TABLE 3.

Relationship between ciprofloxacin and nalidixic acid MICs and GyrA substitution in C. jejuni and C. coli

Resistance phenotypea	Species	GyrA substitutionb	No. of isolates	Ciprofloxacin MIC (μg/ml)				Nalidixic acid MIC (μg/ml)
				50%	90%	Range	Geometric mean	50%	90%	Range	Geometric mean
Nalr Cipr	C. jejuni	Ile-86	157	32	64	2-128	22.7	64	128	8->128	73.2
		Ala-86	4	—c	—	4-32	—	—	—	16->128	—
		Asn-90	10	32	128	8-128	39.4	128	>128	64->128	97.0
	C. coli	Ile-86	111	8	16	4-64	12.0	128	128	32->128	97.3
		Ala-86	1	—	—	8	—	—	—	64	—
Nalr Cips	C. jejuni	Ile-86	1	—	—	1	—	—	—	128	—
		Ala-86	7	—	—	0.25-0.5	—	—	—	64-128	—
	C. coli	Ala-86	5	—	—	0.25-0.5	—	—	—	64	—

^aNal^r Cip^r, resistant to nalidixic acid (MICs ≥ 32 μg/ml) and ciprofloxacin (MICs ≥ 2 μg/ml); Nal^r Cip^s, nalidixic acid resistant (MICs ≥ 32 μg/ml) and ciprofloxacin sensitive (MICs ≤ 1 μg/ml).

^bIle-86, Thr-86→Ile; Ala-86, Thr-86→Ala; Asn-90, Asp-90→Asn.

^c—, the MIC₅₀, MIC₉₀, and geometric mean were not calculated when there were <10 isolates.