Flashcards in Medical Microbiology Deck (109):
What are psychrophiles
Microorganisms that can grow in extremely cold temperatures (-20)
How many chromosomes do prokaryotes have?
What type of ribosomes do prokaryotes have?
What type of ribosomes do eukaryotes have?
How big are prokaryote cells?
1 - 10 um
How big are eukaryote cells?
10 - 100 um
What are the 6 shapes of bacteria?
Give an example of a coccus bacteria?
Give an example of a vibrio bacteria
Give an example of a bacillus bacteria?
Give an example of a coccobacillus?
What are the three growth types for cocci?
What are the 4 components used in the gram stain?
Crystal violet primary stain
What is the primary stain in gram staining and what does it do?
Crystal violet dye - stains all cells purple
What is the mordant used in gram staining and what does it do?
Iodine. It forms insoluble complexes with the crystal violet dye
What is the decolouriser used in gram staining and what does it do?
Removes crystal violet iodine complexes from gram negative but not gram positive
What is the counterstain used in gram staining and what does it do?
Safarin. It stains both cell types pink
What does the peptidoglycan layer contain in gram positive cells?
Teichoic acids and lipteichoic acids
What is the role of the s layer in bacterial cells?
To hide from the immune system
What does the outer membrane of gram negative bacteria contain?
Porins and endotoxin. Endotoxin activates the innate immune system.
Where is the s layer found on gram postive and gram negative bacterial cells?
Peptidoglycan layer of gram positives. Outer membrane of gram negatives.
What is peptidoglycan made up of?
Repeating structure of 2 alternating sugars (nam and nag) crosslinked by peptides
Which enzymes are involved in peptidoglycan synthesis?
Transglycosylases which connect sugars and transpeptidases which form peptide crosslinks
How do beta lactams inhibit cell wall synthesis?
Inhibit transpeptidase reaction
How does vancomycin inhibit cell wall synthesis?
Binds to d-ala-d-ala to stop cross linking
What is the glycocalyx? Give examples
Generic name for extracellular polymers. Capsule and slime layer
What is the capsule used for?
What is the slime layer used for?
What are 3 types of pili?
Type 4 pili
What are fimbriae?
Short pili which are used to attach bacteria to surfaces. They are made up of helically arranged proteins tipped with adhesive proteins.
What are type 4 pili used for?
How do cells move?
Runs and tumbles
When a cell is near an attractant, how do its runs and tumbles change?
Tumbles are less frequent. Runs are longer.
Which type of bacteria form endospores and in what situation?
Gram positive bacteria form endospores when nutrients run out
What are the 4 arrangements of flagella?
What are the 6 shapes of bacterial cells, give examples of each
Bacillus (p aeruginosa)
Vibrio (vibrio cholerae)
What are the 3 growth types for cocci?
Requires salt to grow
Can grow in mild salt concentrations but grow best without salt
Can survive in high sugar environments
Can survive in dry environments (usually fungi)
Grows best between pH 5.4 and 8.5
Optimum is around room temperature but can grow in the fridge
Optimum between 20 and 40 degrees (all animal pathogens)
Optimum 50 to 80 degrees
Has SOD and catalase
Has SOD and catalase
Does not require oxygen but grows best when oxygen is available
Fermentation when oxygen is unavailable
Has SOD but not catalase
Grows equally well with or without oxygen
Has neither SOD nor catalase
Some tolerate oxygen, some killed by it
Has SOD and some have catalase
Grows best in low oxygen conditions
An organism which uses oxygen as the terminal electron acceptor in a respiratory chain
Can aerobes carry out fermentation?
What charge does a biofilm matrix have?
What are persister cells?
They are found in biofilms. They neither grow nor die in the presence of antimicrobials. They are multi drug tolerant (MDT)
Why is natural flora important?
Prevents growth of pathogenic flora by competition and amensalism (secretion of inhibitory substances)
Factors determining microbiome
How is flora on the skin limited?
Lack of nutrients
Disinfectant secretions (lysozyme which cleaves peptidoglycan and cathelicidin which forms pores)
What is the microbiome of the oropharynx?
(Like elevated CO2 and are slow growing)
How are microbes removed from the respiratory tract?
What does the the colon microbiome secrete?
Vitamin k and B
What are antimicrobial secretions?
What is found in granules of NK cells?
Perforin and granzyme
Infectious dose 50. Number of cells that results in disease for 50% of population
How do pathogens attach to host cells?
How do microbes cross the mucosa?
The use M cells
Name the 4 classes of s aureus virulence factors
Name the 2 invasins in s aureus
What does staphylokinase do?
Cleaves plasminogen to plasmin which degrades fibrin clots. Cleaves IgG. Cleaves C3b which inhibits phagocytosis
What does hyaluronidase do?
Lyses hyaluronic acid found in connective tissue which causes tissue breakdown
What 3 substances does s aureus use to evade the immune system?
S aureus protein A
What does coagulase do?
Reacts with thrombin forming staphylothrombin which cleaves fibrinogen to fibrin. S aureus coated with fibrin can evade the immune system
What does staphyloxanthin do?
Antioxidant that protects against ROS
What does s aureus protein do?
Binds to Fc portion of IgG and prevents phagocytosis by preventing opsonisation
What is PVL?
S aureus toxin which is cytotoxic to WBC
Name 3 s aureus toxins
What does pyrogenic toxin cause?
Toxic shock syndrome
How does superantigen cause toxic shock syndrome?
More T cells activated so more cytokines activated
What does exfoliating toxin do?
Cleaves cadherin which forms junctions between skin cells. Leads to skin peeling
Propensity for transmission. Measured by secondary attack rate in a household
Secondary attack rate
Rates of infection among individuals exposed to a first case
Measure of disease causing propensity (ID50)
Propensity to cause severe disease. Measured by fatality ratio or LD50
Time between exposure and onset of symptoms
What are the 5 Is?
Blood heated to release nutrients
Name the 5 selective media
Phenylethyl alcohol agar
Selects out gram negatives by reversibly inhibiting their dna synthesis
Baird parker agar
Contains egg yolk
Lactose fermenting - metal sheen
Non lactose fermenting - colourless
Selects gram negatives (bile salts inhibit growth of gram positives)
Lactose fermenting - produces acid so indicator turns red
Non lactose fermenting - colourless
Likes elevated CO2 conc
Lots of haemolysis
What are 6 biochemical tests?
Cytochrome c oxidase (purple when positive)
Tests for tryptophanase which turns tryptophan into pyruvate, indole and urea. DMAB turns red when indole present
Urease hydrolyses urea to ammonia which increases pH. Indicator turns pink
Mix with plasma, look for clot
Positive - acid or gas production
Acid turns indicator yellow
Gas in collected in upturned durham tube
What are the cons of traditional methods?
Organism must be able to be cultured in vitro (obligate intracellular cannot)
Poor discrimination between similar microbes
What immunological methods are used?
Antigen from patient
Fluorescent antigen from lab
Antigen from lab mixed with patient serum. Antibody against patient antibody fluoresces
What are the molecular methods used?
PCR and real time PCR
Nucleic acid probes
What are the 4 different types of CD4 T cells?
What is the role of Th1 cells?
They recognise mycobacteria derived antigens on macrophages and secrete cytokines which help overcome lysosome binding
What is the role of Th2 response?
Deals with infections at mucosal surfaces, parasite infections and allergies
Deals with extracellular bacteria and fungi