January 7, 1884

Vibrio cholerae

Koch reports a pure culture of the cholera bacillus from Calcutta

The celebrated discovery date is the dateline on a progress letter, not a timestamp from anyone's laboratory notebook.

The fifth dispatch

In his fifth dispatch from Calcutta, dated 7 January 1884, Robert Koch reported that his commission had isolated bacilli from the intestinal contents of clear cholera cases and grown them in pure culture.

The cultures showed form and growth in nutrient gelatin distinctive enough to tell them apart from other bacilli, which gave Koch a way to separate one organism from the crowded microbial mixture of the intestine.

Cause or consequence, still open

The report did not claim the question was settled. Koch still treated it as uncertain whether the cultured organism was specific to cholera, and whether it caused the disease or merely followed it.

He had not reproduced cholera in experimental animals — a gap he acknowledged and attributed to their apparent lack of susceptibility to the human disease.

The comma-like curvature, the claim of consistent presence in cholera cases and the causal argument all came in the next dispatch, dated 2 February.

Not the first to see it

Filippo Pacini had observed and described the cholera vibrio in Florence in 1854, and argued for its pathological importance.

International bacterial nomenclature preserved that priority: the accepted name is Vibrio cholerae Pacini 1854.

The January date belongs to a numbered progress report addressed to the German secretary of state for the interior, Karl Heinrich von Boetticher, rather than to a recorded moment of isolation.

Sources

Researched 24 Aug 2026 8 sources not yet audited Traditional date

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Traditional date. This date is the conventional one, not one fixed by a contemporary record.

What the sources leave uncertain

January 7 is securely documented as the date of Koch's fifth dispatch, not necessarily the exact day on which a technician first obtained the successful culture. Treating it as a laboratory 'discovery day' is conventional shorthand.
Koch's January 7 report announced isolation and pure culture; his stronger specificity and causal argument belongs to the February 2 sixth report.
Koch was long credited as the discoverer, but Pacini had described the organism and its pathogenic role in 1854. The accepted taxonomic name now preserves Pacini's priority.