Question

Escherichia coli present in the human colon is
(a) Parasite
(b) Commensal
(c) Symbiont
(d) Saprophyte

Answer 1

Certain Escherichia coli strains are harmless to the human intestine. As a typical human intestinal habitat, they form part of the usual microbiota of the colon. They support hosts by producing vitamin ${ K }_{ 2 }$ and preventing pathogenic bacteria from colonising the intestine.

Complete step by step answer:
Escherichia coli is commonly called E.coli. It is a Gram-negative, facultatively anaerobic, rod-shaped, coliform bacteria. They belong to the Escherichia genus commonly found in the lower intestine of warm-blooded organisms (endotherms). They live in symbiotic relationships. They're termed commensals.
A parasite is an organism that resides on or in a host organism and receives its food from or at its host's cost. There are three primary groups of human disease-causing parasites: protozoa, helminths and ectoparasites.
Symbiosis is an intimate relationship between two species which benefits at least one species. Mutualism is a symbiotic relationship which benefits both species. Commensalism is a symbiotic relationship in which, although the other species are not affected, one species profits. Symbiont means an organism that lives in symbiosis with one another.
Saprophytes are species which can not produce their own food. They feed on the dead and rotting matter for life. Fungi and a few bacterial species are saprophytes.
So, the correct answer is, ‘(b) Commensal’.

Note: Vitamin ${ K }_{ 2 }$ assists clotting the blood. E.coli within faecal matter is expelled into the atmosphere. Under aerobic conditions, the bacterium grows massively in the fresh faecal matter for 3 days, but its numbers steadily decline afterwards. E.coli is a chemoheterotroph whose chemically defined medium must include a carbon and energy source. E.coli is one of the widely studied prokaryotic model organisms. It is an essential species in the field of biotechnology and microbiology where, for the majority of work with recombinant DNA, it has acted as the host organism. It takes as little as 20 minutes to replicate, under favourable conditions.