Susceptibility of Salmonella typhi to chloramphenicol, ampicillin and cotrimoxazole

Salmonella typhi isolated from the patients admitted to the Hospital for Tropical Diseases, Bangkok, were tested by the tube dilution method and the disc diffusion method against chloramphenicol, ampicillin and cotrimoxazole. Forty-five percent of the S.typhi were resistant to chloramphenicol (MIC greater than or equal to 50 microgram/ml) while 5% were resistant to ampicillin (MIC greater than or equal to 12.5 microgram/ml). Only 1% of the S. typhi was found to be resistant to cotrimoxazole (MIC greater than or equal to 168 microgram of trimethoprim + sulfamethoxazole per ml.) Based on these results, the drug of choice for typhoid fever would be cotrimoxazole, especially when drug sensitivity test is not immediately available.