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.