Four groups of six specific pathogen-free (SPF) pigs were inoculated intranasally with Actinobacillus pleuropneumoniae serotype 2 and treated with either enrofloxacin, tetracycline or penicillin at the onset of clinical disease, or left untreated. A fifth group was left uninoculated. The inoculated control and the penicillin-treated groups developed severe disease, but the groups treated with enrofloxacin and tetracycline recovered rapidly. All the inoculated pigs, except those treated with enrofloxacin developed serum antibodies to A. pleuropneumoniae. On day 28, all five groups were challenged with A. pleuropneumoniae without any subsequent treatment. The previously uninoculated control group and the enrofloxacin-treated group developed severe disease, but the three seropositive groups remained unaffected.
Sjölund M, de la Fuente AJ, Fossum C, Wallgren P, Responses of pigs to a re-challenge with Actinobacillus pleuropneumoniae after being treated with different antimicrobials following their initial exposure, Vet Rec. 2009 May 2;164(18):550-5.