Morphological and biochemical changes in Escherichia coli after exposure to ciprofloxacin.

Examination of morphological and biochemical changes in Escherichia coli KL-16 after exposure to ciprofloxacin revealed distinct concentration-dependent responses. At levels close to the MIC extensive filamentation was seen, whereas at the most bactericidal concentration cells were elongated but not filamented. At higher concentrations ovoid cells were seen. Some cells showed surface vacuoles, but no significant leakage of cell contents was detected. Filamentation and vacuolation were shown to make only a minor contribution to ciprofloxacin-induced cell death, and the data indicate that there are two or more mechanisms involved in the lethal action of ciprofloxacin.