TABLE 4.

Amino acid substitutions in critical positions of gyrA and parC QRDRs in selected S. suis isolates^a

Origin/strain	gyrA		parC		No. of isolates	MIC/MIC range (μg/ml)b
	Ser81c	Glu85	Ser79	Asp83		NAL	ENR	CIP
Diseased pig isolates	Ile	—d	Tyr	—	3	128–128	8–16	16–32
	Lys	Asp	Phe	—	2	64–256	4–8	8–8
	Lys	Asp	Leu	—	1	256	16	16
	Lys	Asp	Tyr	—	1	256	16	16
	Phe	—	Tyr	—	1	128	16	32
	Phe	—	Phe	—	1	128	16	32
	Ala	—	Tyr	—	1	256	4	16
	—	Lys	Phe	—	1	256	16	32
	—	—	Tyr	—	1	256	2	4
Healthy pig isolates	Ile	—	Tyr	Val	1	128	64	64
	Ile	—	Phe	—	5	128–512	16–64	32–64
	Ile	—	Tyr	—	3	256–512	8–8	16–32
	Lys	Asp	Tyr	—	1	512	8	16
	Phe	—	Phe	—	11	128–512	8–32	16–64
	Phe	—	Tyr	—	1	256	16	64
	Tyr	—	Phe	—	9	128–512	8–32	16–64
	Tyr	—	Tyr	—	10	128–256	8–32	16–64
	Tyr	—	—	Tyr	1	128	4	16
	Tyr	—	—	—	1	256	2	4

^aQRDR, quinolone resistance determining region.

^bNAL, nalidixic acid; ENR, enrofloxacin; CIP, ciprofloxacin.

^cThe QRDR DNA sequences of gyrA and parC were compared with the QRDR of gyrA (GenBank: DQ832724) and parC (GenBank: DQ832742) of S. suis type strain ATCC 43765.

^d—, identical to that of reference strain S. suis ATCC 43765.