The emergence in Taiwan of fluoroquinolone resistance in Salmonella enterica serotype choleraesuis

Background Salmonella enterica: serotype choleraesuis is a cause of serious systemic infections. Because fluoroquinolones are the drug of choice for the treatment of severe salmonella infections, the emergence and dissemination of fluoroquinolone-resistant S. enterica serotype choleraesuis have clinical consequences. Methods: In Taiwan, a hospital-based surveillance system has been in place since 1987 to monitor the incidence of S. enterica serotype choleraesuis infections and the antimicrobial susceptibility of the isolates. We investigated the rapid emergence of fluoroquinolone resistance in this serotype in 2000 and 2001. Pigs in Taiwan were evaluated as a potential source of the resistant salmonella. Results: A total of 501 clinical isolates of S. enterica serotype choleraesuis were recovered in our hospital from 1987 through 2000. The proportion of total salmonella isolates made up by S. enterica serotype choleraesuis decreased from an average of 8.4 percent before 1995 to 2.7 percent in 1996 through 1998. During 1999 and 2000, this proportion increased significantly, to an average of 5.0 percent. Ciprofloxacin resistance in S. enterica serotype choleraesuis has been observed since 2000. In the third quarter of 2001, 60 percent of isolates were resistant to ciprofloxacin. Molecular typing indicated that the primary source of S. enterica serotype choleraesuis isolates was herds of swine. All the resistant isolates from humans and swine had mutations that led to the substitution of phenylalanine for serine at position 83 and asparagine for aspartic acid at position 87 in the gene for DNA gyrase A. Conclusions: This investigation in Taiwan indicates that fluoroquinolone-resistant S. enterica serotype choleraesuis can spread from swine to humans. The use of fluoroquinolones in food animals should be prohibited.