A total of 229 Spanish Actinobacillus pleuropneumoniae isolates recovered from diseased pigs with pleuropneumonia from
1997 to 2004 was tested for their susceptibility to 11 antimicrobials in a broth microdilution method. All the isolates were
susceptible to florfenicol andmost of themto cephalothin; however, a high rate of resistancewas observed to tetracycline.Abimodal
or multimodal distribution of isolates over the MIC range were observed for penicillins, tetracycline, trimethoprim, sulfisoxazole
and nalidixic acid, suggesting the development of acquired resistance. Eight resistance patterns were established, and 21.1%of the
isolates were resistant to at least two antimicrobials. In addition, a considerable increase in the resistance to tetracyclines was
observed during the last decade in Spain, when compared with other A. pleuropneumoniae strains isolated during 1987–1988
