In 1966, the penicillin contaminant was traced to whose room below Fleming's lab?

In 1966, the penicillin contaminant was traced to the room of Charles J. La Touche below Fleming’s laboratory.

Fleming noticed in 1928 that a mould had contaminated a staphylococcal culture and destroyed the bacterial colonies around it. The mould produced the antibacterial substance he later called penicillin, but the precise route by which its spores reached the culture remained uncertain for decades.

Charles John Patrick La Touche was a mycologist working at St Mary’s Hospital. His room was directly beneath Fleming’s laboratory, and later investigation suggested that spores could have drifted upward through open doors. In 1966, La Touche told historian Ronald Hare that he had supplied Fleming with thirteen fungal specimens, including ten from his own laboratory; only one showed penicillin-like activity.

The conclusion is best described as the accepted explanation rather than an absolutely witnessed event. Fleming himself had suggested that spores entered through a window facing Praed Street, while later testimony challenged that version. “La Touche” is therefore the key canonical answer, not Merlin Pryce, Fleming’s former assistant.