from Johns Hopkins University in 1930 and continued her research and medical career at Columbia-Presbyterian Hospital in New York City.

Alexander is known for her development of the first effective remedies for Haemophilus influenzae infection,[1] as well as being one of the first scientists to identify and study antibiotic resistance.

Here she met and impressed the director of the laboratory, Septima Smith, who helped to financially support Alexander in medical school.

Alexander was afterwards a resident at Columbia-Presbyterian Medical Center's Babies Hospital in New York City, due to an invitation from Dr. McIntosh, where she stayed for the rest of her career.

[3] While at the Columbia-Presbyterian Babies Hospital, Alexander became the main authority on bacterial infections and the lead microbiologist in the laboratory.

[9] Alexander's work aimed to advance research of infectious diseases and the biology of the microorganisms that cause meningitis in a time before antibiotics or vaccinations.

[3] In the wake of the development of an anti-pneumonia serum at New York's Rockefeller Institute, Alexander reported a cure rate for infants of 75% with influenzal meningitis in 1939.

[10] In the early 1940s, Alexander began researching Haemophilus influenzae (Hib) meningitis, at the time an almost invariably fatal disease in infants and young children.

These experiments led her to develop an improved antiserum for the disease; by combining rabbit serum therapy with the use of sulfa drugs.

She concluded, correctly, that this was caused by random genetic mutations in DNA which were positively selected through evolution; she and Leidy demonstrated the occurrence of transformation in the Hib bacillus, leading to resistance.