Emergence of nalidixic acid resistance in Shigella sonnei isolated from patients having acute diarrheal disease: report from eastern province of Saudi Arabia.

During the 5 years of the study period (October 1999-October 2003), 110 strains of Shigella were isolated from fecal samples of patients having acute diarrheal diseases. Shigella sonnei phase 1 was the most prevalent (88/110, 80.0%) serotype. Resistance to nalidixic acid was not encountered from 1999-2002. Nalidixic acid resistance was observed in 6/13 (46.1%) of the S. sonnei phase 1 strains isolated from April-August 2003. Minimum inhibitory concentration to nalidixic acid among these strains was 48-96 microg/ml. All the six nalidixic acid resistant strains of S. sonnei phase 1 had reduced susceptibility (MIC 0.25 microg/ml) to ciprofloxacin.