[Electron microscopic and microbiological studies on the activity of mezlocillin against Escherichia coli (author's...

Investigations by electron microscopy on thin sections and negative-stained preparations were carried out to show the effect of 6-[(R)-2-[3-methylsulfonyl-2-oxo-imidazolidine-1-carboxamido]-2-phenyl-acetamido]-penicillanic acid sodium salt (mezlocillin, Baypen) on the ultrastructures of gramnegative bacteria (Escherichia coli C 165). Distinct alterations of the bacteria were to be seen depending on concentration and cultivation time. The outer wall of the bacterial cell became irregular. Locally it detached from the plasma membrane. The normal density of the cytoplasmic structures decreased quickly. Owing to their inability to form septa the bacteria grew as extended filaments. These mezlocillin-treated cells could form filaments of up to 100 times the length of normal untreated bacteria. Those bacterial filaments, however, were unable to form colonies as was shown by survival curves carried out in parallel. The filaments, therefore, were irreversibly damaged bacterial forms.