Gram Negative Bacteria Practice Questions
20 free Gram Negative Bacteria practice questions for the Microbiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which structural component is unique to Gram-negative bacteria and contributes to endotoxin activity?
- A Lipoteichoic acid
- B Lipopolysaccharide
- C Peptidoglycan
- D N-acetylglucosamine
Correct answer: Lipopolysaccharide
Lipopolysaccharide (LPS) is found in the outer membrane of Gram-negative bacteria. Its lipid A component acts as an endotoxin, triggering strong immune responses.
Which Gram-negative bacterium is oxidase positive and commonly causes hospital-acquired infections?
- A Acinetobacter baumannii
- B Klebsiella pneumoniae
- C Pseudomonas aeruginosa
- D Proteus mirabilis
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa is oxidase positive and known for causing opportunistic infections, especially in hospital settings. It is also resistant to many antibiotics.
Which Gram-negative diplococcus is a common cause of sexually transmitted infections?
- A Neisseria meningitidis
- B Neisseria gonorrhoeae
- C Moraxella catarrhalis
- D Haemophilus influenzae
Correct answer: Neisseria gonorrhoeae
Neisseria gonorrhoeae is a Gram-negative diplococcus that causes gonorrhea. It is transmitted sexually and infects mucosal surfaces.
Which Gram-negative bacterium is known for producing a green pigment and fruity odor?
- A Klebsiella pneumoniae
- B Escherichia coli
- C Pseudomonas aeruginosa
- D Acinetobacter baumannii
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa produces pigments such as pyocyanin and has a characteristic fruity odor. These features help in its identification.
Which Gram-negative bacterium is the causative agent of enteric fever?
- A Shigella dysenteriae
- B Salmonella typhi
- C Vibrio cholerae
- D Campylobacter jejuni
Correct answer: Salmonella typhi
Salmonella typhi is the causative agent of typhoid fever. It invades intestinal mucosa and spreads systemically through the bloodstream.
Which Gram-negative bacterium is lactose fermenting and appears pink on MacConkey agar?
- A Salmonella typhi
- B Shigella flexneri
- C Proteus vulgaris
- D Escherichia coli
Correct answer: Escherichia coli
Escherichia coli ferments lactose, producing pink colonies on MacConkey agar. This distinguishes it from non-lactose fermenters.
Which curved Gram-negative bacterium produces a toxin that causes profuse rice-water diarrhea?
- A Helicobacter pylori
- B Campylobacter jejuni
- C Shigella sonnei
- D Vibrio cholerae
Correct answer: Vibrio cholerae
Vibrio cholerae is a curved, comma-shaped Gram-negative bacterium. It produces cholera toxin, leading to severe watery diarrhea.
Which Gram-negative bacterium is urease positive and associated with gastric ulcers?
- A Helicobacter pylori
- B Escherichia coli
- C Shigella dysenteriae
- D Salmonella typhi
Correct answer: Helicobacter pylori
Helicobacter pylori produces urease, which neutralizes stomach acid. This allows it to colonize the gastric mucosa and contribute to ulcers.
Which Gram-negative bacterium is known for swarming motility on agar?
- A Proteus mirabilis
- B Klebsiella pneumoniae
- C Escherichia coli
- D Shigella sonnei
Correct answer: Proteus mirabilis
Proteus mirabilis exhibits swarming motility due to its flagella. This results in characteristic spreading growth on agar plates.
Which encapsulated Gram-negative diplococcus is a leading cause of bacterial infection of the cerebrospinal fluid?
- A Neisseria gonorrhoeae
- B Moraxella catarrhalis
- C Haemophilus influenzae
- D Neisseria meningitidis
Correct answer: Neisseria meningitidis
Neisseria meningitidis has a polysaccharide capsule that enhances virulence. It is a major cause of bacterial meningitis.
Which Gram-negative bacterium is non-motile and has a prominent capsule giving mucoid colonies?
- A Escherichia coli
- B Proteus mirabilis
- C Salmonella typhimurium
- D Klebsiella pneumoniae
Correct answer: Klebsiella pneumoniae
Klebsiella pneumoniae is non-motile and produces a thick capsule. This results in mucoid colonies and increased resistance to host defenses.
Which Gram-negative bacterium produces Shiga toxin?
- A Escherichia coli O157:H7
- B Yersinia enterocolitica
- C Plesiomonas shigelloides
- D Campylobacter jejuni
Correct answer: Escherichia coli O157:H7
Certain strains of Escherichia coli, such as O157:H7, produce Shiga toxin. This toxin damages intestinal cells and can cause hemolytic uremic syndrome.
Which Gram-negative bacterium is microaerophilic and associated with foodborne diarrhea?
- A Campylobacter jejuni
- B Vibrio cholerae
- C Shigella dysenteriae
- D Salmonella typhi
Correct answer: Campylobacter jejuni
Campylobacter jejuni is microaerophilic and commonly transmitted through contaminated food. It causes inflammatory diarrhea.
Which Gram-negative bacterium is oxidase positive and requires X and V factors for growth?
- A Haemophilus influenzae
- B Neisseria gonorrhoeae
- C Pseudomonas aeruginosa
- D Klebsiella pneumoniae
Correct answer: Haemophilus influenzae
Haemophilus influenzae requires hemin (X factor) and NAD (V factor) for growth. These requirements are important for laboratory identification.
Which non-motile Gram-negative bacterium invades colonic epithelium and causes bloody diarrhea with mucus?
- A Shigella dysenteriae
- B Salmonella typhi
- C Vibrio cholerae
- D Campylobacter jejuni
Correct answer: Shigella dysenteriae
Shigella dysenteriae invades intestinal epithelial cells and produces shiga toxin. This leads to inflammation and bloody diarrhea.
Which Gram-negative bacterium is a facultative intracellular pathogen commonly transmitted through unpasteurized dairy products?
- A Brucella species
- B Salmonella typhi
- C Shigella sonnei
- D Vibrio cholerae
Correct answer: Brucella species
Brucella species are facultative intracellular bacteria that infect macrophages. They cause brucellosis, often transmitted from animals.
Which Gram-negative bacterium is associated with plague?
- A Francisella tularensis
- B Brucella melitensis
- C Vibrio cholerae
- D Yersinia pestis
Correct answer: Yersinia pestis
Yersinia pestis is the causative agent of plague. It is transmitted by flea bites and can cause bubonic, septicemic, or pneumonic forms.
Which Gram-negative bacterium is a non-lactose fermenter and produces hydrogen sulfide?
- A Escherichia coli
- B Klebsiella pneumoniae
- C Shigella sonnei
- D Salmonella typhi
Correct answer: Salmonella typhi
Salmonella typhi is a non-lactose fermenter that produces hydrogen sulfide. This results in black colonies on certain media like XLD agar.
Which Gram-negative bacterium is known for causing chancroid?
- A Haemophilus ducreyi
- B Neisseria gonorrhoeae
- C Treponema pallidum
- D Chlamydia trachomatis
Correct answer: Haemophilus ducreyi
Haemophilus ducreyi causes chancroid, a sexually transmitted infection characterized by painful ulcers. It is a Gram-negative coccobacillus.
Which Gram-negative bacterium has a bipolar 'safety pin' appearance on staining?
- A Yersinia pestis
- B Salmonella typhi
- C Escherichia coli
- D Vibrio cholerae
Correct answer: Yersinia pestis
Yersinia pestis shows bipolar staining, giving it a 'safety pin' appearance. This is a key diagnostic feature in microscopy.