["Salmonella typhi" resistant to chloramphenicol isolated north of Lisbon (author's transl)].

Thirteen strains of Salmonella typhi phage type A/Tan isolated in a typhoid endemic zone north to Lisbon (November 1977-June 1979) showed a low chloramphenicol resistance (MIC = 32 microgram/ml). None of these strains could transfer chloramphenicol resistance at 28 or 37 degrees C. Production of chloramphenicol-acetyl-transferase by these strains could not be demonstrated. No extrachromosomal DNA was detected by agarose-gel electrophoresis. A chromosomal resistance mechanism is postulated which could act on the permeation system.