Preliminary characterization of Escherichia coli isolated from pigs with diarrhoea in Venezuela

Abstract

The aetiology of neonatal porcine diarrhoea was studied in 15 different herds located in the north-western region of Venezuela. Of 56 strains of Escherichia coli analyzed, 16 (28.6%) were shown to produce heat-stable (ST a) enterotoxin, as detected by infant mouse assay. Only four of these ST a + isolates also possessed the K88 pilus antigen, two were 987P + and none possessed the K99 antigen, leaving 10 ST a + samples in which no pilus antigen was identified. Among the 40 ST a negative samples were six K88 + specimens, one K99 +, four 987P +, one which reacted as K88 + + K99 + and one K88 + + 987P +. Considering as pathogenic any strain showing at least one of the characters studied, pathogenic E. coli were detected with an overall frequency of 42.9%, being more prevalent during the second week of life. An electrophoretic analysis of the plasmid content of the field isolates of E. coli, revealed the presence of numerous species of extrachromosomal DNA, although no direction association could be made between a particular plasmid and any of the pathogenic characteristics identified. Results of Southern blot analysis indicate that the ST a enterotoxin was preferentially encoded within an endemic plasmid of 4.9 Md. Other plasmids present in the E. coli isolates could be related to antibiotic resistance. With the exception of one strain, all E. coli isolates were resistant to more than one of the nine drugs tested; multiresistant E. coli were frequently isolated, including four strains which were resistant to seven antibiotics.