Table 4. Cumulative percentage of Streptococcus suis (n=240) inhibited by eight antimicrobials, and antimicrobial resistance, MIC₅₀, and MIC₉₀ of Streptococcus suis isolates from slaughtered (n=142) and diseased pigs (n=98).

Antimicrobials	Cumulative percentage of strains inhibited at antimicrobial concentration (µg/ml)a)																% resistance			MIC50b)			MIC90b)
	≤0.032	0.064	0.125	0.25	0.5	1	2	4	8	16	32	64	128	256	≥512		Slaughtered	Diseased		Slaughtered	Diseased		Slaughtered	Diseased
Ampicillin	77.1		85.4	89.6	93.4	95.5	98		98.8	99.2	99.6	100					1.4	9.2		0.032	0.032		0.25	1
Ceftiofur		55		63.3	80.4	85.4	90.8	95.8	97	98.2	100						2.1	7.1		0.064	0.25		2	4
Chloramphenicol				0.4		2.5	5.8	26.2	87.4	94.1	97.4	98.6	99.4		100		7.7	19.4		8	8		8	16
Enrofloxacin			0.4	10	61.2	89.1	92		92.4	94.9	98.7	100					6.3	17.3		0.5	0.5		1	16
Erythromycin			7.5	8.7	11.2	11.6			12.4	12.8	13.6			100			83.3	95.9		256	256		256	256
Florfenicol		0.4				1.2	31.6	69.5	87.4	93.6	96.1	97.3	100				26.8	35.7		4	4		8	16
Tetracycline				0.8	1.2	2	3.2		3.6	14.8	45.2	92.7	98.9	99.3	100		97.9	98.0		64	64		64	64
Tiamulin				1.7	20.5	41.3	54.2	57.5	58.3	61.2	65	75.4	89.6	91.7	100		-	-		2	2		256	128

a) Susceptible and resistance breakpoints are indicated in vertical single (sensitive) and double (resistant) lines according to the guidelines of CLSI [5]. Human-derived breakpoints were applied for chloramphenicol and erythromycin, and no breakpoint was established for tiamulin [5], b) MIC₅₀ and MIC₉₀ are the concentrations at which the growth of 50% and 90% of the isolates is inhibited, respectively.