Changes in antimicrobial resistance in fecal bacteria associated with pig transit and holding times at slaughter plants.

Fecal coliforms, fecal streptococci, and antimicrobial resistance (AMR) associated with various pig transit and holding times were investigated at slaughter plants. Changes in the relative abundance of two biotypes of Streptococcus faecium were associated with transit and holding of pigs, although approximately 20% of the isolates were unidentified. The greatest variety of coliforms was isolated from porcine feces after short transit (2 h) or holding (3 h) times and was qualitatively similar to those from pigs on farms. Isolates from pigs with longer average transit or holding times were almost all Escherichia coli (four biotypes). Streptococcal resistance to most antimicrobial agents was significantly greater (P less than 0.05) in isolates from live pigs at slaughter plants than in those from pigs at farms and was apparent after a short transit time (2 h). Streptococci from pigs held an average of 15 h were less resistant to most antimicrobial agents than those from pigs held 3 or 43 h. When compared with short transit times, moderate transit times (6 h) were associated with significantly decreased (P less than 0.05) coliform resistance and decreased resistance transfer but a greater diversity of AMR patterns. Holding pigs overnight (14 h) was associated with lowered coliform resistance to several antimicrobial agents, compared with the resistance of isolates from pigs held 3 or 39 h. A substantial increase (18 to 48%) in the ability to transfer streptomycin resistance was demonstrated in coliforms from pigs held 39 h, when compared with those from pigs held 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)