Epidemiologyof Nalidixic Acid Resistance and TEM-1- and TEM-52-Mediated AmpicillinResistance of Shigella sonnei Isolates Obtained inKorea between 1980 and2000

Abstract

ABSTRACT The resistance to ampicillin and nalidixic acid in Shigella sonnei isolates obtained in Korea during the period 1998 to 2000 was characterized. Recently (J. Y. Oh, H. S. Yu, S. K. Kim, S. Y. Seol, D. T. Cho, and J. C. Lee, J. Clin. Microbiol. 41: 421-423, 2003) ampicillin and nalidixic acid resistance was found in 49 and 70%, respectively, of the 67 S. sonnei isolates obtained during this period. We analyzed 138 S. sonnei isolates collected during the same period. Ampicillin and nalidixic acid resistance was found in 30 and 86% of the isolates, respectively. The ampicillin resistance was mediated by a TEM-1β -lactamase, and TEM-52 extended-spectrum β-lactamase was identified in one sporadic S. sonnei isolate from 1999. bla TEM-1 and bla TEM-52 were located in conjugative R-plasmids. Tn 3 was detected in 41% of the ampicillin-resistant isolates. The R-plasmids from the transconjugants that transferred resistance to ampicillin exhibited different restriction fragment length polymorphism patterns, and a bla TEM-1 probe was hybridized with the different fragments. The nalidixic acid resistance was exclusively associated with an amino acid substitution, Ser83→Leu (TCG→TTG), in gyrA . These findings indicate that the genetically related S. sonnei strains readily acquire resistance to ampicillin, streptomycin, trimethoprim, and sulfamethoxazole but not nalidixic acid through conjugative R-plasmids from difference sources when confronted by antibiotic selective pressures.