Gene Transfer in Bacteria Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Gene Transfer in Bacteria. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Gene Transfer in Bacteria Indian Medical PG Question 1: The initial origin of new drug resistance genes in bacteria most commonly occurs due to:
- A. Translation
- B. Mutation (Correct Answer)
- C. Conjugation
- D. Transduction
Gene Transfer in Bacteria Explanation: ***Mutation***
- **Random genetic changes** in bacteria can alter drug targets or introduce drug-inactivating enzymes, leading to resistance.
- **Spontaneous mutations** in the bacterial genome are the primary source of new resistance genes that did not previously exist in the bacterial population.
- While mutations occur at low frequency, they are the fundamental mechanism by which novel resistance traits first arise.
*Translation*
- This is the process of synthesizing proteins from mRNA; it is a fundamental cellular process and not a cause of drug resistance.
- Errors in translation are generally lethal to the cell and do not typically confer specific drug-resistant phenotypes.
*Conjugation*
- This is a mechanism for **horizontal gene transfer** where bacteria directly transfer genetic material, including resistance genes, via a pilus.
- While conjugation is the **most important mechanism for spreading resistance** in clinical settings, it transfers pre-existing resistance genes rather than creating new ones.
*Transduction*
- This is another form of **horizontal gene transfer** involving bacteriophages (viruses) carrying bacterial genes, including resistance genes, between bacteria.
- Similar to conjugation, transduction is a mechanism for the **transfer** of pre-existing resistance genes, not their original creation.
Gene Transfer in Bacteria Indian Medical PG Question 2: The genetic ability of a bacterium to grow in the presence of several antibiotics is passed in vivo from one bacterium to another by:
- A. Transposition
- B. Conjugation (Correct Answer)
- C. Transduction
- D. Transformation
Gene Transfer in Bacteria Explanation: ***Conjugation***
- This process involves the direct transfer of **genetic material** (often plasmids carrying **resistance genes**) from one bacterium to another through direct cell-to-cell contact, typically via a **pilus**.
- It is a primary mechanism for the spread of **antibiotic resistance** among bacteria, enabling the rapid acquisition of resistance traits.
*Transposition*
- This involves the movement of **transposable elements** (jumping genes) within a bacterium's own genome or between a plasmid and the chromosome.
- While transposons can carry antibiotic resistance genes, their movement is typically within a single cell's DNA, not directly between different bacteria (though they can be part of transferred plasmids).
*Transduction*
- This is the process where **bacteriophages** (viruses that infect bacteria) carry bacterial DNA from one bacterium to another.
- While it can transfer antibiotic resistance genes, it requires a viral vector rather than direct cell-to-cell contact, making it a distinct mechanism from conjugation.
*Transformation*
- This is the uptake of **naked DNA** from the environment by a bacterial cell.
- The DNA can originate from dead bacterial cells, and while it *can* include resistance genes, it's not a direct, active transfer between living bacteria in the way conjugation is.
Gene Transfer in Bacteria Indian Medical PG Question 3: Which of the following is the most widespread method of genetic transfer among bacteria?
- A. Transformation
- B. Transduction
- C. Lysogenic conversion
- D. Conjugation (Correct Answer)
Gene Transfer in Bacteria Explanation: ***Conjugation***
- This method involves **direct cell-to-cell contact** between bacteria, typically through a **pilus**, allowing for the transfer of **plasmids** or chromosomal DNA.
- Its widespread nature is due to the efficient transfer of large amounts of genetic material, including **antibiotic resistance genes**, among diverse bacterial species.
*Transformation*
- This process involves the uptake of **naked DNA** from the environment by a competent bacterial cell.
- While important, it is less common because bacteria must be in a specific **physiological state** (competent) to take up DNA, and the DNA itself can be fragile in the environment.
*Transduction*
- This mechanism involves the transfer of bacterial DNA from one bacterium to another via a **bacteriophage** (virus).
- Its prevalence is limited by the specific range of bacteria that a phage can infect, making it less widespread compared to conjugation.
*Lysogenic conversion*
- This refers to the acquisition of new traits by a bacterium due to the integration of a **prophage** (temperate phage DNA) into its genome.
- While it can alter bacterial phenotypes, it is a specific outcome of phage infection and not a primary mechanism for broad genetic transfer among bacteria.
Gene Transfer in Bacteria Indian Medical PG Question 4: Lysogenic conversion is seen in -
- A. Staphylococcus
- B. Corynebacterium diphtheriae (Correct Answer)
- C. Salmonella
- D. E. coli
Gene Transfer in Bacteria Explanation: ***Corynebacterium diphtheriae***
- **Lysogenic conversion** in *Corynebacterium diphtheriae* is the **classic textbook example**, where a bacteriophage (phage β) carries the **tox gene** for the **diphtheria toxin**, converting a non-pathogenic strain into a toxigenic pathogen.
- The integration of this **prophage** into the bacterial chromosome allows for stable toxin production, leading to the clinical manifestations of diphtheria.
- This is the **most commonly cited example** of lysogenic conversion in medical microbiology education.
*Staphylococcus*
- While *Staphylococcus* can be infected by bacteriophages, **lysogenic conversion** is not the primary mechanism for acquiring major virulence factors.
- Toxins like **TSST-1** and **Panton-Valentine leukocidin (PVL)** are more commonly encoded on **plasmids, pathogenicity islands, or other mobile genetic elements** rather than temperate bacteriophages.
*Salmonella*
- Some *Salmonella* serotypes can undergo **lysogenic conversion** where prophages confer **O-antigen modifications** or other factors.
- However, this is less emphasized in standard medical curricula compared to the diphtheria toxin example.
*E. coli*
- **Shiga toxin-producing *E. coli* (STEC)** strains acquire **Shiga toxins (Stx1 and Stx2)** through lysogenic conversion via **Stx-encoding bacteriophages**.
- While this is indeed a valid and important example of lysogenic conversion, the **diphtheria toxin** case is traditionally presented as the **primary teaching example** in Indian medical PG curricula (Ananthanarayan & Paniker, Jawetz).
- For examination purposes, ***Corynebacterium diphtheriae*** is the expected answer when asked about lysogenic conversion.
Gene Transfer in Bacteria Indian Medical PG Question 5: False regarding bacterial plasmids is:
- A. Extrachromosomal
- B. Transmission to different species
- C. Eliminated by treating with radiation
- D. Can cause lysogenic conversion (Correct Answer)
Gene Transfer in Bacteria Explanation: ***Can cause lysogenic conversion***
- **Lysogenic conversion** is a phenomenon caused by **bacteriophages**, which are viruses that infect bacteria, not by plasmids directly.
- It involves the integration of a **phage genome** into the bacterial chromosome, altering the bacterium's phenotype (e.g., toxin production).
*Extrachromosomal*
- Bacterial plasmids are indeed **extrachromosomal DNA molecules**, meaning they exist independently of the bacterial chromosome.
- This characteristic allows them to be easily transferred between bacteria.
*Transmission of different species*
- Plasmids can be transmitted horizontally between bacteria, even across **different species**, through mechanisms like **conjugation**, **transformation**, or **transduction**.
- This interspecies transmission is a major factor in the spread of **antibiotic resistance**.
*Eliminated by treating with radiation*
- Plasmids, like all DNA, can be eliminated or degraded by treatments such as **radiation** (e.g., UV) or certain chemicals.
- Such treatments disrupt the plasmid DNA structure, preventing its replication or function.
Gene Transfer in Bacteria Indian Medical PG Question 6: What is the primary use of Elek's Gel test?
- A. Influenza
- B. Diphtheria (Correct Answer)
- C. Brucellosis
- D. Cholera
Gene Transfer in Bacteria Explanation: ***Diphtheria***
- **Elek's Gel immunodiffusion test** is a crucial in vitro assay used to detect **toxin production** by *Corynebacterium diphtheriae* strains
- This test helps differentiate **toxigenic strains** (which cause diphtheria) from **non-toxigenic strains**
- Based on the principle of **immunodiffusion** where antitoxin-impregnated filter paper is placed on agar and bacterial strains are streaked perpendicular to it
- **Lines of precipitation** form if the strain produces diphtheria toxin
*Influenza*
- Influenza diagnosis primarily relies on rapid antigen detection tests, PCR, or viral culture
- The Elek test is not used for the identification or toxin detection of *Influenza virus*
*Brucellosis*
- Brucellosis diagnosis is typically confirmed by serological tests (e.g., agglutination tests) or blood cultures
- The Elek test has no role in the diagnosis of *Brucella* infections
*Cholera*
- Cholera is diagnosed by identifying *Vibrio cholerae* in stool samples through culture and biochemical tests
- The Elek test is irrelevant to the diagnosis of cholera
Gene Transfer in Bacteria Indian Medical PG Question 7: Which of the following statements about Corynebacterium diphtheriae is NOT true?
- A. Has metachromatic granules
- B. Toxin mediated by chromosomal gene (Correct Answer)
- C. Toxigenicity demonstrated by elek's test
- D. Does not invade deeper tissues
Gene Transfer in Bacteria Explanation: ***Toxin mediated by chromosomal gene***
- The **diphtheria toxin** is encoded by the **tox gene**, which is a lysogenic bacteriophage (cornyphage) gene, not a chromosomal gene.
- This **bacteriophage** integrates into the bacterial chromosome, making toxigenic *C. diphtheriae* strains lysogenized.
*Has metachromatic granules*
- *Corynebacterium diphtheriae* is known for possessing **metachromatic granules** (also called Babes-Ernst bodies), which are inclusions that stain differently from the rest of the cell.
- These granules are composed of **polyphosphate reserves** and are important for identification.
*Does not invade deeper tissues*
- *Corynebacterium diphtheriae* remains **localized** to the mucosal surface of the upper respiratory tract or skin, forming a **pseudomembrane**.
- Its pathogenicity is primarily due to the **exotoxin** it produces, which then disseminates systemically.
*Toxigenicity demonstrated by elek's test*
- The **Elek test** is a standard laboratory assay used to determine the **toxigenicity** of *Corynebacterium diphtheriae* strains by detecting the production of diphtheria toxin.
- It works by identifying the **immunoprecipitation lines** formed between antitoxin and toxin in an agar medium.
Gene Transfer in Bacteria Indian Medical PG Question 8: All the following terms are used to describe bacterial chromosome Except
- A. Diploid (Correct Answer)
- B. Circular
- C. Nucleoid
- D. Haploid
Gene Transfer in Bacteria Explanation: ***Diploid***
- Bacterial chromosomes are typically **haploid**, meaning they contain only one copy of each gene, not two sets as in diploid organisms.
- While bacteria can sometimes have multiple copies of their chromosome, these copies are usually identical replicas and do not represent distinct sets of genetic information.
*Circular*
- The bacterial chromosome is characteristically a **single, closed circular DNA molecule**.
- This circular structure distinguishes bacterial chromosomes from the linear chromosomes found in eukaryotes.
*Nucleoid*
- The bacterial chromosome is located in a region of the cytoplasm called the **nucleoid**, as bacteria lack a membrane-bound nucleus.
- The nucleoid is where the genetic material is condensed and organized within the bacterial cell.
*Haploid*
- Bacteria are essentially **haploid organisms**, possessing a single set of chromosomes.
- This means they have only one allele for each gene, which can lead to rapid expression of mutations.
Gene Transfer in Bacteria Indian Medical PG Question 9: Darting motility which occurs in V.cholerae, also found in -
- A. Campylobacter jejuni (Correct Answer)
- B. Bacillus anthracis
- C. Shigella
- D. Pneumococcus
Gene Transfer in Bacteria Explanation: ***Campylobacter jejuni***
- *Campylobacter jejuni* is well-known for its **rapid, corkscrew-like motility**, often described as **darting motility**, which is a key characteristic for its identification.
- This characteristic movement is due to its **polar flagella** and helps the bacterium penetrate the intestinal mucosa.
*Shigella*
- *Shigella* species are notable for being **non-motile**, a crucial feature distinguishing them from other enterobacteriaceae.
- Their lack of flagella and motility prevents them from exhibiting darting or any other form of self-propulsion.
*Bacillus anthracis*
- *Bacillus anthracis* is typically described as **non-motile** in its vegetative form.
- While other *Bacillus* species can be motile, *B. anthracis* lacks the flagella necessary for darting motility.
*Pneumococcus*
- *Pneumococcus* (Streptococcus pneumoniae) is a **non-motile** bacterium.
- It does not possess flagella and therefore cannot exhibit darting or any other type of active movement.
Gene Transfer in Bacteria Indian Medical PG Question 10: All of the following statements about cholera are true except -
- A. Culture medium is TCBS Agar
- B. O & H antigens measure carrier state (Correct Answer)
- C. Produces indole and reduces nitrate
- D. Synthesize neuraminidase
Gene Transfer in Bacteria Explanation: ***O & H antigens measure carrier state***
- **O and H antigens** are primarily involved in serotyping *Vibrio cholerae* and are crucial for the initial classification of different strains, particularly differentiating between toxigenic and non-toxigenic strains.
- The detection of **carrier states** in cholera is typically achieved through culturing stool samples for the presence of *Vibrio cholerae*, rather than by measuring O and H antigens, as these antigens reflect the bacterial surface components.
*Culture medium is TCBS Agar*
- **Thiosulfate-citrate-bile salts-sucrose (TCBS) agar** is a selective and differential medium widely used for isolating *Vibrio* species, including *Vibrio cholerae*, from clinical samples and environmental sources.
- It works by inhibiting the growth of most enteric bacteria while allowing *Vibrio* species to grow and produce distinct colonies (e.g., yellow colonies for sucrose-fermenting *V. cholerae*).
*Produces indole and reduces nitrate*
- *Vibrio cholerae* is biochemically characterized by its ability to **produce indole** from tryptophan and to **reduce nitrates** to nitrites, which are important diagnostic markers.
- These metabolic activities are part of the standard battery of biochemical tests used to identify and confirm the presence of *Vibrio cholerae* in laboratory settings.
*Synthesize neuraminidase*
- *Vibrio cholerae* produces **neuraminidase**, an enzyme that cleaves **sialic acid** residues from mucin, potentially enhancing the binding of cholera toxin to intestinal epithelial cells by exposing GM1 ganglioside receptors.
- This enzyme contributes to the pathogen's virulence by modifying the host's intestinal environment, although its direct role in disease pathogenesis is still under investigation.
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