Extraintestinal pathogenic Escherichia coli (ExPEC) strains of human and avian origin show similarities that suggest that the avian strains potentially have zoonotic properties. However, the phylogenetic relationships between avian and human ExPEC strains are poorly documented, so this possibility is difficult to assess. We used PCR-based phylotyping and multilocus sequence typing (MLST) to determine the phylogenetic relationships between 39 avian pathogenic E. coli (APEC) strains of serogroups O1, O2, O18, and O78 and 51 human ExPEC strains. We also compared the virulence genotype and pathogenicity for chickens of APEC strains and human ExPEC strains. Twenty-eight of the 30 APEC strains of serogroups O1, O2, and O18 were classified by MLST into the same subcluster (B2-1) of phylogenetic group B2, whereas the 9 APEC strains of serogroup O78 were in phylogenetic groups D (3 strains) and B1 (6 strains). Human ExPEC strains were closely related to APEC strains in each of these three subclusters. The 28 avian and 25 human strains belonging to phylogenetic subcluster B2-1 all expressed the K1 antigen and presented no significant differences concerning the presence of other virulence factors. Moreover, human strains of this phylogenetic subcluster were highly virulent for chicks, so no host specificity was identified. Thus, APEC strains of serotypes O1:K1, O2:K1, and O18:K1 belong to the same highly pathogenic clonal group as human E. coli strains of the same serotypes isolated from cases of neonatal meningitis, urinary tract infections, and septicemia. These APEC strains constitute a potential zoonotic risk.

The temperature-sensitive hemagglutinin Tsh is a member of the autotransporter group of proteins and was first identified in avian-pathogenic Escherichia coli (APEC) strain 7122. The prevalence of tsh was investigated in 300 E. coli isolates of avian origin and characterized for virulence in a 1-day-old chick lethality test. Results indicate that among the tsh-positive APEC isolates, 90.6% belonged to the highest virulence class. Experimental inoculation of chickens with 7122 and an isogenic tsh mutant demonstrated that Tsh may contribute to the development of lesions within the air sacs of birds but is not required for subsequent generalized infection manifesting as perihepatitis, pericarditis, and septicemia. Conjugation and hybridization experiments revealed that the tsh gene is located on a ColV-type plasmid in many of the APEC strains studied, including strain 7122, near the colicin V genes in most of these strains. DNA sequences flanking the tsh gene of strain 7122 include complete and partial insertion sequences and phage-related DNA sequences, some of which were also found on virulence plasmids and pathogenicity islands present in various E. coli pathotypes and other pathogenic members of the Enterobacteriaceae. These results demonstrate that the tsh gene is frequently located on the ColV virulence plasmid in APEC and suggest a possible role of Tsh in the pathogenicity of E. coli for chickens in the early stages of infection.Avian-pathogenic Escherichia coli (APEC) comprise a specific subset of pathogenic E. coli that cause extraintestinal diseases of poultry. Of the various forms of E. coli disease in poultry, the most common syndrome starts as a respiratory tract infection in 3-to 12-week-old broiler chickens and turkeys and frequently becomes more generalized. The air sacs are the first organs affected, and systemic spreading may result in pericarditis, perihepatitis, and an often fatal septicemia (15,29). APEC infections are frequently enhanced or initiated by predisposing factors, which include environmental conditions and viral or Mycoplasma infection (15, 29). O1, O2, and O78 are the most commonly encountered serogroups among APEC (15,29), and the majority of strains have been shown to belong to a limited number of clonal lineages (69, 70). APEC strains of high virulence are lethal for 1-day-old chicks when administered subcutaneously. Attributes associated with APEC strains include F1 (type 1) and P fimbrial adhesins (16, 21, 53, 66), resistance to serum and phagocytosis (21, 22, 52, 71), the aerobactin siderophore system (21, 41, 65), and colicin V (7, 23, 65, 71) (reviewed in references 15 and 29). Recently the tsh gene, encoding a temperature-sensitive hemagglutinin, first identified by Provence and Curtiss (54), was shown to be associated with APEC but not with E. coli isolated from the feces of healthy chickens (45).The tsh gene was first identified from APEC O78:K80 strain 7122 and, when cloned into E. coli K-12, was shown to impart mannose-resistant hemagglutination of chicken erythrocytes...

f In order to improve the identification of avian pathogenic Escherichia coli (APEC) strains, an extensive characterization of 1,491 E. coli isolates was conducted, based on serotyping, virulence genotyping, and experimental pathogenicity for chickens. The isolates originated from lesions of avian colibacillosis (n ‫؍‬ 1,307) or from the intestines of healthy animals (n ‫؍‬ 184) from France, Spain, and Belgium. A subset (460 isolates) of this collection was defined according to their virulence for chicks. Six serogroups (O1, O2, O5, O8, O18, and O78) accounted for 56.5% of the APEC isolates and 22.5% of the nonpathogenic isolates. Thirteen virulence genes were more frequently present in APEC isolates than in nonpathogenic isolates but, individually, none of them could allow the identification of an isolate as an APEC strain. In order to take into account the diversity of APEC strains, a statistical analysis based on a tree-modeling method was therefore conducted on the sample of 460 pathogenic and nonpathogenic isolates. This resulted in the identification of four different associations of virulence genes that enables the identification of 70.2% of the pathogenic strains. Pathogenic strains were identified with an error margin of 4.3%. The reliability of the link between these four virulence patterns and pathogenicity for chickens was validated on a sample of 395 E. coli isolates from the collection. The genotyping method described here allowed the identification of more APEC isolates with greater reliability than the classical serotyping methods currently used in veterinary laboratories.

In chickens, colibacillosis is caused by avian pathogenic Escherichia coli (APEC) via respiratory tract infection. Many virulence factors, including type 1 (F1A) and P (F11) fimbriae, curli, aerobactin, K1 capsule, and temperature-sensitive hemagglutinin (Tsh) and plasmid DNA regions have been associated with APEC. A strong correlation between serum resistance and virulence has been demonstrated, but roles of virulence factors in serum resistance have not been well elucidated. By using mutants of APEC strains TK3, MT78, and 7122, which belong to serogroups O1, O2, and O78, respectively, we investigated the role of virulence factors in resistance to serum and pathogenicity in chickens. Our results showed that serum resistance is one of the pathogenicity mechanisms of APEC strains. Virulence factors that increased bacterial resistance to serum and colonization of internal organs of infected chickens were O78 lipopolysaccharide of E. coli 7122 and the K1 capsule of E. coli MT78. In contrast, curli, type 1, and P fimbriae did not appear to contribute to serum resistance. We also showed that the iss gene, which was previously demonstrated to increase resistance to serum in certain E. coli strains, is located on plasmid pAPEC-1 of E. coli 7122 but does not play a major role in resistance to serum for strain 7122.Avian pathogenic Escherichia coli (APEC) belongs to the extraintestinal pathogenic group of E. coli. These bacteria cause airsacculitis, omphalitis, peritonitis, salpingitis, synovitis, and colisepticemia in poultry (17). APEC is also associated with cellulitis or necrotic dermatitis of the lower abdomen and thighs and with granuloma. APEC strains belong predominantly to three serogroups, O1, O2, and O78. Virulence factors associated with APEC strains include type 1 and P fimbriae, curli, aerobactin, K1 capsule, and temperature-sensitive hemagglutinin (Tsh) of the autotransporter family (9, 17). Serum resistance also appears to be an important virulence mechanism of APEC, and it may play a major role in the pathogenesis of avian colibacillosis. For instance, serum resistance has often been associated with isolates from septicemic turkeys and chickens (13,33), and a correlation between serum resistance and virulence and lethality in isolates from septicemic chickens and turkeys has been observed (13,15,17).At this time, it is not known if avian E. coli strains differ from mammalian isolates in their mechanisms of serum resistance and virulence. Studies carried out with mammalian E. coli showed that many virulence factors, such as capsules, lipopolysaccharide (LPS), and outer membrane proteins (OMPs), includingOmpA and the ColV plasmid-encoded proteins TraT and Iss, are associated with complement resistance of E. coli (17). TraT is a surface exclusion protein encoded by conjugative plasmids (32), and Iss is a plasmid-encoded OMP homologous to the Bor protein of bacteriophage (32). In APEC, the role of different virulence factors in serum resistance has generally been speculative. Nolan et al. (22) produced an a...

Extraintestinal pathogenic (ExPEC) Escherichia coli strains of serotype O18:K1:H7 are mainly responsible for neonatal meningitis and sepsis in humans and belong to a limited number of closely related clones. The same serotype is also frequently isolated from the extraintestinal lesions of colibacillosis in poultry, but it is not well known to what extent human and avian strains of this particular serotype are related. Twenty-two ExPEC isolates of human origin and 33 isolates of avian origin were compared on the basis of their virulence determinants, lethality for chicks, pulsed-field gel electrophoresis (PFGE) patterns, and classification in the main phylogenetic groups. Both avian and human isolates were lethal for chicks and harbored similar virulence genotypes. A major virulence pattern, identified in 75% of the isolates, was characterized by the presence of F1 variant fimbriae; S fimbriae; IbeA; the aerobactin system; and genomic fragments A9, A12, D1, D7, D10, and D11 and by the absence of P fimbriae, F1C fimbriae, Afa adhesin, and CNF1. All but one of the avian and human isolates also belonged to major phylogenetic group B2. However, various subclonal populations could be distinguished by PFGE in relation to animal species and geographical origin. These results demonstrate that very closely related clones can be recovered from extraintestinal infections in humans and chickens and suggest that avian pathogenic E. coli isolates of serotype O18:K1:H7 are potential human pathogens.