Untitled Study Note | MCQ Quiz | OmpathStudy Kenya

Question 1

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

Accepted Answer

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. ---

Question 2

The presence of a pseudomembrane is a result of

Accepted Answer

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. ---

Question 3

A paroxysm is a and is characteristic of

Accepted Answer

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. ---

Question 4

The Mantoux test is used to identify

Accepted Answer

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. ---

Question 5

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

Accepted Answer

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. ---

Question 6

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

Accepted Answer

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. ---

Question 7

The organism Clostridium perfringens multiplies in foods only under conditions.

Accepted Answer

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. ---

Question 8

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

Accepted Answer

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. ---

Question 9

Woolsorter disease applies to the form of

Accepted Answer

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. ---

Question 10

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

Accepted Answer

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. ---

Question 11

Salpingitis is associated with and can lead to

Accepted Answer

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. ---

Question 12

Ophthalmia is associated with what two STDs?

Accepted Answer

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. ---

Question 13

Toxin-generated S. aureus diseases resulting from contact include

Accepted Answer

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. ---

Question 14

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 patient acquired her infection is

Accepted Answer

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. ---

Question 15

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, suggesting that they are the same strain. A S epidermidis biofilm is thought to be present on the catheter. Which one of the following statements about such an infection is correct?

Accepted Answer

The complex molecular interactions within the biofilm make it difficult to provide effective antimicrobial therapy, and it is likely the catheter will have to be removed to cure the infection — 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. ---

Question 16

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

Accepted Answer

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. ---

Question 17

Which of the following statements about lipopolysaccharide is correct?

Accepted Answer

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. ---

Question 18

Which of the following statements is correct?

Accepted Answer

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). ---

Question 19

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

Accepted Answer

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. ---

Question 20

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?

Accepted Answer

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). ---

Question 21

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?

Accepted Answer

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. ---

Question 22

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

Accepted Answer

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. ---

Question 23

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?

Accepted Answer

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. ---

Question 24

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

Accepted Answer

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. ---

Question 25

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

Accepted Answer

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. ---

Question 26

Scalded skin syndrome is caused by exotoxin (exfoliatins) produced by

Accepted Answer

Staphylococcus aureus — Staphylococcal scalded skin syndrome (SSSS) is caused by exfoliative toxins (ETA and ETB) produced by certain S. aureus strains. These serine proteases cleave desmoglein-1 in the epidermis, causing superficial skin separation and blistering resembling scalding. ---

Question 27

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

Accepted Answer

The mothers previous treatment for syphilis was effective — The pattern shows a nonreactive RPR (indicating no active infection) with a reactive treponemal test (indicating past infection). Treponemal tests remain positive for life after treated syphilis. This serologic pattern indicates successful treatment with "serologic scar." ---

Question 28

Which of the following bacteria has the lowest 50% infective dose (ID50)?

Accepted Answer

Shigella sonnei — Shigella has the lowest ID50 (10-100 organisms) due to acid resistance, allowing survival through stomach acid. Salmonella requires ~10^5 organisms, V. cholerae ~10^8, and C. jejuni ~500-10,000 organisms for infection. ---

Question 29

Which of the following disease is best diagnosed by serologic means?

Accepted Answer

Q Fever — Q fever (Coxiella burnetii) is best diagnosed serologically by detecting antibodies to phase I and II antigens. The organism is difficult to culture due to obligate intracellular nature. TB, gonorrhea, and actinomycosis are diagnosed by culture/microscopy. ---

Question 30

A 30 year old woman has non-bloody diarrhea for the past 14 hours. Which one of the following organisms is least likely to cause this illness?

Accepted Answer

Streptococcus pyogens — S. pyogenes causes pharyngitis, skin infections, and toxic shock syndrome, but not gastroenteritis. C. difficile, Shigella, and Salmonella are all common causes of diarrhea. Note: Shigella typically causes bloody diarrhea but can present with watery diarrhea initially. ---

Question 31

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

Accepted Answer

Infertility — Pelvic inflammatory disease (PID) from N. gonorrhoeae causes tubal scarring and adhesions, leading to infertility (10-20% after one episode, higher with recurrent infections) and increased ectopic pregnancy risk. Chronic pelvic pain is also common. ---

Question 32

The survival of Mycobacterium after ingestion by macrophages is attributed to

Accepted Answer

Bacterial inhibition of phagosome formation and interference with endosomal acidification — Mycobacterium tuberculosis prevents phagosome-lysosome fusion and blocks phagosome acidification through various mechanisms including production of ammonia and inhibition of vacuolar ATPase. This allows intracellular survival within macrophages. ---

Question 33

The molecular basis for effect of cholera toxin on duodenal mucosa cells is

Accepted Answer

Ribosylation of guanosine triphosphate (GTP) binding protein — Cholera toxin's A subunit ADP-ribosylates the Gsα protein (GTP-binding protein), locking it in the active state. This permanently activates adenylate cyclase, causing continuous cAMP production, which drives massive chloride and water secretion into the intestinal lumen. ---

Question 34

The role of bacteria capsule as virulence factor is usually related to their ability to interfere with

Accepted Answer

Phagocytosis — Bacterial capsules (e.g., S. pneumoniae, H. influenzae, N. meningitidis) are antiphagocytic. The hydrophilic polysaccharide layer prevents complement C3b deposition and blocks phagocyte receptors from binding bacterial surface, inhibiting opsonization and phagocytosis until specific anticapsular antibodies develop. ---

Question 35

Which of the following is not most important cause of acute bacterial meningitis?

Accepted Answer

Streptococcus pyrogens — S. pyogenes (Group A Strep) rarely causes meningitis. The three most common causes of bacterial meningitis are S. pneumoniae (most common overall), N. meningitidis (especially in young adults), and H. influenzae type b (reduced since Hib vaccine). ---

Question 36

A 21 year married woman developed a urinary tract infection (UTI). At time of medical advice she was febrile and complained of painful urination and flank pain. Her urine appeared cloudy. Urine culture yield lactose fermenting, indole positive, gram negative bacillus. The effectiveness of the organism responsible for urinary tract infection associated with specific

Accepted Answer

P. fimbriae — P pili (fimbriae) on uropathogenic E. coli bind to P blood group antigens on uroepithelial cells, enabling bacterial adherence and colonization of the urinary tract. P fimbriae are the major virulence factor for ascending UTIs and pyelonephritis. ---

Question 37

The coagulase test is used to differentiate

Accepted Answer

Staphylococcus aureus from Staphylococcus epidermidis — The coagulase test distinguishes S. aureus (coagulase-positive) from coagulase-negative staphylococci like S. epidermidis. Coagulase converts fibrinogen to fibrin, causing plasma clotting. It's a key virulence factor and diagnostic marker for S. aureus. ---

Question 38

During a pandemic of a well-characterized disease, a group of 175 airline passengers flew from Lima, Peru, to Los Angeles. Lunch on the plane included crab salad, which was eaten by about two-thirds of the passengers. After landing in Los Angeles, many of the passengers transferred to other flights with destinations in other parts of California and other Western states. Two of the passengers who stayed in Los Angeles developed severe watery diarrhea. The status of the other passengers was unknown. The likely cause of the diarrhea in the two passengers is

Accepted Answer

Vibrio cholerae type 0139 — The scenario describes a cholera pandemic with severe watery ("rice-water") diarrhea from seafood consumption in an endemic area (Peru). V. cholerae O139 emerged as a pandemic strain. The rapid onset and severe watery diarrhea are characteristic of cholera. ---

Question 39

A 27-year-old man had a rhinoplasty. A nasal tampon was placed to control the bleeding. Approximately 8 hours later, he developed headache, muscle aches, and abdominal cramps with diarrhea. He then developed an erythematous rash (resembling sunburn) over much of his body, including the palms and soles. His blood pressure is 80/50 mm Hg. The nasal tampon remained in place. His liver enzyme tests were elevated, and there was evidence of moderate renal failure. This patient's illness was likely to be caused by which of the following?

Accepted Answer

A superantigen — This is toxic shock syndrome caused by TSST-1, a superantigen that bypasses normal antigen processing and directly cross-links MHC class II with T-cell receptors, causing massive cytokine release. Nasal packing provides the anaerobic niche for toxin-producing S. aureus. ---

Question 40

The organism most likely to be responsible for the patient's disease (Question 39) is

Accepted Answer

Staphylococcus aureus — S. aureus producing TSST-1 causes toxic shock syndrome. Nasal packing creates ideal conditions for bacterial growth and toxin production. The clinical picture (fever, rash, hypotension, multi-organ involvement) is classic for staphylococcal TSS. ---

Question 41

Which of the following is most likely to be associated with the formation of a bacterial biofilm?

Accepted Answer

Airway colonization in a cystic fibrosis patient with a mucoid (alginate-producing) strain of Pseudomonas aeruginosa — Mucoid P. aeruginosa produces alginate exopolysaccharide that forms thick biofilms in CF patient airways. These biofilms protect bacteria from antibiotics and immune clearance, causing chronic infection. Biofilm formation is a hallmark of CF pulmonary infection. ---

Question 42

Regarding bacterial type II secretions systems, which of the following statements is correct?

Accepted Answer

They cause release of effectors of pathogenesis into the extracellular environment, promoting bacterial colonization and multiplication — Type II secretion systems transport folded proteins (toxins, enzymes) from the periplasm to the extracellular space in gram-negative bacteria. Examples include cholera toxin and elastase. Type III systems directly inject proteins into host cells (described in option D). ---

Question 43

A 15-year-old girl develops severe watery diarrhea. The stool looks like "rice water." It is voluminous—more than 1 L in the last 90 minutes. She has no fever and seems otherwise normal except for the effects of loss of fluid and electrolytes. The most likely cause of her illness is

Accepted Answer

A toxin with A and B subunits — This is cholera caused by V. cholerae producing cholera toxin ( an A-B toxin). The "rice-water" appearance, massive volume ( 1L/hour possible), absence of fever, and secretory nature are pathognomonic for cholera. The A subunit ADP-ribosylates Gs protein, causing massive fluid secretion. ---

Question 44

The most important thing that can be done to treat the patient (Question 43) is

Accepted Answer

To treat her with fluid and electrolyte replacement — Immediate oral rehydration therapy (ORT) or IV fluids is life-saving in cholera. Fluid replacement addresses the primary pathology (dehydration and electrolyte loss). Antibiotics (doxycycline or azithromycin) shorten duration but are secondary. Most deaths from cholera are due to inadequate rehydration. ---

Question 45

A 23-year-old woman has a history of recurrent urinary tract infections, including at least one episode of pyelonephritis. Blood typing shows the P blood group antigen. Which of the following is likely to be the primary cause of her infections?

Accepted Answer

Escherichia coli with P-pili (fimbria — P pili (P fimbriae) on uropathogenic E. coli specifically bind to P blood group antigens on uroepithelial cells. Patients with P antigens are more susceptible to pyelonephritis. P-piliated E. coli strains cause 90% of pyelonephritis cases in otherwise healthy individuals. ---

Question 46

A 55-year-old man presents with gradually increasing weight loss, abdominal pain, diarrhea, and arthropathy. During the evaluation process, a small bowel biopsy is done. After processing, examination of the specimen by light microscopy reveals periodic acid-Schiff-positive inclusions in the bowel wall. Which of the following tests could be done to confirm the diagnosis of Whipple disease, caused by Tropheryma whipple?

Accepted Answer

Polymerase chain reaction amplification and sequencing of an appropriate segment of DNA — Tropheryma whipplei cannot be cultured on routine media and is extremely difficult to grow. PCR amplification and sequencing of 16S rRNA gene from tissue specimens is the gold standard for diagnosis of Whipple disease. PAS-positive macrophages support the diagnosis but PCR confirms it. ---

Untitled Study Note | MCQ Quiz | OmpathStudy Kenya

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