Fluoroquinolone-resistant Salmonella sp. in carcasses.

To the Editor: Fluoroquinolone (FQ)-resistant Salmonella has been isolated from patients in Taiwan (–). Recently, a report further indicated that several patients were infected with Salmonella enterica serovar Schwarzengrund with high-level FQ resistance (). S. Schwarzengrund has never been isolated from food animals in Taiwan.

We report the isolation of FQ-resistant strains from pork and broiler carcasses sampled from 2000 to 2003: 27 in 2000, 3 in 2001, 4 in 2002, and 2 in 2003. These isolates made up 18.85% of the 191 Salmonella strains obtained from pork and broiler carcasses in the study period. Of these isolates, 16 FQ-resistant S. Schwarzengrund strains were further analyzed to elucidate the possible mechanism of FQ resistance. Ciprofloxacin MIC levels in these isolates ranged from 4 to 16 μg/mL, and all had high-level nalidixic acid resistance (>1,024 μg/mL). All of the 16 investigated strains displayed mutations possibly associated with high-level FQ resistance. The mutation sites included 2 sites (Ser83Phe and Asp87Gly) in the quinolone resistance–determining region (QRDR) of gyrA, 2 sites (Thr57Ser and Ser80Arg) in the QRDR of parC, and 1 site (Ser458Pro) in the QRDR of parE, respectively. Four strains had mutations in the QRDR of gyrA and parC only but not in the QRDR of parE (Table).

Table

Characteristics of ciprofloxacin-resistant Salmonella enterica serovar Schwarzengrund strains from carcasses*†

Strain no.	Origin*	Year isolated	Antimicrobial drug resistance profile	Quinolone MICs (μg/mL)				Substitutions in QRDR‡
				NAL	FLU	ENR	CIP	gyrA	parC	parE
A5	B, M	2000	CmSxtTc	1,024	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A16	P, E	2000	ApCmNSxtTc	2,048	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A17	P, E	2000	ApCmNSxtTc	2,048	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A18	P, E	2000	ApCmNSxtTc	2,048	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A19	P, E	2000	ApCmCnNSxtTc	1,024	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A20	P, E	2000	ApCmNSxtTc	2,048	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A29	B, S	2000	CmNSxtTc	1,024	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A36	B, S	2000	ApCmSxtTc	1,024	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A41	P, S	2000	ApCmCnNSxtTc	1,024	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A45	P, S	2000	ApCmNSxtTc	1,024	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg
A51	P, S	2000	ApCmCnNSxtTc	1,024	512	16	4	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg
A56	B, M	2000	ApCmCnNSxtTc	2,048	512	64	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg
A61	P, S	2000	CmSxtTc	1,024	512	32	8	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
A62	P, S	2000	ApCmCnSxtTc	2,048	512	64	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg
B16	P, E	2001	ApCmCnCroTc	2,048	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro
B73	P, N	2003	ApCmCnNSxtTc	2,048	512	32	16	Ser83Phe; Asp87Gly	Thr57Ser; Ser80Arg	Ser458Pro

*QRDR, quinolone resistance–determining region; B, broiler; M, middle Taiwan; P, pork; E, east Taiwan; S, south Taiwan; N, north Taiwan.
†Antimicrobial agents are ampicillin (Ap), chloramphenicol (Cm), ciprofloxacin (CIP), enrofloxacin (ENR), flumequine (FLU), gentamicin (Cn), ceftriaxone (Cro), nalidixic acid (NAL),neomycin (N), trimethoprim/sulfamethoxazole (Sxt), and tetracycline (Tc).
‡No gyrB substitutions were detected.

In conclusion, high-level FQ resistance was detected in S. Schwarzengrund isolated from pork and chicken in Taiwan. Specific mutation sites of gyrA, parC, and parE were associated with high-level FQ resistance in all the isolates investigated. Our results warrant further investigation of the public health consequences of FQ use in food animals in Taiwan.