FIG 1.

Occurrence of multidrug-resistant E. coli strains in beef cattle raised without antibiotics. (A) Fecal samples were collected from beef cattle on two research farms, the North Florida Research and Education Center (NFREC, blue dot) and the Beef Research Unit (BRU, orange dot). (B) Prevalences of cefotaxime-resistant bacteria (CRB) and cefotaxime-resistant E. coli strains in beef cattle. Isolates carrying the CMY-2 or/and CTX-M gene(s) were identified by PCR genotyping. (C) Antimicrobial susceptibility testing (AST) against 13 different antibiotics belonging to 8 classes (S, sulfonamides; A, aminoglycosides; T, tetracyclines; F, fluoroquinolones; C, chloramphenicol; PEN, penicillisn; CEP, cephalosporins; P, polymyxins) was conducted following the CLSI guidelines. Thirty-six isolates, 22 from the BRU (orange) and 14 from the NFREC (blue), were selected based on origin and animal source. Colored blocks represent resistance, intermediate susceptibility, and susceptibility. MICs of cefotaxime were determined by the broth microdilution method. The presence (+) and absence (−) of CMY-2 and CTX-M genes in the isolates are indicated to the right of the AST results.