
Pada tahun 1925, Ermol'eva ditunjuk sebagai kepala Departemen Biokimia Mikroba di Akademi Ilmu Pengetahuan USSR. Di sana, ia memulai penelitiannya tentang bakteriofag dan agen antimikroba yang terjadi secara alami — terutama lisozim. Selama Perang Dunia II, ia mengisolasi strain penisilin Penicillium crustosum. Ini pertama kali digunakan di rumah sakit Soviet pada tahun 1943. Pada tahun 1942, ia mempublikasikan hasil eksperimen yang dilakukan pada dirinya sendiri, di mana ia menginfeksi dirinya dengan minum larutan Vibrio cholerae dan sembuh setelah perawatan. Hasil penelitiannya dipandang penting dalam tindakan pencegahan terhadap kolera dalam upaya perang Rusia di Front Timur Perang Dunia II.
Pada tahun 1947, Ermol'eva menjadi direktur Institut Antibiotik yang baru dibentuk dari Kementerian Kesehatan Publik Uni Soviet. Dari tahun 1952 sampai kematiannya, ia memimpin Departemen Mikrobiologi Institut Kedokteran Pasca Sarjana di Moskow (sekarang Akademi Kedokteran Rusia Pendidikan Pascasarjana). Ermol'eva menikah dengan mikrobiolog Lev Zilber, yang saudara laki-lakinya, novelis Veniamin Kaverin menggunakan karir Ermol'eva dan suaminya sebagai dasar untuk akun fiksalisasi dalam bukunya Open Book trilogi (1949-56). Penggambaran Tatiana yang "hidup dan realistis", karakter yang didasarkan pada Ermol'eva, mempopulerkan mikrobiologi sebagai kemungkinan karier di antara para gadis di Uni Soviet.
In 1925, Ermol'eva was appointed head of the Department of Microbial Biochemistry at the USSR Academy of Sciences. There, she began her research on bacteriophages and naturally-occurring antimicrobial agents—lysozyme in particular. During the Second World War, she isolated a penicillin-producing strain of Penicillium crustosum. It was first used in Soviet hospitals in 1943. In 1942, she published the results of an experiment performed on herself, where she infected herself by drinking a solution of Vibrio cholerae and recovered after treatment. The results of her research were seen as essential in preventative measures against cholera in Russia's war efforts in the Eastern Front of World War II.
In 1947, Ermol'eva became the director of the newly formed Institute of Antibiotics of the USSR Ministry of Public Health. From 1952 until her death, she headed the Department of Microbiology of the Central Post-Graduate Medical Institute in Moscow (now the Russian Medical Academy of Postgraduate Education). Ermol'eva was married to the microbiologist Lev Zilber, whose brother, the novelist Veniamin Kaverin used the career of Ermol'eva and her husband as a basis for a fictionalized account in his trilogy Open Book (1949–56). The "lively and realistic" depiction of Tatiana, the character based on Ermol'eva, popularized microbiology as a possible career among girls in the Soviet Union.