Abstract
SUMMARY: Klebsiella aerogenes strain V9A carries determinants AK and TK, giving resistance to ampicillin and tetracycline, and a plasmid FKlac, but no active sex factor. F− and I-type sex factors were able to transfer TK from V9A to Escherichia coli K12 and between strains of K12, and TK behaved as a separate plasmid with its own replicon. AK could not be transferred, except possibly by a sex factor carrying its own A determinant, but the evidence for such transfer was inconclusive. It is suggested that AK is either a chromosomal gene or is in a plasmid with a cell attachment in Klebsiella not represented in E. coli K12. AK produces a β-lactamase.