Biofilm model experiments in vitro with Escherichia coli and Shigella strains

Escherichia coli and Shigella were cultured together in a glucose-free minimal medium completed only by hog gastric mucin. In mixed cultures inoculated simultaneously one member of the pair more or less overgrew the other. This organism remained predominant when superinfected with its strain pair after 1, 3, 5 or 7 days incubation. Other signs of the quasi biofilm character of such cultures are the higher level of free polysaccharides and enhanced viscosity in the medium and higher streptomycin resistance of the culture. Around the bacteria a capsule-like material can morphologically be demonstrated.