Comparison of fluoroquinolone resistance genes of Salmonella enterica serovar Choleraesuis isolates in Japan and Taiwan.

*Corresponding author: Mailing address: National Veterinary Assay Laboratory, Ministry of Agriculture, Forestry and Fisheries, 115-1 Tokura, Kokubunji, Tokyo 185-8511, Japan. Tel: +81-42321-1841, Fax: +81-42-321-1769, E-mail: [email protected] In Japan’s neighbor Taiwan, the occurrence and spread of fluoroquinolone-resistant Salmonella enterica serovar Choleraesuis infection in human and pigs was reported in 2002, pointing out the genetic relevance between human and porcine isolates during 2000 and 2001 (1). In 2001, we isolated the fluoroquinolone-resistant S. Choleraesuis from swine in Japan (3). At that time, no published was available on fluoroquinolone-resistant isolates of human origin in Japan. A considerable amount of pork meats each year (40% of all imported pork meats) were imported from Taiwan before an outbreak of foot-and-mouth disease there in 1997. In addition, business and sightseeing trips to Taiwan by Japanese travelers have seen large increases. To clarify the relevance of the fluoroquinolone-resistant S. Choleraesuis isolates between Japan and Taiwan, we examined the antimicrobial susceptibility and the sequence of the regions encoding the target enzymes of fluoroquinolones. Seven isolates of S. Choleraesuis in Japan and Taiwan, including two fluoroquinolone-resistant isolates (13-PLS-6, Japan; CGSC18, Taiwan), were used in this study. The Japanese isolates were originated from swine and the Taiwanese isolates from patients. Antimicrobial susceptibility of S. Choleraesuis isolates against ampicillin (AMP), cefazolin, cefuroxime, ceftiofur, dihydrostreptomycin (DSM), kanamycin (KM), gentamicin, destomycin A (DMA), apramycin (APM), colistin, oxytetracycline (OTC), chloramphenicol (CHL), bicozamycin, nalidixic acid (NA), oxolinic acid (OA), enrofloxacin, ofloxacin, ciprofloxacin, sulphadimethoxine (SDMX), trimethoprim (TMP), and olaquindox were tested by an agar dilution methods in accordance with NCCLS guidelines (4). The 13-PLS-6 strain was resistant to seven antimicrobials (AMP-CHL-DSM-KM-OTC-SDMX-TMP) in addition to showing quinolone resistance. With regard to antimicrobial resistance type, the three NA-resistant isolates in Taiwan were resistant to DMA and APM together with the seven antimicrobial resistances of 13-PLS-6. The Salmonella isolates resistant to the two antimicrobials (DMA and APM) were rarely prevalent in Japan (2). Mutations in quinolone resistance-determining region (QRDR) of the gyrA and parC gene were detected by direct DNA sequencing. In both fluoroquinolone-resistant isolates, two point mutations in the gyrA gene and a mutation in the parC gene were detected, as shown in Table 1. All of the fluoroquinolone-resistant isolates described in the previous report (1) had the same type of mutation in the gyrA gene (83Phe and 87Asn as CGSC18), differing from the gyrA mutation of 13-PLS-6. We suspected the relevance of fluoroquinolone isolates in both countries, but these isolates did not seem relevant genetically. In recent years, the worldwide spread of antimicrobial-