Characterization of IcmF of the type VI secretion system in an avian pathogenic Escherichia coli (APEC) strain

Abstract

The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome–lysosome fusion inLegionella pneumophila. InVibrio choleraeit is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcpandclpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenicEscherichia coli(APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenicE. coli(ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APECicmFmutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. TheicmFmutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in theicmFmutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.