Cephalexin-Induced Morphological Alterations in the Surface Structures of Staphylococcus aureus and Escherichia coli Demonstrated by Scanning Electron Microscopy

Abstract

The scanning electron microscope was used to investigate the alteratiwns in surface morphology of Staphylococcus aureus 209P and Escherichia coli NIH induced by the action of cephalexin known to interfere with cell-Wall synthesis. Exposure to cephalexin produced a series of changes on the surface morphology in proportion to the concentrations of cephalexin added. Untreated S. aureus cells had smootb contours. Exposure to 1μg/ml of cephalexin during the logarithmic phase of growth in S. aureus did not produce any detectable changes. Upon exposure of S. aureus to 5μg/ml or 10μg/ml, some cells were larger than noarmal and showed abnormal cell division-like structures in part. When S. aureus was exposed to 50μg/ml, cell division was completely inhibited, and no formation of grape-like clusters was obsersed. Untreated E. coli cells appeared to have smooth and regular contours. E. coli propagated almost nor-mally upon exposure of the organisms to 1μg/ml of cephalexin. Filamentous structures were observed with the exposure of E. coli to 12.5μg/ml or 25μg/ml, but spheroplast-like structures were not observed. Exposure to, 100μg/ml of cephalexin resulted in the formation of marked filament us cells and sphero-plast-like structures having multiple small saccular outpouehings. Scanning electron microscope demonstrated more completely the morphological abnormalities induced by cephalexin.