Induction of phenotypically determined resistance of Neisseria gonorrhoeae to human serum by factors in human serum.

Of 47 human sera tested, 13 converted serum-sensitive gonococci [strain BS4 (agar)] to serum resistance in vitro in 3 h at 37 degrees C, as had previously been demonstrated for most samples of guinea pig serum. The resistance-inducing activity of human serum was lower than that of guinea pig serum but, like the latter, did not operate at 8 degrees C, was greater at pH 6.6 than at pH 7.1, was increased by freezing and thawing, and depended on high and low molecular weight serum fractions; the latter fraction had a molecular weight between 1000 and 5000, and was acid- and heat-labile.