General microbiology Flashcards
What does the cell wall in gram positive bacteria consist of?
A thick peptidoglycan layer
Contains Teichoic acid
No periplasmic space
Vulnerable to lysozyme and penicillin
What does the cell wall in gram negative bacteria consist of?
Thin peptidoglycan layer and a layer of LPS
Contains murein lipoproteins
Have a periplasmic space and porin channels
NOT sensitive to lysozyme and penicillin attack
Gram staining: What is it, what do we use and what are the colors?
Gram staining, is a method of staining used to differentiate bacterial species into two large groups (gram-positive and gram-negative). The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique.
Gram staining differentiates bacteria by the chemical and physical properties of their cell walls by detecting peptidoglycan, which is present in the cell wall of gram-positive bacteria.
Gram-positive bacteria retain the crystal violet dye, and thus are stained violet/blue, while the gram-negative bacteria do not; after washing, a counterstain is added (commonly safranin) that will stain these gram-negative bacteria a pink/red color
What are the steps in Gram staining?
1: Crystal violet stain (a blue dye) for 1-2 min
2: Wash off with water and iodine (Lugol) for 1 min
3: Wash off with water and alcohol (95%)
4: Counter-stain with safrain (a red dye). Wait 1 min and wash off
What links the peptidoglycans in the cell wall? is there any antibiotics that work against it?
Transpeptidase (inhibited by pencillin: Beta-lactam).
What are the structure of LPS?
Lipid A (endotoxin)
Core polysaccaride
O-specific side chain (Antigen determinant O-antigen) - 40 unit repeats
Endotoxin can cause fever, diarrhea and possible endotoxic shock (septic shock)!
What are the different clarifications of bacteria based on morphology?
Round = cocci
Rods: Bacilli
Short bacilli are called coccobacilli
Spiral shaped
PleomorphicWhat are the 3 different types of symbiosis?
• mutualism: advantageous for both (reciprocal benefit)
• commensalism: do not damage each other (neutral)
• parasitism: advantageous for microorganism
(unilateral benefit)
damages to macroorganisms → disease
What are the 3 different types of classification of parasites?
– obligate parasites: in defined host (range of hosts)
always pathogenic, never found in the normal flora
– facultative parasites: depending on the condition of both host and microbe, presence of predisposing /risk factors, members of the normal flora
– opportunistic parasites: member of the environment, not pathogenic for healthy people, take advantage in case of host disorders (usually immunosuppression)
How do we make a “simple stain”?
methylene blue for 1 min
What is consider to be a synonym to endotoxin?
Lipid A for LPS in gram negative bacteria
Structure of peptidoglycan
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Different types of hemolysis
Used for streptococcus species. Blood agar is a solid growth medium that contains red blood cells. The medium is used to detect bacteria that produce enzymes to break apart the blood cells. This process is also termed hemolysis. The degree to which the blood cells are hemolyzed is used to distinguish bacteria from one another.
Alpha hemolysis (α-hemolysis) is present, the agar under the colony is dark and greenish. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha hemolysis. This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin.
Beta hemolysis (β-hemolysis), sometimes called complete hemolysis, is a complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. E.g. Staphylococcus aureus, Streptococcus pyogenes, Bacillus cereus
If an organism does not induce hemolysis, the agar under and around the colony is unchanged, and the organism is called non-hemolytic or said to display gamma hemolysis (γ-hemolysis)
https: //en.wikipedia.org/wiki/Hemolysis_(microbiology)#/media/File:Streptococcal_hemolysis.jpg
https: //upload.wikimedia.org/wikipedia/commons/0/03/Gram-Positive_Classification.png
What is the “simple stain”?
Methylene blue - everything will have the same colour
What are the 3 types of nutrient types of bacteria?
Autotrophic: make organic from inorganic
Paratrophic: survive only in living cells
Hetrotrophic: require organic meterials carbon and nitrogen sources
