Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2261: All of the following statements about Botulism are true except:

A. Constipation is seen
B. Detection of toxin in the serum can aid in diagnosis
C. Honey ingestion causes infant botulism
D. Botulism is caused by endotoxin (Correct Answer)

Explanation: ***Botulism is caused by endotoxin*** - Botulism is caused by **exotoxins** produced by *Clostridium botulinum*, specifically neurotoxins, not endotoxins. - **Endotoxins** are lipopolysaccharides found in the cell walls of gram-negative bacteria, whereas botulinum toxin is a protein secreted by gram-positive *C. botulinum*. *Constipation is seen* - **Constipation** is a common symptom in both adult and infant botulism due to the neurotoxin's effect on the parasympathetic nervous system, leading to reduced gut motility. - The toxin inhibits acetylcholine release, affecting smooth muscle contraction in the GI tract. *Detection of toxin in the serum can aid in diagnosis* - The **diagnosis of botulism** can be confirmed by detecting the botulinum toxin in the patient's serum, stool, or gastric aspirate. - Identifying the toxin directly is crucial for diagnosis, especially in cases of suspected foodborne or wound botulism. *Honey ingestion causes infant botulism* - **Infant botulism** is commonly associated with the ingestion of honey, as it can contain *Clostridium botulinum* spores. - An infant's immature gut flora allows these spores to germinate and produce toxin in the intestine, leading to characteristic symptoms.

Question 2262: In cystic fibrosis, the most common organism which causes early infection is

A. Streptococcus
B. Staphylococcus (Correct Answer)
C. Klebsiella
D. Pseudomonas

Explanation: ***Staphylococcus*** - **Methicillin-sensitive Staphylococcus aureus (MSSA)** is the most common pathogen isolated in the lungs of young children with **cystic fibrosis** during early infection. - It can cause significant pulmonary morbidity in these patients, making its early detection and management crucial. *Streptococcus* - While *Streptococcus pneumoniae* can cause **respiratory infections**, it is not typically the most common organism associated with early colonization and infection in cystic fibrosis patients. - Early infections in CF are more often dominated by other bacterial species that thrive in the altered **mucus environment**. *Klebsiella* - **Klebsiella species** are Gram-negative bacteria that can cause **nosocomial infections** and are sometimes seen in CF, but they are not the primary cause of early-onset infections. - **Klebsiella** is more commonly associated with opportunistic infections in individuals with compromised immune systems or prolonged hospital stays rather than initial colonization in CF. *Pseudomonas* - **Pseudomonas aeruginosa** is a major pathogen in cystic fibrosis, but it typically establishes chronic infection **later in life** or after initial colonization by other bacteria. - While highly problematic due to its **biofilm formation** and resistance, it is generally preceded by *Staphylococcus aureus* in initial infections.

Question 2263: Phagosome-lysosome fusion in TB-infected macrophages is inhibited by -

A. Cord factor (Correct Answer)
B. Wax D
C. Muramyl dipeptide
D. Peritrichous flagella

Explanation: ***Cord factor*** - **Cord factor** (trehalose dimycolate) is a major **virulence factor** of *Mycobacterium tuberculosis* that inhibits the maturation of the phagosome and subsequent fusion with the lysosome within macrophages. - This prevents the phagocytosed bacteria from being exposed to the harsh acidic and enzymatic environment of the lysosome, allowing them to **survive and replicate intracellularly**. *Peritrichous flagella* - **Peritrichous flagella** refers to the arrangement of flagella distributed all around a bacterial cell surface, used for motility. - *Mycobacterium tuberculosis* is a **non-motile** organism that lacks flagella entirely, making this completely unrelated to its pathogenesis or phagosome-lysosome fusion inhibition. *Wax D* - **Wax D** is a component of the **mycobacterial cell wall**, specifically a mycolic acid-arabinogalactan-peptidoglycan complex, but it is not the primary factor responsible for inhibiting phagosome-lysosome fusion. - While it contributes to the overall immune-modulating properties of the mycobacterium, **cord factor** is more directly implicated in this specific mechanism. *Muramyl dipeptide* - **Muramyl dipeptide** is the minimal active structure of peptidoglycan that is capable of inducing an immune response by activating **NOD2 receptors**. - It acts as an **adjuvant** and immunostimulant, but it does not directly inhibit phagosome-lysosome fusion; rather, it triggers host immune pathways.

Question 2264: Ehrlichia chaffeensis is the causative agent of -

A. HME (Correct Answer)
B. Glandular fever
C. HGE
D. None of the options

Explanation: ***HME (Human Monocytic Ehrlichiosis)*** - **Ehrlichia chaffeensis** is the primary causative agent of **Human Monocytic Ehrlichiosis**, a tick-borne illness. - This bacterium primarily infects **monocytes** and macrophages, leading to characteristic intracellular inclusions called **morulae**. *Glandular fever* - Glandular fever, also known as **infectious mononucleosis**, is predominantly caused by the **Epstein-Barr virus (EBV)**. - It is characterized by fever, sore throat, lymphadenopathy, and fatigue, and is not caused by bacteria. *HGE (Human Granulocytic Ehrlichiosis)* - **Human Granulocytic Ehrlichiosis (HGE)** is caused by **Anaplasma phagocytophilum**, not *Ehrlichia chaffeensis*. - HGE primarily targets **neutrophils** (granulocytes), differentiating it from HME which targets monocytes. *None of the options* - This option is incorrect because *Ehrlichia chaffeensis* is indeed the causative agent of HME, as described above.

Question 2265: Which of the following microorganisms causes Buruli ulcer?

A. Mycobacterium marinum
B. Mycobacterium ulcerans (Correct Answer)
C. Mycobacterium fortuitum
D. Mycobacterium kansasii

Explanation: ***Mycobacterium ulcerans*** - **Buruli ulcer** is caused by the bacterium *Mycobacterium ulcerans*, which produces a toxin called **mycolactone** that causes tissue destruction. - This disease is characterized by chronic, necrotizing skin and soft tissue lesions, often leading to large skin ulcers. *Mycobacterium marinum* - This bacterium is primarily associated with **"swimming pool granuloma"** or **"fish tank granuloma"**, an infection contracted from contaminated water. - It typically causes skin lesions or nodules, but these are generally less severe and non-ulcerative compared to Buruli ulcer. *Mycobacterium fortuitum* - *Mycobacterium fortuitum* is a **rapidly growing mycobacterium** that commonly causes skin and soft tissue infections, often following trauma or surgical procedures. - It is not associated with the characteristic large, necrotizing ulcers of Buruli ulcer. *Mycobacterium kansasii* - *Mycobacterium kansasii* is a common cause of **non-tuberculous mycobacterial lung disease**, particularly in immunocompromised individuals. - While it can occasionally cause extrapulmonary infections, it rarely causes skin lesions and is not associated with Buruli ulcer.

Question 2266: CSF in meningococcal meningitis shows -

A. Gm '-ve' Diplococci in pus cells (Correct Answer)
B. Gm '+ve' bacilli
C. Gm '+ve' Diplococci, in pus cells
D. Gm '-ve' bacilli

Explanation: ***Gm '-ve' Diplococci in pus cells*** - Meningococcal meningitis is caused by *Neisseria meningitidis*, which are characteristic **Gram-negative diplococci**. - In active infection, these bacteria are typically found **intracellularly within polymorphonuclear leukocytes** (pus cells) in the cerebrospinal fluid. *Gm '+ve' bacilli* - This description would suggest a Gram-positive rod-shaped bacterium, such as *Listeria monocytogenes*, which is not the causative agent of meningococcal meningitis. - The morphology and Gram stain reaction are incorrect for *Neisseria meningitidis*. *Gm '+ve' Diplococci, in pus cells* - This describes organisms like *Streptococcus pneumoniae*, which are **Gram-positive diplococci** and a common cause of bacterial meningitis. - However, meningococcal meningitis is specifically caused by **Gram-negative** organisms. *Gm '-ve' bacilli* - This describes Gram-negative rod-shaped bacteria, such as *Haemophilus influenzae* or *Escherichia coli*. - While these can cause meningitis, *Neisseria meningitidis* is specifically a **diplococcus** (spherical in pairs), not a bacillus (rod-shaped).

Question 2267: Most common organism causing UTI:

A. E. coli (Correct Answer)
B. Klebsiella
C. Streptococci
D. Staphylococcus saprophyticus

Explanation: ***E. coli*** - **Uropathogenic *E. coli*** (UPEC) is responsible for 75-95% of all urinary tract infections (UTIs) due to its virulence factors like **fimbriae** that allow adherence to uroepithelial cells. - Its presence in the urethra colonizes the region and ascends to the bladder, making it the most common causative agent. *Klebsiella* - **Klebsiella pneumoniae** is a common cause of UTIs, especially in complicated cases or in patients with indwelling catheters, but it is not the most frequent overall. - It ranks significantly lower than *E. coli* in incidence. *Streptococci* - While certain **Streptococcus species** can cause UTIs, they are a less common cause compared to gram-negative rods like *E. coli*. - For example, **Enterococcus faecalis** (a Group D Streptococcus) can cause UTIs, especially in hospital-acquired infections, but *E. coli* is still more prevalent. *Staphylococci saprophyticus* - **Staphylococcus saprophyticus** is a common cause of UTIs in young, sexually active women but is not the most common organism overall across all demographics. - Its incidence is significant in specific populations but doesn't rival that of *E. coli* generally.

Question 2268: Which organism has not been successfully cultured so far?

A. Leptospira
B. Treponema pallidum (Correct Answer)
C. Staphylococcus
D. Bordetella

Explanation: ***Treponema pallidum*** - This organism, the causative agent of **syphilis**, is notoriously difficult to culture and cannot be routinely grown on artificial media in clinical or standard laboratory settings. - Its complex nutritional requirements and slow growth rate make standard laboratory culture methods ineffective; it is typically maintained in vivo in rabbit testicular tissue for research purposes. *Leptospira* - **Leptospira organisms** can be cultured in specialized media, such as Fletcher's or EMJH media, under aerobic conditions. - They require long incubation periods (weeks) and are identified by their characteristic corkscrew motility. *Staphylococcus* - **Staphylococcus species** are readily cultured on common laboratory media, such as blood agar, and are known for their rapid growth and characteristic colony morphology. - They are gram-positive cocci that grow in grape-like clusters. *Bordetella* - **Bordetella pertussis**, the cause of whooping cough, can be cultured on specific enriched media like Bordet-Gengou agar or charcoal blood agar. - It requires a humid environment and a relatively long incubation period (3-7 days).

Question 2269: Which of the following is true about tetanus acquired through traumatic wound?

A. The patient should be given tetanus toxoid intravenously
B. Causes positive Nagler reaction.
C. Clostridium tetani travels via the nerves to the anterior horn cells in spinal cord. (Correct Answer)
D. The tetanospasmin component of the exotoxin acts on the post-synaptic neurones and prevents impulse transmission.

Explanation: ***Clostridium tetani travels via the nerves to the anterior horn cells in spinal cord.*** - After entering the body through a wound, **Clostridium tetani** multiplies locally and produces **tetanospasmin**, which then travels via the **peripheral nerves** to the central nervous system. - The toxin specifically targets the **anterior horn cells** in the spinal cord, where it interferes with neurotransmitter release. *The tetanospasmin component of the exotoxin act on the post-synaptic neurones and prevents impulse transmission.* - **Tetanospasmin** acts predominantly on **pre-synaptic terminals**, preventing the release of inhibitory neurotransmitters like **GABA** and **glycine**. - Its action leads to **uncontrolled excitation** of motor neurons, causing muscle spasms, rather than preventing impulse transmission. *The patient should be given tetanus toxoid intravenously* - **Tetanus toxoid** is given **intramuscularly** as part of routine immunization or prophylaxis, not intravenously. - In a patient with active tetanus or high-risk wounds, **Tetanus Immune Globulin (TIG)**, which contains pre-formed antibodies, is given intravenously or intramuscularly to neutralize circulating toxin. *Causes positive Nagler reaction.* - The **Nagler reaction** is a test used to identify **Clostridium perfringens**, which produces alpha-toxin (lecithinase), and is not relevant for **Clostridium tetani**. - **Clostridium tetani** does not produce the alpha-toxin that causes a positive Nagler reaction; it produces **tetanospasmin**.

Question 2270: Q fever is caused by -

A. Pseudomonas
B. Rickettsia typhi
C. Coxiella burnetii (Correct Answer)
D. Francisella

Explanation: ***Coxiella burnetii*** - **Q fever** is an infectious disease caused by the gram-negative bacterium **Coxiella burnetii**. - This bacterium is highly resistant and can survive in the environment, primarily transmitted through **inhalation of contaminated aerosols from infected animals** (e.g., cattle, sheep, goats). *Pseudomonas* - **Pseudomonas aeruginosa** is a common opportunistic pathogen known for causing a wide range of infections, particularly in hospitalized or immunocompromised individuals. - It is often associated with **nosocomial infections**, such as pneumonia, urinary tract infections, and wound infections, and is not the causative agent of Q fever. *Rickettsia typhi* - **Rickettsia typhi** is the causative agent of **endemic (murine) typhus**, a common rickettsial disease. - It is transmitted to humans through the bite of **fleas** that have fed on infected rodents. *Francisella* - The genus **Francisella** includes **Francisella tularensis**, the bacterium responsible for **tularemia**, also known as "rabbit fever." - Tularemia is a zoonotic disease transmitted to humans through contact with infected animals, insect bites, or inhalation, but it is distinct from Q fever.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

Neisseria and Moraxella

Practice Questions

Corynebacterium and Listeria

Practice Questions

Bacillus and Clostridium

Practice Questions

Enterobacteriaceae

Practice Questions

Vibrio, Aeromonas, and Plesiomonas

Practice Questions

Pseudomonas and Related Bacteria

Practice Questions

Haemophilus and HACEK Group

Practice Questions

Bordetella and Brucella

Practice Questions

Mycobacteria

Practice Questions

Spirochetes

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free