactobacilli and two strains of enterococci isolated from the small intestine of pigs, was studied by a free zone electrophoretic technique in a rotating quartz electrophoresis tube. Most lactobacilli strains of low surface hydrophobicity (i.e. hydrophilic strains) showed high electrophoretic mobility values but no visible capsule, while most strains of intermediate and high surface hydrophobicity showed low mobility. Some strains, hydrophobic as well as hydrophilic, had mobility values equal or close to zero. Electrophoretic mobilities of strains of extremely high surface hydrophobicity were difficult to determine due to cell clumping during electrophoresis. These strains adhered best in vitro to isolated pig intestinal epithelial cells. Both enterococcal strains from pig showed high electrophoretic mobility values. In conclusion, a rapid, accurate and highly reproducible method is described for the determination of the net surface charge density of procaryotes. High electrophoretic mobility of hydrophilic strains suggests surface accumulation of highly negative charged surface polymers such as capsule or slime material. However, none of the porcine strains showed visible capsule, as did the hydrophilic laboratory strain Lactobacillus casei NCTC 10302. Electrophoretic methods have a great potential in studies of adhesion mechanisms of bacteria to different surfaces as well as isolation of capsule variants within a heterogenous bacterial population.