Q.72 Which ONE of the following statements about E.coli is NOT true ?
(A) E.coli was the first disease- causing bacterium identified by Robert Koch
(B) E.coli is part of the normal microbiota of humans
(C) Certain E.coli strains can cause bloody diarrohea
(D) E.coli is beneficial to human

E. coli was NOT the first disease-causing bacterium identified by Robert Koch (A).

Question Breakdown

This GATE Life Sciences question tests historical microbiology facts about E. coli’s dual role as commensal and pathogen, versus Robert Koch’s foundational discoveries establishing germ theory.

Option Analysis

(A) E.coli was the first disease-causing bacterium identified by Robert Koch

FALSE. Robert Koch identified Bacillus anthracis (1876, anthrax) as first pathogen, then Mycobacterium tuberculosis (1882). E. coli discovered by Escherich (1885) as normal gut flora.​

(B) E.coli is part of normal human microbiota

TRUE. Non-pathogenic strains dominant in large intestine (10⁹ CFU/g feces), aid vitamin K synthesis, prevent pathogen colonization.

(C) Certain E.coli strains cause bloody diarrhea

TRUE. Enterohemorrhagic E. coli (EHEC) O157:H7 produces Shiga toxins, causes hemorrhagic colitis, hemolytic uremic syndrome (HUS).

(D) E.coli is beneficial to humans

TRUE. K-12, B strains produce vitamin K, compete with pathogens, used in recombinant DNA technology, probiotics.

Correct Choice

(A)

E.coli first disease-causing bacterium Robert Koch is false—Koch discovered anthrax (1876) and TB (1882); E. coli found later as normal flora.

Historical Timeline

E.coli Facts Table

Pathotypes vs Commensals

GATE Exam Relevance

Microbiology PYQ tests historical facts + clinical correlations. Key: Koch’s postulates established with anthrax → TB → cholera. E. coli = model organism (lab) + opportunistic pathogen (EHEC). Memorize O157:H7 for bloody diarrhea.

Answer: (A)