Study of the adhesion and invasion capacities of an invasive avian pathogenic escherichia coli strain (APEC) to in vitro cultivated HEP-2 cells

ABSTRACT

An avian pathogenic Escherichia coli strain (APEC), designated strain sep17, was isolated from the liver of a chicken suffering from septicaemia. Its biological characteristics, including antimicrobial drug resistances, colicin production, plasmid profile, adhesion and invasion capacities to in vitro cultivated HEp-2 cells, and PCR detection of DNA sequences related to pathogenicity genes (fimA, tsh, papA, crl, csgA, afa, sfa, eae, lpfAO157/OI-141, lpfAO157/OI-154, toxB, iha, ial, efa, inv, invA/invE and ibeA) were determined. This strain (Lac+, TcR, fimA, csgA, crl, lpfAO157/OI-154) harbored a 70 MDa plasmid and was able to adhere to and invade in vitro cultured HEp-2 cells. Transference of this 70 MDa plasmid by conjugation rendered a non-pathogenic recipient strain HB101 (Lac-, SmR, csgA) capable of adhering to and invading the same type of cell. Scanning electron microscopy and light microscopy confirmed the adhesion capacity of the wild and the transconjugant strains, while the in vitro invasion technique and light microscopy confi rmed the invasion capacity of these strains. The FAS technique, which is used to visualize actin accumulation on cells where the adhesion process occurs, was negative for all those strains. None of the genes detected in strain sep17 were transferred by conjugation, which indicates that they are chromosomally located and are not related to the adhesion and invasion processes. The presence and absence of pathogenicity-related genes are discussed.