microbiology Flashcards
(44 cards)
Q: What are the three main shapes of bacteria?
A: Cocci (spherical), Bacilli (rod-shaped), Spirochaetes (spiral-shaped).
Q: Name bacterial arrangements with examples.
Clusters: Staphylococci
Chains: Streptococci
Pairs: Diplococci
Tetrads: Micrococci
name the two parts of bacterial names
genus name- group with similar overall characteristics, species name sub group with same biochemical charac.
Q: What is Gram staining and who developed it?
A technique to differentiate bacteria based on cell wall composition, developed by Christian Gram in 1884
How do Gram-positive and Gram-negative bacteria differ?
Gram-positive: Thick peptidoglycan cell wall, stains purple/holds on to the stain.
Gram-negative: Thin cell wall, stains pink/red
Q: What are the different types of media used for bacterial growth?
Undefined media: Supports broad growth, e.g., Horse Blood Agar.
Chemically defined media: Synthetic or complex broths.
Functional types: Supportive, enriched, selective, differential.
Physical nature: liquid, semi-solid, solid/agar
Q: What are the oxygen requirements for bacterial growth?
Aerobes: Require oxygen.
Anaerobes: Die in oxygen presence (e.g., Fusobacterium sp.).
Aerotolerant: Grow without oxygen using co2 but are not harmed by it.
Microaerophiles: Grow in low oxygen concentrations.
What are methods to quantify bacterial growth?
Microscopic cell counting using a gridded slide.
Serial dilution and plating.
Optical density measurement (spectrophotometer at 600nm).
qPCR (gene expression measurement).
What are the traditional methods used to identify bacteria?
Morphology – Observing bacterial shape and arrangement under a microscope.
Gram Stain – Identifying if the bacteria are Gram-positive (purple) or Gram-negative (pink).
Biochemical Testing – Testing bacterial metabolism and enzyme production, such as:
Catalase test (distinguishes Staphylococcus from Streptococcus).
Coagulase test (Staphylococcus aureus is coagulase-positive).
Q: How is a bacterial sample grown for traditional identification?
Grow in broth – Bacteria are cultured in a basic broth (e.g., Tryptic Soy Broth or Luria Broth) overnight at 37°C.
Plate onto agar – A portion of the culture is streaked onto an all-purpose agar medium (e.g., Horse Blood Agar).
Observe colony characteristics – Shape, color, hemolysis (if applicable).
Perform Gram stain & biochemical tests – Helps narrow down the species.
What are the modern techniques for bacterial identification?
PCR (Polymerase Chain Reaction) –
Detects bacterial DNA, particularly the 16S rRNA gene, which is unique to different bacteria.
Used since the early 2000s.
MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Spectrometry) –
Analyzes the protein composition of bacterial cells.
Faster and more accurate than traditional methods.
Q: What are the four phases of bacterial growth?
Lag phase – Bacteria adjust to the environment.
Exponential phase – Rapid bacterial division.
Stationary phase – Nutrient depletion slows growth. no of cells growing=no of cells dying
Death phase – Bacteria die due to lack of nutrients.
What are the four phases of bacterial growth in oral cavity?
Lag phase = immediately after meal, or after initial infection, adjusting to new
influx of nutrients, or new conditions, respectively.
Exponential phase = High nutrient availability post-meal, or post-adjustment,
respectively. Cells dividing at exponential rate (2,4,8,16 etc.)
Stationary = period of fasting in between meals, nutrients limited, bacteria
susceptible to antimicrobials. Lack of available space and competition for
resources also triggers this phase.
Death phase = variable between bacteria e.g., Streptococcus gordonii cannot
survive for prolonged periods without nutrients, but others can by forming
colonies.
what is a significant disease causing species in oral cavity
streptocpcci, gram +ve, cocci shaped, some can lyse RBC, related to poor oral health e.g. gordonii, salivarius, sanguis and disease causing ones are pyogenes, mutans.
Q: Which bacterial species are associated with tooth decay?
Streptococcus mutans
Streptococcus pyogenes
Q: Which bacteria cause gum disease?which ones are for advanced periodontitis?
Treponema denticola (advanced)
Porphyromonas gingivalis (advanced)
Fusobacterium nucleatum
Prevotella intermedia
Selenomonas sputigena.
bacteria causing the juvenile periodontitis?
microaerophile Actinobacillus actinomycetemcomitans
Q: What is a biofilm?
A: A matrix-encased community of microbes that accumulate on a surface.
Q: How does a biofilm function?
A: It distributes nutrients, protects against the immune system, and acts as a unified microbial community.
Q: What is dental plaque?
A: A biofilm of various bacterial species that forms on teeth.
Q: What are the four stages of biofilm formation?
Adhesion – Bacteria attach to the surface using receptors.
Early colonisers – Initial bacterial species settle.
Later colonisers – More species join.
Mature plaque – The biofilm becomes structured and resilient.
Q: What is the salivary pellicle, and what does it do?
A: A thin protein layer that forms on the tooth seconds after brushing, allowing bacteria to attach.
Q: What compounds are found in the salivary pellicle?
A: Over 100 salivary glycoproteins, lipids, proline-rich peptides, amylase, and glucan.
how does salivary pellicle causes bacterial attachment?
receptors on glycoproteins bind glucose binding proteins which in turn bind to receptors on bacterial cells.
