Robert Koch discovered the cholera bacterium in 1883. Sent by the German government to investigate a cholera epidemic, Koch first worked in Alexandria, Egypt, and then traveled to Calcutta, India, where he studied victims of a more severe outbreak. He found the same curved bacterium repeatedly in the intestines of people who had died from cholera.
Koch isolated the organism in pure culture in January 1884 and described its distinctive comma-like shape. The bacterium became known as the comma bacillus and is now called Vibrio cholerae. Koch reported his findings in February 1884, but the discovery is conventionally dated to 1883 because that was the year his cholera investigation and identification began.
A historical complication is that Italian physician Filippo Pacini had described the cholera bacterium in 1854, but his work was largely overlooked. Koch’s achievement was to connect the organism convincingly with cholera during a major epidemic and establish its medical importance. He could not fully satisfy every later version of Koch’s postulates because laboratory animals generally do not develop human cholera.