Hattie Elizabeth Alexander (April 5, 1901 – June 24, 1968) was an American pediatrician and microbiologist. She is known for her development of the first effective remedies for Haemophilus influenzae infection, as well as being one of the first scientists to identify and study antibiotic resistance.
Alexander was born in Baltimore, Maryland, and graduated from Goucher College in 1923. She worked for the United States Public Health Service and the Maryland Public Health Service, and then enrolled at Johns Hopkins University medical school, where she received her M.D. in 1930. In 1932, she became an instructor and researcher in the Department of Pediatrics at Columbia University, where she spent her entire professional career.
In the early 1940s, Alexander began researching Haemophilus influenzae (Hib), at the time an almost invariably fatal disease in infants and young children. She developed an improved antiserum for the disease; by combining antiserum therapy with the use of sulfa drugs, and developing standardized techniques for diagnosis and treatment, she and her associate Grace Leidy helped reduce the mortality rate from Hib from nearly 100 percent to less than 25 percent. Later, Alexander and Leidy studied the effect of antibiotics on Hib, finding streptomycin to be highly effective. The combined use of the antiserum, sulfa drugs, and antibiotics significantly lowered the mortality rate from Hib.
In the course of her research on antibiotics, Alexander noted and reported the appearance of antibiotic-resistant strains of Hib. 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.
Alexander received numerous honors and awards for her work, including the E. Mead Johnson Award (1942) and the Oscar B. Hunter Memorial Award (1962). In 1964, she became the first woman to be elected president of the American Pediatric Society. She died of liver cancer in New York City in 1968.