Resistance of Shigella dysenteriae type 1 to ampicillin and other antimicrobial agents: strains isolated during a dysentery outbreak in a hospital in Mexico City.

In June 1972, an epidemic of dysentery began in a hospital ward lodging 22 children with tuberculosis. Fifteen of them developed the disease and five children died. The age of the children ranged from five months to four years. A rectal swab culture taken from all hospitalized children three weeks after the initiation of the outbreak revealed Shigella dysenteriae type 1 in five of the patients (28%). The strains isolated were susceptible to cephalothin, gentamicin, kanamycin, colistin, trimethoprim, and nalidixic acid, but were resistant to ampicillin (greater than 5,000 mug/ml), chloramphenicol (300 mug/ml), streptomycin (400 mug/ml), tetracycline (100 mug/ml), and sulfadiazine (1,000 mug per disk). Transfer experiments to Escherichia coli K-12 indicated that these strains were infected with two different plasmids; one was responsible for resistance to chloramphenicol, tetracycline, streptomycin, and sulfonamides, and the other caused resistance to ampicillin. The epidemiological and clinical importance of these findings is emphasized.