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A total of 45 strains of Escherichia coli isolates from chickens with colisepticemia were examined for virulence factors commonly found in pathogenic groups of E. coli. These strains were studied for the following: pathogenicity in 1-day-old chicks; toxin, hemolysin, and colicin production; cell invasiveness and adherence; hemagglutination for fimbriae detection; serum resistance; aerobactin production in iron-limited conditions; and plasmid content. The characteristics exhibited by virulent strains were invasion for HeLa and chicken fibroblast cells, serum resistance, colicin V, and aerobactin production. None of the isolates were toxigenic or positive in hemagglutination tests. The molecular genetic studies of the virulence factors by agarose electrophoresis showed that the plasmids of these strains are of high molecular weight.

Extraintestinal pathogenic Escherichia coli (ExPEC) is one of the main etiological agents of bloodstream infections caused by Gram-negative bacilli. In the present study, 20 E. coli isolates from human hemocultures were characterized to identify genetic features associated with virulence (pathogenicity islands markers, phylogenetic group, virulence genes, plasmid profiles, and conjugative plasmids) and these results were compared with commensal isolates. The most prevalent pathogenicity island, in strains from hemoculture, were PAI IV536, described by many researchers as a stable island in enterobacteria. Among virulence genes, iutA gene was found more frequently and this gene enconding the aerobactin siderophore receptor. According to the phylogenetic classification, group B2 was the most commonly found. Additionally, through plasmid analysis, 14 isolates showed plasmids and 3 of these were shown to be conjugative. Although in stool samples of healthy people the presence of commensal strains is common, human intestinal tract may serve as a reservoir for ExPEC.

In this study, we compared Escherichia coli isolates from chickens with avian cellulitis with those from feces of healthy chickens. Cellulitis-derived strains presented phenotypic and genotypic characteristics of greater virulence than did the fecal isolates. Phylogenetic analysis by repetitive extragenic palindromic-PCR showed that, in agreement with their virulence characteristics, the cellulitis isolates form two clonal groups distinct from the fecal isolates.Escherichia coli causes a variety of diseases in poultry, including respiratory tract infection, omphalitis, swollen-head syndrome, enteritis, septicemia, and cellulitis (3, 7), and these diseases are responsible for major economic losses in the chicken industry. Cellulitis lesions cause carcass downgrading and condemnation losses estimated at $40 million annually (7) in the United States. In Brazil, cellulitis is responsible for 45.2% of the broiler carcasses condemned for skin lesions (2), and the economic losses are estimated at $10 million annually.Some clones of E. coli may be more effective in causing cellulitis, since experimental inoculation of isolates from cellulitis lesions reproduced this disease with a significantly greater frequency (100%) than did inoculation of isolates from airsacculitis lesions (42%) or inoculation of fecal isolates (8%) (9). However, E. coli strains isolated from cellulitis lesions expressed many virulence-associated factors similar to those presented by strains isolated from other colibacillosis lesions and from feces (6, 8), which shows that the expression of these virulence factors by themselves cannot explain the differences in pathogenicity presented by these isolates.Since avian colibacillosis in its different forms occurs worldwide, we can gain a better understanding of its pathogenesis by a phylogenetic analysis of the clonal relations among E. coli isolates in several regions and in different countries. In this study, we used phenotypic and genotypic methods to examine the presence of virulence factors in E. coli isolates obtained in Southern Brazil from broiler chickens and determined by repetitive extragenic palindromic (REP)-PCR the genetic relationship among these isolates and avian fecal isolates.Fifty-two broiler chickens presenting cellulitis were collected from 52 different flocks in Southern Brazil, and from each animal one E. coli strain was isolated from pure culture and maintained by standard procedures. Twelve E. coli strains were obtained from the feces of healthy chickens. Isolates were grown on brain heart infusion agar (Difco) for 18 h at 37°C for phenotypic or genotypic analysis.The following phenotypic properties of the E. coli isolates were evaluated by standard methods (1, 9, 11): antibiotic resistance, pathogenicity to 1-day-old chickens, motility, ability to experimentally reproduce cellulitis (applied to 20 isolates), production of hemolysins, presence of K1 capsule, hemagglutination, production of aerobactin, resistance to chicken serum, and production of cytotoxins to Vero cells. All ...