Resistance of Shigella, Salmonella, and other selected enteric pathogens to antimicrobial agents.

Antimicrobial agents are commonly used therapeutically and prophylactically for travelers' diarrhea. Resistance of enteric pathogens to these agents may prevent the success of such therapy, with the result depending upon the level of resistance and the drug concentrations achieved in the gastrointestinal tract. Data from a number of geographic locations were collected in order to determine whether consistent trends exist and whether predictions can be made regarding the susceptibility of various enteric pathogens worldwide. These data showed marked variability in the prevalence of resistance. Among Shigella, the percentage of strains resistant to commonly used agents varied within the following ranges: ampicillin, 7% (Dacca) to 87% (Thailand); tetracycline, 11% (Sri Lanka) to 91% (Mexico); and trimethoprim-sulfamethoxazole, 0 (Dacca, 1980) to 55% (Dacca, 1984). Resistance in Salmonella strains showed a similar marked variability. Few strains of enteroxigenic Escherichia coli (less than or equal to 10%) were resistant to trimethoprim-sulfamethoxazole. Relatively recent isolates of all pathogens examined tended to be more resistant than earlier isolates to trimethoprim-sulfamethoxazole as well as to other agents.