Journal of Microbiology

Isolation of Norfloxacin Resistant Escherichia coli from the Han River and Characterization of Resistance Mechanism: Yoosun Jung , Hyunjin Hong , Hyeran Nam , Yeonhee Lee; J. Microbiol. 2002;40(1):63-69.

Abstract: A total of twenty-five norfloxacin resistant Escherichia coli were isolated from Joongrang-chun stream, a branch of the Han River in Seoul, Korea from May to July in 2000 and their norfloxacin resistance mechanism was characterized for target site mutation, permeability, and efflux pump. Fourteen isolates contained the same three mutations, Ser83->Leu and Asp87->Asn in GyrA and Ser90->Ile in ParC. Six isolates had Ser83->Leu and Asp87->Tyr in GyrA and Ser80->Ile in ParC while one isolate had Ser83->Leu and Val103->Ala in GyrA and Ser80->Ile in ParC. Two isolates had mutation(s) in GyrA without any mutation in ParC. Two isolates had Ser80->Arg in ParC instead of the commonly found Ser80->Ile. Every norfloxacin resistant isolate had an efflux system but the correlation between the efflux activity and MIC was not observed. The amount of OmpF for norfloxacin permeability decreased in resistant isolates compared to the susceptible strains. When amplified polymorphic DNA (RAPD) and pulse field gel electrophoresis (PFGE) were performed, these isolates showed no similarity to each other or clinical isolates.

Characterization of Quinolone-Resistant Clinical Isolates of Escherichia coli in Korea: Yoojung Oh , Seohyung Park , Misun Ha , Yeonhee Lee; J. Microbiol. 2002;40(2):98-103.

Abstract: Twenty-eight clinical isolates of Escherichia coli, composed of thirteen norfloxacin resistant isolates (MIC of >16 ug/ml), one intermediately resistant isolate (MIC of 8 ug/ml), and fourteen susceptible isolates (MIC of <4 ug/ml), were randomly selected to study the norfloxacin resistance mechanism and phylogeny in clinical isolates in Korea. Eleven norfloxacin resistant isolates and one susceptible isolate were multi-drug resistant (MDR). Every norfloxacin resistant isolate with MIC higher than 32 ug/ml had the same three mutations: Ser83->Leu and Asp87->Asn or Tyr in GyrA and Ser80->Ile in ParC. Whereas a resistant isolate with MIC of 16 ug/ml had three mutations but Asp87 in GyrA was replaced with Gly instead of Asn. The intermediately resistant isolate had the same two mutations in GyrA but a different mutation in ParC, Glu84->Lys. Among the susceptible isolates, two isolates with MIC of 4 ug/ml had one mutation: Ser83->Leu in GyrA, and no mutation was found in the susceptible isolates. Resistant isolates showed higher efflux activity than the susceptible ones, with random amplification of polymorphic DNA (RAPD), six susceptible isolates form a separate group from the rest of the isolates.

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