In his laboratory he watched as succeeding generations of Staphylococcus aureus (hospital staph) developed cell walls increasingly impervious to the drug that he had discovered.
Savā laboratorijā viņš novēroja, ka ar katru nākamo paaudzi Staphylococcus aureus baktēriju šūnapvalks kļuva arvien izturīgāks pret viņa iegūto preparātu.