Table 1.

Antimicrobial classes and resistance breakpoints of drugs used between 2004 and 2012 in the antimicrobial susceptibility testing of Escherichia coli isolated from chicken carcasses and chicken retail meat by the National Antimicrobial Resistance Monitoring System.

Class	Drug	Abbreviation	Years Tested	Resistance Breakpoint
β-lactams	Ampicillin	AMP	2004–2012	≥32
	Amoxicillin–Clavulanic Acid	AMC	2004–2012	≥32
	Ceftriaxone	AXO	2004–2012	≥4
	Cefoxitin	FOX	2004–2012	≥32
	Ceftiofur	TIO	2004–2012	≥8
Aminoglycosides	Amikacin	AMI	2004–2010	≥64
	Gentamicin	GEN	2004–2012	≥16
	Kanamycin	KAN	2004–2012	≥64
	Streptomycin	STR	2004–2012	≥64
Sulfonamides	Trimethoprim–Sulfamethoxazole	COT	2004–2012	≥4
	Sulfisoxazole	FIS	2004–2012*	≥512
Quinolones	Ciprofloxacin	CIP	2004–2012	≥1
	Nalidixic Acid	NAL	2004–2012	≥32
Tetracyclines	Tetracycline	TET	2004–2012	≥16
Phenicols	Chloramphenicol	CHL	2004–2012	≥32
Macrolides	Azithromycin	AZI	2011–2012	≥32

^*Except 2007 slaughter isolates.