ESCHERICHIA-COLI CELLULITIS IN BROILER-CHICKENS - CLONAL RELATIONSHIPS AMONG STRAINS AND ANALYSIS OF VIRULENCE-ASSOCIATED FACTORS OF ISOLATES FROM DISEASED BIRDS

Thirty-nine Escherichia coli isolates from broiler chickens with cellu litis were serotyped and analyzed for clonal relationships by multiloc us enzyme electrophoresis. The isolates were further characterized wit h respect to hemagglutination (HA); serum resistance; antibiotic susce ptibility; production of aerobactin, colicin V, and hemolysin; express ion K1 or K5 capsule; sensitivity to cloacin DF13 after treatment with diphenylamine; expression of iron-regulated outer membrane proteins; and virulence in 1-day-old chickens. In addition, the isolates were ex amined for the presence of DNA sequences related to F1A (fim) and P (p ap) fimbriae, aerobactin synthesis (iuc) and transport (iut), hemolysi n operon hly, and TraT lipoprotein-induced serum resistance (traT). On ly 38.4% of the isolates were typeable with standard O antisera, and o f these, serogroups O25 and O78 were the most frequently observed. Mul tilocus enzyme electrophoresis, based on 20 enzymes, resolved 17 elect rophoretic types, forming seven clusters. Isolates from four of these clusters fell into E. coli clone complexes that have been previously r eported to be commonly associated with avian colibacillosis. All isola tes expressed two to five iron-regulated outer membrane proteins, were resistant to serum and cloacin DF13, and possessed DNA sequences homo logous to fim and iuc/iut. Most isolates (72%) were positive for traT, and a majority produced colicin V and aerobactin (92 and 82%, respect ively). Assays for the presence of fim and pap DNA sequences, for HA, and for virulence gave variable results but suggest that cellulitis is olates may express F1A and/or other mannose-resistant HA fimbriae diff erent from P and may be virulent in 1-day-old chickens. Our results su pport the hypothesis that cellulitis in broilers in many cases is caus ed by E. coli clones identical to other pathogenic avian E. coli strai ns. Certain clones may be specific to cellulitis, because 25% of the i solates tested belong to clusters not related to known clone complexes .