Bifidobacteria in the intestinal tract of infants: an in-vitro study

Abstract

Strains of Escherichia coli and Proteus mirabilis that appeared to have similar sensitivity to ampicillin when tested by conventional techniques, behaved differently when dense cultures were exposed to ampicillin and opacity readings were taken. These differences were accompanied by distinctive morphological changes revealed by the stereoscan electron microscope. The morphological changes and the very rapid fall in opacity of Escherichia on exposure to ampicillin suggest that lysis of enterobacteria by penicillins is not wholly due to destruction of osmotically sensitive spheroplasts liberated through defects in the cell wall.