Koch's identification of the cholera bacillus

A fifth cholera pandemic began in 1881 and spread from India through Egypt to Africa and Europe, and east to China and Japan. In 1883 Robert Koch, still busy with his work on tuberculosis, was sent to Egypt as leader of the German Cholera Commission to investigate an outbreak there. By then he had the methods for such work: pure cultures grown on solid media such as potato, and new stains that made bacteria easier to see and identify.

In Egypt Koch identified a curved microbe that he called Kommabazillen, comma bacilli. He then went on to Calcutta, where he found the same bacilli in the stools of cholera patients, and he brought pure cultures of the organism back to Germany. In 1884 he also proposed that the bacteria caused the disease through a poison. That part was proved only in 1959, when S. N. De showed that a bacteria-free filtrate of cholera cultures made tied-off loops of rabbit intestine swell with fluid.

Koch was not the first to see the organism. During the epidemic of 1854 in Florence, Filippo Pacini had found a curved bacillus in the stools of cholera victims under the microscope and named it Vibrio cholerae. His drawings leave little doubt that he saw the right organism, but his work was largely ignored. Koch's comma bacillus was later renamed Vibrio cholerae in belated recognition of Pacini.

The findings were soon put to use. From what he had learned of the vibrio and how it spread, Koch drew up rules for controlling cholera epidemics, which the Great Powers approved at Dresden in 1893, and he received a prize of 100,000 marks for the cholera work. In 1887 Joseph Kinyoun set up a one-room laboratory in the Marine Hospital on Staten Island and diagnosed cholera using Koch's methods. When cholera threatened New York in 1892, harbor quarantine backed by laboratory diagnosis kept an outbreak from taking hold.