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Free-ranging cottontail rabbits (Sylvilagus floridanus) from two areas in central Pennsylvania were sampled over a 4-year period. Large numbers of coliforms were isolated from the intestinal tracts of these animals; in 136 of the 141 rabbits sampled, Escherichia coli was found to be a major component of the alimentary flora. Four serogroups (O7, O77, O73, and O103) were predominant among the isolates and were considered resistant coliflora of this species of cottontail rabbit.

Twenty Holstein calves were assigned alternately at birth to diets of 1) fermented colostrum, 2) colostrum treated with 1% propionic acid, 3) whole milk, or 4) whole milk treated with Lactobacillus acidophilus (frozen concentrate culture) at 5 x 10(8) organisms per litter. Diets were fed once daily for 3 wk at 10% of birth weight as the sole source of nutritients. Fecal samples were collected at 0, 7, 14, and 21 days of age and analyzed for coliform and lactobacilli numbers. Fermented colostrum diets did not alter coliform counts in feces of healthy calves. Fecal coliform counts of calves fed L. acidophilus decreased with time. Average fecal lactobacilli counts were lower for the colostrum diets than milk diets. The apparent lowered incidence of scours frequently reported in calves fed fermented colostrum diets was not reflected in major changes in fecal microflora under the conditions of this study.

Five strains of Escherichia coli were tested for the presence of the K88ac or K88ab antigens by immunoelectrophoresis and immunodiffusion. The K88ac antigen of 0A2 and Sojka Abbotstown gave an anodic line in the immunoelectrophoresis test and a line in immunodiffusion with homologous K88ac antisera. The K88ab antigens of 0G7, 0E68, and Moon 263 also gave anodic lines in immunoelectrophoresis, and were detectable by immunodiffusions. The 0 groups of these strains were also demonstrated by immunoelectrophoresis and immunodiffusion with homologous 0 antisera. Lack of complete inactivation at 100 degrees C of both the K88ac and K88ab antigens was noted in this study.

A study was undertaken to determine whether virulence in mice could be used to assess the pathogenicity of a variety of Escherichia coli serotypes. Sixty-one E. coli strains isolated from animals, poultry, or humans were serotyped to determine their O, K, and H antigens, and were administered to mice via the intraperitoneal route with and without a mucin adjuvant. The ld(50) dose was then determined for each serotype. The results indicated that the source of the serotype may be associated with virulence for mice. Serotypes isolated from nonenteric, systemic sources showed a greater virulence for mice inoculated intraperitoneally than did the enteric and the nonenteric, nonsystemic (localized) isolates. It was observed that not all serotypes belonging to a specific serogroup were virulent for mice and that the presence or absence of a K antigen had no effect on the virulence of strains of one serotype.

Immunochemical properties of Escherichia coli O antibodies present in bovine serum and colostrum were investigated. Dam and calf serum samples plus colostral whey samples were fractionated by gel filtration, and the 7S and 19S fractions isolated. Antibody activity against the O antigens of four recognized E. coli bovine pathogens was determined by the indirect hemagglutination test on the whole serum and colostral whey samples and the 7S and 19S fractions thereof. Mercaptoethanol reduction was used to chemically study the immunochemistry of the E. coli O antibodies. The E. coli O antibodies in dam serum were entirely 19S macroglobulins and appeared to be IgM immunoglobulins. The antibodies in colostrum and calf serum were both 7S and 19S globulins. Reasons for believing these 7S antibodies may be IgG, and the 19S antibodies IgA, immunoglobulins are presented.

Twelve hundred bacterial cultures from thirty newborn calves were examined serologically to determine the experimental pathogenicity of E. coli serotypes as well as the influence of enteric bacteria naturally present in the calves. Serotype O115:K.:H18 was pathogenic, O9:K35:H1O was not, and unclassified E. coli OX28 was questionable. Klebsiella sp. and E. coli OX28 occurred naturally in the calves and was responsible for some mortality. Contact exposure in two groups of calves was not successful. All calves had a detectable gamma-globulin level whether or not they had nursed the dam. Antibody to four E. coli O groups was present at a gamma-globulin level above 0.78 gm% but not belw 0.60 gm%. Antibody was associated with survival of calves given E. coli serotype 115:K.:H18 but not the less virulent 9:K35:H1O. There was no correlation between antibody level and bactericidal activity of the serums. The latter did not appear to offer resistance to infection by itself, but antibody level and bactericidal activity to E. coli O115 and O78 did protect all calves experimentally infected with different serotypes.

Cultures of Escherichia coli isolated from colibacillosis in pigs in Canada and the U.S.A. and previously identified as unclassified E. coli OX36 were found to belong to a new E. coli O group 157. Strains of E. coli V145, GIRI, C308 and V17 which had a weak relationship to E. coli O116 also were found to belong to O157. The increased incidence of E. coli O157 in colibacillosis of swine stresses the inclusion of this O group among those enteropathogenic for swine.

Of 3,200 cultures of Escherichia coli isolated from streams in Pennsylvania over a 7-year period, 82.46% or 2,639 were O serogrouped. The largest number of cultures (33.4%) belonged to O groups 1 to 26, and the second highest number (16.8%) belonged to O groups 60 to 88. The individual E. coli O groups most frequently isolated were ADO3, 18ac, 2a, 3, 7, 73, 139, and OX13. Practically every known standard E. coli O group was found in the streams. It was not possible to identify the K and H antigen of every E. coli isolate. Serotypes of E. coli O2a:K1:H6, O26:K60:H11, O55:K59:H27, O86:K62:H2, 112ab:K68:H2, 125ab:K70:H21, 128ab:K67:H2, and O138:K81:H14 known to be pathogenic for humans and animals were identified. Cultures having the same K antigen but a different H antigen for enteropathogenic E. coli O groups 6, 18ab, 18ac, 111ab, 126, 127a, 139, 141, and 147 were also isolated.

An unclassified serogroup of Escherichia coli, OX1, was identified in 151 of 196 isolates from 20 rabbits affected with fatal diarrhea and four with no visible illness. No other known pathogenic bacteria or protozoa were isolated from these rabbits. Six strains of OX1 produced a positive reaction comparable to a known positive-reacting E. coli O26:K60 strain when injected into ligated intestinal loops of young rabbits.