Occurrence of virulence-related sequences and phylogenetic analysis of commensal and pathogenic avian Escherichia coli strains (APEC) / Ocorrência de seqüências relacionadas com a virulência e análise filogenética de estirpes comensais e patogênicas de Escherichia coli aviário (APEC)

The presence of iron uptake (irp-2, fyuA, sitA, fepC, iucA), adhesion (iha, lpfA O157/O141, lpfA O157/O154, efa, toxB) and invasion (inv, ial-related DNA sequences and assignment to the four main Escherichia coli phylogenetic groups (A, B1, B2 e D) were determined in 30 commensal E. coli strains isolated from healthy chickens and in 49 APEC strains isolated from chickens presenting clinical signs of septicemia (n=24) swollen head syndrome (n=14) and omphalitis (n=11) by PCR. None of the strains presented DNA sequences related to the inv, ial, efa, and toxB genes. DNA sequences related to lpfA O157/O154, iucA, fepC, and irp-2 genes were significantly found among pathogenic strains, where iucA gene was associated with septicemia and swollen head syndrome and fepC and irp-2 genes were associated with swollen head syndrome strains. Phylogenetic typing showed that commensal and omphalitis strains belonged mainly to phylogenetic Group A and swollen head syndrome to phylogenetic Group D. Septicemic strains were assigned in phylogenetic Groups A and D. These data could suggest that clonal lineage of septicemic APEC strains have a multiple ancestor origin; one from a pathogenic bacteria ancestor and other from a non-pathogenic ancestor that evolved by the acquisition of virulence related sequences through horizontal gene transfer. Swollen head syndrome may constitute a pathogenic clonal group. By the other side, omphalitis strains probably constitute a non-pathogenic clonal group, and could cause omphalitis as an opportunistic infection. The sharing of virulence related sequences by human pathogenic E. coli and APEC strains could indicate that APEC strains could be a source of virulence genes to human strains and could represent a zoonotic risk.(AU)

A presença de seqüências de DNA associadas à capacidade de captação de ferro (irp-2, fyuA, sitA, fepC, iucA), adesão (iha, lpfA O157/O141, lpfA O157/O154, efa, toxB) e de invasão (inv, ial) e a classificação dentro dos quatro grupos filogenéticos principais de Escherichia coli (Grupos A, B1, B2 e D) foram determinadas, através de PCR, em 30 amostras comensais de E. coli isoladas de frangos e de 49 linhagens APEC (24 isoladas de frangos com septicemia, 14 isoladas de frangos com síndrome da cabeça inchada e 11 isoladas de embriões de galinhas com onfalite). Nenhuma das linhagens apresentou os genes inv, ial, efa, e toxB. Os genes lpfA O157/O154, iucA, fepC e irp-2 foram encontrados em freqüências significativas entre as amostras patogênicas. O gene iucA foi associado com amostras causadoras de septicemia e de síndrome da cabeça inchada. Os genes fepC e irp-2 foram associados a amostras causadoras de síndrome da cabeça inchada. A análise filogenética demonstrou que linhagens comensais e causadoras de onfalite pertenceram principalmente ao Grupo filogenético A, não patogênico. Amostras causadoras de síndrome da cabeça inchada pertenceram, em sua maioria, ao Grupo patogênico D. Linhagens causadoras de septicemia pertenceram aos Grupos A e D. Estes dados sugerem que linhagens APEC causadoras de septicemia provavelmente têm uma origem ancestral múltipla: uma derivada de uma linhagem patogênica e outra de uma linhagem não patogênica que possivelmente evoluiu através da aquisição horizontal de genes de virulência. Amostras causadoras de síndrome da cabeça inchada possivelmente constituem um grupo clonal patogênico. Por outro lado, amostras causadoras de onfalite possivelmente constituem um grupo clonal não patogênico, que, possivelmente causam onfalite devido a uma infecção oportunista. A presença de genes de virulência também encontrados em E. coli de origem humana pode indicar a possível ocorrência de zoonoses causadas por APEC.(AU)

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

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.