Infectious Diseases

Infectious Diseases Indian Medical PG Question 1: Which of the following is NOT a mechanism of antibiotic resistance?

• A. Efflux pump activity
• B. Inactivation by enzymes such as beta-lactamase
• C. Modification of drug target sites
• D. Increased drug absorption (Correct Answer)

Infectious Diseases Explanation: ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].

Infectious Diseases Indian Medical PG Question 2: Which of the following statements about antibiotic resistance in N. gonorrhoeae is FALSE?

• A. Ceftriaxone resistance typically involves alterations in the penA gene
• B. Resistance to fluoroquinolones is often due to mutations in gyrA and parC genes
• C. Spectinomycin resistance remains extremely rare globally
• D. Tetracycline resistance is primarily mediated by beta-lactamase production (Correct Answer)

Infectious Diseases Explanation: ***Tetracycline resistance is primarily mediated by beta-lactamase production*** - This statement is **FALSE**. Beta-lactamases (such as TEM-1 and TEM-135) in *N. gonorrhoeae* confer resistance to **penicillins and related beta-lactam antibiotics**, not tetracyclines. - **Tetracycline resistance** in *N. gonorrhoeae* is mediated by two distinct mechanisms: **plasmid-borne TetM determinants** (conferring high-level resistance through ribosomal protection) and **chromosomal mutations** (affecting mtrR, penB, and rpsJ genes, leading to increased efflux or altered ribosomal targets). - Beta-lactamase production and tetracycline resistance are independent resistance mechanisms. *Ceftriaxone resistance typically involves alterations in the penA gene* - This is **TRUE**. Ceftriaxone resistance in *N. gonorrhoeae* is primarily associated with **mosaic _penA_ alleles** encoding altered penicillin-binding protein 2 (PBP2). - These mosaic alleles result in decreased affinity of PBP2 for cephalosporins, reducing drug effectiveness. - Additional mechanisms include mtrR mutations (increasing efflux) and penB mutations (decreasing permeability). *Resistance to fluoroquinolones is often due to mutations in gyrA and parC genes* - This is **TRUE**. Fluoroquinolone resistance in *N. gonorrhoeae* primarily results from mutations in the **quinolone resistance-determining regions (QRDRs)** of **_gyrA_** and **_parC_** genes. - These genes encode subunits of DNA gyrase and topoisomerase IV respectively, the primary targets of fluoroquinolones. - The most common mutation is S91F in GyrA, with additional mutations in ParC contributing to higher-level resistance. *Spectinomycin resistance remains extremely rare globally* - This is **TRUE**. Spectinomycin resistance in *N. gonorrhoeae* remains **extremely rare worldwide**, with only sporadic case reports. - Resistance is mediated by mutations in the **16S rRNA gene** (particularly at position 1192), but this mechanism has not become widespread. - Spectinomycin remains a valuable alternative therapy, particularly for patients with cephalosporin allergies or in areas with cephalosporin resistance.

Infectious Diseases Indian Medical PG Question 3: A healthcare worker develops fever, night sweats, and cough. Sputum shows acid-fast bacilli. What is the next diagnostic test?

• A. Gram stain
• B. Serology for TB
• C. NAAT for TB (Correct Answer)
• D. Sputum culture

Infectious Diseases Explanation: ***NAAT for TB*** - Nucleic Acid Amplification Tests (**NAAT**) rapidly confirm the presence of **Mycobacterium tuberculosis** DNA or RNA, crucial after an **acid-fast bacilli (AFB) smear** is positive [1]. - This test offers high sensitivity and specificity and can also detect **drug resistance**, guiding immediate treatment decisions [1]. *Gram stain* - A **Gram stain** is not appropriate for **Mycobacterium tuberculosis** because these bacteria have a unique cell wall that makes them **acid-fast**, not readily stained by the Gram method. - The initial finding of **acid-fast bacilli** already indicates a general type of organism, making a Gram stain redundant and uninformative for TB. *Serology for TB* - **Serological tests for TB** (detecting antibodies to M. tuberculosis) are generally **not recommended** for the diagnosis of active pulmonary TB due to their **poor sensitivity and specificity**. - They have limited utility in diagnosing active disease and are not endorsed by major health organizations for this purpose. *Sputum culture* - **Sputum culture** is the **gold standard** for confirming TB diagnosis and for **drug susceptibility testing**, but it is a **slow process** (taking several weeks) [2]. - While essential for definitive diagnosis and resistance profiling, it is not the **"next" rapid diagnostic test** required given the positive AFB smear.

Infectious Diseases Indian Medical PG Question 4: Why is a regimen of four drugs recommended for a TB patient on the first visit?

• A. To prevent emergence of drug-resistant strains (Correct Answer)
• B. To reduce bacterial load effectively
• C. To minimize treatment duration
• D. None of the options

Infectious Diseases Explanation: ***To prevent emergence of drug-resistant strains*** - Using a **four-drug regimen** at the initial stage significantly reduces the likelihood of **Mycobacterium tuberculosis** developing resistance to any single drug. - This strategy ensures that even if a small number of bacteria are naturally resistant to one drug, the other drugs will still be effective in killing them, preventing the proliferation of **resistant strains**. *To minimize treatment duration* - While a multi-drug regimen is effective, its primary goal is not to minimize treatment duration but rather to ensure **eradication of the infection** and prevent resistance. - Treatment duration is determined by the need to kill both actively multiplying and dormant bacteria, which typically takes several months even with multiple drugs. *To reduce bacterial load effectively* - Reducing bacterial load is certainly a goal of TB treatment, but the use of four drugs is specifically aimed at achieving this while simultaneously preventing **drug resistance**. - A single effective drug could reduce bacterial load, but it would quickly lead to the emergence of resistant bacteria, making the long-term goal of **cure** impossible. *None of the options* - This option is incorrect because the primary reason for a **four-drug regimen** in TB treatment is indeed to prevent the emergence of **drug-resistant strains**.

Infectious Diseases Indian Medical PG Question 5: Which of the following is the best parameter to predict virulence of acute infectious illness?

• A. Incidence
• B. Secondary attack rate
• C. Case fatality rate (Correct Answer)
• D. Crude death rate

Infectious Diseases Explanation: ***Case fatality rate*** - The **case fatality rate (CFR)** directly measures the **proportion of individuals diagnosed with a disease who die from it**, reflecting the pathogen's ability to cause death. - A higher CFR indicates greater **virulence** and a more severe disease outcome, making it the most direct predictor of an illness's ability to harm. *Incidence* - **Incidence** measures how often a disease occurs in a population over a specified period, indicating the **risk of contracting the disease**. - It does not provide information about the **severity** or **lethality** of the disease once contracted. *Secondary attack rate* - The **secondary attack rate** quantifies the probability that infection will occur among susceptible individuals within a particular group exposed to a primary case. - While it measures **transmissibility** and the potential for spread within a close group, it does not reflect the **virulence** or severity of the illness itself. *Crude death rate* - The **crude death rate** is the total number of deaths from all causes in a population over a given period, divided by the total population. - This parameter measures **overall mortality** in a population and is not specific to the deaths caused by a particular infectious illness, nor does it solely reflect its virulence.

Infectious Diseases Flashcard 1 of 5

Question: ICU inpatients of community acquired pneumonia are treated with:_____ + azithromycin or fluoroquinolone

Answer: -lactam

Infectious Diseases Flashcard 2 of 5

Question: In which opportunistic infections can ART be started immediately?_____

Answer: MAC, cryptosporidiosis, microsporidiosis and PML

Infectious Diseases Flashcard 3 of 5

Question: List of pathogens that can cause endocarditis in IVDUs:_____Candida albicans

Answer: Staphylococcus aureus

Infectious Diseases Flashcard 4 of 5

Question: _____ are susceptible to acute bacterial endocarditis of the tricuspid valve from staphylococcus aureus

Answer: IV drug users

Infectious Diseases Flashcard 5 of 5

Question: Secondary bacterial pneumonia is typically _____, Haemophilus influenzae, or Strep pneumo superimposed on Influenza

Answer: Staph aureus