Bacterial Pathogenesis Multiple Choice Question And Answers

Bacterial Genetics

Question 1. Jumping gene is:

1. Transposon
2. Episome
3. Cosmid
4. Plasmid

Answer. (1) (Transposon)

Read And Learn More: Micro Biology And Immunology Multiple Choice Question And Answers

Question 2. Function of CRISPR is:

1. Bacterial genome editing to protect against infecting viruses
2. Bacterial genome editing to protect against human immune system
3. Mechanisms used by viruses to produce reassortants
4. Genotypic mixing seen in viruses for genetic reactivation

Answer. (2) (Bacterial genome…)

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats):

• The sequences contain snippets of DNA from viruses that have attacked the bacterium.
• These snippets are used by the bacterium to detect and destroy DNA from similar viruses during subsequent attacks.
• In short, this is a prokaryotic immune system that confers the bacteria resistance to foreign genetic elements such as those present within plasmids and phages.

Question 3. Transfer of nuclear material by transduction through:

1. Transposons
2. Plasmids
3. Bacteriophage
4. Insertion sequences

Answer. (3) (Bacteriophage)

• Transduction refers to transfer of genetic material from one bacterium to other by mean of bacteriophage.

Question 4. Bacteria used in Griffith experiment is:

1. Streptococcus pyogenes
2. Capsulated Streptococcus pneumoniae
3. Staphylococcus aureus
4. MRSA
5. Non-capsulated Streptococcus pneumoniae

Answer. (2, 5) (Capsulated S. pneumoniae, Non-capsulated S. pneumoniae)

Capsulated dead S. pneumoniae + non-capsulated live S. pneumoniae → Transformation of gene coding capsule from dead to live pneumococci → Results in capsulated live pneumococci

Question 5. Pick the true statement regarding Plasmids:

1. Nonself-replicative
2. Acts as Messenger RNA
3. Involved in conjugational transfer between strains
4. Involved in transformation

Answer. (3) (Involved in Conjugational…)

Plasmids are self-replicative extra-chromosomal elements frequently transferred by conjugation.

Question 6. Nontoxigenic C. diphtheriae changes to toxigenicC. diphtheriae by the help of bacteriophage… by which method this conversion occur?

1. Transfection
2. Transduction
3. Conjugation
4. Recombinant technology

Answer. (2) (Transduction)

• Transduction is the transfer of bacterial genes from one bacteria to other by bacteriophage
• Lysogenic Conversion would have been a better answer here. It is the process by which the phage DNA is integrated to bacterial DNA and remains as lysogenic phage. In such case, certain phage gene (e.g. gene coding for diphtheria toxin) imparts toxigenicity to the bacteria.

Question 7. Movement of DNA from one bacteria to another connection tube or pilus is called:

1. Transformation
2. Transduction
3. Conjugation
4. Lysogenic conversion

Answer. (3) (Conjugation)

Question 8. Mechanism of direct transfer of free DNA:

1. Transformation
2. Conjugation
3. Transduction
4. None

Answer. (1) (Transformation)

• Transformation is the process of the transfer of free DNA itself from one bacterium to another.

Question 9. Horizontal transmission of ‘R’ factor is by:

1. Transduction
2. Transformation
3. Conjugation
4. Fusion

Answer. (3) (Conjugation)

Conjugation is the process where there is transfer of genetic elements from one bacterium (male) to another (female) along sex pilus or conjugation tube—Horizontal genetic transfer.

• Antimicrobial Resistance

Question 10. New Delhi metallo-Beta-Lactamase enzyme confers resistance to which antibiotic?

1. Colistin
2. Amoxicillin
3. Carbapenems
4. Vancomycin

Answer. (3) (Carbapenems)

• New Delhi metallo-Beta-Lactamase enzyme confers resistance to carbapenems.

Question 11. All the following are bacteriostatic except?

1. Vancomycin
2. Clindamycin
3. Tetracycline
4. Linezolid

Answer. (1) (Vancomycin)

Vancomycin is a cell-wall-acting antibiotic, it is primarily bactericidal.

Primarily bacteriostatic antibiotic include: Clindamycin, Tetracycline, Linezolid,

Sulfonamide, Macrolide, Chloramphenicol

Question 12. The mechanism of action of vancomycin is inhibition/alteration of:

1. Cell wall synthesis
2. mRNA synthesis
3. Cell membrane integrity
4. Protein synthesis via 50s ribosomal subunit

Answer. (1) (Cell wall synthesis)

Vancomycin acts by inhibition of cell wall synthesis by binding to D-Ala-D-Ala of tetrapeptide side chain of peptidoglycan.

Question 13. Most common method of bacteria responsible for drug resistance:

1. Conjugation
2. Transduction
3. Transformation
4. Enzyme inactivation
5. Mutation

Answer. (1, 4) (Conjugation, Enzyme inactivation)

Transferrable resistance by conjugation is the most common method of transfer of bacterial-resistant genes. Enzyme inactivation is the most common mechanisms of bacteria drug resistance.

Question 14. Not true about bacterial drug resistance mechanism:

1. Most common mechanism is production of neutralizing enzymes
2. If resistance is plasmid mediated, it is always transferred vertically
3. Alteration of target seen in pneumococcal resistance
4. Complete removal of target is cause of resistance to Vancomycin

Answer. (2) (If resistance is plasmid mediated, it is always transferred vertically)

• If resistance is chromosomally mediated, it is usually transferred vertically from parent to daughter bacteria.
• If resistance is plasmid mediated, it is usually transferred by horizontal route mainly by conjugation.
  About Other Options
• Clinically, enzymatic drug inactivation is the most common mechanism for acquired microbial resistance by bacteria.
  Most common mechanism of bacterial drug resistance:
• Pneumococcal resistance: is mainly due to Alteration of target, i.e. Penicillin-binding protein (PBP)
• Resistance to Vancomycin is due to complete removal of target D alanyl-D alanine present the bacterial cell wall is the target site for Vancomycin, which binds there and inhibits it and thus inhibits the cell wall synthesis.

Question 15. Multiple drug resistance is spread by:

1. Transformation
2. Transduction
3. Mutation
4. Conjugation

Answer. (4) (Conjugation)

• Resistance (R) factors are extrachromosomal plasmids responsible for spread of multiple drug resistance among bacteria.
• They are circular double-stranded DNA carry genes for variety of enzymes that can destroy antibiotics.
• R factor consists of 2 components: Resistance transfer factor (RTF) and resistant determinant (r).
• The resistance transfer factor is responsible for conjugational transfer while each r determinant carries resistance for one of the several antibiotics.

Question 16. A patient is on ceftriaxone and amikacin, ESBL Klebsiella has grown from culture. What will you do next?

1. Continue with same antibiotic but in higher dose
2. Change ceftriaxone and add ceftazidime
3. Start imipenem in place of ceftriaxone
4. Remove Amikacin

Answer. (3) (Start Imipenem in place of ceftriaxone)

• ESBL (Extended-spectrum beta-lactamases) are resistant to all Penicillin and 1st/2nd/3rd cephalosporin and monobactam
• Which can be overcome by addition of β lactamase inhibitor like clavulinic acid
• Other alternate which can be given are:
  • Carbapenems like Imipenem and meropenem
  • Cephamycins (like cefoxitin and cefotetan )
  • Different class of antibiotics like aminoglycoside

Question 17. Drug against ESBL-producing Pseudomonas:

1. Ceftriaxone + Piperacillin
2. Ceftriaxone + Tazobactam
3. Piperacillin + Tazobactam
4. Ceftriaxone + Piperacillin + Tazobactam

Answer. (3) (Piperacillin + Taz…)

Extended Spectrum-β-Lactamases (ESBL) producing Pseudomonas can be treated with an antipseudomonal β lactam (e.g. piperacillin) plus β lactamase inhibitor such as tazobactam combination therapy.

Question 18. MIC (minimum inhibitory concentration) can be calculated by all of the following antibiotic sensitivity methods except:

1. E test
2. Agar dilution method
3. Kirby-Bauer’s disk diffusion method
4. Broth dilution method

Answer. (3) (Kirby-Bauer’s disk diffusion method)

• Kirby-Bauer’s disk diffusion method is used to know the zone of inhibition of the streaked organism surrounding the disk by which we can know whether the organism is sensitive or resistant to the antibiotic disk. However, we cannot know the MIC.
• MIC (Minimal inhibitory concentration) of the antibiotic is defined as the lowest concentration of an antimicrobial agent that will inhibit the visible growth of a microorganism.
• MIC is calculated by: (1) Agar dilution method, (3) Broth dilution method and (3) Epsilometer (E test)

Question 19. For antibiotic sensitivity test, the organism broth prepared should match with:

1. McFarland standard 0.5
2. McFarland standard 1
3. McFarland standard 2
4. McFarland standard 3

Answer. (1) (McFarland standard 0.5)

• In microbiology, McFarland standards are used as a reference to adjust the turbidity of bacterial suspensions so that the number of bacteria will be within a given range.
• A 0.5 McFarland standard is prepared by mixing 0.05 mL of barium chloride dihydrate with 9.95 mL of 1% sulfuric acid and its equivalent to 150 million no. of bacteria/mL in a broth.
• For antibiotic sensitivity test, the organism broth prepared should match with- 0.5 McFarland standard.

Question 20. Beta-lactamase is produced by:

1. E. coli
2. Gonococcus
3. Staphylococcus aureus
4. All of the above

Answer. (4) (All of the above)

Beta-lactamase enzymes are plasmid coded, produced by both gram positive and gram-negative organisms.

Question 21. Which of the following disease(s) is/are not toxin mediated?

1. Diphtheria
2. Tetanus
3. Pertussis
4. Anthrax
5. Syphilis

Answer. (5) (Syphilis)

Syphilis is caused by T. pallidum. Refer chapter review.

Question 22. A strain of E. coli isolated from urine is resistant to third-generation cephalosporins.

The mechanism of development of resistance is:

1. Extended-spectrum Beta-Lactamases
2. Decreased permeability
3. Active efflux of Beta-Lactam agents
4. Alteration of PBP

Answer. (1) (Extended spectrum Beta-Lactamases)

Out of several mechanisms of beta-lactam resistance in E. coli, Beta-Lactamase production is the MOST COMMON; particularly Extended spectrum Beta-Lactamases (ESBL).