Effects of global regulatory proteins and environmental conditionson fimbrial gene expression of F1651 and F1652 producedby Escherichia coli causing septicaemia in pigs

Abstract Escherichia coli O115:F165 strains are associated with septicaemia in young pigs and possess at least two types of fimbriae. F165 1 fimbriae belong to the P fimbrial family and F165 2 fimbriae belong to the S fimbrial family. Regulatory regions of foo (F165 1 ) and fot (F165 2 ) fimbrial gene clusters from wild-type strain 4787 were sequenced and characterised. Expression of F165 1 and F165 2 fimbrial genes was analysed by using lacZ and/or luxAB as reporter genes under the control of the native fimbrial promoters. Differential expression of fimbrial genes was observed. Global regulatory mechanisms such as catabolite repression, leucine-responsive regulatory protein (Lrp), methylation and DNA supercoiling were demonstrated to influence foo and fot expression. foo and fot expression was optimal at 37 °C and under aerobic conditions. Expression of foo was higher on minimal medium, whereas fot expression was higher on complex Luria-Bertani medium. This could reflect an in vivo differential expression.