Antimicrobial Resistance — MCQs

Antimicrobial Resistance Indian Medical PG Practice Questions and MCQs

Question 61: Which of the following microorganisms will be resistant to meropenem and aminoglycosides but sensitive to piperacillin tazobactam and cotrimoxazole?

A. Pseudomonas
B. Acinetobacter
C. Burkholderia cepacia
D. Stenotrophomonas (Correct Answer)

Explanation: ***Stenotrophomonas maltophilia*** - *Stenotrophomonas maltophilia* exhibits **intrinsic resistance to carbapenems (like meropenem)** due to the presence of L1 and L2 metallo-beta-lactamases and chromosomally encoded beta-lactamases. - It is **resistant to aminoglycosides** via aminoglycoside-modifying enzymes and efflux pump mechanisms. - **Trimethoprim-sulfamethoxazole (cotrimoxazole) is the drug of choice** with consistent susceptibility, making it the first-line treatment. - **Susceptibility to piperacillin-tazobactam is variable** - while some isolates may show in vitro susceptibility, clinical efficacy is inconsistent and it is not considered a reliable first-line agent. Among the options given, this organism best fits the described pattern. *Pseudomonas aeruginosa* - **Generally susceptible to carbapenems (meropenem) and aminoglycosides**, which are important therapeutic options. - Does not match the resistance pattern described in the question. *Acinetobacter baumannii* - Shows **multidrug resistance including carbapenems and aminoglycosides** in most clinical isolates. - However, typically also **resistant to piperacillin-tazobactam and cotrimoxazole**, making it inconsistent with the described susceptibility pattern. *Burkholderia cepacia complex* - Exhibits **intrinsic resistance to multiple antibiotics** including aminoglycosides and often carbapenems. - **Variable and often resistant to piperacillin-tazobactam**, and susceptibility to cotrimoxazole is inconsistent. - Does not reliably match the described antibiotic profile.

Question 62: Which antimicrobial resistance mechanism is most commonly associated with extended-spectrum cephalosporin resistance in Neisseria gonorrhoeae?

A. PenA mosaic alleles (Correct Answer)
B. mtrR promoter mutation
C. 23S rRNA methylation
D. TetM plasmid

Explanation: ***PenA mosaic alleles*** - **PenA mosaic alleles** are altered forms of the gene encoding **penicillin-binding protein 2 (PBP2)**, which is the primary target of cephalosporin antibiotics in *Neisseria gonorrhoeae*. These mosaic alleles result from recombination events with homologous genes from commensal *Neisseria* species. - The altered PBP2 has **reduced affinity for cephalosporins**, making the bacteria resistant to this class of antibiotics, including extended-spectrum cephalosporins. *mtrR promoter mutation* - A **mutation in the *mtrR* promoter** typically leads to overexpression of the **MtrCDE efflux pump**, which pumps out various antimicrobial agents, including some macrolides, disinfectants, and bile salts. - While it contributes to multidrug resistance, its primary role is not in mediating high-level resistance to extended-spectrum cephalosporins in *N. gonorrhoeae*. *23S rRNA methylation* - **23S rRNA methylation** is a common mechanism of resistance to **macrolide antibiotics** (e.g., azithromycin), which bind to the 50S ribosomal subunit. - This mechanism interferes with macrolide binding to the ribosome, but it does not directly affect the activity of cephalosporins, which target bacterial cell wall synthesis. *TetM plasmid* - The **TetM plasmid** confers resistance to **tetracycline antibiotics** by protecting the bacterial ribosome from their action. TetM is a ribosomal protection protein. - This plasmid is a well-known mechanism of tetracycline resistance in many bacteria, including *N. gonorrhoeae*, but it is not involved in resistance to cephalosporins.

Question 63: A high-risk STI clinic sees increasing antibiotic resistance in N. gonorrhoeae isolates. Which laboratory strategy would best inform local treatment guidelines?

A. Periodic random sampling of cases
B. Selective culture of treatment failures
C. Culture with antimicrobial susceptibility testing from all anatomical sites (Correct Answer)
D. Universal NAAT testing only

Explanation: ***Culture with antimicrobial susceptibility testing from all anatomical sites*** - This approach allows for comprehensive determination of the **antibiotic resistance patterns** of *N. gonorrhoeae* isolates across all potential infection sites. - Tracking resistance from samples obtained from the **cervix, urethra, rectum, and pharynx** provides crucial data to adapt local treatment guidelines effectively and monitor the emergence of new resistant strains. *Periodic random sampling of cases* - While helpful for general surveillance, **random sampling** may not adequately capture the full spectrum of resistance patterns, especially for less common or emerging resistant strains. - This strategy might miss critical shifts in resistance if the sampling frequency is too low or the sample size is not representative of the population. *Selective culture of treatment failures* - This method is useful for confirming resistance in individual cases where treatment has failed, but it only provides information on a subset of the *N. gonorrhoeae* population already identified as problematic. - It does not offer a comprehensive picture of the **overall resistance epidemiology** in the clinic's patient population for proactive guideline adjustments. *Universal NAAT testing only* - **Nucleic Acid Amplification Tests (NAATs)** are highly sensitive for detecting *N. gonorrhoeae* DNA or RNA, but they do not provide information on antibiotic susceptibility. - Relying solely on NAATs would prevent the clinic from monitoring resistance trends and making informed decisions about **empirical treatment regimens**.

Question 64: What is the primary mechanism of antibiotic resistance in Neisseria gonorrhoeae?

A. Efflux pump mechanisms only
B. Altered penicillin-binding proteins (PBPs) (Correct Answer)
C. Ribosomal protection proteins only
D. Plasmid-mediated beta-lactamase production only

Explanation: ***Altered penicillin-binding proteins (PBPs)*** - Alterations in **penicillin-binding proteins (PBPs)**, particularly the mosaic *penA* gene, represent the **most clinically significant mechanism** of resistance in *N. gonorrhoeae* today. - These chromosomal mutations reduce the affinity of beta-lactam antibiotics (including **cephalosporins**) for their target, preventing inhibition of cell wall synthesis. - This mechanism is responsible for **reduced susceptibility and resistance to extended-spectrum cephalosporins** (ceftriaxone, cefixime), which are currently the recommended first-line treatment. - PBP alterations are now **widespread globally** and represent the primary concern for treatment failure. *Plasmid-mediated beta-lactamase production only* - Beta-lactamase production (PPNG strains) was historically important for **penicillin resistance** in the 1970s-1980s. - While still present, this mechanism is **less relevant clinically** today since penicillin is no longer used for gonorrhea treatment. - The word "only" makes this incorrect, as *N. gonorrhoeae* employs multiple resistance mechanisms simultaneously. *Efflux pump mechanisms only* - The **MtrCDE efflux pump system** contributes to resistance by expelling multiple antibiotic classes from the bacterial cell. - Efflux pumps enhance resistance to **hydrophobic antibiotics** including azithromycin and some beta-lactams. - However, they are typically part of a **multifactorial resistance pattern** rather than the sole mechanism, making "only" incorrect. *Ribosomal protection proteins only* - Ribosomal protection (e.g., *tetM* gene) confers resistance to **tetracyclines**. - This mechanism is important for tetracycline resistance but is **not the primary concern** for current gonorrhea treatment. - The word "only" makes this incorrect, as resistance involves multiple mechanisms.

Question 65: Vertical transmission of resistance to ciprofloxacin occurs :-

A. Transduction
B. Mutation (Correct Answer)
C. Conjugation
D. Transformation

Explanation: ***Mutation*** - Vertical transmission of resistance occurs when a bacterium with a **resistance gene**, such as one conferring resistance to **ciprofloxacin**, replicates and passes that gene to its progeny. - This typically happens through **spontaneous mutations** in the bacterial genome that alter the drug's target or uptake, and these mutations are then inherited by subsequent generations. *Transduction* - **Transduction** involves the transfer of genetic material, including resistance genes, via **bacteriophages** (viruses that infect bacteria). - This is a **horizontal gene transfer** mechanism, not a vertical one. *Conjugation* - **Conjugation** is the direct transfer of genetic material, often in the form of **plasmids**, from one bacterium to another through direct cell-to-cell contact. - This is a form of **horizontal gene transfer**, not vertical transmission. *Transformation* - **Transformation** is the uptake of **free DNA** from the environment by a bacterium, which can then integrate this DNA into its own genome. - This mechanism is also a type of **horizontal gene transfer**, not vertical transmission of resistance to daughter cells during replication.

Question 66: Organism showing marked resistance to multidrug therapy -

A. Haemophilus ducreyi
B. Calymmatobacterium granulomatosis
C. Treponema pallidum
D. Gonococci (Correct Answer)

Explanation: ***Gonococci*** - **Gonococci (Neisseria gonorrhoeae)** increasingly show **resistance to multiple antibiotics**, including penicillin, tetracycline, macrolides, and some cephalosporins, making treatment challenging. - The Centers for Disease Control and Prevention (CDC) recommends **dual therapy with ceftriaxone and azithromycin** to overcome rising resistance. *Haemophilus ducreyi* - **Haemophilus ducreyi**, the causative agent of **chancroid**, is typically susceptible to macrolides and cephalosporins, with **less reported multidrug resistance** compared to gonococci. - Single-dose therapy with **azithromycin or ceftriaxone** is usually effective. *Calymmatobacterium granulomatosis* - Now known as **Klebsiella granulomatis**, this organism causes **donovanosis (granuloma inguinale)**, and it is generally sensitive to **doxycycline**, **azithromycin**, or ciprofloxacin. - While prolonged treatment may be needed, **widespread multidrug resistance** is not characteristic. *Treponema pallidum* - **Treponema pallidum**, which causes **syphilis**, remains exquisitely susceptible to **penicillin**, which is the gold standard treatment. - There is **no significant reported multidrug resistance** to penicillin, although macrolide resistance has emerged in some regions.

Question 67: Burkholderia cepacia is intrinsically resistant to:

A. Ciprofloxacin
B. Ceftriaxone
C. Polymyxin B (Correct Answer)
D. Ampicillin

Explanation: ***Polymyxin B*** - *Burkholderia cepacia* demonstrates **classic intrinsic resistance** to **polymyxins (Polymyxin B and Colistin/Polymyxin E)** - **Mechanism**: Modifications in the **lipopolysaccharide (LPS) structure** of the outer membrane, particularly alterations in lipid A, reduce polymyxin binding - This resistance is **chromosomally encoded** and present in all strains, making polymyxins completely ineffective against *B. cepacia* infections - This is the **most characteristic example** of intrinsic resistance in this organism *Ciprofloxacin* - *B. cepacia* is **NOT intrinsically resistant** to ciprofloxacin - Ciprofloxacin may retain activity and is sometimes used in susceptible strains - Resistance can develop through **acquired mechanisms** (efflux pumps, DNA gyrase mutations), but this is not inherent to all strains - Susceptibility testing is essential before use *Ceftriaxone* - *B. cepacia* shows resistance to third-generation cephalosporins like ceftriaxone through **multiple resistance mechanisms** including chromosomal AmpC beta-lactamases and efflux pumps - While this resistance is widespread, it's **less characteristic** as a defining feature compared to polymyxin resistance - The beta-lactam resistance pattern in *B. cepacia* is complex and variable *Ampicillin* - *B. cepacia* is resistant to aminopenicillins like ampicillin through **chromosomal beta-lactamase production** and poor outer membrane permeability - While present in most strains, this resistance mechanism is **common to many Gram-negative bacteria** and not a distinguishing feature - Ampicillin is not considered for *B. cepacia* treatment

Question 68: 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

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.

Question 69: The most common mechanism of resistance to drugs in Staphylococcus is

A. Transformation
B. Transduction (Correct Answer)
C. Episomes
D. Conjugation

Explanation: ***Correct Option: Transduction*** - **Transduction** is the transfer of genetic material via **bacteriophages** and is the **most common mechanism** of horizontal gene transfer in *Staphylococcus aureus*. - Bacteriophages play a crucial role in disseminating **antibiotic resistance genes** in staphylococci, including genes for **methicillin resistance (mecA)**, **toxins**, and **beta-lactamase**. - Phage-mediated transfer is responsible for spreading many **virulence factors** and **resistance determinants** among staphylococcal populations. *Incorrect Option: Episomes* - **Episomes** are plasmids capable of integrating into the bacterial chromosome or existing autonomously. - While episomes can **carry resistance genes**, they are a **genetic element**, not a **mechanism of transfer**. - The question asks about the mechanism, not the vehicle carrying resistance genes. *Incorrect Option: Transformation* - **Transformation** involves uptake of **naked DNA** from the environment. - *Staphylococcus* species are **not naturally competent** for transformation under normal conditions. - This is not a significant mechanism of resistance acquisition in staphylococci. *Incorrect Option: Conjugation* - **Conjugation** requires direct cell-to-cell contact through a **conjugative pilus**. - While possible in *Staphylococcus*, it is **less common** compared to transduction. - Conjugation is more characteristic of **Gram-negative bacteria** and enterococci among Gram-positives.

Question 70: All of the following are antibiotic sensitivity testing methods except:

A. Culture dilution (Correct Answer)
B. Agar dilution
C. Tube dilution
D. Epsilometer test

Explanation: ***Culture dilution*** - This is not a recognized or standard method for **antibiotic sensitivity testing**. The term itself does not correspond to any established laboratory procedure used to determine bacterial susceptibility to antimicrobial agents. - Standard methods include techniques that involve diluting either the antibiotic or the bacterial culture in specific media to determine the minimum inhibitory concentration (MIC) or to observe growth inhibition. *Agar dilution* - This is a standard method used to determine the **minimum inhibitory concentration (MIC)** of an antibiotic for a specific bacterium. - Serially diluted concentrations of the antibiotic are incorporated into **agar plates**, which are then inoculated with a standardized bacterial suspension. *Tube dilution* - This method, also known as **broth macrodilution** or **microdilution**, is used to determine the **MIC** and often the **minimum bactericidal concentration (MBC)**. - Serially diluted concentrations of the antibiotic are added to tubes (macro) or wells (micro) containing nutrient broth and a standardized bacterial inoculum. *Epsilometer test* - Commonly known as the **E-test**, this is a quantitative method that uses a plastic strip impregnated with a **gradient of antibiotic concentrations**. - When placed on an inoculated agar plate, an elliptical zone of inhibition forms, and the **MIC** is read at the point where the zone intersects the strip.

Practice by Chapter

Mechanisms of Antimicrobial Resistance

Practice Questions

Beta-lactamase Producing Organisms

Practice Questions

Methicillin-Resistant Staphylococcus aureus

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Vancomycin-Resistant Enterococci

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Carbapenem-Resistant Enterobacteriaceae

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Multi-drug Resistant Tuberculosis

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Antimicrobial Stewardship

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Detection of Antimicrobial Resistance

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Global Surveillance of Resistance

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New Antimicrobial Development

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Alternative Approaches to Antimicrobial Therapy

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One Health Approach to Resistance

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