Microbiology
10 questionsA 4 year old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility. What is the etiological agent?
What does the hookworm primarily feed on?
Infective form of Hookworms?
Cutaneous larva migrans is due to ?
What type of spore is produced by Ascomycota during sexual reproduction?
The fungus with septate hyphae and dichotomous branching is?
In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?
Which of the following statements about Penicillium marneffei is incorrect?
Color of granules in mycetoma caused by Actinomadura pelletierrii -
Which of the following conditions is NOT caused by Aspergillus?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 681: A 4 year old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility. What is the etiological agent?
- A. Giardia lamblia (Correct Answer)
- B. Trichomonas tenax
- C. Balantidium coli
- D. Entamoeba histolytica
Explanation: **Giardia lamblia** - The presence of **trophozoites** with characteristic **falling leaf motility** in stool microscopy is pathognomonic for **Giardia lamblia** infection. - **Giardiasis** commonly causes **acute watery diarrhea** and **abdominal cramps** in children, often acquired through contaminated water or food. *Entamoeba histolytica* - **Entamoeba histolytica** causes **amoebic dysentery**, characterized by bloody diarrhea, unlike the watery diarrhea described. - Its trophozoites exhibit **directional motility** with pseudopods and may contain ingested red blood cells, not falling leaf motility. *Trichomonas tenax* - **Trichomonas tenax** is found in the **oral cavity** and is not associated with intestinal infections or diarrhea. - Its typical habitat and clinical presentation are entirely different from the symptoms described. *Balantidium coli* - **Balantidium coli** is a large, ciliated protozoan whose trophozoites have a **distinctive kidney-shaped macronucleus** and rotary motility with cilia. - It causes **balantidiasis**, which can range from asymptomatic to dysentery, but its trophozoite morphology and motility are distinct from falling leaf.
Question 682: What does the hookworm primarily feed on?
- A. Plasma proteins
- B. Lymphatic fluid
- C. Interstitial fluid
- D. Blood from intestinal mucosa (Correct Answer)
Explanation: ***Blood from intestinal mucosa*** - Hookworms attach to the **intestinal wall** and ingest host blood, leading to blood loss and potential **anemia**. - They produce **anticoagulants** to facilitate continuous feeding from the mucosal capillaries. *Plasma proteins* - While plasma contains proteins, hookworms primarily feed directly on **whole blood**, not just isolated plasma proteins. - Feeding mainly on plasma proteins would not explain the significant **iron-deficiency anemia** associated with hookworm infection. *Lymphatic fluid* - Hookworms reside in the **small intestine** and do not typically feed on lymphatic fluid. - Other parasites, like **filarial worms**, are known to inhabit and obstruct the lymphatic system. *Interstitial fluid* - Interstitial fluid is found in the spaces between cells; hookworms feed from the **vascular supply** within the intestinal mucosa. - Feeding on interstitial fluid would not cause the characteristic **blood loss** seen in hookworm infections.
Question 683: Infective form of Hookworms?
- A. Egg
- B. Rhabditiform larva
- C. Filariform larva (Correct Answer)
- D. Adult worm
Explanation: ***Filariform larva*** - The **filariform larva (L3)** is the infective stage of hookworms, capable of penetrating intact skin. - Upon penetration, these larvae migrate through the bloodstream to the lungs, then up the bronchial tree to be swallowed, eventually maturing in the intestines. *Egg* - Hookworm **eggs** are passed in the feces of infected individuals and are not infective to humans directly. - They require favorable conditions (warm, moist soil) to embryonate and hatch into rhabditiform larvae. *Rhabditiform larva* - The **rhabditiform larva (L1)** is the first larval stage that hatches from the egg in the soil. - It is a non-infective, free-living stage that feeds on bacteria and molts twice to become the infective filariform larva. *Adult worm* - **Adult worms** reside in the small intestine of the host and are not the infective form. - They attach to the intestinal mucosa and feed on blood, causing the characteristic anemia associated with hookworm infection.
Question 684: Cutaneous larva migrans is due to ?
- A. W.bancrofti
- B. B. Malayi
- C. D. medinensis
- D. Ancylostoma braziliense (Correct Answer)
Explanation: ***Ancylostoma braziliense*** - **Cutaneous larva migrans** is primarily caused by the larvae of **dog and cat hookworms**, especially *Ancylostoma braziliense*. - Humans become **accidental hosts** when these larvae penetrate the skin but cannot complete their life cycle, leading to **serpiginous tracks**. *W. bancrofti* - This parasite, **Wuchereria bancrofti**, is a filarial nematode that causes **lymphatic filariasis** (elephantiasis). - Its effects are characterized by **lymphedema** and **hydrocele**, not migrating skin lesions. *B. Malayi* - **Brugia malayi** is another filarial nematode responsible for **lymphatic filariasis** in humans, similar to *W. bancrofti*. - It primarily causes **swelling of the limbs** and scrotum, not cutaneous larva migrans. *D. medinensis* - **Dracunculus medinensis** is the parasite that causes **dracunculiasis**, also known as **Guinea worm disease**. - This infection is characterized by a **painful blister** and subsequent emergence of the adult worm, which is distinct from creeping eruptions.
Question 685: What type of spore is produced by Ascomycota during sexual reproduction?
- A. Asexual spores
- B. Ascospores (Correct Answer)
- C. Conidia
- D. None of the options
Explanation: ***Ascospores*** - **Ascospores** are the sexual spores produced by fungi belonging to the phylum **Ascomycota** during their sexual reproductive cycle. - These spores are formed inside a sac-like structure called an **ascus** after **karyogamy (nuclear fusion)** and **meiosis**. - Each ascus typically contains **4-8 ascospores** arranged in a characteristic pattern. - Examples of Ascomycota include *Aspergillus*, *Penicillium*, *Candida*, and yeasts like *Saccharomyces*. *Asexual spores* - **Asexual spores** are produced during **asexual reproduction** without the fusion of gametes or meiosis. - Examples include **conidia** and **sporangiospores**, which allow for rapid proliferation and dispersal. *Conidia* - **Conidia** are a specific type of **asexual spore**, not sexual spores. - They are formed exogenously on specialized structures called **conidiophores**. - While Ascomycota can produce conidia asexually, the question asks specifically about sexual reproduction. *None of the options* - This option is incorrect because **ascospores** are indeed the sexual spores of Ascomycota.
Question 686: The fungus with septate hyphae and dichotomous branching is?
- A. Aspergillus (Correct Answer)
- B. Penicillium
- C. Mucor
- D. Rhizopus
Explanation: ***Aspergillus*** - *Aspergillus* species are characterized by their **septate hyphae** and **acute-angle branching** (branching at approximately 45-degree angles), which are key distinguishing features in histopathology. - This branching pattern is sometimes referred to as "dichotomous branching" in medical literature, though true dichotomous branching is more characteristic of certain tissue forms. - This fungal morphology is often seen in infections such as **invasive aspergillosis** in immunocompromised patients. *Penicillium* - *Penicillium* also has **septate hyphae**, but its branching pattern is typically *not acute-angled or dichotomous*. - It is more commonly known for its **brush-like** conidiophores (penicillus) in culture rather than distinctive tissue branching patterns. *Mucor* - *Mucor* is a type of **zygomycete** (now classified under Mucorales) and is characterized by **aseptate or sparsely septate hyphae** with **irregular, right-angle branching**. - This is a key histological feature distinguishing it from *Aspergillus* in cases of **mucormycosis**. *Rhizopus* - Similar to *Mucor*, *Rhizopus* is also a zygomycete with **aseptate or sparsely septate hyphae** and **irregular, wide-angle branching**. - It is often identified in culture by the presence of **rhizoids** (root-like structures) and sporangiophores.
Question 687: In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?
- A. Aspergillus (Correct Answer)
- B. Mucor
- C. Penicillium
- D. Candida
Explanation: ***Aspergillus*** - *Aspergillus* species are characterized by their distinctive **acute-angled (dichotomous) septate hyphae** when observed microscopically in tissue sections or clinical samples. - This morphological feature is crucial for differentiating *Aspergillus* infections, such as **aspergillosis**, from other fungal infections. *Mucor* - *Mucor* (along with *Rhizopus* and *Lichtheimia*) belongs to the Zygomycetes class, which are characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching, not acute-angled septate hyphae. - These fungi are associated with **mucormycosis**, often seen in immunocompromised patients, particularly those with diabetes. *Penicillium* - *Penicillium* is a common mold known for producing penicillin and typically appears as **septate hyphae** but is more often recognized by its branching, brush-like conidiophores (penicilli) in culture rather than a distinct acute-angled septate hyphal morphology in clinical samples causing invasive disease. - While it can cause opportunistic infections, its hyphae are less commonly described as having uniquely acute angles compared to *Aspergillus*. *Candida* - *Candida* species are typically observed as **yeast cells (oval budding forms)**, often forming **pseudohyphae** (elongated yeast cells that remain attached) or true hyphae under specific conditions, but not as acute-angled septate hyphae. - *Candida* is a common cause of superficial and invasive candidiasis, and its microscopic appearance is distinct from filamentous fungi.
Question 688: Which of the following statements about Penicillium marneffei is incorrect?
- A. Forms black colonies (Correct Answer)
- B. Is a dimorphic fungus
- C. Amphotericin B is used for treatment
- D. Causes severe infections in immunocompromised patients
Explanation: ***Forms black colonies*** - *Penicillium marneffei* typically forms colonies that are often **reddish-beige** or **pigmented red-diffusible**, not black. - The production of a characteristic **red-to-burgundy pigment** is a key identifying feature of this fungus, especially in culture. *Is a dimorphic fungus* - This statement is correct. *Penicillium marneffei* is a **thermally dimorphic fungus**, meaning it grows as a mould at 25°C (room temperature) and as yeast-like cells at 37°C (body temperature). - This dimorphism is crucial for its pathogenesis and identification. *Amphotericin B is used for treatment* - This statement is correct. **Amphotericin B** is a commonly used antifungal agent for the treatment of severe *Penicillium marneffei* infections, particularly in immunocompromised patients. - It is often followed by a maintenance regimen with an azole antifungal like itraconazole. *Causes severe infections in immunocompromised patients* - This statement is correct. *Penicillium marneffei* is an **opportunistic pathogen** that primarily causes severe, disseminated infections in individuals with compromised immune systems, especially those with HIV/AIDS. - Endemic regions include Southeast Asia, where it is a leading cause of systemic mycosis in HIV-positive patients.
Question 689: Color of granules in mycetoma caused by Actinomadura pelletierrii -
- A. Black
- B. Yellow
- C. Red (Correct Answer)
- D. Brown
Explanation: ***Red*** - *Actinomadura pelletierrii* is a common cause of **actinomycetoma** and is characterized by producing **red granules** in the lesions. - The color of these granules is a key diagnostic feature, helping differentiate it from other causes of mycetoma. *Black* - **Black granules** are typically associated with **eumycetoma** caused by **dematiaceous fungi** such as *Madurella mycetomatis*. - This color indicates the presence of **melanin**, a pigment produced by these fungal species. *Yellow* - **Yellow granules** are commonly seen in actinomycetoma caused by organisms such as *Nocardia brasiliensis* or sometimes *Actinomadura madurae*. - This color helps differentiate these specific actinomycetes from other types that produce different granule colors. *Brown* - While varying shades of color can occur, **brown granules** are not the characteristic color produced by *Actinomadura pelletierrii*. - Some *Streptomyces* species or certain eumycetoma agents can occasionally produce brownish granules, but red is specific for *A. pelletierrii*.
Question 690: Which of the following conditions is NOT caused by Aspergillus?
- A. Otomycosis
- B. Dermatophytosis (Correct Answer)
- C. Allergic sinusitis
- D. Bronchopulmonary allergy
Explanation: ***Dermatophytosis*** - This condition is caused by **dermatophytes** (e.g., *Trichophyton*, *Microsporum*, *Epidermophyton*), which are a specific group of fungi that metabolize keratin. - *Aspergillus* species are generally **opportunistic molds** but do not typically cause dermatophytosis, which is a superficial fungal infection of the skin, hair, or nails. *Otomycosis* - **Otomycosis** is a fungal infection of the external ear canal, and *Aspergillus* species are a common cause, particularly *Aspergillus niger*. - It can lead to ear pain, discharge, itching, and hearing impairment. *Allergic sinusitis* - **Allergic fungal sinusitis (AFS)** is a common form of fungal sinusitis where *Aspergillus* species are significant contributors, often leading to a thick, tenacious allergic mucin. - This condition is an IgE-mediated hypersensitivity reaction to the fungal elements in the nasal and sinus cavities. *Bronchopulmonary allergy* - **Allergic bronchopulmonary aspergillosis (ABPA)** is a hypersensitivity reaction to *Aspergillus fumigatus* antigens that colonize the airways, particularly in individuals with asthma or cystic fibrosis. - It results in recurrent episodes of wheezing, cough, and transient pulmonary infiltrates, and can lead to bronchiectasis if left untreated.