MCQs Bacteriology (61-70): Sexually Transmitted Infections

61. A 70-year-old woman with severe chronic lung disease presented in the OPD of Tribhuvan University Teaching Hospital with fever, productive cough with purulent sputum, and worsening hypoxemia. A sputum sample was collected and sent to the microbiology lab. The lab reported plenty of polymorphonuclear leukocytes with both intracellular and extracellular gram-negative diplococci. This organism grows well on 5% sheep blood agar and chocolate agar. Later, a butyrate esterase test was done and found to be positive. What is the most likely organism to be involved in this illness?

a. Haemophilus influenzae

b. Moraxella catarrhalis

c. Neisseria gonorrhoeae

d. Neisseria lactamica

e. Neisseria meningitidis

62. A 32-year-old woman who is 10 weeks pregnant presents to the Obstetrics clinic for prenatal care. She has a history of treatment for syphilis 7 years previously. The results of serologic tests for syphilis are as follows: Non-treponemal test (RPR): Nonreactive; Treponemal test (TP-PA): Reactive. Which of the following statements is most correct?

a. The baby is at high risk for congenital syphilis

b. The mother needs a lumbar puncture and a VDRL test of her CSF for neurosyphilis

c. The mother needs to be treated again for syphilis

d. The mother’s previous treatment for syphilis was effective

63. A 26-year-old sexually active woman presents to the OPD with purulent vaginal discharge and dysuria. While history taking, she admitted that she had unprotected sexual intercourse with a new partner a week ago. Which of the following diagnostic tests will be the most sensitive method to find the etiologic agents involved in this case?

a. An enzyme immunoassay

b. Bacterial culture on selective media

c. Gram's stain

d. Molecular diagnostic methods

e. Serology

64. A 20-year-old woman who reports unprotected sex with a new partner 2 weeks previously develops fever and left lower quadrant abdominal pain with onset in association with her menstrual period. Neisseria gonorrhoeae is cultured from her endocervix. The diagnosis is gonococcal pelvic inflammatory disease. What is a common sequela of this infection?

a. Cancer of the cervix

b. Infertility

c. Urethral stricture

d. Uterine fibroid tumors

e. Vaginal-rectal fistula

65. A 40-year-old man is suffering from multiple episodes of disseminated gonococcal infection for the last few years. Cultures of his urethra and knee fluid yield Neisseria gonorrhoeae. What is the most likely cause for this infection?

a. A polymorphonuclear cell chemotactic factor deficiency

b. Absence of lymphocyte adenosine deaminase activity

c. Deficiency of a late-acting complement component (C5, C6, C7, or C8)

d. Myeloperoxidase deficiency

e. Selective IgA deficiency

66. Infection with which of the following agents can result in a biological false-positive non-treponemal (VDRL or RPR) test for syphilis?

a. Borrelia burgdorferi

b. Epstein-Barr virus

c. Streptococcus pyogenes

d. Varicella-zoster virus

e. All of the above

67. A false-positive non-treponemal (VDRL or RPR) test for syphilis is a common diagnostic problem. In which of the following conditions can you expect false-positive VDRL or RPR results?

a. Leprosy

b. Lupus erythematosus

c. Malaria

d. Measles

e. All of the above

68. A 22-year-old woman presents with a 2 cm ulcer on her labia majora. The lesion is painless and has a raised border. The differential diagnosis of this lesion includes:

a. Adenovirus infection

b. Chlamydia trachomatis infection

c. Neisseria gonorrhoeae infection

d. Papillomavirus infection

e. Treponema pallidum infection

69. After returning from a community posting in a rural village in Nepal, a 20-year-old medical student was admitted to the hospital with chief complaints of fever (39°C) and headache. While history taking, he stated that he had been swimming in a pond while in the village where cows are also taken for bathing. Based on the clinical examination, leptospirosis is suspected. Which of the following tests will help to confirm the diagnosis?

a. Culture of CSF on blood and chocolate agar

b. Culture of urine on human diploid fibroblast cells

c. Testing acute and convalescent-phase sera for anti-leptospiral antibodies

d. Testing acute and convalescent-phase sera using the RPR test

e. Testing serum by dark-field examination for the presence of leptospires

70. Which of the following animals is a reservoir/source of Leptospira interrogans?

a. Cattle

b. Dogs

c. Mice

d. Swine

e. All of the above

Answer Key & Explanations

**61. Correct Answer: b (*Moraxella catarrhalis*)**

• Explanation: Moraxella catarrhalis is a gram-negative diplococcus that frequently causes respiratory tract infections in elderly patients with chronic obstructive pulmonary disease (COPD). While it morphologically resembles Neisseria species under the microscope, it can grow on standard blood and chocolate agar (unlike fastidious Neisseria species like N. gonorrhoeae). The definitive biochemical marker here is a positive butyrate esterase test, which easily differentiates M. catarrhalis from Neisseria species.

**62. Correct Answer: d (The mother’s previous treatment for syphilis was effective)**

• Explanation: Treponemal tests (like TP-PA or FTA-ABS) measure specific antibodies against Treponema pallidum structural antigens. Once a patient is infected, these tests usually remain reactive for life, regardless of successful treatment. Non-treponemal tests (like RPR or VDRL) track anti-cardiolipin antibodies, which fluctuate with disease activity and revert to nonreactive after successful eradication. A nonreactive RPR coupled with a reactive TP-PA in a patient treated years ago confirms past, successfully cleared syphilis with no current risk of congenital transmission.

**63. Correct Answer: d (Molecular diagnostic methods)**

• Explanation: Nucleic Acid Amplification Tests (NAATs), or molecular diagnostic methods, are the gold standard for investigating suspected urogenital infections like gonorrhea and chlamydia. They offer significantly higher sensitivity than traditional bacterial cultures, do not depend on maintaining pathogen viability during transport, and are far more reliable than a cervical Gram stain, which has a drastically low sensitivity in female patients.

**64. Correct Answer: b (Infertility)**

• Explanation: Pelvic Inflammatory Disease (PID) happens when a lower genital tract infection travels upward to colonize the endometrium and fallopian tubes. This triggers intense local inflammation, leading to mucosal scarring, structural adhesions, and tubal occlusion. Consequently, a prominent and devastating long-term sequela of untreated or recurrent gonococcal PID is infertility and an increased risk of ectopic pregnancies.

**65. Correct Answer: c (Deficiency of a late-acting complement component C5, C6, C7, or C8)**

• Explanation: The immune system relies heavily on the Membrane Attack Complex (MAC), comprised of late complement components C5b through C9, to clear structurally complex, thin-walled Neisseria species (N. gonorrhoeae and N. meningitidis). Individuals with a genetic deficiency in these late-acting complement proteins cannot assemble the MAC to lyse these bacteria, leaving them highly susceptible to recurrent, disseminated neisserial infections.

**66. Correct Answer: e (All of the above)**

• Explanation: Non-treponemal screening tests like RPR and VDRL detect cardiolipin-cholesterol-lecithin antibodies rather than direct treponemal targets. Because cardiolipin is a phospholipid present in both host mitochondrial membranes and various microorganisms, diverse infections—including Lyme disease (Borrelia burgdorferi), infectious mononucleosis (EBV), acute viral syndromes (Varicella-zoster), and severe bacterial infections—can trigger transient, cross-reactive antibodies that result in a biological false-positive.

**67. Correct Answer: e (All of the above)**

• Explanation: Beyond acute infections, biological false-positive VDRL or RPR results are frequently driven by chronic medical conditions. Chronic conditions such as lepromatous leprosy, autoimmune disorders like systemic lupus erythematosus (SLE) due to anti-phospholipid antibodies, malaria, and acute exanthems like measles cause widespread tissue inflammation and cellular breakdown, releasing cardiolipin into circulation and mimicking a reactive syphilis screen.

**68. Correct Answer: e (*Treponema pallidum* infection)**

• Explanation: A classic, 2 cm, indurated, painless ulcer on the external genitalia with clean bases and firmly raised margins is the definition of a hard chancre, the hallmark clinical manifestation of primary syphilis caused by the spirochete Treponema pallidum. Conversely, chancroid (caused by Haemophilus ducreyi) presents as an extremely painful ulcer, while lesions from Chlamydia trachomatis (lymphogranuloma venereum) are usually small, transient, and quickly disappear before prominent lymphadenopathy occurs.

**69. Correct Answer: c (Testing acute and convalescent-phase sera for anti-leptospiral antibodies)**

• Explanation: Confirming a clinical suspicion of leptospirosis is most reliably accomplished by tracking seroconversion or a significant (fourfold or greater) rise in specific antibody titers between acute and convalescent-phase serum samples using tests like the Microscopic Aggglutination Test (MAT) or ELISA. Leptospires are fastidious and will not grow on routine blood or chocolate agar, nor can they be cultured on standard viral fibroblast lines. Dark-field microscopy of blood or serum yields an incredibly high rate of false results due to misinterpreting normal fibrin strands as spirochetes.

**70. Correct Answer: e (All of the above)**

• Explanation: Leptospira interrogans is a highly successful zoonotic pathogen that establishes chronic renal infections in a broad spectrum of wild and domestic animal hosts. These reservoir animals—including cattle, dogs, rodents (mice/rats), and swine—persistently shed the spirochetes in their urine. Humans become incidental hosts through direct skin contact with water, mud, or agricultural environments contaminated by this infectious animal waste.