She pursued a PhD in medicine at Groningen, graduating on 3 July 1925 after submitting a thesis on the cause of rat-bite fever.

One of her early discoveries was a large group of women who were being treated for gonorrhea despite actually suffering from the minor infection vulvovaginitis, due to sloppy laboratory tests.

Proper diagnosis enabled the women to return to work and avoid the embarrassment and social stigma of a sexually transmitted infection.

In 1940 she was promoted by van Loghem to professor of microbiology of infectious diseases in Amsterdam with the speech Ziektekiemen.

[3] The next year she spoke at an event celebrating his 25th anniversary as professor and in 1948 she took over his professorship of bacteriology, epidemiology and immunology.