LightCycler gyrA mutation assay (GAMA) identifies heterogeneity in GyrA in Salmonella enterica serotypes Typhi and Paratyphi A with decreased susceptibility to ciprofloxacin.

Mutations in gyrA in strains of Salmonella enterica serotypes Typhi and Paratyphi A have been characterised by a LightCycler-based PCR-hybridisation gyrA mutation assay (GAMA) and by DNA sequencing. Four mutations (Ser-83 to Phe, Asp-87 to Asn, Ser-83 to Tyr and Asp-87 to Gly) have been identified in 13 strains of Typhi and three strains of Paratyphi A resistant to nalidixic acid (=nal(r)) and with decreased susceptibility to ciprofloxacin (=Cp(L)), with the mutation Ser-83 to Phe predominating. The results have demonstrated heterogeneity in gyrA in nal(r) Cp(L) strains of Typhi and Paratyphi A and may be useful for epidemiological investigations. No mutations in gyrA were identified in four Cp(L) strains of S. Typhi that were sensitive to nalidixic acid. The mechanism of decreased susceptibility to ciprofloxacin in these strains is under investigation.