Bacteriology Practice Questions

Q: All of the following statements about Botulism are true except:

Botulism is caused by endotoxin. ***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.

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

Staphylococcus. ***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.

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

Cord factor. ***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.

Q: Which of the following microorganisms causes Buruli ulcer?

Mycobacterium ulcerans. ***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.

Q: CSF in meningococcal meningitis shows -

Gm '-ve' Diplococci in pus cells. ***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).

Q: Most common organism causing UTI:

E. coli. ***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.

Q: In generalized tetanus, how do toxins typically enter the body?

Both. ***Both*** - Tetanus toxins, specifically **tetanospasmin**, can enter the systemic circulation via both the **bloodstream** and the **lymphatic system** from the site of the anaerobic wound [1]. - Once in the general circulation, these toxins are then able to reach the **central nervous system**, where they exert their neurotoxic effects. *Lymphatics* - While toxins *can* enter via the lymphatic system, it's not the sole route; the **bloodstream** also plays a significant role [1]. - The lymphatic system primarily drains interstitial fluid and transports immune cells, but toxins can also be absorbed this way. *Blood stream* - Toxins *can* enter via the bloodstream, but this is not the only route; the **lymphatic system** also contributes to systemic spread [1]. - Direct absorption into capillaries at the wound site allows toxins to quickly enter the general circulation. *None of the options* - This is incorrect as tetanus toxins are known to spread systemically via **both the lymphatic and circulatory systems** [1]. - Systemic absorption is crucial for the toxins to reach the spinal cord and brain, leading to generalized symptoms.

Q: A 1 week old female infant with symptoms of vomiting and anorexia has a temperature of 102°F. A bulging fontanel is noted on physical examination. The most likely agent is?

Streptococcus agalactiae. ***Streptococcus agalactiae*** - This organism, also known as **Group B Streptococcus (GBS)**, is the **most common cause of bacterial meningitis** and sepsis in neonates (0-3 months). - The symptoms (fever, vomiting, anorexia, bulging fontanel) are classic signs of **meningitis** in a 1-week-old infant. *Haemophilus influenzae type b* - While a significant cause of meningitis, **Hib meningitis** is rare in infants under 2 months due to the presence of maternal antibodies and the later onset of vaccination. - Its incidence has also drastically decreased due to routine **Hib vaccination**. *Listeria monocytogenes* - **Listeria monocytogenes** can cause meningitis in neonates and is often acquired transplacentally or during birth. - While a possibility, it is generally **less common than GBS** as a cause of early-onset neonatal sepsis and meningitis. *Neisseria meningitidis* - **Meningococcal meningitis** is rare in infants under 3 months, with incidence increasing in older infants and young children. - This organism is more commonly associated with outbreaks and rapid progression in older populations.

Q: Which organism has not been successfully cultured so far?

Treponema pallidum. ***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 1

All of the following statements about Botulism are true except:

Accepted Answer

Botulism is caused by endotoxin

Answer

Constipation is seen

Answer

Detection of toxin in the serum can aid in diagnosis

Answer

Honey ingestion causes infant botulism

Question 2

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

Accepted Answer

Staphylococcus

Answer

Streptococcus

Answer

Klebsiella

Answer

Pseudomonas

Question 3

Phagosome-lysosome fusion in TB-infected macrophages is inhibited by -

Accepted Answer

Cord factor

Answer

Wax D

Answer

Muramyl dipeptide

Answer

Peritrichous flagella

Question 4

Which of the following microorganisms causes Buruli ulcer?

Accepted Answer

Mycobacterium ulcerans

Answer

Mycobacterium marinum

Answer

Mycobacterium fortuitum

Answer

Mycobacterium kansasii

Question 5

CSF in meningococcal meningitis shows -

Accepted Answer

Gm '-ve' Diplococci in pus cells

Answer

Gm '+ve' bacilli

Answer

Gm '+ve' Diplococci, in pus cells

Answer

Gm '-ve' bacilli

Question 6

Most common organism causing UTI:

Accepted Answer

E. coli

Answer

Klebsiella

Answer

Streptococci

Answer

Staphylococcus saprophyticus

Question 7

In generalized tetanus, how do toxins typically enter the body?

Accepted Answer

Both

Answer

Lymphatics

Answer

Blood stream

Answer

None of the options

Question 8

A 1 week old female infant with symptoms of vomiting and anorexia has a temperature of 102°F. A bulging fontanel is noted on physical examination. The most likely agent is?

Accepted Answer

Streptococcus agalactiae

Answer

Haemophilus influenzae type b

Answer

Listeria monocytogenes

Answer

Neisseria meningitidis

Question 9

Which organism has not been successfully cultured so far?

Accepted Answer

Treponema pallidum

Answer

Leptospira

Answer

Staphylococcus

Answer

Bordetella

Question 10

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

Accepted Answer

Clostridium tetani travels via the nerves to the anterior horn cells in spinal cord.

Answer

The patient should be given tetanus toxoid intravenously

Answer

Causes positive Nagler reaction.

Answer

The tetanospasmin component of the exotoxin acts on the post-synaptic neurones and prevents impulse transmission.

Bacteriology — MCQs

Bacteriology — MCQs

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