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Journal of Clinical Microbiology, June 2005, p. 2798-2804, Vol. 43, No. 6
0095-1137/05/$08.00+0     doi:10.1128/JCM.43.6.2798-2804.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Epidemiologic Relationship between Fluoroquinolone-Resistant Salmonella enterica Serovar Choleraesuis Strains Isolated from Humans and Pigs in Taiwan (1997 to 2002)

Graduate Institute of Veterinary Public Health, National Chung Hsing University, Taichung 402, Taiwan,¹ The Central Branch Office, Center for Disease Control, Taichung 408, Taiwan,² Department of Veterinary Medicine, National Taiwan University, Taipei 106, Taiwan,³ Department of Microbiology and Immunology, School of Medicine, Taipei Medical University, Taipei 110, Taiwan,⁴ Division of Pediatric Infectious Diseases, Department of Pediatrics, Chang Gung Children's Hospital, Taoyuan 333, Taiwan,⁵ Department of Applied Microbiology, National Chiayi University, Chiayi 600, Taiwan,⁶ Graduate Institute of Veterinary Pathology, National Chung Hsing University, Taichung 402, Taiwan,⁷ Department of Biological Science and Technology, School of Medicine, China Medical University, Taichung 404, Taiwan⁸

Received 3 October 2004/ Returned for modification 14 January 2005/ Accepted 13 February 2005

The emergence of ciprofloxacin-resistant Salmonella enterica serovar Choleraesuis in recent years has become an important public health issue in Taiwan. The resistant strains that cause human infections are considered to be from pigs. In this study, we characterized 157 swine and 42 human Salmonella serovar Choleraesuis isolates by pulsed-field gel electrophoresis (PFGE) and drug susceptibility testing to investigate the epidemiologic relationship among the isolates. By PFGE analyses, two major clusters (clusters GA and GB) were identified. Isolates in cluster GA were of both human and swine origins, while those in cluster GB were from pigs only. Among the various genotypes identified, genotype gt-1a was the most prevalent, which was found in 71% (30 of 42) and 48% (76 of 157) of human and swine isolates, respectively. The susceptibility tests for the 106 gt-1a isolates identified 44 susceptibility profiles and showed that 73% of human isolates and 34% of swine isolates were resistant to three fluoroquinolones (ciprofloxacin, enrofloxacin, and norfloxacin). Our findings indicate that a clonal group of Salmonella serovar Choleraesuis may have been circulating in human and swine populations in Taiwan for years and that the fluoroquinolone-resistant Salmonella serovar Choleraesuis strains most likely evolved from a gt-1a clone that emerged in 2000 and that then caused widespread infections in humans and pigs. Nevertheless, it is still debatable whether those Salmonella infections in humans are caused by isolates derived from pigs, on the basis of the higher fluoroquinolone and other antimicrobial resistance percentages in human isolates than in pig isolates.