Detection of mutations in the gyrA of clinical Salmonella spp.

The high prevalence of resistance to nalidixic acid and reduced susceptibility to ciprofloxacin of Salmonella spp. obtained from stool samples of neonates presenting with acute diarrhea in 2001 at the King Edward VIII hospital in Durban, South Africa, prompted this study to determine if there were any mutations in the QRDR of these isolates and to search for the qnrA gene. All isolates with nalidixic acid MICs > 48 μg/ml had the single mutation D87N, or D87G in the QRDR of the gyrA gene, and only 2 strains had an additional mutation; S83L and S83F respectively. The mutation S83T was present in only one isolate with the nalidixic acid MIC of 10 μg/ml whilst the 6 other strains with nalidixic acid MICs < 10 μg/ml had no changes in the QRDR of the gyrA gene. The qnrA gene was not found. These findings indicate that there are mutations in the gyrA of Salmonella isolates which could contribute to resistance to nalidixic acid with reduced susceptibility to ciprofloxacin and there is the co-expression of quinolone and extended-spectrum ß-lactam resistance among Salmonella spp