The United States Department of Agriculture, or USDA, helped locate new penicillin-producing strains. During Florey and Heatley’s 1941 American visit, USDA scientists contributed expertise in mould identification and searched collections and samples for strains that could yield more penicillin.
A key figure was Charles Thom, a mycologist at the USDA’s Bureau of Plant Industry. Thom had identified the mould associated with Fleming’s original work and helped examine Penicillium cultures. The search mattered because the Oxford strain produced penicillin in very small quantities, making large-scale treatment and manufacturing difficult.
USDA researchers helped identify a more productive strain, designated NRRL 1951, from a mould found on a cantaloupe in Peoria, Illinois. This strain became an important ancestor of many commercial penicillin strains. Improving the organism was only one part of the challenge: manufacturers also had to refine submerged fermentation, extraction and purification.
The USDA is sometimes confused with the NIH, CDC or FDA. Those agencies have major roles in American health and biomedical research, but the penicillin-strain work described here was associated with the USDA’s agricultural and mycological laboratories. Agriculture was central because industrial penicillin depended on cultivating a useful mould at scale.