Decreased susceptibility to fluoroquinolones and gyrA gene mutation in the Salmonella enterica serovar Typhi and Paratyphi A isolated in Katmandu, Nepal, in 2003.

Typhoid fever is the most common clinical diagnosis among febrile patients presenting to hospital in Katmandu. Salmonella enterica serovar Typhi (S. enterica serovar Typhi) and Salmonella enterica serovar Paratyphi A (S. enterica serovar Paratyphi A) with decreased susceptibility to fluoroquinolones and resistance to nalidixic acid are common in recent years. In the present study, we examined the in vitro susceptibility to fluoroquinolones and the presence of gyrA gene mutations in 30 clinical strains of S. Typhi and 39 of S. Paratyphi A, all of which were isolated in Katmandu, Nepal, in 2003. In those strains, we found that 73.3% and 94.9% of S. Typhi and S. Paratyphi A strains contained gyrA gene mutation, and showed the resistance to a quinolone, nalidixic acid, and decreased susceptibility to fluoroquinolones, ciprofloxacin, and levofloxacin. Although fluoroquinolones may still be useful as antibiotics for the treatment of typhoid fever, clinicians should be aware of the possibility of treatment failures of infections with S. Typhi and S. Paratyphi A strains with decreased susceptibility to fluoroquinolones.