Purpose: To determine if antimicrobial resistance patterns in E. coli observed in pigs upon arrival at the abattoir were reflective of those observed in ceca from the same cohort of pigs post-slaughter.
Methods: Pigs were sampled at a large, Midwestern abattoir, by convenience. Before placement, 10 random pen (lairage) swab samples were taken. At placement, 10 fecal swabs were taken from voided manure pats (arrival). After 2 h, pigs moved by group to processing; 10 ceca were randomly removed and 50 ml of cecal fluid (CF) was collected. Samples were transported on ice, swabbed onto blood agar/Tergitol-7, incubated at 35°C for 24 h, examined for typical E. coli phenotypes (rough, smooth, mucoid, and hemolytic), and 1 - 4 colonies of each phenotype was selected. Antimicrobial susceptibility testing (AST) was conducted using broth microdilution (TREK SensititreTM) per manufacturer’s instructions and CSLSI or NARMS breakpoints.
Results: Samples were collected from 14 truck lots over eight dates representing n = 139 unique animals at arrival, n = 80 at lairage, and n = 140 post-slaughter (CF). Of the n = 359 samples, n = 345 were positive for E. coli; n = 138 arrival, n = 131 CF and n = 76 lairage. Isolates (n = 953) were recovered; n = 813 were classified by phenotype: n = 531 rough, n = 197 smooth, n = 62 mucoid, and n = 23 hemolytic. Only n = 736 isolates were recovered for AST. The top 3 AST patterns by location were Tetracycline (cecal), StreptomycinTetracycline (cecal), and AmpicillinStreptomycinTetracycline (arrival). AST patterns varied by phenotype and location. Four isolates (all CF) were resistant to nine antimicrobials and n = 33 (n = 21 arrival, n = 8 CF, n = 4 lairage) were pan-susceptible.
Significance: AST patterns were identified post-slaughter (CF) that were not identified at arrival and vice versa suggesting that E. coli AST surveillance post-slaughter may not be a surrogate for on-farm testing.