PRODUCTION OF TOXINS (ENTEROTOXINS, VEROTOXINS, AND NECROTOXINS) AND COLICINS BY ESCHERICHIA-COLI STRAINS ISOLATED FROM SEPTICEMIC AND HEALTHY CHICKENS - RELATIONSHIP WITH IN-VIVO PATHOGENICITY

Since the mechanism of virulence of Escherichia coli strains pathogeni c to birds is not fully understood, the prevalence of toxic factors pr oduced by E. coli strains pathogenic to other animals was investigated . A total of 625 E. coli strains isolated from visceral organs of chic kens with colisepticemia and from feces of healthy chickens in Spain w ere tested for production of enterotoxins (heat labile [LT] and heat s table [STa]), verotoxins (VT1, VT2, and VT2v), cytotoxic necrotizing f actors (CNF1 and CNF2), alpha-hemolysin (Hly), enterohemolysin (EntHly ), colicin V (Col V) and other types of colicins, and necrotic and let hal activities. Only 45 (7%) of avian E. coli strains were toxigenic: 20 strains produced a cytotoxic response in HeLa but not in Vero cells , indicating the production of a cytotoxin not related to the VTs; 16 were EntHly(+); 5 produced a new cytotonic product that causes the app earance of whitish vacuola in Vero and HeLa cells; 5 synthesized solub le factors that cause lethal activity in mice; and 1 elaborated LT. No ne of 625 avian E. coli strains was positive for production of VTs or CNFs. In contrast, colicinogenicity occurred in 335 (73%) of the 458 s epticemic strains and 97 (58%) of 167 fecal isolates (P < 0.01), and t his property was correlated,vith in vivo pathogenicity of strains. Thu s, 80% (P < 0.001) and 66% (P < 0.001) of strains producing Col V and other types of colicins were characterized as being of high pathogenic ity, whereas only 15% of the noncolicinogenic strains were classified as highly pathogenic. Our results clearly support the special pathogen icity theory, because 60% of the E. coli strains belonging to 18 serog roups (01, 02, 05, 08, 012, 014, 015, 018, 020, 053, 078, 081, 083, 01 02, 0103, 0115, 0116, and 0132) most frequently identified among clini cal septicemic strains were classified as highly pathogenic in in vivo assays, whereas only 24% of the strains with 0 serogroups less preval ent among diseased chickens were considered highly pathogenic (P < O.0 1).