Untitled Study Note – 46 MCQs | Kenya MBChB

46 Year 2: Microbiology exam questions on Untitled Study Note for medical students. Includes MCQs, answers, explanations and written questions. Sample: Which on

This MCQ set contains 46 questions on Untitled Study Note in the Year 2: Microbiology unit. Each question includes the correct answer and a detailed explanation for active recall and exam preparation.

Q1: Which one of the following is a complication of streptococcus pharyngitis?

  1. A. Rheumatic fever
  2. B. Pseudomembrane blockage
  3. C. Tubercle formation
  4. D. Meningococcemia
  5. E. Waterhouse-Friderichsen syndrome

Correct answer: A – Rheumatic fever

Rheumatic fever is a nonsuppurative complication of Group A Streptococcus (Streptococcus pyogenes) pharyngitis. It occurs 2-4 weeks after untreated strep throat due to molecular mimicry, where antibodies against streptococcal M protein cross-react with cardiac tissue, causing carditis, arthritis, and chorea. ---

Q2: The presence of a pseudomembrane is a result of

  1. A. Strep throat
  2. B. Meningitis
  3. C. Scarlet fever
  4. D. Diphtheria
  5. E. Psittacosis

Correct answer: D – Diphtheria

Corynebacterium diphtheriae produces diphtheria toxin that causes local tissue necrosis in the pharynx, forming a characteristic gray-white pseudomembrane composed of fibrin, dead cells, bacteria, and inflammatory exudate. This membrane adheres firmly to underlying tissue and can cause airway obstruction. ---

Q3: A paroxysm is a and is characteristic of

  1. A. Fever; meningitis
  2. B. Rapid-fire cough; meningitis
  3. C. Fever; pneumonia
  4. D. Headache; pertussis
  5. E. Rapid-fire cough; pertussis

Correct answer: E – Rapid-fire cough; pertussis

A paroxysm is a sudden, uncontrollable series of coughs characteristic of pertussis (whooping cough) caused by Bordetella pertussis. The paroxysmal stage features severe coughing fits followed by an inspiratory "whoop" sound, often accompanied by post-tussive vomiting. ---

Q4: The Mantoux test is used to identify

  1. A. TB exposure
  2. B. Q fever
  3. C. Ornithosis
  4. D. Pertussis
  5. E. Meningitis

Correct answer: A – TB exposure

The Mantoux test (tuberculin skin test) detects delayed-type hypersensitivity to tuberculin purified protein derivative (PPD), indicating prior exposure to Mycobacterium tuberculosis. A positive result shows induration at the injection site 48-72 hours after intradermal injection. ---

Q5: This bacterial species is the most common cause of "typical" pneumonia.

  1. A. H. influenzae
  2. B. S. pneumoniae
  3. C. M. pneumoniae
  4. D. L. pneumophila
  5. E. pertussis

Correct answer: B – S. pneumoniae

Streptococcus pneumoniae (pneumococcus) is the most common cause of community-acquired bacterial pneumonia. It presents with typical features: acute onset, high fever, productive cough with rusty sputum, pleuritic chest pain, and lobar consolidation on chest X-ray. ---

Q6: To treat patients who have ingested botulism toxin, large doses of must be administered.

  1. A. Antibiotic
  2. B. Aspirin
  3. C. Pepto-Bismol
  4. D. Antitoxin
  5. E. Electrolytes

Correct answer: D – Antitoxin

Botulism requires administration of botulinum antitoxin (trivalent or heptavalent). The antitoxin neutralizes circulating toxin but cannot reverse already bound toxin. Early administration is critical. Antibiotics are ineffective against the preformed toxin. ---

Q7: The organism Clostridium perfringens multiplies in foods only under conditions.

  1. A. Aerobic
  2. B. Freezing
  3. C. Anaerobic
  4. D. Saline
  5. E. Permissive

Correct answer: C – Anaerobic

Clostridium perfringens is an obligate anaerobe that multiplies only in oxygen-free environments. Improper food storage (inadequate cooling or reheating) creates anaerobic conditions that allow spore germination and toxin production, leading to food poisoning. ---

Q8: A spore-forming, motile rod that can cause foodborne illness in a diarrheal or emetic form is Bacillus

  1. A. Anthracis
  2. B. Abortus
  3. C. Enterocolitica
  4. D. Cereus
  5. E. Botulinum

Correct answer: D – Cereus

Bacillus cereus causes two forms of food poisoning: the emetic form (1-6 hours, associated with fried rice) caused by cereulide toxin, and the diarrheal form (8-16 hours, associated with meats and vegetables) caused by enterotoxins. ---

Q9: Woolsorter disease applies to the form of

  1. A. Inhalation; tularemia
  2. B. Toxic; myonecrosis
  3. C. Intestinal; anthrax
  4. D. Inhalation; anthrax
  5. E. Ingested; leptospirosis

Correct answer: D – Inhalation; anthrax

Woolsorter's disease is pulmonary anthrax caused by inhaling Bacillus anthracis spores from contaminated animal products (wool, hides). It causes severe hemorrhagic mediastinitis, septic shock, and high mortality. The name comes from textile workers who processed contaminated wool. ---

Q10: Which one of the following describes the mode of action of tetanospasmin?

  1. A. It inhibits muscle contraction
  2. B. It damages and lyses red blood cells
  3. C. It disrupts cell tissues
  4. D. It inhibits muscle relaxation
  5. E. It lyses white blood cells

Correct answer: D – It inhibits muscle relaxation

Tetanospasmin (tetanus toxin) blocks release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells in the spinal cord by cleaving synaptobrevin. This prevents muscle relaxation, causing sustained muscle contraction (spastic paralysis) and characteristic lockjaw. ---

Q11: Salpingitis is associated with and can lead to

  1. A. Syphilis; gumma formation
  2. B. Gonorrhea; sterility
  3. C. Chlamydia; ophthalmia
  4. D. Chancroid; soft chancre
  5. E. Gonorrhea; pharyngitis

Correct answer: B – Gonorrhea; sterility

Salpingitis (fallopian tube inflammation) is commonly caused by Neisseria gonorrhoeae as part of pelvic inflammatory disease (PID). Chronic inflammation causes scarring and tubal obstruction, leading to infertility and increased ectopic pregnancy risk. ---

Q12: Ophthalmia is associated with what two STDs?

  1. A. Syphilis and chlamydia
  2. B. Gonorrhea and chlamydia
  3. C. Syphilis and chancroid
  4. D. Syphilis and gonorrhea
  5. E. Chlamydia and chancroid

Correct answer: B – Gonorrhea and chlamydia

Ophthalmia neonatorum (neonatal conjunctivitis) is caused by Neisseria gonorrhoeae and Chlamydia trachomatis acquired during passage through an infected birth canal. Both can cause severe conjunctivitis and, if untreated, corneal scarring and blindness. ---

Q13: Toxin-generated S. aureus diseases resulting from contact include

  1. A. Purpuric fever
  2. B. Scalded skin syndrome
  3. C. Toxic shock syndrome
  4. D. Pseudomembranous colitis
  5. E. Both B and C are correct

Correct answer: E – Both B and C are correct

Staphylococcus aureus produces exfoliative toxins causing scalded skin syndrome (bullous impetigo, Ritter's disease) and toxic shock syndrome toxin-1 (TSST-1) causing toxic shock syndrome. Both are toxin-mediated diseases that can result from skin colonization or infection. ---

Q14: A 22-year-old woman who works in a plant nursery presents with a history of fever and cough for 2 months. Over this period of time she has lost 5 kg. Chest radiography shows bilateral upper lobe infiltrates with cavities. A stain of her sputum shows acid-fast bacilli. The likely means by which the p

  1. A. Sexual activity
  2. B. Ingesting the microorganisms in her food
  3. C. Holding onto contaminated hand rails when she takes public transportation
  4. D. Handling potting soil
  5. E. Breathing aerosolized droplets containing the microorganism

Correct answer: E – Breathing aerosolized droplets containing the microorganism

The patient has pulmonary tuberculosis caused by Mycobacterium tuberculosis. TB is transmitted by inhalation of aerosolized droplet nuclei (1-5 μm) from an infectious person's cough, sneeze, or speech. The upper lobe cavitation, chronic symptoms, weight loss, and acid-fast bacilli confirm the diagnosis. ---

Q15: A 65-year-old woman has a long-term central venous catheter for intravenous therapy. She develops fever and subsequently has multiple blood cultures positive for Staphylococcus epidermidis. All of the S epidermidis isolates have the same colony morphology and antimicrobial susceptibility pattern, su

  1. A. The biofilm containing the S epidermidis is likely to wash off the catheter
  2. B. Production of an extracellular polysaccharide inhibits growth of the S epidermidis, limiting the infection
  3. C. The S epidermidis in the biofilm are likely to be more susceptible to antimicrobial therapy because the bacteria have decreased rates of metabolism
  4. D. The quorum-sensing ability of S epidermidis results in increased susceptibility to antimicrobial therapy
  5. E. The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy, and it is likely the catheter will

Correct answer: E – The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy, and it is likely the catheter will

S. epidermidis biofilms on catheters are highly resistant to antibiotics due to reduced metabolic activity, limited antibiotic penetration through polysaccharide matrix, and altered bacterial physiology. Catheter removal is usually necessary for cure because antibiotics alone cannot eradicate biofilm infections. ---

Q16: The first microorganism to satisfy Koch's postulates (in the late 19th century) was

  1. A. Treponema pallidum
  2. B. Stenotrophomonas maltophilia
  3. C. Mycobacterium leprae
  4. D. Bacillus anthracis
  5. E. Neisseria gonorrhoeae

Correct answer: D – Bacillus anthracis

Robert Koch first proved Bacillus anthracis as the causative agent of anthrax in 1876, establishing Koch's postulates. He isolated the organism from diseased animals, cultured it in pure form, reproduced the disease in healthy animals, and re-isolated the same organism. ---

Q17: Which of the following statements about lipopolysaccharide is correct?

  1. A. It interacts with macrophages and monocytes yielding release of cytokines
  2. B. The toxic component is the O side chain
  3. C. It forms holes in red blood cell membranes yielding hemolysis
  4. D. It causes hypothermia
  5. E. It causes paralysis

Correct answer: A – It interacts with macrophages and monocytes yielding release of cytokines

Lipopolysaccharide (LPS/endotoxin) binds to TLR4 on macrophages and monocytes via LPS-binding protein and CD14, triggering massive cytokine release (TNF-α, IL-1, IL-6). This causes fever, shock, and DIC. The toxic component is Lipid A, not the O antigen. ---

Q18: Which of the following statements is correct?

  1. A. Lipopolysaccharide is part of the cell wall of Escherichia coli
  2. B. Cholera toxin is attached to the flagella of Vibrio cholerae
  3. C. The lecithinase of Clostridium perfringens causes diarrhea
  4. D. Toxic shock syndrome toxin-1 is produced by hemolytic stains of Staphylococcus epidermidis
  5. E. coli is a gram-negative bacterium with LPS in its outer membran

Correct answer: A – Lipopolysaccharide is part of the cell wall of Escherichia coli

E. coli is a gram-negative bacterium with LPS in its outer membrane. Cholera toxin is secreted (not on flagella), lecithinase causes tissue necrosis (not diarrhea), and TSST-1 is produced by S. aureus (not S. epidermidis). ---

Q19: Which of the following best describes the mechanism of action of diphtheria toxin?

  1. A. Forms pores in red blood cells causing hemolysis
  2. B. Degrades lecithin in eukaryotic cell membranes
  3. C. Causes release of tumor necrosis factor
  4. D. Inhibits elongation factor 2
  5. E. Causes increased adenylate cyclase activity

Correct answer: D – Inhibits elongation factor 2

Diphtheria toxin is an A-B toxin. The A subunit catalyzes ADP-ribosylation of elongation factor 2 (EF-2), irreversibly inactivating it and blocking protein synthesis. One toxin molecule can kill a cell by halting translation. ---

Q20: Certain microorganisms are never considered to be members of the normal flora. They are always considered to be pathogens. Which one of the following organisms fits into that category?

  1. A. Streptococcus pneumoniae
  2. B. Escherichia coli
  3. C. Mycobacterium tuberculosis
  4. D. Staphylococcus aureus
  5. E. Neisseria meningitides

Correct answer: C – Mycobacterium tuberculosis

M. tuberculosis is always pathogenic and never part of normal flora. The others can be normal flora: S. pneumoniae (nasopharynx), E. coli (intestine), S. aureus (skin/nose), N. meningitidis (nasopharynx up to 10% of population). ---

Q21: An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. You are called upon to investigate. According to your knowledge of the normal flora, what is the most likely source of the organism?

  1. A. Nose
  2. B. Colon
  3. C. Hand
  4. D. Throat

Correct answer: A – Nose

The anterior nares (nose) is the primary reservoir for S. aureus colonization, occurring in 20-40% of healthy adults. Healthcare workers can transmit the organism from their nose to patients via hands, making nasal carriage the most likely source in nosocomial outbreaks. ---

Q22: Each of the following agent is a recognized cause of diarrhea except?

  1. A. Clostridium perfringens
  2. B. Vibrio cholera
  3. C. Enterococcus faecalis
  4. D. Escherichia coli
  5. E. perfringens, V. cholerae, and

Correct answer: C – Enterococcus faecalis

Enterococcus faecalis is normal intestinal flora and causes urinary tract infections, endocarditis, and intra-abdominal infections, but not diarrhea. C. perfringens, V. cholerae, and E. coli are all well-recognized diarrheal pathogens. ---

Q23: The identification of bacteria by serological test is based on the presence of specific antigens. Which of the following bacterial components is least likely to contain useful antigens?

  1. A. Capsule
  2. B. Cell wall
  3. C. Flagella
  4. D. Ribosome

Correct answer: D – Ribosome

Ribosomes are internal structures with highly conserved proteins across species, making them poor serological markers. Capsule (K antigens), cell wall (O antigens for LPS), and flagella (H antigens) are surface-exposed and variable, making them excellent for serotyping. ---

Q24: Which of the following species of Pasteurella species has been associated with infection of female genital tract and newborn?

  1. A. Pasteurella multocida
  2. B. Pasteurella ureae
  3. C. Pasteurella bettyae
  4. D. Pasteurella bettyae

Correct answer: C – Pasteurella bettyae

Pasteurella bettyae (formerly CDC group HB-5) is associated with genital tract infections and neonatal infections. P. multocida is primarily associated with animal bites and respiratory infections, not genital tract infections. ---

Q25: Each of the following statements about the classification of streptococci is correct except

  1. A. Pneumococci (Streptococcus pneumonia
  2. B. are alpha-hemolytic and can be serotyped on the basis of their polysaccharide capsule
  3. C. Enterococci are group D streptococci and can be classified by their ability to grow 6.5% sodium chloride
  4. D. Viridans streptococci are identified by Lancefield grouping, which is based on the carbohydrate in the cell wall
  5. E. Although pneumococci and the viridans streptococci are alpha-hemolytic, they can be differentiated by the bile solubility test and their susceptibilit

Correct answer: D – Viridans streptococci are identified by Lancefield grouping, which is based on the carbohydrate in the cell wall

Viridans streptococci lack Lancefield group antigens and cannot be classified by Lancefield grouping. They are identified by biochemical tests, hemolysis pattern, and optochin resistance. Lancefield grouping applies to beta-hemolytic streptococci. ---

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