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Nine epidemiologically unrelated isolates {1 Salmonella Bredeney from turkeys, and 8 Escherichia coli [3 environmental isolates (2 from chickens, 1 from pigs), and 5 isolates from cattle with neonatal diarrhea]} were examined both pheno- and genotypically for extended-spectrum β-lactam (ESBL) resistance. Resistance phenotypes (ampicillin, aztreonam, cefotaxime, cefpodoxime, ceftazidime, and ceftriaxone) suggested the presence of an ESBL enzyme, but cefoxitin MICs (≥ 32 mg/L) suggested the presence of an AmpC-like enzyme. Synergism experiments with benzo(b)thiophene-2-boronic acid (BZBTH2B) and isoelectric focusing (IEF) revealed the presence of an AmpC β-lactamase with a pI ≥ 9. amp C multiplex PCR, sequence, and Southern analyses indicated that only the Salmonella isolate had a plasmid-encoded AmpC β-lactamase CMY-2 on a nonconjugative 60-MDa plasmid. PCR …