Mycobacteria — MCQs
A healthcare worker develops fever, night sweats, and cough. Sputum shows acid-fast bacilli. What is the next diagnostic test?
A patient presented with cough and evening rise of temperature since one month. Which among the following is the definitive diagnostic test for tuberculosis?
Which of the following is the PRIMARY causative agent of tuberculosis in humans?
A patient was diagnosed to have single skin lesion of Leprosy without any AFB positive bacteria from the scrapings. What should be the treatment of this patient according to latest guidelines?
Which of the following organisms is classified as a strongly acid-fast bacterium?
Which organism is considered the PRIMARY prototype for Ziehl-Neelsen (acid-fast) staining identification?
A man presents with fever, weight loss, and cough; the Mantoux test reads an induration of 17 x 19 mm, and sputum cytology is negative for acid-fast bacilli. What is the most likely diagnosis?
An 11-year-old boy presented with a cough for 15 days. On examination, he was found to have cervical lymphadenopathy. Lymph node biopsy showed the following findings. What could be the diagnosis?
Paucibacillary leprosy treatment includes
HACEK group of organisms includes all, except:
Mycobacteria Indian Medical PG Practice Questions and MCQs
Question 1: 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
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.
Question 2: A patient presented with cough and evening rise of temperature since one month. Which among the following is the definitive diagnostic test for tuberculosis?
- A. Gram's staining
- B. Culture (Correct Answer)
- C. Tuberculin testing
- D. Guinea-pig inoculation
Explanation: ***Culture*** - **Culture** of *Mycobacterium tuberculosis* from clinical specimens is considered the **gold standard** or **definitive diagnostic test** for tuberculosis - It allows for **species identification**, **comprehensive drug susceptibility testing (DST)** for first-line and second-line drugs, which is crucial for guiding treatment, especially in MDR-TB - Culture is essential for **confirming the diagnosis** when molecular tests are inconclusive and for **monitoring treatment response** - Though culture takes **2-8 weeks** (liquid media like MGIT is faster than solid media like LJ medium), it remains the reference standard *Gram's staining* - **Not effective** for *Mycobacterium tuberculosis* because its cell wall contains a high concentration of **mycolic acid**, making it impervious to the Gram stain - Mycobacteria appear as **gram-negative or gram-variable** "ghosts" with Gram staining - Specialized staining like **acid-fast stain (Ziehl-Neelsen or Auramine-Rhodamine)** is used to visualize the bacilli, but staining alone is **not definitive** - it only suggests mycobacterial infection *Tuberculin testing* - **Tuberculin skin testing (TST)** or Mantoux test detects a **delayed-type hypersensitivity reaction** to tuberculin purified protein derivative (PPD) and indicates **exposure or latent infection**, not necessarily active disease - Cannot distinguish between **latent TB infection (LTBI)** and **active TB disease** - A positive TST can result from **BCG vaccination** or exposure to **nontubercous mycobacteria (NTM)**, reducing specificity - Useful for **screening** but not diagnostic of active disease *Guinea-pig inoculation* - Historically used for **isolation and identification** of *Mycobacterium tuberculosis*, but is a **slow, expensive, and largely obsolete method** - Involves inoculating a susceptible animal with a suspect sample and observing for disease development over **6-8 weeks** - **Lower sensitivity** than modern culture and molecular methods, and raises ethical concerns - Replaced by faster techniques like **liquid culture systems** and **molecular diagnostics (CBNAAT/GeneXpert)**
Question 3: Which of the following is the PRIMARY causative agent of tuberculosis in humans?
- A. M. Bovis
- B. M. Tuberculosis (Correct Answer)
- C. M. Leprae
- D. M. Avium
Explanation: ***M. tuberculosis*** - **_Mycobacterium tuberculosis_** is the principal and most common bacterial agent responsible for causing **tuberculosis** in humans worldwide. - It primarily affects the **lungs** but can also cause extrapulmonary disease in other organs. *M. Bovis* - **_Mycobacterium bovis_** primarily causes **tuberculosis in cattle** and can be transmitted to humans, often through contaminated milk, but it is a less common cause than _M. tuberculosis_. - Human infection by _M. bovis_ usually manifests as **extrapulmonary tuberculosis**, especially in the lymph nodes or bones. *M. Leprae* - **_Mycobacterium leprae_** is the causative agent of **leprosy** (Hansen's disease), a chronic infectious disease affecting the skin, peripheral nerves, upper respiratory tract, eyes, and testes. - It does not cause tuberculosis. *M. Avium* - **_Mycobacterium avium_** is part of the **_Mycobacterium avium_ complex (MAC)**, which commonly causes disseminated disease in individuals with **HIV/AIDS** or other forms of severe immunocompromise. - While it can cause lung disease, it is distinct from tuberculosis caused by _M. tuberculosis_ and is generally not considered the primary causative agent of classic human tuberculosis.
Question 4: A patient was diagnosed to have single skin lesion of Leprosy without any AFB positive bacteria from the scrapings. What should be the treatment of this patient according to latest guidelines?
- A. (Rifampicin + Dapsone) for 12 months
- B. (Rifampicin + Dapsone + Clofazamine) for 6 months
- C. (Rifampicin + Dapsone + Clofazamine) for 12 months
- D. (Rifampicin + Dapsone) for 6 months (Correct Answer)
Explanation: ***(Rifampicin + Dapsone) for 6 months*** - This regimen is the standard **Multi-Drug Therapy (MDT)** for **paucibacillary (PB) leprosy**, which is characterized by a **single skin lesion** and **negative acid-fast bacilli (AFB)** on scrapings. - The 6-month duration is effective in eradicating the infection with high cure rates and low relapse rates. * (Rifampicin + Dapsone) for 12 months* - This 12-month regimen is unnecessarily prolonged for paucibacillary leprosy, increasing the risk of side effects and reducing patient adherence without additional clinical benefit compared to the 6-month regimen. - While Rifampicin and Dapsone are correct drugs for PB leprosy, the duration is not aligned with current WHO guidelines for this specific presentation. * (Rifampicin + Dapsone + Clofazamine) for 6 months* - The addition of **Clofazamine** makes this the regimen for **multibacillary (MB) leprosy**, which presents with multiple skin lesions or positive AFB smears. - This patient's presentation of a **single lesion** and **negative AFB** clearly indicates paucibacillary leprosy, for which Clofazamine is not typically included. * (Rifampicin + Dapsone + Clofazamine) for 12 months* - This is the standard regimen for **multibacillary (MB) leprosy**, due to the presence of Clofazamine and the 12-month duration. - It is not appropriate for a patient with a **single, AFB-negative lesion**, as this presentation denotes paucibacillary leprosy requiring a shorter, two-drug treatment.
Question 5: Which of the following organisms is classified as a strongly acid-fast bacterium?
- A. Mycobacteria (Correct Answer)
- B. Nocardia
- C. Cryptosporidia
- D. Mycoplasma
Explanation: ***Mycobacteria*** - **Mycobacteria** are characterized by their **mycolic acid-rich cell wall**, which makes them **strongly acid-fast** and resistant to decolorization by strong acid-alcohol (3% HCl in ethanol) after staining with carbol fuchsin. - This property is crucial for their identification in clinical samples, particularly for diagnosing diseases like **tuberculosis** (caused by *Mycobacterium tuberculosis*) and **leprosy** (caused by *Mycobacterium leprae*). - The Ziehl-Neelsen stain is the standard method for identifying strongly acid-fast bacteria. *Nocardia* - **Nocardia** are **Gram-positive, aerobic bacteria** that exhibit **partial acid-fastness**, meaning they resist decolorization with weaker acid solutions (1% H₂SO₄) but NOT strong acid-alcohol. - They are known to cause opportunistic infections, particularly in immunocompromised individuals, leading to pulmonary or systemic disease. - Modified acid-fast staining with weaker acid is used to differentiate them from strongly acid-fast Mycobacteria. *Cryptosporidia* - **Cryptosporidia** are **protozoan parasites**, not bacteria, though they do show acid-fast properties in their oocysts due to unique cell wall structure. - They are commonly associated with **gastrointestinal infections** and are identified using specific staining techniques for parasites. *Mycoplasma* - **Mycoplasma** are unique bacteria due to their complete **lack of a cell wall**, which makes them pleomorphic and resistant to antibiotics that target cell wall synthesis. - They are **not acid-fast** and are typically identified through specialized culture methods or molecular tests.
Question 6: Which organism is considered the PRIMARY prototype for Ziehl-Neelsen (acid-fast) staining identification?
- A. Escherichia coli
- B. Mycobacterium tuberculosis (Correct Answer)
- C. Streptococcus pneumoniae
- D. Clostridium difficile
Explanation: ***Mycobacterium tuberculosis*** - The **Ziehl-Neelsen (ZN) stain** is the classic **acid-fast staining** technique used to identify **Mycobacterium species**, particularly **M. tuberculosis** - **Mycobacteria** possess high content of **mycolic acid** (60-90 carbon fatty acids) in their cell wall, making them resistant to decolorization by acid-alcohol - After staining with **carbol fuchsin** (heated), acid-fast bacilli retain the **red/pink color** while non-acid-fast organisms are decolorized and counterstained blue - M. tuberculosis is the **prototype organism** for acid-fast staining and remains the primary clinical application of ZN stain - **Note:** Modified ZN stain (using weaker 1% H2SO4) is used for **weakly acid-fast organisms** like Nocardia and Cryptosporidium *Streptococcus pneumoniae* - This is a **Gram-positive coccus** identified by **Gram staining**, not acid-fast staining - Appears as lancet-shaped diplococci on Gram stain - Lacks mycolic acid in cell wall and cannot retain carbol fuchsin after acid-alcohol decolorization *Escherichia coli* - This is a **Gram-negative bacillus** with thin peptidoglycan layer and outer membrane - Identified by **Gram staining** (appears pink/red) and biochemical tests - Not acid-fast and would be completely decolorized in ZN staining procedure *Clostridium difficile* - This is an **anaerobic, Gram-positive, spore-forming bacillus** - Identified by **Gram staining** and anaerobic culture - Lacks mycolic acid and acid-fast properties, making it unsuitable for ZN staining
Question 7: A man presents with fever, weight loss, and cough; the Mantoux test reads an induration of 17 x 19 mm, and sputum cytology is negative for acid-fast bacilli. What is the most likely diagnosis?
- A. Pulmonary tuberculosis (Correct Answer)
- B. Histoplasmosis
- C. Influenza
- D. Bacterial pneumonia
Explanation: ***Pulmonary tuberculosis*** - The combination of **fever**, **weight loss**, and **cough** are classic symptoms of tuberculosis [1]. - A **Mantoux induration of 17x19 mm** indicates a significant cell-mediated immune response to *Mycobacterium tuberculosis*, supporting the diagnosis even with initial negative sputum cytology [2]. *Histoplasmosis* - While it can cause fever, weight loss, and cough, a **positive Mantoux test** is not characteristic of histoplasmosis. - Diagnosis typically involves fungal cultures, serology, or antigen detection, not tuberculin skin testing. *Influenza* - Influenza is an **acute viral infection** presenting with sudden onset of fever, cough, and myalgia, but **chronic weight loss** is not a typical feature. - The **Mantoux test** being positive does not point towards influenza. *Bacterial pneumonia* - This typically presents with an **acute onset** of fever, productive cough, and dyspnea, while **weight loss** and a **positive Mantoux test** are not typical findings. - It rapidly responds to antibiotics, unlike the more chronic presentation suggested here.
Question 8: An 11-year-old boy presented with a cough for 15 days. On examination, he was found to have cervical lymphadenopathy. Lymph node biopsy showed the following findings. What could be the diagnosis?
- A. Leprosy
- B. Sarcoidosis
- C. Syphilis
- D. Tuberculosis (Correct Answer)
Explanation: ***Tuberculosis*** - The image likely displays **granulomatous inflammation** with **caseous necrosis**, which is highly characteristic of **tuberculosis**, especially in someone presenting with a persistent cough and lymphadenopathy. - The presence of **cervical lymphadenopathy** along with a **cough** for 15 days in an 11-year-old boy points towards extrapulmonary tuberculosis or primary tuberculosis infection affecting the mediastinal lymph nodes with cervical involvement. *Leprosy* - While leprosy also causes granulomas, it typically manifests as skin lesions and nerve involvement, and lymphadenopathy is less common or specific as the primary initial presentation. - The granulomas in leprosy are often **epithelioid** with **foamy histiocytes** and numerous acid-fast bacilli, which are not explicitly described or obvious in the provided context for a definitive diagnosis without special stains. *Sarcoidosis* - Sarcoidosis involves **non-caseating granulomas**, meaning there is no central necrosis, which is a key differentiating feature from the caseating necrosis often seen in tuberculosis. - Although sarcoidosis can cause lymphadenopathy and cough, the microscopic features in the image, particularly if showing necrosis, would argue against sarcoidosis. *Syphilis* - Syphilis can cause lymphadenopathy (especially in secondary syphilis), but the characteristic histological finding is usually a **plasma cell-rich infiltrate** with **endarteritis obliterans**, not typically prominent granulomas with caseous necrosis. - Clinical presentation with cough and chronic lymphadenopathy in an 11-year-old would also make syphilis a less likely primary consideration without other suggestive signs.
Question 9: Paucibacillary leprosy treatment includes
- A. Rifampicin 600 mg once a month for 6 months + Dapsone 100 mg daily for 6 months (Correct Answer)
- B. Rifampicin 600 mg daily + Dapsone 100 mg daily for 6 months
- C. Rifampicin 600 mg + Dapsone 100 mg + Clofazimine for 12 months
- D. Dapsone 100 mg daily + Clofazimine 300 mg daily for 6 months
Explanation: ***Rifampicin 600 mg once a month for 6 months + Dapsone 100 mg daily for 6 months*** - The World Health Organization (WHO) recommends **multi-drug therapy (MDT)** for paucibacillary leprosy, which comprises **Rifampicin 600 mg once monthly** and **Dapsone 100 mg daily** for a total of **6 months**. - This regimen is crucial for effective bacterial eradication and preventing drug resistance in paucibacillary forms of the disease, which have **five or fewer skin lesions**. - The once-monthly Rifampicin dosing is due to its **potent bactericidal activity** and **prolonged post-antibiotic effect**. *Rifampicin 600 mg daily + Dapsone 100 mg daily for 6 months* - While both drugs are part of the paucibacillary regimen, **Rifampicin** is administered **monthly**, not **daily**. - Daily Rifampicin administration is not the WHO standard and could potentially increase the risk of **side effects** and **drug toxicity** without additional therapeutic benefit in paucibacillary leprosy. *Rifampicin 600 mg + Dapsone 100 mg + Clofazimine for 12 months* - The addition of **Clofazimine** is characteristic of the **multibacillary leprosy** regimen, not paucibacillary. - **Multibacillary leprosy** involves extensive disease (more than 5 skin lesions) with higher bacterial load and requires a **12-month treatment** duration with three drugs including Clofazimine. *Dapsone 100 mg daily + Clofazimine 300 mg daily for 6 months* - This regimen excludes **Rifampicin**, which is a critical component of treatment for both paucibacillary and multibacillary leprosy due to its **strong bactericidal action**. - Furthermore, **Clofazimine** is typically included in **multibacillary regimens** and is not part of the standard paucibacillary protocol.
Question 10: HACEK group of organisms includes all, except:
- A. Cardiobacterium hominis
- B. Eikenella corrodens
- C. Haemophilus parainfluenzae
- D. Haemophilus ducreyi (Correct Answer)
Explanation: ***Haemophilus ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection, and is not considered part of the HACEK group. - The **HACEK group** consists of fastidious, gram-negative bacteria known for causing **endocarditis**. *Haemophilus parainfluenzae* - *Haemophilus parainfluenzae* is one of the five genera included in the **HACEK group** acronym, specifically the 'H'. - This organism is a known cause of **infective endocarditis**, particularly in patients with pre-existing valvular disease. *Cardiobacterium hominis* - *Cardiobacterium hominis* is represented by the 'C' in the **HACEK group** acronym. - It is a significant cause of **culture-negative endocarditis** due to its fastidious nature and slow growth. *Eikenella corrodens* - *Eikenella corrodens* is the 'E' in the **HACEK group** acronym. - It is often associated with **oral cavity infections**, human bite wounds, and can cause **endocarditis** in susceptible individuals.
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