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Antimicrobial Agents and Chemotherapy, November 2003, p. 3567-3573, Vol. 47, No. 11
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.11.3567-3573.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Mutations in Topoisomerase Genes of Fluoroquinolone-Resistant Salmonellae in Hong Kong

J. M. Ling,* E. W. Chan, A. W. Lam, and A. F. Cheng

Department of Microbiology, The Chinese University of Hong Kong, The Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China

Received 31 March 2003/ Returned for modification 15 May 2003/ Accepted 22 August 2003

A total of 88 salmonella isolates (72 clinical isolates for which the ciprofloxacin MIC was >0.06 µg/ml, 15 isolates for which the ciprofloxacin MIC was <=0.06 µg/ml, and Salmonella enterica serotype Typhimurium ATCC 13311) were studied for the presence of genetic alterations in four quinolone resistance genes, gyrA, gyrB, parC, and parE, by multiplex PCR amplimer conformation analysis. The genetic alterations were confirmed by direct nucleotide sequencing. A considerable number of strains had a mutation in parC, the first to be reported in salmonellae. Seven of the isolates sensitive to 0.06 µg of ciprofloxacin per ml had a novel mutation at codon 57 of parC (Tyr57->Ser) which was also found in 29 isolates for which ciprofloxacin MICs were >0.06 µg/ml. Thirty-two isolates had a single gyrA mutation (Ser83->Phe, Ser83->Tyr, Asp87->Asn, Asp87->Tyr, or Asp87->Gly), 34 had both a gyrA mutation and a parC mutation (29 isolates with a parC mutation of Tyr57->Ser and 5 isolates with a parC mutation of Ser80->Arg). Six isolates which were isolated recently (from 1998 to 2001) were resistant to 4 µg of ciprofloxacin per ml. Two of these isolates had double gyrA mutations (Ser83->Phe and Asp87->Asn) and a parC mutation (Ser80->Arg) (MICs, 8 to 32 µg/ml), and four of these isolates had double gyrA mutations (Ser83->Phe and Asp87->Gly), one parC mutation (Ser80->Arg), and one parE mutation (Ser458->Pro) (MICs, 16 to 64 µg/ml). All six of these isolates and those with a Ser80->Arg parC mutation were S. enterica serotype Typhimurium. One S. enterica serotype Typhi isolate harbored a single gyrA mutation (Ser83->Phe), and an S. enterica serotype Paratyphi A isolate harbored a gyrA mutation (Ser83->Tyr) and a parC mutation (Tyr57->Ser); both of these isolates had decreased susceptibilities to the fluoroquinolones. The MICs of ciprofloxacin, levofloxacin, and sparfloxacin were in general the lowest of those of the six fluoroquinolones tested. Isolates with a single gyrA mutation were less resistant to fluoroquinolones than those with an additional parC mutation (Tyr57->Ser or Ser80->Arg), while those with double gyrA mutations were more resistant.

* Corresponding author. Mailing address: Department of Microbiology, The Chinese University of Hong Kong, The Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR, China. Phone: (852) 2632 3333. Fax: (852) 2647 3227. E-mail: meilunling{at}cuhk.edu.hk.

Antimicrobial Agents and Chemotherapy, November 2003, p. 3567-3573, Vol. 47, No. 11
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.11.3567-3573.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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