LIGHT AND ELECTRON MICROSCOPY OF THE EARLY RESPONSE OF <i>ESCHERICHIA COLI</i> TO A 6β‐AMIDINOPENICILLANIC ACID (FL 1060)

Abstract

The morphological response of E. coli to a new antibiotic, 6β‐[(hexahydro‐1H‐azepin‐1‐yl)‐methyleneamino]‐penicillanic acid (FL 1060), has been investigated and compared with the response to benzylpenicillin and ampicillin. At high concentrations of FL 1060 (1000 μg/ml) in osmotically stabilized media, E. coli responds in the same way as to penicillins by forming “rabbit ears” and spheroplasts. At lower concentrations down to the IC50 value (0.02 μg/ml), the cells, even in unstabilized media, first become ellipsoidal and later spherical. After 2–3 hours, lysis of the cells occurs. This is rather late, as compared to the early lysis obtained with penicillins. Electron microscopical investigations show no characteristic changes in the subcellular pattern. During the second hour of treatment, the bacterial culture contains a considerable number of cells presenting asymmetrical cell divisions. During the same period, nuclear stainings show abnormal nuclear regions with impaired segregation, resulting in chromatine bridges and horseshoe‐shaped chromatine regions. The results support the conception that, on cells in the pre‐lytic stage, FL 1060 interferes with the balance between lengthwise growth and cell division through cross wall formation.