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118 clinical strains of Shigella were serotyped, in which 116 strains were tested to be S.flexneri. The susceptibilities of the S.flexneri strains to quinolones were measured by the disk-diffusion method. It was found that most S.flexneri strains were susceptible to norfloxacin and ciprofloxacin, but resistant to nalidixic acid. To study the correlation between gyrA mutations and quinolones resistance, a fragment within the gyrA gene was amplified by PCR. The SSCP (Single-Strand Conformation Polymorphism) analysis was applied to detect mutations in PCR products of different strains. The mutations were then confirmed by DNA sequencing. Altogether, two types of mutation were revealed, in which one type was single mutation (C42-T), and the other was double mutations (C42-T and A54-G). By statistical analysis, C42-T (encoding Ser83-Leu substitution) was shown to have correlation with nalidixic-acid resistance in the clinical strains of Shigella, while A54-G (encoding Asp87-Gly substitution) was shown to have correlations with both norfloxacin resistance and ciprofloxacin resistance.
118 clinical strains of Shigella were serotyped, in which 116 strains were tested to be S.flexneri. The susceptibilities of the S.flexneri strains to quinolones were measured by the disk-diffusion method. It was found that most S.flexneri strains were susceptible to norfloxacin and ciprofloxacin, but resistant to nalidixic acid. To study the correlation between gyrA mutations and quinolones resistance, a fragment within the gyrA gene was amplified by PCR. The SSCP (Single-Strand Conformation Polymorphism) was was applied to detect mutations in PCR products of different strains. The mutations were then confirmed by DNA sequencing. Altogether, two types of mutation were revealed, in which one type was single mutation (C42-T), and the other was double mutations (C42-T and A54-G By statistical analysis, C42-T (encoding Ser83-Leu substitution) was shown to have correlation with nalidixic-acid resistance in the clinical strain of Shigella, while A54-G (encoding Asp87-Gly substitution ) was shown to have correlations with both norfloxacin resistance and ciprofloxacin resistance.