Virginiamycin susceptibility of Serpulina hyodysenteriae, in vitro and in vivo
Rønne, H.; Jensen, J.C.
Veterinary Record 131(11): 239-240
1992
ISSN/ISBN: 0042-4900 PMID: 1441115 Document Number: 393227
Clinical and bacteriological monitoring of swine dysentery (SD) was carried out for 16 weeks in a herd which had suffered from SD for several years; the herd was managed as a continuous production of finishing pigs. Rectal swabs were taken from pigs showing typical clinical signs of SD. Virginiamycin 20 ppm was added to the feed for 11 weeks. Minimum inhibitory concentrations (MICs) of virginiamycin on S. hyodysenteriae isolates from this herd, from 20 representative Danish field cases of SD and for type strain B78 were determined; 19 different Danish isolates had MIC values of 2 micro g/ml or more and 2 isolates (isolated during the virginiamycin feeding) from the infected herd had MIC values of 2 micro g/ml and were, therefore, among the most sensitive to virginiamycin. S. hyodysenteriae was isolated from 75% of rectal swabs taken from pigs with typical clinical signs of SD before virginiamycin was added to to the feed and from 57.6% of swabs taken after the addition of virginiamycin. However, data were not sufficient to show a statistical decrease in the isolation rate. Thus control of clinical SD was not achieved during virginiamycin feeding.