R factors derived from Shigella flexneri strains.

Of 2492 Shigelle flexneri strains isolated from dysenteric patients in Hungary in the years 1972-1974, 767 (30.8%) were resistant to 1-5 antibiotics. Resistance was due to R factors in 79.2% of the strains. Fertility inhibition experiments with F specific phages showed R factors to be fi+ in 12.9% and fi- and 87.1%. Of the antibiotic markers, the chloramphenicol-tetracycline resistance determinant was the most common (46.4%). Chloramphenicol resistance determinants were carried out by fi- R factors.