Table 2.

Percent resistant, MIC₅₀ and MIC₉₀ of Staphylococcus aureus overall and isolated from avian, bovine, equine, and porcine sources (n = 221)

Class and/or Antimicrobial	Range tested (μg/mL)	Resistance breakpoint (μg/mL)	All (n = 221)	Avian (n = 25)	Bovine (n = 123)	Equine (n = 21)	Porcine (n = 22)
Amoxicillin/Clavulanate	2–16	8	0	0	0	0	0
MIC50a				2	2	2	2
Ampicillin/Sulbactam	4–64	32	0	0	0	0	0
MIC50a				4	4	4	4
Cephalothin	4–64	32	0	0	0	0	0
MIC50a				4	4	4	4
Penicillin	0.06–0.5	0.25	31	20	26	43	100b
MIC50				0.06	0.06	0.06	1
MIC90				1	0.5	1	1
Ciprofloxacin	0.25–16	4	< 1	0	0	5	0c
MIC50				0.25	0.25	0.25	0.5
MIC90				0.5	0.5	0.5	0.5
Enrofloxacin	0.25–16	4	< 1	0	0	0c	0
MIC50				0.25	0.25	0.25	0.25
MIC90				0.25	0.25	0.5	0.25
Clindamycin	0.25–16	4	7	0	0	5	64b
MIC50a				0.25	0.25	0.25	16
Erythromycin	0.25–16	8	8	4d	0	5	68b
MIC50a				0.25	0.25	0.25	32
Amikacin	8–64	64	0	0	0	0	0
MIC50a				8	8	8	8
Gentamicin	2–16	16	0	0	0	0	0
MIC50a				2	2	2	2
Chloramphenicol	4–32	32	0	0	0	0	0c
MIC50				4	4	8	8
MIC90				8	8	8	8
Rifampin	0.5–8	4	0	0	0	0	0
MIC50a				0.5	0.5	0.5	0.5
Tetracycline	2–32	16	12	24d	1	10	82b
MIC50				2	2	2	32
MIC90				64	2	2	64
Trimethoprim/Sulfamethoxazole	19–76	76	0	0	0	0	0
MIC50a				19	19	19	19

^aThe MIC₉₀ values were identical to the MIC₅₀.

^bSignificantly higher MICs (P < 0.008) than avian, bovine, and equine isolates.

^cSignificantly higher MICs (P < 0.008) than avian and bovine isolates.

^dSignificantly higher MICs (P < 0.008) than bovine isolates.