Ferdinand Cohn found the bacterial spores that survive boiling

Person: Ferdinand Cohn
Lived: 1828–1898
Field: Microbiology & botany
From: German (Prussian Silesia)

The story

Ferdinand Cohn was born in 1828 in Breslau, then in Prussia and now Wrocław in Poland, the eldest son of a poor Jewish merchant. He grew up in the city's Jewish quarter and entered the University of Breslau at fourteen, but rules barring Jews from advanced degrees there forced him to take his doctorate in botany at the University of Berlin in 1847. He returned to Breslau, where he spent his career and became one of the founders of modern bacteriology.

Cohn was puzzled by a stubborn problem. Scientists trying to sterilise broths and infusions by boiling them found that some bacteria still appeared afterwards. To some, this looked like evidence that life could arise spontaneously. Cohn investigated why certain bacteria in hay infusions survived high temperatures, and studied Bacillus subtilis growing on cheese that had been boiled.

He showed that certain bacilli can change into a resting form, the endospore, when conditions become harmful to the active cell. These spores are remarkably tough. They can resist heat, drying, freezing, radiation and most disinfectants, and can survive boiling for hours. When conditions improve, they germinate and grow again. His work supported the challenges by Louis Pasteur and John Tyndall to the old idea of spontaneous generation: the bacteria were not appearing from nothing, they were surviving as spores.

This discovery has very practical consequences. Because spores can outlast ordinary boiling, sterilisation must go further. Endospores can be destroyed by autoclaving, which uses steam under pressure to reach temperatures above the boiling point of water. Hospitals and laboratories even use the spores of a heat-loving bacterium as test indicators, to check that an autoclave has truly sterilised its load.

Several dangerous bacteria form spores, including Clostridium botulinum. Understanding that spores exist, and that they demand stronger measures than simple boiling, is part of the foundation on which safe sterilisation of surgical instruments, laboratory equipment and other materials rests.

Cohn died in Breslau in 1898. His careful work on these tiny survivors remains one of the building blocks of microbiology and infection control.

Why it matters

Knowing that bacterial spores survive boiling is why hospitals and laboratories sterilise with pressurised steam and test their equipment, protecting patients from infection.

About Ferdinand Cohn

Breslau botanist, barred from a doctorate at home as a Jew, who classified bacteria, discovered heat-resistant spores and championed Robert Koch, becoming a founder of bacteriology.

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Ferdinand Cohn

1828–1898 · Microbiology & botany

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