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Synopsis A study has been made of the intestinal flora of chickens aged between 2 and 6½ weeks. No major differences were found when rations containing 9 or 25% fish meal were compared or when two different sources of fish meal were used. Throughout the period investigated, it was confirmed that the lactobacilli are the only group of organisms generally present in the small intestine in numbers exceeding 104/g. Clostridia were regularly found at 102 to 104/g, but Clostridium welchii was isolated from only occasional samples. In the caeca, the total number of bacteria present at 2, 3, 4 and 6½ weeks was about 1011/g. Of these it was generally possible to isolate more than 20% using an anaerobic roll‐tube technique and oxygen‐free CO2. Many different types of anaerobes were isolated including strictly anaerobic budding bacteria which had not previously been studied. During the growth of the bird the flora changed. Anaerobic streptococci (peptostreptococci) predominated at 2 weeks but gradually decreased so ...

Nineteen antisera produced in pigs against 14 enteropathogenic and five nonenterotoxigenic porcine strains of Escherichia coli were tested for their ability to inhibit gut loop fluid accumulation induced by homologous and heterologous organisms. In addition, four antisera produced in pigs by an intensive series of intravenous inoculations and three by a less intensive series of intramuscular injections of a polyvalent E. coli vaccine were evaluated. Antisera were also produced in rabbits against eight strains of porcine enteropathogens and tested in pig gut loops. Fluid inhibiting activity was detected in prevaccinal sera of pigs but not of rabbits. This activity was significantly increased following immunization. When single strains of E. coli were used for immunization the activity of the antisera against heterologous organisms varied considerably from one test strain to another and was usually much less than that against the homologous organism. The activity against heterologous organisms could not be associated with relatedness of the O, K and H antigens of the vaccine and the test strains. Antisera produced against a vaccine made by combining three strains were shown to exert inhibitory effects on heterologous organisms similar to those against homologous organisms. Considerably less activity against homologous and heterologous organisms was present in antisera produced by the series of intramuscular compared with the series of intravenous injections.

Minimal inhibitory concentration (M.I.C.) values as determined by an agar-plate-dilution method for 60 bacterial isolates, consisting of Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus of animal origin against 20 antimicrobial drugs are presented. Of all the drugs, gentamicin had the best in vitro antibacterial activity in terms of M.I.C. when considering all the species of organisms together, while spectinomycin had the least activity.An inoculum replicator was a convenient tool in carrying out the agar-plate-dilution method.A comparison of the M.I.C. values of 42 isolates of S. typhimurium with the results obtained by low level method and the Bauer-Kir-by method showed that with few exceptions, there is a general agreement.

The coliflora of three groups of young pigs was shown to be dominated by a small number of Escherichia coli types, as determined by their O antigen, that maintained a tenure of several days or weeks. The pattern of successive waves of E. coli was similar in littermates but, in general, each pig harboured a unique sequence of E. coli types. The E. coli flora from a litter was also shown to be dominated by a small number of E. coli types whose tenure averaged several weeks. A limited amount of information indicated that an enteropathogenic strain of E. coli may occur in this sequence of events and thus appears to be influenced by the same factors as other E. coli strains. The coliflora of two sows appeared to be more complex than those of their progeny and did not seem to follow the same pattern of population change. The coliflora of young pigs differed from the coliflora of man in that there appeared to be no E. coli strains in pigs fitting the description of resident strains.Forty-two percent of all isolates were found to produce colicins and it appeared that this property was more commonly encountered in dominant strains of E. coli

Summary The effect of cultural conditions on the size of the zone of inhibition surrounding growth of colicine-producing organisms was examined. The size of the zone was not altered by the addition of 5 per cent. bovine blood to tryptic soy agar, but was slightly increased by raising the temperature of incubation from 37° to 40°C and substantially increased by extending incubation of producer organisms from 24 to 48 hr. A colicine typing system based on colicine production by field strains of E. coli was evolved and compared with serological typing in epidemiological investigations of E. coli on pigs. Colicine-producing isolates belonging to particular serological types generally belonged to the same colicine type. However, isolates belonging to a number of serological types frequently belonged to the same colicine type. A colicine typing system based on the sensitivity of field strains of E. coli to nine standard colicinogenic strains was too unreliable to serve as the basis for a colicine typing system.

The effect of chlortetracycline fed at concentrations of 10 or 20 grams per ton on the antibiotic resistance of fecal coliforms from weaned pigs from four different farms was studied. At admission to experimental quarters, coliforms resistant to at least one antibiotic predominated in all groups of animals. In pigs from three farms, chlortetracycline caused a reduction in the proportion of sensitive coliforms excreted, the extent of reduction depending on feeding practices on the farm of origin. In another experiment using pigs from a fourth farm, almost all coliforms isolated were resistant. Of all resistant strains isolated, those carrying resistance to a multiplicity of antibiotics predominated, and resistance to tracycline unaccompanied by that to other agents was relatively infrequent. Special studies of hemolytic coliforms from pigs from one farm identified two particular antibiotic sensitive types. No further isolations of these types were made once chlortetracycline administration began although 21 additional isolates were made from littermates receiving unsupplemented ration. These findings suggest that the elimination of sensitive strains resulting from chlortetracycline administration was due to a replacement of these strains by different resistant types rather than by acquisition of resistance by previously sensitive strains.

Three hundred and seventy strains of fecal Escherichia coli were isolated from pigs in one barn and 475, 539 and 490 strains were isolated at each of three successive samplings in another barn. The majority of the E. coli isolates obtained at any one sampling belonged to a small number of E. coli types. Three repeated samplings in one barn indicated that the dominant E. coli types harboured by pigs in this barn were constantly changing. The results also suggested that, within a particular barn, a successive batch of pigs could experience the same sequence of E. coli types. Colicin production appeared to be associated with dominant strains and the proportion of colicin producers in different investigations ranged from 36 to 68%.

The various manifestations of poultry diseases associated with Escherichia coli have been recently reviewed (20). The etiology and pathogenesis of the disease, with special reference to 0 groups concerned, were studied by workers in the U.S.A. (2,5,11) and Great Britain (14,21) and on the Continent (19,22). Although the disease has been recognized in Canada, no serological identification of strains has been published. This paper reports biochemical and serological findings of E. coli strains of avian origin isolated mainly in Ontario (95%). A considerable increase in the incidence of disease associated with E. coli has become evident in Ontario. Perhaps this is due, in part, to increased awareness of the disease entities described in the literature (7,8,10,12,13,20). There is little doubt that colisepticemia and other E. coli disease syndromes are difficult to define because of their complex pathogenesis (1,4,6). In this respect, an effort was made to isolate strains of E. coli from cases in which it was considered significant as a cause of disease, as done by workers in Great Britain (21). The association of certain carbohydrate fermentation patterns, particularly of dulcitol and salicin, was studied in relation to the virulence of the organisms (15,18).