Morphological Changes in Staphylococcus aureus and Escherichia coli Exposed to Cephalexin

Abstract

The action of cephalexin against Staphylococcus aureus No. 50774 and Escherichia coli NIH had been studied by phase contrast microscopy and electron microscopy. S. aureus grown on the cephalexin-containing agar exhibited abnormal cell division when observed nuder the phase contrast microscope. Exposure of E. coli to cephalexin resulted in the formation of long fiaments and spheroplasts The degree of morphological changes was found to be dependent on the concentration of cephalexin added. Electron micrescopic studies revealed that S. aureus upon exposure to cephalexin produced a swelling of the cross wall, which resulted in lysis of the cell or the production of a protoplast. E. coli exposed to cephalexin produced long filamentous forms. A number of mesosomes were seen in the firamentous forms. However, the presence of a cross wall or plasma membrane partitioning the elongated cell thus formed was never observed. The above-mentioned lindings offer morphological evidence that the antibacterial action of cephalexin is ascribed to the inhibition of cell division and possibly cell wall svnthesis.