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
What are the 4 types of O2 requirements for bacteria?
1: Obligate aerob: requires oxygen to grow.
2: Obligate anaerob: killed by normal atmospheric concentrations of oxygen (20.95% O2). Dont need O2 to grow.
3: Facultative anaerob: an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absen
4: Microaerophil / aerotolerant (more CO2 required). Microaerophiles require oxygen (typically 2-10% O2) for growth
Aerobs: possessing catalase and superoxide-dismutase enzymes. Carbohydrate metabolism
Anaerobs: no enzymes to neutralise toxic oxygenic materials. Fermentation!
Ability to neutralise toxic oxygen forms:
Superoxide dismutase (2 O2- + 2 H+ H2O2 + O2)
Catalase (2 H2O2 2 H2O + O2)
What are the 4 stages in growth of bacteria?
I. Lag phase (adaptation)
II. Log phase (exponential growth)
III. Stationer phase (cell number steady)
IV. Declination phase (decrease in number)
What types of agar do we use?
1: Simple
2: Blood: For the cultivation of fastidious bacteria (eg. Streptococcus pneumoniae). 5 % sterile blood RBC + protein: nutrient, FFA-neutralisation
3: Chocolate: For more fastidious bacteria (eg. Haemophilus influenzae). Heating blood agar. Release of haem
all in a petri dish
How do we describe colonies in a petri dish?
colony size colony shape (round, cloud-like) colony consistence (smooth, dry, rough) colony colour (pigment production) hemolysis: alpha and beta smell (lime tree, garlic)
How can anaerobic bacteria be cultivated?
Anaerostat: N2-CO2 gas mixture insted of air
Liquid media: Removing O2 by 10-20 min boiling. Inoculation after cooling. Isolation with paraffine waw.
Chemical method: Decrease redox potential.
Biological method: Fortner- technology. One half of the petri dish with an very aerob bacteria, the second half with an anaerobic one.
What is the deal with biofilms?
Make slime on suitable surfaces. Made of a polysaccharide matrix.
99% of microorganism in water live as biofilms on surfaces
Advantage for bacteria: Protection against antibiotics, immune system. Nutrient trap
Catheters, canules, branuls, impalntations, prosthesis, pacemakers, artificial heart valves!
Frequent exchange!
Diseases involving biofilm:
Native heart valve endocarditis (Streptococcus, S. aureus, KNS, Enterococcus, Gram -, Candida, Aspergillus)
Implantates: venous canules (central or periferial), urinary catheters (Enterococcus, Gram Pseudomonas, Serratia, Citrobacter), artificial valve, intrauterine devices (IUD), dental implantates (titanium), contact lenses, implanted eye lense, hip protesis, …
Chronic bacterial prostatitis
CF (cystic fibrosis): Pseudomonas aeruginosa, S. aureus, Burkholderia, H. influenzae (alginate formation!)
periodontitis, dental plaque
Disinfectant are compared relative to?
The effect of phenol - “phenol coefficient”
To calculate phenol coefficient, the concentration of phenol at which the compound kills the test organism in 10 minutes, but not in 5 minutes, is divided by the concentration of the test compound that kills the organism under the same conditions (or, probably more common, dividing the dilution factor at which the tested substance shows activity by the dilution factor at which phenol shows comparable activity)
Name som physical sterilization methods
Heat
1: Burning at over 1000C (burning until red glow for metal devices and glass)
2: Dry heat: More hours. E.g 180C (1h), 160C (2h) or 140C (3h). For inflammable materials.
3: Wet heat: Autoclave (hot saturated stea). 121C at 1 atm for 30 min or 134C at 2 atm for 10 min.
4: Chilling and cold: Doest not kill but limits growth.
Radiation
1: Gamma radiation. Dangerous and expensive
2: UV radiation. Destroy germs in air or operation theatres and laboratories.
Name some chemical sterilization methods
Gas sterilization: Previously ethylene-oxide, nowadays β-propiolactone. Reactive alkyling agents (formaldehyde). Although; carcinogenic, requires ventilation for days (min. 48 h)
Cold sterilization with chemicals: Glutaric aldehyde. Billman solution. Sterilization time -> 3 h
Plasma sterilization: Ions and free radicals in gas phase. H2O2 vaporize. No toxic products.
