Bacteriology Practice Questions

Q: Trench fever is caused by which of the following organisms?

Bartonella quintana. ***Bartonella quintana*** - **Trench fever**, also known as **Wolhynian fever** or quintan fever, is caused by *Bartonella quintana* (formerly *Rickettsia quintana*). - It is a **louse-borne illness** characterized by recurrent fevers, headache, and bone pain, especially in the shins. - The organism was reclassified from Rickettsia to Bartonella based on molecular and phylogenetic studies. *Borrelia recurrentis* - This bacterium is the causative agent of **epidemic relapsing fever**, also transmitted by body lice. - While it causes relapsing fevers, its clinical presentation and causative organism are distinct from trench fever. *Tunga penetrans* - This is a species of **flea** commonly known as the **jigger flea** or sand flea. - It causes a parasitic skin infection called **tungiasis**, characterized by intense itching and inflammation, and is not associated with trench fever. *Rickettsia prowazekii* - This bacterium is the etiologic agent of **epidemic typhus**, also a louse-borne disease. - While *Rickettsia prowazekii* causes a severe febrile illness, it presents differently from trench fever with symptoms like a characteristic rash and neurological complications.

Q: Patient having gastroenteritis after eating contaminated food. Microscopy showed gram-positive bacillus with subterminal spore. The bacteria is

Clostridium perfringens. ***Clostridium perfringens*** - This bacterium is a **Gram-positive, anaerobic bacillus** known for forming **subterminal spores**, matching the microscopy description. - It is a common cause of **food poisoning (gastroenteritis)** after consumption of contaminated meat or poultry. - The clinical presentation and microscopic findings are characteristic of *C. perfringens* infection. *Clostridium tetani* - While also a **Gram-positive bacillus**, *C. tetani* produces **terminal spores** (drumstick appearance), **not subterminal spores** as seen in this case. - It causes **tetanus**, not gastroenteritis, producing a neurotoxin that leads to muscle spasms and paralysis. *Corynebacterium* - Bacteria in this genus are **Gram-positive rods** but are **non-spore forming**, so they do not match the microscopy findings. - *Corynebacterium diphtheriae* causes diphtheria, an upper respiratory tract infection, not gastroenteritis. *Staphylococcus* - This is a genus of **Gram-positive cocci** (spherical bacteria), **not bacilli** (rods), and they do not form spores. - *Staphylococcus aureus* can cause food poisoning, but it would not appear as a Gram-positive bacillus with spores on microscopy.

Q: Osteomyelitis of spine is caused by the most common organism?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common causative organism for **hematogenous osteomyelitis** in adults, including osteomyelitis of the spine. - It frequently gains access to bone through the bloodstream, leading to infection of the vertebral bodies. *Streptococcus* - While various species of **_Streptococcus_** can cause bone infections, they are **less common** than **_Staphylococcus aureus_** in vertebral osteomyelitis. - **Group A Streptococcus** primarily causes soft tissue infections, and **_S. pneumoniae_** is more associated with pneumonia and meningitis. *Pseudomonas* - **_Pseudomonas aeruginosa_** is a common cause of osteomyelitis, particularly in specific risk groups such as intravenous drug users, patients with puncture wounds (especially through footwear), or those with implanted medical devices. - It is **not the most common** overall cause of general osteomyelitis of the spine. *Mycobacterium tuberculosis* - **_Mycobacterium tuberculosis_** causes tuberculous spondylitis **(Pott's disease)**, which commonly affects the spine, leading to characteristic vertebral destruction and kyphosis. - While significant globally, it is **not the most common bacterial cause** of acute pyogenic vertebral osteomyelitis.

Q: All of the following species of Borrelia are associated with tick-borne relapsing fever, except:

Borrelia recurrentis. ***Borrelia recurrentis*** - This species is primarily associated with **louse-borne relapsing fever**, not tick-borne. - *Borrelia recurrentis* is transmitted by the human body louse (*Pediculus humanus humanus*). - It causes **epidemic relapsing fever**, particularly in conditions of overcrowding and poor hygiene. *Borrelia hermsii* - This is a well-known species that causes **tick-borne relapsing fever** in North America, transmitted by *Ornithodoros* ticks. - It is associated with **endemic outbreaks** of relapsing fever in specific geographic regions. *Borrelia turicatae* - This species is also a cause of **tick-borne relapsing fever** in North America, endemic to the southern United States. - It is transmitted by the soft tick *Ornithodoros turicata*. *Borrelia duttoni* - This species is a primary cause of **tick-borne relapsing fever** in Africa, primarily transmitted by *Ornithodoros moubata*. - It leads to cycles of fever and remission characteristic of relapsing fever.

Q: True about typhoid is -

Vi polysaccharide of bacterial cell used for vaccination. ***Vi polysaccharide of bacterial cell used for vaccination*** - The **Vi antigen** (capsular polysaccharide) from *Salmonella typhi* is used in **subunit vaccines** to induce protective immunity against typhoid fever. - This vaccine is effective and is recommended for travelers to endemic areas and high-risk individuals. *Chronic carrier is 10-15%* - The percentage of individuals who become **chronic carriers** after acute typhoid fever is much lower, typically around **1-5%**. - Chronic carriage is defined as shedding *Salmonella typhi* in stool or urine for more than one year. *Widal test is specific* - The **Widal test** detects antibodies against O and H antigens of *Salmonella typhi*, but it is **not specific** due to cross-reactions with other infections and prior vaccination. - Its utility is limited by low sensitivity and specificity, especially in endemic areas, making culture or PCR more reliable. *Incubation period 3-6 weeks* - The typical **incubation period** for typhoid fever is much shorter, usually ranging from **6 to 30 days**, with an average of 1-3 weeks. - A 3-6 week incubation period would be uncharacteristically long for typhoid fever.

Q: Most common organism causing SBP after E. coli is

Streptococcus. ***Streptococcus*** - After **E. coli**, **Streptococcus species** are the most common pathogens isolated in cases of **spontaneous bacterial peritonitis (SBP)**. - This includes various Streptococcal strains, which can translocate from the gut lumen into the ascetic fluid. *Bacteroids* - **Bacteroides fragilis** and other Bacteroids species are obligate anaerobes and are more commonly associated with **secondary peritonitis** due to bowel perforation, rather than SBP. - While they are abundant in the gut, their recovery in SBP is rare, suggesting a different pathogenic mechanism. *Enterococcus* - **Enterococci** are found in the gut flora and can cause SBP, but they are less common than Streptococcus species as the second leading cause. - Infections with Enterococcus are often seen in patients with **nosocomial infections** or those with prior antibiotic exposure. *Klebsiella* - **Klebsiella pneumoniae** is a common Gram-negative bacterium that can cause SBP, but it is typically the third most common Gram-negative cause after E. coli. - While significant, it does not surpass Streptococcus as the second most common overall cause of SBP following E. coli.

Q: A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?

Staphylococcus aureus. ***Staphylococcus aureus*** - *S. aureus* is the most common cause of **osteomyelitis** in children, accounting for the symptoms of bone pain, limp, fever, and periosteal erosion. - The organism frequently gains access to bone via **hematogenous spread** from a superficial infection or direct inoculation through trauma. *Salmonella enteritidis* - While *Salmonella* can cause osteomyelitis, especially in patients with **sickle cell disease**, there is no indication of this predisposing factor in the girl's history. - *Salmonella* osteomyelitis is less common than that caused by *S. aureus* in the general pediatric population. *Staphylococcus saprophyticus* - *S. saprophyticus* is primarily associated with **urinary tract infections (UTIs)**, particularly in young, sexually active females. - It is an uncommon cause of osteomyelitis and typically not the primary pathogen in bone infections. *Listeria monocytogenes* - *Listeria monocytogenes* is known to cause severe infections in **immunocompromised individuals**, neonates, and pregnant women. - While it can cause osteomyelitis, it is a rare cause in an otherwise healthy 12-year-old and would usually be associated with specific risk factors.

Q: Griffith classification is based on

M, T, R antigens. ***M, T, R antigens*** - **Griffith classification** (also known as Griffith serotyping) is based on the surface protein antigens: **M, T, and R antigens**. - This system is used for **typing within Group A Streptococcus** (*Streptococcus pyogenes*) to further subdivide strains. - **M protein** is the most important virulence factor and provides the basis for typing into over 100 different M types. - **T and R antigens** are additional surface proteins used for supplementary typing when M typing is not definitive. *'C'-carbohydrate* - The **C-carbohydrate** (also called C-substance) is the basis for **Lancefield grouping**, not Griffith classification. - Lancefield grouping divides streptococci into serogroups (A, B, C, etc.) based on cell wall polysaccharide antigens. - This is a **different classification system** from Griffith typing - broader and more general. *Type of hemolysis* - **Hemolysis pattern** (alpha, beta, gamma) is a phenotypic characteristic observed on blood agar. - While useful for preliminary identification, it is not the basis for Griffith classification. - *Streptococcus pyogenes* shows beta-hemolysis but this doesn't subdivide strains further. *O requirement* - **Oxygen requirement** refers to metabolic characteristics (aerobic, anaerobic, facultative). - This is unrelated to any serological classification system including Griffith typing. - *Streptococcus pyogenes* is a facultative anaerobe.

Q: NOT a cause of bacterial community acquired pneumonia:

Blastomyces. ***Blastomyces*** - *Blastomyces*, a **dimorphic fungus**, causes **blastomycosis**, which is a **fungal infection**, not a bacterial infection. - While it can cause community-acquired pneumonia with pulmonary symptoms, it is **NOT a bacterial pathogen** and therefore not a cause of **bacterial community-acquired pneumonia**. - The question asks specifically about bacterial causes, making this the correct answer. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** is the **most common bacterial cause** of **community-acquired pneumonia (CAP)**. - Infection typically presents with **acute onset** of fever, chills, productive cough, and lobar consolidation on chest X-ray. *Mycoplasma pneumoniae* - **_Mycoplasma pneumoniae_** is a common cause of **atypical bacterial community-acquired pneumonia**, often referred to as "**walking pneumonia**". - It typically causes milder symptoms, including a **persistent dry cough** and malaise, and is prevalent in younger adults and children. *Moraxella catarrhalis* - **_Moraxella catarrhalis_** is a **bacterial pathogen** that causes **community-acquired pneumonia**, especially in patients with **chronic obstructive pulmonary disease (COPD)**. - It can also cause **bronchitis**, otitis media, and sinusitis.

Q: All are important causes of UTI except-

Streptococcus viridans. ***Streptococcus viridans*** - *Streptococcus viridans* is a common inhabitant of the **oral flora** and is a frequent cause of **bacterial endocarditis**, especially in individuals with damaged heart valves. - It is **rarely associated with urinary tract infections** because it lacks specific virulence factors to colonize the urinary tract effectively. *Proteus* - *Proteus* species, particularly *Proteus mirabilis*, are well-known causes of UTIs, often associated with **struvite stones** due to their production of **urease**, an enzyme that increases urine pH. - Their motility, mediated by **flagella**, also aids in ascending the urinary tract. *Klebsiella* - *Klebsiella pneumoniae* is a significant Gram-negative bacterium that commonly causes UTIs, particularly in **hospital-acquired infections** and in patients with catheters or underlying medical conditions. - It is known for its **capsule**, which provides resistance against phagocytosis, contributing to its pathogenicity. *E. coli* - **Uropathogenic *E. coli*** (UPEC) is the **most common cause of UTIs**, accounting for 80-90% of community-acquired cases. - Its virulence factors, such as **P fimbriae (pili)**, enable it to adhere to uroepithelial cells and colonize the bladder and kidneys effectively.

Question 1

Trench fever is caused by which of the following organisms?

Accepted Answer

Bartonella quintana

Answer

Borrelia recurrentis

Answer

Tunga penetrans

Answer

Rickettsia prowazekii

Question 2

Patient having gastroenteritis after eating contaminated food. Microscopy showed gram-positive bacillus with subterminal spore. The bacteria is

Accepted Answer

Clostridium perfringens

Answer

Clostridium tetani

Answer

Corynebacterium

Answer

Staphylococcus

Question 3

Osteomyelitis of spine is caused by the most common organism?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus

Answer

Pseudomonas

Answer

Mycobacterium tuberculosis

Question 4

All of the following species of Borrelia are associated with tick-borne relapsing fever, except:

Accepted Answer

Borrelia recurrentis

Answer

Borrelia hermsii

Answer

Borrelia turicatae

Answer

Borrelia duttoni

Question 5

True about typhoid is -

Accepted Answer

Vi polysaccharide of bacterial cell used for vaccination

Answer

Chronic carrier is 10-15%

Answer

Widal test is specific

Answer

Incubation period 3-6 weeks

Question 6

Most common organism causing SBP after E. coli is

Accepted Answer

Streptococcus

Answer

Bacteroids

Answer

Enterococcus

Answer

Klebsiella

Question 7

A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?

Accepted Answer

Staphylococcus aureus

Answer

Salmonella enteritidis

Answer

Staphylococcus saprophyticus

Answer

Listeria monocytogenes

Question 8

Griffith classification is based on

Accepted Answer

M, T, R antigens

Answer

Type of hemolysis

Answer

O requirement

Answer

'C'-carbohydrate

Question 9

NOT a cause of bacterial community acquired pneumonia:

Accepted Answer

Blastomyces

Answer

Streptococcus pneumoniae

Answer

Mycoplasma pneumoniae

Answer

Moraxella catarrhalis

Question 10

All are important causes of UTI except-

Accepted Answer

Streptococcus viridans

Answer

Proteus

Answer

Klebsiella

Answer

E coli

Bacteriology — MCQs

Bacteriology — MCQs

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