Antimicrobial resistance of Shigellae isolated in Michigan

Patterns of antimicrobial resistance were studied for 213 strains of shigellae isolated in rural and urban areas of Michigan by quantitative techniques: 66% of these organisms were resistant to ampicillin, tetracycline, cephalexin, or chloramphenicol or had multiple resistance to various combinations of these antibiotics. The incidence of resistant organisms was higher in the Detroit-Wayne County area, which is the most urban part of the state. Nalidixic acid and oxolinic acid were noted to be quite effective in vitro against shigellae and perhaps warrant further clinical study as potential agents for therapy of shigellosis, especially in view of the appearance of isolates with multiple resistance. Sulfamethoxazole alone was effective against only 62% of the Shigella isolates tested, but mixture with trimethoprim in a 20:1 ratio yielded a highly active in vitro combination.