Microbiology Flashcards
What do bacteria have instead of a nucleus?
Nucleoid- DNA and associated proteins
No nuclear membrane
Co transcription and translation via DNA dependent RNA polymerase
How is the chromosome arranged in a bacteria?
Single circular chromosome organised by gyrases
What are DNA gyrases?
Essential bacterial enzymes that catalyses the DNA dependant negative super coiling of double stranded closed circular DNA (part of topsomerases)
What are extra chromosomal replications called?
Plasmids
Where do most biochemical processes take place in a prokaryote?
The cell membrane as tehre are no membrane bound organelles
How is energy generated in a bacterial cell?
Electrons are released from high energy compounds in the cytoplasm. They reach the membrane and are passed through a series of electron acceptors.
The energy released from this pumps H+ ions outside of the membrane producing an electrochamical gradient.
Inflow of protons generates ATP.
NB: This occurs on the surface of the cell- therefore if you damage the membrane you will damage/kill the bacteria
What is peptidoglycan made from?
2 Sugars NAM = N-acetyl muramic acid NAG = N-acetyl glucosamine and peptide bridges with 5 types of protein Repeated polysaccharide structure
Why do bacteria require a cell wall?
High osmotic pressure and concentrated cytoplasm
What is the target for penicillin?
Peptidoglycan cell wall
Describe the cell wall in a gram positive bacteria?
Thick multilayered peptidogylcan
Rope structure
Survive 8-10 atmospheres
Describe the cell wall in a gram negative bacteria?
Thin peptidoglycan layer
Survive 5-6 atmospheres
2 cell membranes (inner and outer)
Lipopolysaccharide extensively on outer membrane
What is the role of glycolipids?
Lipid A and core polysaccharide
Structural support but also as an antigen, bacterial toxin
What are flagella and fimbrae?
Proteinachious extensions
Which bacteria have flagella and what is the function?
Both gram positive and gram negative
Huge SA to help with attachment and adhesion of bacteria together
Some inject RNA and toxins
Useful for motility
What is a fimbrae/pillus and which bacteria have which one?
Non flagella proteinacious abhendage
Fibrae = gram positive
Pillus = gram negative (=> biofilm formation)
Used for adherence and sex in both
Where does prokaryotic protein synthesis take place and what are the features?
Cytoplasmic membrane
Co-transcription/translation
No polyadenylation of transcript (addition of poly A tails to mRNA)
Rapid => higher mutation rate
What is required for binary fission?
Food: C, H, O, N, Inorganic salts (metal), Trace elements (Zn, Cu, Mn, Ni) and vitamins (Folic acid and Niacin)
Specific temp, pH, osmotic protection and oxygen concentration
What are the 4 phases of binary fission?
1) Lag phase
2) Exponential phase
3) Stationary phase- all nutrients used up
4) Decline phase- bacteria die and produce toxins. No more nutrients
What is a bacteria called that works at low, high and body temp?
Low = Psycrophiles
High = Thermophiles
Body temp = mesophiles
What is the preferred pH and osmotic protection for human commensal bacteria?
- 8-7.2 pH
0. 85% NaCl
What is a microaerophile?
A bacterium which requires oxygen at a less than atmospheric pressure
Bacteria can sense there population density. T or F?
True
What is multicellularity?
Colony development and differentiation
What are planktonic cells?
Free flowing bacteria in suspension
What is a biofilm?
A group of microorganisms that stick together on a surface
If cocci divide in one plane they produce…?
Chains eg Streptococci
If cocci divide in 3 planes they produce…?
Clumps eg staph aureus
If cocci divide in right angled planes they produce…?
Socina => Perfect packets of 4
What is a bacillus and how are they commonly found?
Rod shaped bacterium
Normally gram positive in chains
Give an example of a curved rod bacterium and the gram stain?
Vibro Cholerae
Gram negative
Give 2 examples of spiral shaped bacterium?
Rigid = Spirillium Flexible = Spirochaete
What is a fusiform bacteria?
A long elongated form
What are capsules made from and what is there function?
Carbohydrates,
Physical and chemical protection
What are spores?
Innert structures resistant to physical and chemical challenge. Resistant to disinfectant so survive a long time outside the body.
Produced by C diff
How are spores produced and released?
Binary fission -> Sporulation -> Prespore (dehydrated and condensed) -> endospore -> cell lysis -> germination of spore
What is gram staining?
The retention of crystal violet/iodine staining by gram positive bacteria
How is gram staining carried out?
1) Add cyrstal violet (the greater the PG the greater the uptake)
2) Add decolouring agent eg ethanol/acetone for 10-15 seconds. Decolourises the cell that has not taken up crystal violet
3) Add water to stop the decolourising process
4) Add the iodine complex to see colourless structures
What are the limitations of gram staining?
Not all organisms stain well eg mycobacterium have a lipid rich waxy cell wall, treponema pallidum (causes syphilis
What is an aerobic bacteria?
Grows in air/oxygen
What is an obligate aerobe?
Must have oxygen
What is an obligate anaerobe?
Killed by oxygen.
Respiration uses another electron acceptor (nitrogen)
Smaller reduction potential, less proton motive force across membranes and less energy released per molocule oxidised. (Alternative is fermentation)
What is a facultative anaerobe?
Tolerates oxygen
What is a capnophile?
Prefer CO2 conditions
What is a selective media?
a culture medium containing ingredients that inhibit growth of contaminants or microorganisms other than that desired.
What is a differential media?
a medium that can allow different types of organism to be distinguished by their different forms of growth.
What type of medium is Mannitol salt agar and what organism is it used to identify?
Selective
Staphylococci
What type of medium is Salmonella Shingella and what organism is it used to identify?
Selective
Bile salts and inhibits coliforms eg ecoli
What is haemolysis used to identify?
Streptococci
What is alpha, beta and gamma haemolysis?
Alpha = blaching of erythrocytes Beta = Bacteria digest erythrocytes around them = group A strep Gamma = no haemolysis
What type of medium is MacConkay agar and what organism is it used to identify?
Differential
Identification of enetrobacteriaceae
What type of medium is Eosin and methylene blue and what organism is it used to identify?
Differential
Identification of lactose fermenters like E coli
What is the linnaean classification?
King Philip came over from great spain Kingdom Phylum Class Order Family Genus Species
What biochemical tests/markers can hep identify bacteria?
Metabolic profiling
Exoenzyme production
Now all automater
What is a serological test and what are the advantages?
Agglutination reaction of IgM antibody with a specific antigen on bacteria
+ Rapid detection 24 hours, can identify different stereotypes of bacteria, works well if you know what you’re looking for
What is genome sequencing?
Sequence DNA targetusing PCR and primers and compare with many organisms that have already been sequenced
What is MALDI-TOF and what is it used for?
Used for identifying peptides an their patterns of arrangement. Works like a mass spectrometer.
Very precise identification of bacteria and cost effective
What is Multi locus sequence typing used for?
Checking resistance of an organism => targeted prescribing
What are the 8 steps to pathogenesis of bacteria?
1) Reservoir of pathogen
2) Enter host
3) Colonise/invade host
4) Overcome host defences
5) Multiply complete life cycle
6) Damage the host
7) Exit the host
8) Released and spread
What is an endogenous pathogen?
Pathogens which live in the body normally but become pathogenic
What is virulence?
The capacity of a microbe to cause damage to the host. LD50 is the level at which 50% of infected organisms die
What is a microbiome?
Natural microorganisms that live within the body
What is an exogeneous organism?
Not normal flora but can be beneficial and give protection from other microorganisms.
Can also be pathogenic
What is a pathogen?
A disease causing organism
What is a commensal?
An organism that is part of the normal flora. Often mutualistic symbiosis and an endogeneous organism
What is a contaminant?
Organism in a culture by accident
What is an opportunistic pathogen?
Organism that causes infection when opportunity/ change in natural immunity arises
Give 2 examples of common fungal pathogens?
Candida (budding yeast)
Linked to prescriptions of antibiotics because more nutrients are available and inhaler use as steroids suppress the immune system
Aspergillus (mould)
Infection in the immunocomprimised
Give 3 examples of protozoa?
Malaria, toxoplasma, Leishmaniasis
GI infection: cryptosporidiosis
Gram positive or gram negative: Neisseria?
-
Gram positive or gram negative: Escherichia?
-
Gram positive or gram negative: Streptococcus?
+
Gram positive or gram negative: Klebsiella?
-
Gram positive or gram negative: Enterobacter?
-
Gram positive or gram negative: salmonella?
-
Gram positive or gram negative: Staphylococcus?
+
Gram positive or gram negative: Enterococcus?
+
Gram positive or gram negative: Shingella?
-
Gram positive or gram negative: Haemophylous?
-
Gram positive or gram negative: Clostridium?
+
Gram positive or gram negative: Fusobacterium?
+
Gram positive bacteria produce endo/exotoxin?
Exotoxin
Gram negative bacteria produce endo/exotoxin?
Endotoxin
What is the most common cause of bacterial meningitis?
Neisseria Meningitidis
Gram negative cocci (aerobic diplococci)
What causes gonorrhoea?
Neisseria Gonorrhoea
Gram negative cocci (aerobic diplococci)
Becoming resistant to azithromycin
What is a colliform?
Species of gram negative bacilli that look like E coli on a gram film
What are the characteristics of coliforms?
Grow best aerobically but can grow anaerobically
Part of normal bowel flora
Differentiated from each other by biochemical reactions and the antigenic structure of the cell wall.
Where is a O antigen, K antigen and a H antigen found on a coliform?
O on the cell wall
H on flagella
K on the capsule
Gram positive or gram negative: Proteus?
-
When is endotoxin released?
Released from the cell wall when gram negative bacteria die
What is the first line antibiotic for coliforms?
Gentamycin
What is SIRS?
Systemic inflamatory response syndrome (Endotoxin shock)
What happens in SIRS?
Endotoxin, LPS, Peptidoglycan bind to receptors on macrophages. Endotoxins can also bind to T cells
=> Release of inflamatory cytokines and an immune response
Is a fever considered benifical in infection?
Yes as the higher temperature slows bacterial growth
What is sepsis?
Step up from SIRS.
1) Small blood vesels become leaky => oedema and reduced blood volume
2) Lower blood volume => lower BP and increased work of the heart to perfuse tissues
3) Poor perfusion means blood supply to less essential organs is shut down
4) COagulation cascade is activated => clotting in small vessels uses all the clotting factors => increased risk of haemorrhage
Which strep species show alpha haemolysis?
S. pneumoniae and S. viridans
Which strep species show beta haemolysis?
Strep group A, B, C, F, G
Which strep species show gamma haemolysis?
Strep group B and enterococci
What is VRE?
Vancomycin resistant Enterococci.
Common outbreaks in hospitals
Where is enterococci usually found?
Part of normal bowel flora and a common cause of UTI
What infections does S aureus usually cause?
Bone and joint infections
Skin and wound infections
Food poisoning
What infections are associated with staph epidemidis?
Infections associated with external devices eg heart valves and catheters.
Lives on skin and mucus membranes
Is staph aureus a aerobic bacteria?
Yes
What is MRSA and which patients are more likely to get it?
Methacillin resistant staph aureus
Elderly, immunocomprimised, burns and surgical patients
Dialasis and IV lines are risk factors
What type of organism is clostridium?
Gram positive ANAEROBIC organism which produces spores which can survive for months and exotoxins which cause severe tissue dammage
When does C diff perliferate?
In the absence of normal gut flora
Clostridium difficile causes what?
Chronic diarrhoea in elderly
Clostridium perfringes causes what?
Gangrene
Clostridium tetani causes what?
Tenanus
