Microbiology Flashcards
What are the three domains into which life is split?
- Bacteria
- Archaea
- Eukaryotes
What are the main pathogens that can affect humans?
. Bacteria
. Viruses
. Fungi
. Protozoa
. Prions
What is “Virulence”?
The level of infectivity of a pathogen
What is a bacterial cell wall composed of?
Peptidoglycan
What is peptidoglycan?
The main constitute of a bacterial cell wall.
It is essentially a sugar caging-repeating polysaccharide structure with peptide cross links- providing a rigid structure and a barrier
Which two types of bacterial cell wall exist?
Gram Positive
Gram Negative
(There are also bacteria without a cell wall)
How can gram positive and negative bacteria differentiated?
By performing a gram stain
What is a gram stain?
A test that is used to differentiate between a gram positive and negative bacteria.
what is involved in gram staining?
Crystal violet dye is used to stain the cell wall - specifically the peptidoglycan layer.
the extent to which the dye is retained determines the type of bacteria.
Gram positive- thick peptidoglycan layer due to this it stays a purple colour.
Gram negative- thin peptiidoglycan layer due to this it turns a pink colour
Gram positive bacteria have a ________ peptidoglycan layer allowing them to deal with ______ internal pressure.
Thick
Higher
Of both gram positive and negative which of the two has a larger periplasmic space?
Gram Negative
(they have two different periplasmic spaces)
Which class of bacteria have two membranes?
Gram Negative
(Outer membrane and Plasma membrane)
What exists on the outside of gram negative bacteria that confers antigenic properties?
Lipid polysaccharides (endotoxins)
Why are gram positive bacteria more susceptible to antibiotics?
The outside peptidoglycan layer can act as a target for antibiotics such as penicillin
What happens when antibiotics bind to the peptidoglyan layer of gam positive bacteria?
The peptide cross links within peptidoglycan are broken down
What are flagella and fimbriae (pili)?
Extracellular proteinaceous extensions
What are some of the functions of flagella and fimbriea?
Increase bacterial surface area
Can act as a syringe to inject proteins and RNA into cells
Passage of DNA from one bacterium to another - horizontal gene transfer
Motility (only flagella)
What 5 key factors so bacteria require to grow and thrive?
- Food (C, O, H, N, salts and vitamins etc.)
- Correct temperature
- pH
- Osmotic pressure
- Oxygen content
What are aerobic bacteria?
Bacteria that require oxygen to grow
What are microaerophiles?
Bacteria that only require minimal oxygen to grow
What are facultative anaerobes?
Bacteria that can use oxygen if it is available, but do not require it to function
What are obligate anaerobes?
Bacteria that do not require oxygen at all
What are the stages in the chain of infection?
- Infectious microbe
- Reservoir
- Portal of exit
- Mode of transmission
- Portal of entry
- Susceptible host
What are the only 5 ways in which infection can be spread?
- Inhalation
- Ingestion
- Inoculation (vaccination or artificial introduction) - direct or indirect
- Mother to infant - vertical transmission
- Intercourse - STI or STD
In what 5 situations (clinically) is hand washing necessary?
- Before patient contact
- Before aseptic task
- After bodily fluid exposure
- After patient contact
- After contact with patient surroundings - when leaving zone
What are black bags for?
General/domestic waste
What are orange bags for?
Clinical waste
For serious airbourne pathogens, those infected should be kept within a ________ ________ room
Negative Pressure
What is the definition of disinfection?
Any process by which the level of microorganisms is reduced to a safe level
What is the definition of sterilisation?
A process by which all microorganisms are killed or removed to render the object incapable of causing infection
What are the three bacterial shapes?
- Bacilli
- Cocci
- Spiral shaped
In what two ways can cocci divide?
- In two planes - produce chains
- In three planes - produce clusters
All bacilli are gram _________ bacteria
Positive
What bacterium causes the disease cholera?
Vibrio chlolera
(Vibrio family of 34 members)
What are rigid spiral bacteria called?
Spirillum
What are flexible spiral bacteria called?
Spirochaete
How are the flagella utilised differently between spirullum and spirochaete?
Spirillum - tufts at each end to aid movement
Spirochaete - within periplasm causign cork-screw motion - efficient at travelling through secretions
What are fusiform bacteria?
Bacteria with a thin strand structure that play a part in the natural gut flora
Why are fusiform bacteria potentially dangerous?
By crossing the placenta in pregancy, they can cause still births and even cancer
With gram positive bacteria there is only one type of membrane, what is it?
Cytoplasmic membrane
In a gram stain, what happens if the stain is clear?
There is no cell wall
During a gram stain, why is it important to keep the time constant when removing the stain?
Eventually all the stain will be removed from any bacterial type
What is selctive media?
This is a growth medium that contains specific nutrients for a specific type of microbe to grow over others
What is differential media?
Allows all types of bacteria to grow and contains a range of nutrients, but allows for differentitaion between bacterial species
How can streptococcus be identified?
Through levels of haemolysis shown by bacteria
What is haemolysis?
Destruction of red blod cells
What is alpha haemolysis?
Partial haemolysis - greening of colonies
What is beta haemolysis?
Total haemolysis - the most aggressive
What is gamma haemolysis?
No haemolysis
Describe polymerase chain reaction (PCR)
Primers bind to specific DNA segments of interest
Successful binding meads to amplification of the DNA target which replicates many times
Real-time PCR uses fluorescence and allows the amplification response to be monitored
What is multi locus sequence typing (MLST)?
This allows sequences of bacterial DNA and entire genomes to be sequenced and uploaded to a database
This allows previously sequenced sections to be matched to newly scanned sequences
What is MALDI-TOF?
Matrix assisted laser desorption ionisation time of flight
This profiles the protein components in a sample
The sample is ionised and travels in vacuum
The componenets will travel at different speeds and deflect to different degrees based on their charge and mass providing a classic signature
Microorganisms can be classed depending on where they originate in relation to the body. What are these classifications?
. Endogenous - originate from within the body
. Exogenous - originates outwith host
What are commensal organisms?
Organisms that are endogenous, part of the natural flora and often form mutalistic relations with the host
What are opportunistic organisms?
Exogenous organisms that infect the host when there is an opportunity such as immunocompromisation
What are contaminants?
Organisms that enter a culture by accident - can be confusing
Fungal infections are generally associated with which two groups?
- Moulds - e.g. aspergillus
- Yeast - e.g. candida spp
Aerobic gram negative cocci appear in which formation?
Diplococci
What are the two (out of 10) pathogenic aerobic gram negative cocci species?
- Neisseria meningitidis - can cause meningitis
- Neisseria gonorrhoea - can cause gonorrhoea
What are coliforms?
Gram negative bacteria - rod shaped and non-spore forming
Can grow either anerobially or aerobically - better aerobically
Many part of the natural bowel flora
Should not enter sterile areas as can cause disease e.g. peritonitis, UTI, biliary tract infection etc
What is the first line antibiotic used for any infection caused by coliforms?
Gentamicin
What is it on the outside of gram negative bacteria that stimulates the immune system?
Lipopolysaccharides (endotoxins) composed of O antigens and lipids
Why can it be advantageous for gram negative bacteria to stimulate the immune system?
Vascularity, available nutrients and protein production can increase
Describe the mechanism of fever production
1.Endotoxin interacts with macrophages to stimulate immune response and cytokine release
2. Cytokines cause adverse effects of sepsis and travel to the hypothalamus
3. Prostaglandin E is produced which means the body perceives itself as cold
4. Shivering is stimulated which generates heat and rasies the body temperature
Describe the process of sepsis
. Small blood vessels become leaky meaning fluid is lost into tissues - due to inflammation
. This causes hypovolaemia
. Blood pressure is reduced
. Organ perfusion becomes inadequate and organ shutdwon may occur
. Blood clotting system activates leading to clot formation
. Clotting factors become used up leading to haemorrhage
When will septic shock occur?
After cell death lipopolysaccarides are released (causing inflammation), yet this also happens with valid treatment
But, due to the sudden disintegration of many cells septic shock will occur due to the huge immune response initiated
What is group A streptococci?
The most pathogenic streptococci
What is the most important group of non-haemolytic streptococci?
Enterococci
(enterococcus faecalis and faecium)
What is Clostridium spp and why is it hard to treat?
Gram positive anaerobic baccili - part of normal bowel flora
Spores are produced - can live outside body
Endotoxins produced can cause severe body damage
Antibiotic resistant (spore production) and general resistance
What are the two main classes of antiobiotic that related to their function?
- Bacteriostatic - inhibits growth
- Bacteriocidal - kills bacteria
What are narrow spectrum antibiotics?
Antibiotics which are very specific in the bacteria that they target
Which types of antibiotics will target the cell wall?
. B lactam (includes penicillins)
. Glycopeptide
Describe how penicillin halts cell wall production
Peptide cross links exist in the cell wall
These are formed from D alanine to D alanine terminal proteins
Such terminal proteins are formed when transpeptidase cleaves this dipeptide, releasing energy and creating the bond
Penicillin resembles a terminal protein such as this and can bind irreversible to transpeptidase which halts cell wall production
What are beta lactam antibiotics?
Antiobiotics containing the beta-lactam ring in their molecular structure
Common in penicillins, co-amoxiclav, cephalosporins etc.
Name a penicillin which targets gram positive bacteria well
Flucloxacillin
(IV or oral)
Name 3 penicillins which can target either gram positive or negative bacteria
. Amoxicillin
. Co-amoxiclav (amoxicillin/clavulanic acid)
. Tazocin (Tazobactam/piperacillin)
What are the 3 forms of penicillin?
. Benzylpenicillin (penicillin G) - IV
. Phenoxymethyl penicillin (penicillin V) - oral
. Benzathine penicillin - IM
What is flucloxacillin commonly prescribed for?
Skin infections from staph and strep
Deals with gram positive bacteria
What is the purpose of clavulanic aid in co-amoxiclav?
B lactamases are microorganisms that destroy the B lactam ring of antibiotics including amoxicllin renderinging them useless
Clavulanic acid inhibits B lactamases which allows the B lactam ring to remain intact.
Essentially co-amoxiclav is a “work around” to allow amoxicillin to work where it wouldn’t normally
What is special about temocillin?
It is resistant to B lactamases
It will generally target coliforms
Cephalosporins are very attractive antibiotics due to their bacteriostatic and bacteriocidal properties as well as being B lactamase resistant. However, what is their major disadvantage?
They are broad spectrum so cause damage to the natural flora
This clears the environment for dangerous bacteria which they cannot kill
They remove the competition for harmful bacteria
Do glycopeptide antibiotics possess a B lactam ring in their structure?
No
Give two examples of glycopeptides
- Vancomycin
- Teicoplanin
How do glycopeptides function?
.They bind to the end of peptides
.This prevents peptide binding proteins such as transpeptidase from binding to their substate (the protein)
.Proteins cannot be incorporated into the cell wall
.Peptidoglycan cannot be synthesised
.Cross links are reduced and the cell wall is weakened
Why can glycopeptides only function on gram postitive bacteria?
The outer membrane in gram egative bacteria blocks any activity they could have on the peptidoglycan layer
Describe how antibiotics can target bacterial protein synthesis
Human ribosomes are different to bacterial ribosomes
Antibiotics are taken into bacterial cells by active transport
They bind to the 30S subunt and prevent tRNA from binding at receptor sites
The chain of elonagtion is inhibited
What type of antibiotic is gentamicin and why is it bactericidal?
Aminoglycoside
Gentamicin targets protein synthesis
When it binds to the 30S subunit in the ribosome, it inhibits protein sythesis
This binding is permanent so bacteria die
What is the mode of action for the tetracyclines?
They are transported into the cell and bind to the 30S subunit of the ribosome.
This blocks tRNA binding sites and stops chain elongation
They are bacteriostatic
Give an example of a tetracycline antibiotic
. Doxycycline
. Tetracycline
. Minocycline
What is the mode of action for macrolides?
They are taken into cells and bind to the 50S subunit in bacterial ribosomes
They can be lipophilic antibiotics and can easily pass through cell membrane to “find” bacteria hiding from the immune system
Give an example of a macrolide antibiotic
. Erythromycin
. Clarithromycin
. Azithromycin
Describe how quinolone work
They bind to the alpha subunit of DNA gyrase and prevent supercoiling of DNA which indrectly inhibts DNA synthesis
They are bactericidal
What is an example of a fluroquinolone?
. Ciprofloxacin
. Levofloxacin
Why is the use of fluroquinolones very restricted?
They are broad spectrum
Why is folic acid required by bacterial cell and which antibiotics can prevent its synthesis?
Required to syntheiss key cell components
Sulphonamides and trimethoprim
What are the serious side effects of gentamicin?
Renal damage and damage to cranial nerve VIII
Which antibiotics are associated with increased risk of C diff
. Cephalosporins
. Co-amoxiclav
. Ciprofloxacin
. Clindamycin
What is a biofilm?
A protective layer around a microorganism that allows it to grow in different environments
What are persistor cells?
Cells that are extremely resisatnt to antibiotics
This is because they are encased within biofilms and cannot be targeted by antibiotics when in a dormant or inactive state - which they often are
What are some methods that bateria use for horizontal gene transfer?
. Transformation - genetic material is released into the extracellular space
. Transduction - via bacteriophages (viruses that use bacteria to replicate within)
. Conjugation - exchange of plasmids through direct comtact via sexual pilus
What are the two different types, or stages, of resistance?
. Cross resistance - resistant to single antibiotic(s) using the same mechanism
. Multiple resistance - resistant to multiple unrelated antibiotics
What is MRSA?
Methicillin Resistant S. aureus
A “superbug”
It has an altered target site, so is difficult to trea
