Escherichia coli serotypes in pigs in South Africa.

This retrospective study was based on 674 cases of colibacillosis in pigs submitted to the diagnostic bacteriology laboratory of the Onderstepoort Veterinary Institute (OVI) over the 20-year period ranging from 1971-1991. During this time, 28,840 cases from various livestock species were received, of which 4162 (14.4%) were from pigs. The 674 porcine cases selected for this study were included if an E. coli infection had been suspected by the referring veterinarian, and typable E. coli strains were then isolated by this laboratory. Enteritis (45.5%) and septicaemia (46.9%) were the most common syndromes, with agalactiae (1.4%) and abortion (1.1 %) representing a far lower prevalence. Oedema-disease signs were described by the submitting veterinarian in only 12 cases. Samples were received from weaners and sucklers in relatively equal numbers until 1981, but subsequently samples from sucklers declined, while those from weaners remained high. There were 69 different somatic and capsulated (OK) antigen groups associated with E. coli infections in pigs. Escherichia coli O149 was the most common isolate (45.8%), while E. coli O141 was the next most common isolate (18.3%). This was followed by O9 (8.9%), O20 (5.2%) and O8 (3.1%). All other serotypes together accounted for less than 20% of the total number of cases, and were isolated fewer than 20 times each. The fimbrial attachment factor, F4 (K88) was found associated with 46.9% of isolates.

Resistance to various antibiotics of Salmonella and Escherichia coli isolated from registrable farm feeds.

Resistance to 20 antibiotics of 128 Salmonella and 97 Escherichia coli isolates from various registrable farm feeds was determined. A high frequency of comparatively low levels of resistance was found in both the Salmonella and E. coli isolates. This, together with an elevated frequency of multiple resistance, indicates that problems related to an effective transfer in bacterial populations of resistance to certain antibiotics are a distinct possibility. The addition of antibiotics, such as penicillin and tetracyclines, to animal feeds can create conditions for rapid selection amongst bacteria resistant to antibiotics. The numbers of resistant bacteria in the animal environment may be increased and may lead to the development of veterinary and human health problems from the possible transfer of antimicrobial resistance from animal pathogens to human pathogens or spreading in the human population of animal pathogens resistant to antibiotics. There is a need for caution in the use of antibiotics, particularly in animal feeds. Extended survey of, and epidemiological research on, farm feeds, manufacturing mills and animal production units are emphasized.

The serological and immunological relationship of type strains A and D of Pasteurella multocida to field isolates from sheep.

Investigations with antisera prepared in rabbits and sheep and active immunity experiments in mice showed that strains of Pasteurella multocida which, according to the haemagglutination test, are serologically related, do not necessarily give rise to cross immunity. Conversely, it was found that serologically unrelated strains may exhibit an appreciable degree of cross protection. The unreliability of the haemagglutination test as an indicator of immunological identity of strains was further confirmed in that peritoneal fluid from immunized mice showed passive protection properties despite the absence of haemagglutinating antibodies. There was no consistent agreement between the results obtained with antisera prepared in different species and active immunity experiments in mice, and this leads to the conclusion that different species probably vary quantitatively and qualitatively in their immune response to immunization with P. multocida. Attempts to determine whether combined bacterins afforded a better immunity than monovalent bacterins were inconclusive.

Relation between macrophage migration inhibition and immunity to Brucella abortus in guinea-pigs.

Relation between macrophage migration inhibition and immunity to Brucella abortus in guinea-pigs. Onderstepoort Journal of Veterinary Research 43 (4), 175-184 (1976). A soluble protein antigen was prepared from Brucella melitensis Rev I with which macrophage migration inhibition (MMI) assays were successfully done using guinea-pig peritoneal exudate cells. By comparing the MMI, agglutinin response and immunity of groups and of individual guinea-pigs which had been immunized with either B. melitensis Rev I live vaccine or B. melitensis Rev I inactivated antigen, an association between the MMI and resistance to infection was demonstrated.