SUMMARY: Antibodies prepared against competent and non-competent Haemophilus influenzae were compared as to their effect on DNA binding and transformation. The gamma globulin fraction of rabbit antisera prepared against competent bacteria inhibited irreversible binding of DNA and transformation to 21% and 7%, respectively, of the control values. Antibodies against non-competent bacteria had an insignificant effect on irreversible binding or transformation. The transforming ability of DNA was not altered by exposure to competent organism antibodies. The antibody activity was reduced to one-third of the control value by heating for 10 min in a boiling water bath. Bacterial agglutinating ability of the antibodies was completely removed by papain treatment, while only 10% of the anti-transforming activity was destroyed. The kinetics and dose-response of anti-bodies on inhibition of irreversible uptake and transformation are reported. It was concluded that antigenic determinants related to irreversible binding and at least one additional step in the uptake of transforming DNA are integral components of the competent state of H. influenzae.
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