A total of 118 nalidixic-acid (NA)-resistant Salmonella strains consisting of 68 domestic strains and 50 imported strains isolated during 1988-1998 in Tokyo were examined regarding their annual incidence, serovars, drug-resistance patterns, and minimum inhibitory concentrations (MIC) to fluoroquinolones (NFLX, OFLX, ENX, and CPFX).
NA-resistant strains accounted for 1.3% of all Salmonella (5, 302 strains) isolated from domestic cases, and 2.5% of all Salmonella (1, 981 strains) isolated from imported cases. The incidence of NAresistant strains has increased since 1995, and it has been remarkable in imported cases.
The results of the serotyping showed that the NA-resistant strains were classified into 25 serovars, excluding untypable strains. Among those, S. Enteritidis (21 strains), S. Blockley (13 strains), S. Litchifield (13 strains) S. Typhimurium (13 strains), S. Hadar (9 strains) and S. Virchow (8 strains) were predominant.
Drug-resistance patterns of NA-resistant strains, including other drugs (CP, TC, SM, KM, ABPC, ST, FOM, and NFLX) tested varied among the 26 types. Among those, multidrug-resistant strains accounted for 61.9% (73 strains), and one strain among them was high-resistant to NFLX.
MIC distribution of NA-resistant strains to fluoroquinolones showed that the ranges of all drugs were 4-128 times higher than NA-sensitive strains used for controls.