Flagellum expression and swimming activity by the zoonotic pathogen Escherichia albertii

Flagella are the well-known structural appendages used by bacteria for motility. Although generally reported to be non-motile, the enteropathogenic bacterial species Escherichia albertii produces flagella intermittently. We found that E. albertii expressed flagella under specific environmental conditions. After several generations (involving 4 to 12-h incubations), six of the twelve strains we investigated displayed swimming motility in various aquatic environments, including pond water containing nutrients from pigeon droppings (10% suspension) as well as in 20 × -diluted tryptic soy broth. The most significant motility determinant was a temperature between 15 and 30 °C. At 20 °C in the 10% pigeon-dropping suspension, microscopic observations revealed that some cells (1%-95% of six strains) showed swimming motility. Electron microscopy showed that the E. albertii cells expressed flagella. Lower concentrations of some substrates (including nutrients) may be of secondary importance for E. albertii flagella expression. Interestingly, the non-motile strains (n = 6/12) contained pseudogenes corresponding to essential flagella structural proteins. After being released from its host into surface water, E. albertii may express flagella to move toward nutrient sources or new hosts.