Summary: The transmission of the ability to produce hydrogen sulphide was demonstrated in 11 out of 32 HS-positive strains collected during the years 1950 to 1971 at the International Escherichia Centre (WHO) in Copenhagen. The ability to ferment raffinose was co-transferred in some cases but not in others. Those of the 11 strains which were resistant to tetracycline also transmitted that determinant.

Three strains carrying the HS, raffinose and tetracycline resistance characters were examined especially as regards characterization of the transfer factors. It was suggested that one strain contained two compatible transfer factors, one carrying the HS and raffinose markers, and the other the resistance determinant. In the second strain, an factor transferred the resistance to tetracycline and an F-like factor was responsible for transfer of the HS-raffinose markers. The third strain harboured two compatible F-like factors, one transferring the HS and raffinose markers and the other the tetracycline resistance. In one case, only the raffinose character was transferred, and the factor responsible for that transfer was incompatible with the factor carrying the resistance determinant. It was thus inferred that in this case the raffinose character had been substituted for the resistance determinant on the factor that normally transfers this latter character.


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