AP-Micro Bacterial Classification 2 — Questions and Answers
Question 1: Which bacterial structure is the primary target of the Gram stain procedure?
- Cell membrane
- Peptidoglycan cell wall (Correct answer)
- Outer membrane
- Capsule
Correct answer: Peptidoglycan cell wall
The Gram stain differentiates bacteria based on the thickness of their peptidoglycan cell wall.
Question 2: Bacteria classified as obligate anaerobes would be killed by exposure to which condition?
- High salt concentration
- Acidic pH
- Molecular oxygen (Correct answer)
- UV radiation
Correct answer: Molecular oxygen
Obligate anaerobes lack the enzymes needed to detoxify reactive oxygen species, so oxygen is lethal to them.
Question 3: Which of the following best describes the classification of Mycobacterium tuberculosis?
- Gram-negative rod
- Gram-positive coccus
- Acid-fast bacillus (Correct answer)
- Spirochete
Correct answer: Acid-fast bacillus
Mycobacterium tuberculosis stains acid-fast due to its waxy mycolic acid-rich cell wall rather than staining in a typical Gram reaction.
Question 4: A bacterium that grows optimally at temperatures between 20°C and 45°C is classified as a:
- Psychrophile
- Mesophile (Correct answer)
- Thermophile
- Hyperthermophile
Correct answer: Mesophile
Mesophiles thrive at moderate temperatures (20–45°C) and include most human pathogens.
Question 5: Which feature distinguishes Archaea from Bacteria at the molecular level?
- Presence of ribosomes
- Circular chromosome
- Ether-linked membrane lipids (Correct answer)
- Binary fission reproduction
Correct answer: Ether-linked membrane lipids
Archaea have ether-linked lipids in their membranes, whereas Bacteria have ester-linked lipids.
Question 6: The Bergey's Manual of Systematic Bacteriology classifies bacteria primarily based on:
- Colony morphology alone
- Phylogenetic and phenotypic characteristics (Correct answer)
- Pathogenicity and virulence
- Geographic origin
Correct answer: Phylogenetic and phenotypic characteristics
Bergey's Manual uses a combination of genetic (16S rRNA phylogeny) and phenotypic data to classify prokaryotes.
Question 7: A microbiologist identifies a bacterium as coagulase-positive. This result is most useful in identifying which organism?
- Streptococcus pyogenes
- Staphylococcus aureus (Correct answer)
- Escherichia coli
- Bacillus anthracis
Correct answer: Staphylococcus aureus
Coagulase positivity is a key biochemical marker that distinguishes Staphylococcus aureus from other staphylococci.
AP-Micro Bacterial Classification 2
Which bacterial structure is the primary target of the Gram stain procedure?