The effect of some beta-lactam antibiotics on Escherichia coli studied by flow cytometry

The effects of three beta-lactam antibiotics on Escherichia coli were studied by means of flow cytometry. Since these agents block bacterial cell wall synthesis in such manner as to prevent septal formation without appreciably affecting nucleic acid synthesis, the resulting cell elongation caused by these agents can be assessed by nucleic acid fluorescent staining. It was shown by this technique that the somatic effects of cefazolin, cefamandole and moxalactam were related both to the antibiotic concentration and time of exposure to the drugs and were observable within 30 minutes of the initial exposure of the cultures to these agents. These results demonstrate that fluorescent cytometry can provide accurate assessment of the effects of compounds that inhibit cell wall formation. This technology could be a useful tool for comparing antibiotic somatic effects on bacteria and for rapidly and reliably determining their sensitivity and resistance to these agents.