General Microbiology — MCQs

General Microbiology Indian Medical PG Practice Questions and MCQs

Question 451: Nucleic acid is not found in which of the following?

A. Virus
B. Fungus
C. Prions (Correct Answer)
D. Bacteria

Explanation: ***Prions*** - **Prions** are infectious protein particles composed solely of misfolded proteins, lacking any **nucleic acid** (DNA or RNA). - They replicate by inducing normal cellular proteins to misfold into the abnormal, pathogenic prion form. *Virus* - **Viruses** are obligate intracellular parasites that contain either **DNA or RNA** as their genetic material, enclosed within a protein coat. - This nucleic acid is essential for directing the synthesis of new viral particles within a host cell. *Bacteria* - **Bacteria** are prokaryotic organisms that contain **DNA** as their genetic material, typically in a single circular chromosome located in the nucleoid region. - They also contain plasmids, which are small, extrachromosomal DNA molecules. *Fungus* - **Fungi** are eukaryotic organisms that contain **DNA** organized into multiple chromosomes within a membrane-bound nucleus. - Their genetic material directs all cellular activities and reproduction.

Question 452: Who propounded the germ theory of disease?

A. Louis Pasteur (Correct Answer)
B. Robert Koch
C. Anton van Leeuwenhoek
D. Ambroise Paré

Explanation: ***Louis Pasteur*** - **Louis Pasteur** performed definitive experiments (e.g., swan-neck flask experiments) that disproved **spontaneous generation** and firmly established microorganisms as the cause of infectious diseases. - His work on **fermentation**, pasteurization, and vaccines provided irrefutable evidence for the concept that specific microbes cause specific diseases. *Anton van Leeuwenhoek* - **Anton van Leeuwenhoek** is known for being one of the first to observe and describe **microorganisms** ("animalcules") using single-lens microscopes. - While he saw microbes, he did not establish the link between these microbes and the causation of disease. *Robert Koch* - **Robert Koch** provided crucial evidence for the germ theory through his work on **anthrax, tuberculosis, and cholera**. - He formulated **Koch's postulates**, a set of criteria to establish a causal relationship between a specific microorganism and a specific disease, building upon Pasteur's initial propounding of the theory. *Ambroise Paré* - **Ambroise Paré** was a prominent **French surgeon** from the 16th century, often considered one of the fathers of modern surgery. - His contributions were primarily in surgical techniques, wound care, and anatomy, long before the development of the germ theory.

Question 453: Which of the following organisms does not fulfill Koch's postulates?

A. E.coli
B. T. pallidum (Correct Answer)
C. M. tuberculosis
D. All of the options

Explanation: ***T. pallidum*** - **_Treponema pallidum_**, the causative agent of **syphilis**, cannot be cultured on artificial media, failing the third Koch's postulate. - Its inability to grow in pure culture makes it difficult to reproducibly cause disease in an experimental host by direct inoculation of a cultured organism. *M. tuberculosis* - **_Mycobacterium tuberculosis_** can be isolated and grown in **pure culture** on specific media like Löwenstein-Jensen medium. - It also consistently causes tuberculosis when inoculated into susceptible animals, fulfilling Koch's postulates. *E.coli* - **_Escherichia coli_** is readily cultured in various laboratory media and can be isolated from infected hosts. - Specific pathogenic strains of _E. coli_ (e.g., EHEC) fulfill Koch's postulates by reproducing disease in animal models. *All of the options* - This option is incorrect because both **_M. tuberculosis_** and **_E. coli_** largely fulfill Koch's postulates. - The primary exception among the given options is **_T. pallidum_** due to its unculturable nature.

Practice by Chapter

History and Scope of Microbiology

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Classification of Microorganisms

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Bacterial Morphology and Structure

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Bacterial Physiology and Metabolism

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Bacterial Genetics

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Microbial Growth and Nutrition

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Sterilization and Disinfection

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Bacterial Identification Methods

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Normal Microbiota and Pathogenicity

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Antimicrobial Susceptibility Testing

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