Bacteriology Practice Questions

Q: The gram stain given below shows which organism most likely? (AIIMS May 2016)

Neisseria meningitidis. ***Neisseria meningitidis*** - The image shows **Gram-negative diplococci** (pink/red, paired cocci) both extracellularly and **intracellularly within neutrophils** (large pink cells). This morphology is classic for *Neisseria meningitidis* in cerebrospinal fluid. - *N. meningitidis* is a common cause of **bacterial meningitis**, and its presence as intracellular Gram-negative diplococci in CSF is diagnostic. *Staphylococcus aureus* - *Staphylococcus aureus* are **Gram-positive cocci** (purple/blue), typically appearing in **clusters** like grapes. The organisms in the image are Gram-negative and often in pairs. - While *S. aureus* can cause meningitis, its characteristic Gram stain appearance is distinctly different from what is shown. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* are **Gram-positive cocci** (purple/blue) typically arranged in **pairs (diplococci)** or short chains. The organisms in the image are Gram-negative. - Although *S. pneumoniae* is a common cause of bacterial meningitis, its Gram stain morphology is different (Gram-positive). *Streptococcus pyogenes* - *Streptococcus pyogenes* are **Gram-positive cocci** (purple/blue) arranged in **chains**. The organisms in the image are Gram-negative and appear as diplococci. - *S. pyogenes* is more commonly associated with pharyngitis and skin infections, and rarely causes meningitis, but its Gram stain morphology is not consistent with the image.

Q: A 24-year-old female presented with an ulcer in the genital area. A giemsa stained cervical smear was prepared. Identify the causative agent: (AIIMS Nov 2015)

Haemophilus ducreyi. ***Hemophilus ducreyi*** - The image shows numerous small, pleomorphic, gram-negative coccobacilli arranged in **'school of fish'** or parallel chains, characteristic of **_Haemophilus ducreyi_** on a Giemsa-stained smear. - This morphology, especially from a genital ulcer, is highly indicative of **chancroid**, caused by _H. ducreyi_. *Gardnerella vaginalis* - _Gardnerella vaginalis_ is associated with **bacterial vaginosis** and is characterized by the presence of **"clue cells"** (vaginal epithelial cells covered with coccobacilli) on microscopy. - It does not form the "school of fish" arrangement seen in the image, nor does it typically cause ulcerative lesions. *Chlamydia* - **_Chlamydia trachomatis_** causes various infections, including genital ulcers in cases of **lymphogranuloma venereum (LGV)**, but it is an obligate intracellular bacterium. - It would appear as **intracellular inclusions** on a Giemsa stain and would not show extracellular coccobacillary forms arranged in clusters as depicted. *Calymmatobacterium granulomatosis* - Previously known as _Calymmatobacterium granulomatosis_, now designated as **_Klebsiella granulomatis_**, this bacterium causes **granuloma inguinale (donovanosis)**, characterized by large, beefy-red ulcers. - Diagnostic features on Giemsa stain include **Donovan bodies** (intracellular bacilli within macrophages), which are not a prominent feature in the provided image.

Q: A 23-year-old female presents with fever and altered sensorium for two days with rashes on legs as shown. Her BP is 70/50 mm Hg and neck stiffness is present. Lumbar puncture reveals cloudy CSF with 4200 cells/ $\mu \mathrm{L}$, protein level 198 and glucose $21 \mathrm{mg} /$ dL. Which of the following correctly describes the organism causing this condition?

Gram negative diplococci (kidney shaped), oxidase positive. ***Gram negative diplococci (kidney shaped), oxidase positive*** - The clinical presentation of **fever**, **altered sensorium**, **neck stiffness**, **petechial rash** (shown on legs), **hypotension**, and characteristic CSF findings (cloudy, high protein, low glucose, high cell count) is highly suggestive of **meningococcal meningitis**. - **Neisseria meningitidis**, the causative agent, is a **Gram-negative diplococcus** with a characteristic **kidney-bean shape** and is **oxidase-positive**. *Gram positive cocci catalase negative, bacitracin sensitive* - This description refers to **Streptococcus pyogenes** (Group A Streptococcus), which causes pharyngitis, skin infections, and rarely meningitis. - S. pyogenes meningitis is **uncommon** and does not typically present with the widespread **petechial rash** characteristic of meningococcemia. *Gram positive diplococci (lanceolate), catalase negative, optochin sensitive* - This describes **Streptococcus pneumoniae**, which is a common cause of **bacterial meningitis**, especially in adults and children. - While S. pneumoniae can cause similar CSF findings, it does not typically present with the prominent **petechial rash** and **meningococcemia** seen in this case. *Gram negative diplococci, ferments glucose only (not maltose)* - This describes **Neisseria gonorrhoeae**, which ferments **glucose** but **not maltose**, unlike N. meningitidis which ferments both. - N. gonorrhoeae typically causes **sexually transmitted infections** (urethritis, cervicitis) and rarely causes meningitis, making it unsuitable for this clinical scenario.

Q: All are correct about the condition shown in the image except:

Aspirated material shows LCL bodies. ***Correct: Aspirated material shows LCL bodies*** - **"LCL bodies" is NOT a recognized diagnostic term** for lymphogranuloma venereum (LGV) - The aspirated material from buboes in LGV shows **Chlamydia trachomatis elementary bodies and reticulate bodies**, along with inflammatory cells - This is the EXCEPTION as it is an incorrect statement about LGV *Incorrect: Groove sign of LGV* - The **groove sign is a classic clinical feature** of LGV - Formed by enlarged inguinal lymph nodes above and below the inguinal (Poupart's) ligament, creating a characteristic depression - This is a TRUE statement about LGV *Incorrect: Most common cause of this infection is L2 biovar* - LGV is caused by **Chlamydia trachomatis serovars L1, L2, and L3** - **L2 serovar is the most prevalent cause** of LGV infections worldwide - This is a TRUE statement about LGV *Incorrect: Females develop esthiomene* - **Esthiomene is a late complication** of chronic untreated LGV in females - Characterized by progressive genital elephantiasis, ulceration, and destruction of vulvo-perineal tissues - Results from persistent lymphatic obstruction and chronic inflammation - This is a TRUE statement about LGV

Q: All are correct about the organism shown in the image except: (Recent NEET Pattern 2016-17)

Pneumonic plague is the predominant presentation. **Pneumonic plague is the predominant presentation** - **Bubonic plague** is the most common form of plague, accounting for approximately 80-90% of cases. - While pneumonic plague is highly dangerous and can be transmitted person-to-person, it is **not the predominant clinical form** globally. *Safety pin appearance* - The image shows bipolar staining, which gives *Yersinia pestis* its characteristic **"safety pin" appearance** under microscopy. - This is a classic diagnostic feature when stained with **Giemsa or Wayson stain**. *Direct immunofluorescence for F1 antigen in sputum* - **F1 antigen** is a major virulence factor of *Yersinia pestis* and is produced in large quantities by the bacterium. - **Direct immunofluorescence (DIF)** for detecting F1 antigen in patient samples like sputum is a rapid and specific diagnostic method for plague, especially pneumonic plague. *Doxycycline is used for prophylaxis in house-hold contacts of pneumonic plague* - Due to the high transmissibility and severity of pneumonic plague, **post-exposure prophylaxis (PEP)** is crucial for close contacts. - **Doxycycline** is a recommended antibiotic for PEP alongside other options like ciprofloxacin or levofloxacin.

Q: The following organism shown leads to development of:

Syphilis. ***Syphilis*** - The image displays **spirochetes**, which are characteristic of *Treponema pallidum*, the causative agent of **syphilis**. - **Syphilis** is a sexually transmitted infection that progresses through primary, secondary, latent, and tertiary stages. *Leptospirosis* - Caused by **Leptospira** species, which are also spirochetes but typically have hooked ends and are associated with exposure to contaminated water or animal urine. - Symptoms include fever, headaches, muscle aches, and occasionally severe conditions like Weil's disease (jaundice, renal failure, hemorrhage). *Lyme disease* - Caused by **Borrelia burgdorferi**, another spirochete transmitted by **ticks**. - Characterized by an expanding rash (**erythema migrans**), flu-like symptoms, and can lead to arthritis, neurological problems, and cardiac issues if untreated. *Relapsing fever* - Caused by various species of **Borrelia**, transmitted by **lice or ticks**. - Characterized by recurrent episodes of fever, headache, and muscle pain due to antigenic variation of the bacteria.

Q: The following colony is seen with:

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - The image displays characteristic **"fried egg" colonies**, which are typical for *Mycoplasma pneumoniae* when grown on appropriate agar. This morphology is due to the colony's center growing down into the agar while the periphery spreads on the surface. - This organism is a common cause of **atypical pneumonia** and lacks a cell wall. *Mycoplasma hominis* - While *Mycoplasma hominis* also forms "fried egg" colonies, they are typically **larger** and may develop more rapidly than *M. pneumoniae* colonies. - *M. hominis* is primarily associated with **genitourinary tract infections** and not typically found causing respiratory infections in the general population. *Mycoplasma genitalium* - *Mycoplasma genitalium* colonies are generally **much smaller** and more difficult to observe, often requiring specialized microscopy or staining techniques to visualize due to their extremely slow growth and small size. - This species is mainly implicated in **urogenital infections** like non-gonococcal urethritis. *Mycoplasma fermentans* - *Mycoplasma fermentans* also produces "fried egg" shaped colonies, but they are generally **smaller and less distinct** than those of *M. pneumoniae*. - This species has been associated with various conditions, including **arthritis** and opportunistic infections in immunocompromised individuals, but its colony morphology is not as classically defined as the "fried egg" for *M. pneumoniae* in typical clinical identification.

Q: A 35-year-old patient presents to the OPD 24 hours after a fight with a stranger in which he was bitten. GCS is 15/15 and following injury is noted on left forearm. He complains of extreme pain and tenderness in the injury. Swab from the injury was plated in chocolate agar and incubated in 10% carbon dioxide for 48 hours. Small colonies with pitting appearance were noted. Which of the following organism is responsible?

Eikenella corrodens. ***Eikenella corrodens*** - The context of a **human bite wound** and the characteristic **pitting of agar** by bacterial colonies are classic identifiers for *Eikenella corrodens*. - This organism is a common inhabitant of the **oral flora** and is frequently implicated in infections resulting from human bites. *Flavobacterium meningosepticum* - This organism is more commonly associated with **nosocomial infections**, particularly in newborns and immunocompromised patients, and severe infections like meningitis or sepsis, not typically human bite wounds. - While it can grow on chocolate agar, its colonial morphology does **not typically involve pitting** of the agar. *Capnocytophaga gingivalis* - This organism is also part of the normal oral flora and can cause infections related to human bites, especially in immunocompromised individuals. - However, while it can grow on chocolate agar, it characteristically exhibits **gliding motility** and ferments carbohydrates, but does not typically cause the striking **pitting** seen with *Eikenella corrodens*. *Streptobacillus moniliformis* - *Streptobacillus moniliformis* is associated with **rat bite fever** (Haverhill fever if contracted through contaminated food or water) and not typically human bite wounds. - It often produces **"fried egg" colonies** with a dense center and a lacy edge, which is distinct from the pitting observed here.

Q: All are true about the organism whose colonies are shown below except:

Warm agglutinin production. ***Warm agglutinin production*** - This is the **EXCEPTION** - Mycoplasma pneumoniae produces **COLD agglutinins**, not warm agglutinins - **Cold agglutinins** are IgM antibodies that agglutinate red blood cells at temperatures below 37°C and are a characteristic feature of **Mycoplasma pneumoniae** infection - **Warm agglutinins** are associated with autoimmune hemolytic anemia, not Mycoplasma infections - This is the FALSE statement, making it the correct answer in this EXCEPT question *Mulberry shaped colony* - **TRUE statement** - Mycoplasma colonies have a characteristic **"fried egg" or mulberry appearance** with a dense central zone and a flat peripheral zone - This distinctive colony morphology is due to the organisms growing into the agar surface while spreading on top - This is a key identifying feature of Mycoplasma species on culture media *Lack cell wall* - **TRUE statement** - Mycoplasma are unique among bacteria in that they **completely lack a cell wall** - This absence of cell wall makes them resistant to **beta-lactam antibiotics** (penicillins, cephalosporins) that target cell wall synthesis - The lack of cell wall also contributes to their **pleomorphism** (variable shape) and osmotic fragility - Their cell membrane contains **sterols**, which is unusual for prokaryotes *Divide by binary fission* - **TRUE statement** - Mycoplasma reproduce by **binary fission**, the standard method of bacterial reproduction - Despite lacking a cell wall, they still undergo typical prokaryotic cell division - They are the **smallest self-replicating organisms** capable of independent growth

Q: A blood smear from a patient with fever shows the following spirochetes on microscopy. Identify the organism:

Borrelia. ***Borrelia*** - The image distinctly shows **large, coarse, and irregularly coiled spirochetes**, which are characteristic morphological features of *Borrelia* species. These are larger than other spirochetes and their coils are less tightly wound. - *Borrelia* species cause diseases like **Lyme disease** (*B. burgdorferi*) and **relapsing fever** (*B. recurrentis*), which are diagnosed by identifying these distinctive spirochetes in blood smears or tissue samples. *Treponema pallidum* - This bacterium is characterized by **thinner, tightly coiled, and regularly spaced spirals**, appearing more delicate than the organisms shown in the image. - **Darkfield microscopy** is typically used for direct visualization of *Treponema pallidum* due to its thinness and inability to be stained by Gram stain. *Leptospira* - *Leptospira* are typically **thin, tightly coiled spirochetes** with characteristic **hooked ends**, which are not visible in the provided image. - They are known for causing **leptospirosis**, a zoonotic disease. *Brucella* - *Brucella* are **small, Gram-negative coccobacilli** and are not spirochetes at all. - They cause **brucellosis**, which is a systemic infection with different microscopic appearances.

Question 1

The gram stain given below shows which organism most likely? (AIIMS May 2016)

Accepted Answer

Neisseria meningitidis

Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Streptococcus pyogenes

Question 2

A 24-year-old female presented with an ulcer in the genital area. A giemsa stained cervical smear was prepared. Identify the causative agent: (AIIMS Nov 2015)

Accepted Answer

Haemophilus ducreyi

Answer

Gardnerella vaginalis

Answer

Chlamydia

Answer

Calymmatobacterium granulomatosis

Question 3

A 23-year-old female presents with fever and altered sensorium for two days with rashes on legs as shown. Her BP is 70/50 mm Hg and neck stiffness is present. Lumbar puncture reveals cloudy CSF with 4200 cells/ $\mu \mathrm{L}$, protein level 198 and glucose $21 \mathrm{mg} /$ dL. Which of the following correctly describes the organism causing this condition?

Accepted Answer

Gram negative diplococci (kidney shaped), oxidase positive

Answer

Gram positive cocci catalase negative, bacitracin sensitive

Answer

Gram positive diplococci (lanceolate), catalase negative, optochin sensitive

Answer

Gram negative diplococci, ferments glucose only (not maltose)

Question 4

All are correct about the condition shown in the image except:

Accepted Answer

Aspirated material shows LCL bodies

Answer

Groove sign of LGV

Answer

Most common cause of this infection is L2 biovar

Answer

Females develop esthiomene

Question 5

All are correct about the organism shown in the image except: (Recent NEET Pattern 2016-17)

Accepted Answer

Pneumonic plague is the predominant presentation

Answer

Safety pin appearance

Answer

Direct immunofluorescence for F1 antigen in sputum

Answer

Doxycycline is used for prophylaxis in house-hold contacts of pneumonic plague

Question 6

The following organism shown leads to development of:

Accepted Answer

Syphilis

Answer

Leptospirosis

Answer

Lyme disease

Answer

Relapsing fever

Question 7

The following colony is seen with:

Accepted Answer

Mycoplasma pneumoniae

Answer

Mycoplasma hominis

Answer

Mycoplasma genitalium

Answer

Mycoplasma fermentans

Question 8

A 35-year-old patient presents to the OPD 24 hours after a fight with a stranger in which he was bitten. GCS is 15/15 and following injury is noted on left forearm. He complains of extreme pain and tenderness in the injury. Swab from the injury was plated in chocolate agar and incubated in 10% carbon dioxide for 48 hours. Small colonies with pitting appearance were noted. Which of the following organism is responsible?

Accepted Answer

Eikenella corrodens

Answer

Flavobacterium meningosepticum

Answer

Capnocytophaga gingivalis

Answer

Streptobacillus moniliformis

Question 9

All are true about the organism whose colonies are shown below except:

Accepted Answer

Warm agglutinin production

Answer

Mulberry shaped colony

Answer

Lack cell wall

Answer

Divide by binary fission

Question 10

A blood smear from a patient with fever shows the following spirochetes on microscopy. Identify the organism:

Accepted Answer

Borrelia

Answer

Treponema pallidum

Answer

Leptospira

Answer

Brucella

Bacteriology — MCQs

Bacteriology — MCQs

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