Microbiology Techniques Flashcards
6 cards from real Laboratory Science practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Microbiology Techniques flashcards as text
What is the purpose of the Gram stain in clinical microbiology?
Answer: Differentiate bacteria into gram-positive and gram-negative based on cell wall structure
The Gram stain differentiates bacteria by their cell wall peptidoglycan thickness: gram-positive cells retain crystal violet (purple) while gram-negative cells stain red with safranin counterstain.
Which growth medium is selective for gram-negative enteric bacteria while inhibiting gram-positive organisms?
Answer: MacConkey agar
MacConkey agar contains bile salts and crystal violet that inhibit gram-positive bacteria, while lactose and pH indicator differentiate lactose-fermenting from non-fermenting gram-negatives.
What does a positive catalase test (bubbling with H₂O₂) indicate?
Answer: The organism produces catalase enzyme, suggesting Staphylococcus (not Streptococcus)
Catalase-positive organisms (like Staphylococcus) produce catalase that converts H₂O₂ to O₂ and water; Streptococcus is catalase-negative, a key differentiator.
Which temperature is standard for incubating most clinical bacterial cultures?
Answer: 35–37°C
Most pathogenic bacteria grow optimally at 35–37°C (human body temperature), making this the standard incubation temperature for clinical cultures.
What is the purpose of a streak plate technique in microbiology?
Answer: Isolate individual bacterial colonies from a mixed culture
The streak plate technique dilutes bacteria across successive sectors, producing isolated single colonies from a mixed specimen for pure culture isolation and identification.
Which test is used to differentiate Staphylococcus aureus from other coagulase-negative staphylococci?
Answer: Coagulase test
S. aureus produces coagulase enzyme that clots plasma, while coagulase-negative staphylococci (like S. epidermidis) do not, making the coagulase test the primary identifier.