EVALUATION OF ANTIBIOTICS FOR THE ELIMINATION OF THE TONSILLAR CARRIER STATE OF STREPTOCOCCUS-SUIS IN PIGS

Seventy clinically normal 13-day-old crossbred pigs from 10 litters fr om a Streptococcus suis-infected herd were randomly assigned by litter and weight to 7 groups of 10 pigs each to determine whether different antibiotic regimens would eliminate the tonsillar carrier state of S. suis. Six antimicrobial regimens were tested: penicillin intramuscula rly (IM) once daily (s.i.d.) for 3 consecutive days; penicillin IM s.i .d. for 5 consecutive days; ampicillin IM s.i.d. for 5 consecutive day s; ampicillin per os s.i.d. for 5 consecutive days; ampicillin intrana sally s.i.d. for 5 consecutive days; and ceftiofur sodium IM s.i.d. fo r 5 consecutive days. The seventh group consisted of untreated control pigs. Tonsillar swab samples were collected before treatment, and ton sillar tissue samples were collected after treatment for cultural exam ination for S. suis. Streptococcus suis was identified in pigs from al l groups prior to treatment and after treatment. Pigs did not have cli nical signs of disease during the study. All antimicrobial treatments tested in this study failed to eliminate the tonsillar carrier state o f S. suis. Early weaning and medication used in this study were not ef fective for the elimination of the tonsillar carrier state of S. suis in pigs. Optimization of management and environment of pigs coupled wi th strategic medication of clinically ill animals should be used for c ontrol and prevention of mortality caused by streptococcosis.