Welcome, PharmD students, to this MCQ quiz focusing on the Principles of Important Gram-Negative Bacteria! These microorganisms are a diverse group, characterized by their unique cell wall structure, and are responsible for a wide array of human infections. Understanding their classification, key genera and species, virulence factors, the diseases they cause, and their inherent resistance mechanisms is crucial for effective diagnosis and guiding antimicrobial therapy. This quiz will test your knowledge on these fundamental aspects of Gram-negative bacteriology. Let’s begin!
1. The Gram stain differentiates bacteria based on the thickness of which cell wall component, which is thinner in Gram-negative bacteria?
- a) Lipopolysaccharide (LPS)
- b) Peptidoglycan
- c) Mycolic acid
- d) Teichoic acid
Answer: b) Peptidoglycan
2. A distinctive feature of the Gram-negative cell envelope is the presence of:
- a) A thick, multi-layered peptidoglycan cell wall.
- b) An outer membrane containing lipopolysaccharide (LPS) and porin channels.
- c) Lipoteichoic acids anchored to the cytoplasmic membrane.
- d) Cholesterol in the cell membrane.
Answer: b) An outer membrane containing lipopolysaccharide (LPS) and porin channels.
3. The lipid A portion of lipopolysaccharide (LPS) in Gram-negative bacteria is also known as _______ and is responsible for many of the toxic effects seen in severe infections.
- a) Exotoxin
- b) Endotoxin
- c) Capsule
- d) Spore coat
Answer: b) Endotoxin
4. The space located between the inner (cytoplasmic) membrane and the outer membrane of Gram-negative bacteria is called the:
- a) Nucleoid region
- b) Mesosome
- c) Periplasmic space
- d) Glycocalyx
Answer: c) Periplasmic space
5. Which of the following is a characteristic of the Enterobacterales order (e.g., E. coli, Klebsiella)?
- a) They are all Gram-positive cocci.
- b) They are Gram-negative rods that typically ferment glucose and are often found in the gastrointestinal tract.
- c) They are strict anaerobes.
- d) They lack an outer membrane.
Answer: b) They are Gram-negative rods that typically ferment glucose and are often found in the gastrointestinal tract.
6. Escherichia coli is a versatile Gram-negative bacterium. While many strains are commensal, pathogenic strains are a leading cause of:
- a) Strep throat and skin infections.
- b) Urinary tract infections, traveler’s diarrhea, and neonatal meningitis.
- c) Tuberculosis and leprosy.
- d) Fungal pneumonia.
Answer: b) Urinary tract infections, traveler’s diarrhea, and neonatal meningitis.
7. Klebsiella pneumoniae is particularly known for which characteristic that can contribute to its virulence and resistance?
- a) Production of a potent neurotoxin.
- b) Formation of a prominent polysaccharide capsule, which is antiphagocytic.
- c) Its inability to grow on standard laboratory media.
- d) Its classification as a Gram-positive coccus.
Answer: b) Formation of a prominent polysaccharide capsule, which is antiphagocytic.
8. Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen often associated with:
- a) Infections in healthy individuals in the community.
- b) Healthcare-associated infections, particularly in immunocompromised patients, burn victims, and those with cystic fibrosis.
- c) Foodborne gastroenteritis primarily.
- d) Sexually transmitted infections.
Answer: b) Healthcare-associated infections, particularly in immunocompromised patients, burn victims, and those with cystic fibrosis.
9. A key feature of Pseudomonas aeruginosa that contributes to its antibiotic resistance is its:
- a) Lack of an outer membrane.
- b) Low outer membrane permeability, expression of efflux pumps, and production of beta-lactamases (e.g., AmpC).
- c) Inability to form biofilms.
- d) High susceptibility to penicillin G.
Answer: b) Low outer membrane permeability, expression of efflux pumps, and production of beta-lactamases (e.g., AmpC).
10. The term “non-fermenter” when applied to Gram-negative bacilli like Pseudomonas aeruginosa means that they:
- a) Cannot grow in the presence of oxygen.
- b) Do not ferment carbohydrates (like glucose) for energy production, often relying on oxidative metabolism.
- c) Only ferment lactose.
- d) Are unable to synthesize their own ATP.
Answer: b) Do not ferment carbohydrates (like glucose) for energy production, often relying on oxidative metabolism.
11. Pili or fimbriae on the surface of Gram-negative bacteria are primarily involved in:
- a) ATP synthesis.
- b) Adherence to host cells and surfaces, a critical step in colonization and infection.
- c) Motility through liquid media.
- d) Endospore formation.
Answer: b) Adherence to host cells and surfaces, a critical step in colonization and infection.
12. Acinetobacter baumannii is a Gram-negative coccobacillus that has gained notoriety as a cause of:
- a) Mild skin rashes in children.
- b) Difficult-to-treat, multidrug-resistant healthcare-associated infections, especially in intensive care units.
- c) Common food poisoning outbreaks.
- d) Sexually transmitted urethritis.
Answer: b) Difficult-to-treat, multidrug-resistant healthcare-associated infections, especially in intensive care units.
13. Stenotrophomonas maltophilia is an environmental Gram-negative bacterium that is intrinsically resistant to many antibiotics, including carbapenems, due to mechanisms such as:
- a) Its Gram-positive cell wall structure.
- b) Production of metallo-beta-lactamases and efflux pumps.
- c) Lack of porin channels.
- d) Its inability to grow at 37°C.
Answer: b) Production of metallo-beta-lactamases and efflux pumps.
14. The Enterobacterales order includes genera like Enterobacter, Citrobacter, and Serratia. These organisms are often associated with:
- a) Only causing infections in animals.
- b) Opportunistic healthcare-associated infections and can possess inducible AmpC beta-lactamases.
- c) Being highly susceptible to all penicillins.
- d) Being strict anaerobes.
Answer: b) Opportunistic healthcare-associated infections and can possess inducible AmpC beta-lactamases.
15. Proteus mirabilis, another member of Enterobacterales, is well known for causing urinary tract infections and is characterized by its ability to:
- a) Produce a potent neurotoxin.
- b) “Swarm” across agar plates and produce urease, which can lead to kidney stone formation.
- c) Ferment lactose rapidly.
- d) Only infect the respiratory tract.
Answer: b) “Swarm” across agar plates and produce urease, which can lead to kidney stone formation.
16. Salmonella enterica serovars are Gram-negative bacteria primarily associated with:
- a) Skin infections.
- b) Gastroenteritis (food poisoning) and enteric fever (typhoid fever).
- c) Respiratory infections in cystic fibrosis patients.
- d) Causing dental caries.
Answer: b) Gastroenteritis (food poisoning) and enteric fever (typhoid fever).
17. Shigella species are Gram-negative bacteria that cause bacillary dysentery, characterized by:
- a) Mild, watery diarrhea.
- b) Invasive infection of the colonic mucosa, leading to bloody, mucoid stools, fever, and abdominal cramps.
- c) Production of a potent neurotoxin causing paralysis.
- d) Chronic skin ulcers.
Answer: b) Invasive infection of the colonic mucosa, leading to bloody, mucoid stools, fever, and abdominal cramps.
18. Haemophilus influenzae, particularly non-type b strains after the Hib vaccine, is a Gram-negative coccobacillus that commonly causes:
- a) Gastroenteritis.
- b) Otitis media, sinusitis, bronchitis, and pneumonia.
- c) Urinary tract infections.
- d) Endocarditis in healthy adults.
Answer: b) Otitis media, sinusitis, bronchitis, and pneumonia.
19. Neisseria gonorrhoeae is a Gram-negative diplococcus responsible for:
- a) Meningitis.
- b) The sexually transmitted infection gonorrhea.
- c) Food poisoning.
- d) Whooping cough.
Answer: b) The sexually transmitted infection gonorrhea.
20. Neisseria meningitidis is a Gram-negative diplococcus that is a leading cause of:
- a) Urinary tract infections.
- b) Bacterial meningitis and meningococcemia (sepsis).
- c) Gastric ulcers.
- d) Athlete’s foot.
Answer: b) Bacterial meningitis and meningococcemia (sepsis).
21. Bordetella pertussis, a small Gram-negative coccobacillus, is the causative agent of:
- a) Diphtheria
- b) Tetanus
- c) Pertussis (whooping cough)
- d) Legionnaires’ disease
Answer: c) Pertussis (whooping cough)
22. Helicobacter pylori is a spiral-shaped Gram-negative bacterium that colonizes the stomach and is a major cause of:
- a) Acute gastroenteritis.
- b) Peptic ulcer disease and is a risk factor for gastric cancer.
- c) Traveler’s diarrhea.
- d) Urinary tract infections.
Answer: b) Peptic ulcer disease and is a risk factor for gastric cancer.
23. Legionella pneumophila is a Gram-negative bacterium that typically causes atypical pneumonia (Legionnaires’ disease) and is often acquired from:
- a) Contaminated food.
- b) Aerosolized contaminated water sources (e.g., air conditioning systems, showers).
- c) Direct contact with an infected person.
- d) Animal bites.
Answer: b) Aerosolized contaminated water sources (e.g., air conditioning systems, showers).
24. Bacteroides fragilis is an example of a(n) _______ Gram-negative bacterium that is a common component of the human colonic flora and can cause infections if it spreads to normally sterile sites.
- a) aerobic coccus
- b) aerobic bacillus
- c) anaerobic bacillus
- d) microaerophilic spirochete
Answer: c) anaerobic bacillus
25. The interaction of Gram-negative bacteria with the host immune system is often initiated by host cell recognition of LPS via:
- a) Ribosomal RNA.
- b) Toll-like receptors (TLRs), particularly TLR4.
- c) Peptidoglycan transpeptidases.
- d) Bacterial flagellin only.
Answer: b) Toll-like receptors (TLRs), particularly TLR4.
26. Which of the following is a characteristic virulence factor of Pseudomonas aeruginosa that contributes to tissue damage and immune evasion?
- a) Production of Shiga toxin.
- b) Formation of a thick polysaccharide capsule (in mucoid strains, especially in CF patients) and production of exotoxins like Exotoxin A.
- c) Lack of motility.
- d) Strict intracellular parasitism.
Answer: b) Formation of a thick polysaccharide capsule (in mucoid strains, especially in CF patients) and production of exotoxins like Exotoxin A.
27. Extended-spectrum β-lactamases (ESBLs), commonly found in Enterobacterales like E. coli and Klebsiella, mediate resistance to:
- a) Vancomycin.
- b) Penicillins, and first-, second-, and third-generation cephalosporins.
- c) Daptomycin.
- d) Linezolid.
Answer: b) Penicillins, and first-, second-, and third-generation cephalosporins.
28. The ability of some Enterobacterales like Proteus spp. to produce urease contributes to:
- a) Lactose fermentation.
- b) The formation of kidney stones (struvite stones) by increasing urine pH.
- c) Resistance to fluoroquinolones.
- d) Biofilm formation on heart valves.
Answer: b) The formation of kidney stones (struvite stones) by increasing urine pH.
29. Type III secretion systems, found in many pathogenic Gram-negative bacteria like Salmonella and Pseudomonas, are used to:
- a) Import nutrients from the environment.
- b) Inject bacterial effector proteins (toxins/virulence factors) directly into host cells.
- c) Form endospores.
- d) Mediate conjugation.
Answer: b) Inject bacterial effector proteins (toxins/virulence factors) directly into host cells.
30. Which characteristic of Neisseria meningitidis is a major virulence factor contributing to its ability to cause invasive disease like meningitis?
- a) Its ability to ferment lactose.
- b) The presence of a polysaccharide capsule that helps evade phagocytosis.
- c) Its strict anaerobic nature.
- d) Its Gram-positive cell wall.
Answer: b) The presence of a polysaccharide capsule that helps evade phagocytosis.
31. The O antigen, core polysaccharide, and lipid A are components of which major Gram-negative bacterial structure?
- a) Flagella
- b) Pili
- c) Lipopolysaccharide (LPS)
- d) Peptidoglycan
Answer: c) Lipopolysaccharide (LPS)
32. Enterobacter species are known for potentially possessing inducible AmpC β-lactamases, which can lead to resistance developing during therapy with:
- a) Aminoglycosides.
- b) Third-generation cephalosporins (e.g., ceftriaxone, ceftazidime).
- c) Vancomycin.
- d) Trimethoprim/sulfamethoxazole.
Answer: b) Third-generation cephalosporins (e.g., ceftriaxone, ceftazidime).
33. Which of the following is a principle regarding infections caused by Pseudomonas aeruginosa?
- a) They are easily treated with oral penicillin.
- b) They often require combination antibiotic therapy, especially for serious infections, due to intrinsic and acquired resistance.
- c) They are exclusively community-acquired.
- d) They are always susceptible to trimethoprim/sulfamethoxazole.
Answer: b) They often require combination antibiotic therapy, especially for serious infections, due to intrinsic and acquired resistance.
34. Carbapenem-resistant Enterobacterales (CRE) are a significant concern because:
- a) Carbapenems are often last-line agents for multidrug-resistant Gram-negative infections, and resistance leaves few options.
- b) They are only found in animals.
- c) They are easily treated with older penicillins.
- d) They primarily cause skin infections.
Answer: a) Carbapenems are often last-line agents for multidrug-resistant Gram-negative infections, and resistance leaves few options.
35. Citrobacter freundii is an Enterobacterales member that can cause opportunistic infections and is notable for its ability to:
- a) Produce a red pigment.
- b) Hydrolyze urea rapidly, similar to Proteus.
- c) Possess an inducible AmpC β-lactamase, similar to Enterobacter.
- d) Not ferment glucose.
Answer: c) Possess an inducible AmpC β-lactamase, similar to Enterobacter.
36. The interactions of Gram-negative bacteria with the host immune system, particularly the inflammatory response triggered by LPS, can lead to the clinical syndrome of:
- a) Allergic rhinitis.
- b) Sepsis and septic shock.
- c) Type 1 diabetes.
- d) Osteoarthritis.
Answer: b) Sepsis and septic shock.
37. Serratia marcescens is an Enterobacterales known for causing opportunistic infections and sometimes producing a characteristic:
- a) Green pigment.
- b) Red pigment (prodigiosin).
- c) Swarming motility.
- d) Potent neurotoxin.
Answer: b) Red pigment (prodigiosin).
38. Which Gram-negative bacterium is a common cause of healthcare-associated pneumonia, particularly ventilator-associated pneumonia (VAP), and is known for its environmental resilience?
- a) Streptococcus pyogenes
- b) Acinetobacter baumannii
- c) Listeria monocytogenes
- d) Mycoplasma pneumoniae
Answer: b) Acinetobacter baumannii
39. The term “pleomorphic” as applied to some Gram-negative bacteria like Haemophilus indicates that they:
- a) Are perfectly spherical.
- b) Exhibit variability in shape and size.
- c) Always occur in chains.
- d) Are obligate intracellular parasites.
Answer: b) Exhibit variability in shape and size.
40. A key principle for managing infections caused by multidrug-resistant Gram-negative bacteria is the importance of:
- a) Using subtherapeutic doses of antibiotics.
- b) Infection control measures to prevent spread, antimicrobial stewardship, and often consultation with infectious disease specialists.
- c) Relying solely on outdated antibiotics.
- d) Treating all colonized patients.
Answer: b) Infection control measures to prevent spread, antimicrobial stewardship, and often consultation with infectious disease specialists.
41. The presence of porin channels in the outer membrane of Gram-negative bacteria is crucial for:
- a) Allowing entry of small, hydrophilic nutrients and some antibiotics.
- b) Preventing all substances from entering the periplasm.
- c) Anchoring the flagella.
- d) Synthesizing LPS.
Answer: a) Allowing entry of small, hydrophilic nutrients and some antibiotics.
42. Mutations or loss of porin channels can contribute to antibiotic resistance in Gram-negative bacteria by:
- a) Increasing the uptake of antibiotics.
- b) Decreasing the permeability of the outer membrane to certain antibiotics, reducing their intracellular concentration.
- c) Enhancing the activity of beta-lactamases.
- d) Modifying the antibiotic target site.
Answer: b) Decreasing the permeability of the outer membrane to certain antibiotics, reducing their intracellular concentration.
43. Which group of Enterobacterales is generally lactose non-fermenting and includes important human pathogens like Salmonella and Shigella?
- a) Escherichia coli and Klebsiella pneumoniae
- b) While some classifications vary, historically these are distinct from strong lactose fermenters.
- c) Enterobacter cloacae
- d) Citrobacter freundii
Answer: b) While some classifications vary, historically these are distinct from strong lactose fermenters. (This is a classic microbiology distinction taught).
44. The primary mode of transmission for most Salmonella gastroenteritis is:
- a) Airborne droplets.
- b) Consumption of contaminated food (especially poultry, eggs) or water.
- c) Sexual contact.
- d) Tick bites.
Answer: b) Consumption of contaminated food (especially poultry, eggs) or water.
45. Efflux pumps are protein complexes in bacteria that actively transport substances, including antibiotics, out of the cell. This is a significant resistance mechanism in many Gram-negative bacteria against antibiotics like:
- a) Vancomycin (too large for many common efflux pumps)
- b) Fluoroquinolones, tetracyclines, and macrolides (in some G-).
- c) Penicillin G only.
- d) Daptomycin.
Answer: b) Fluoroquinolones, tetracyclines, and macrolides (in some G-).
46. One reason why Gram-negative bacteria are intrinsically more resistant to some antibiotics (like vancomycin) compared to Gram-positives is:
- a) Their thicker peptidoglycan layer.
- b) The presence of the outer membrane, which acts as a permeability barrier.
- c) Their lack of ribosomes.
- d) Their ability to form spores.
Answer: b) The presence of the outer membrane, which acts as a permeability barrier.
47. Biofilm formation by Gram-negative bacteria like Pseudomonas aeruginosa is a virulence factor because it:
- a) Makes the bacteria more susceptible to antibiotics.
- b) Protects bacteria from host immune responses and antimicrobial agents.
- c) Helps bacteria move rapidly.
- d) Is essential for lactose fermentation.
Answer: b) Protects bacteria from host immune responses and antimicrobial agents.
48. The interaction between Helicobacter pylori and the gastric mucosa, leading to inflammation and ulcers, involves virulence factors such as:
- a) Endospore formation.
- b) Urease (to neutralize stomach acid), adhesins, and toxins like CagA and VacA.
- c) A thick polysaccharide capsule preventing phagocytosis in the stomach.
- d) Rapid fermentation of lactose.
Answer: b) Urease (to neutralize stomach acid), adhesins, and toxins like CagA and VacA.
49. Which of the following is NOT a typical characteristic or disease association for the Enterobacterales group?
- a) Gram-negative rods.
- b) Common cause of urinary tract infections.
- c) Frequent cause of whooping cough.
- d) Many are facultative anaerobes.
Answer: c) Frequent cause of whooping cough. (Whooping cough is caused by Bordetella pertussis).
50. Understanding the principles of important Gram-negative bacteria is crucial for pharmacists to:
- a) Perform surgical debridement of infected wounds.
- b) Appreciate the rationale for empiric antibiotic choices, interpret culture and susceptibility reports, and counsel on preventing and managing infections.
- c) Design new vaccines for all Gram-negative pathogens.
- d) Only handle antibiotics targeting Gram-positive bacteria.
Answer: b) Appreciate the rationale for empiric antibiotic choices, interpret culture and susceptibility reports, and counsel on preventing and managing infections.