topic 6 : microbiology and pathogens Flashcards
why are microorganisms cultured?
they are too small to be seen by the naked eye
what is the definition of a pathogen
microorganisms that cause diseases
what is a culture?
measures growth of microorganisms (bacteria and fungi) in a culture/nutrient medium under controlled conditions
what is a nutrient/culture medium?
substance used for the culture of microorganisms which can be in a liquid form (nutrient broth) or solid form (nutrient agar)
selective media
only a selected group of microorganisms
- has specific nutrients for the bacteria
what does inoculation mean?
getting bacteria on agar/broth with inoculating loop (which scrapes bacteria from solid surface to medium)
definition of sterile
free from living microorganisms and their spores
how to obtain a pure culture?
- desired microorganism must be isolated
- growing under anaerobic/aerobic conditions means that only certain bacteria survive
- medium can favour the growth of one organisms by controlling the nutrients or adding growth inhibitors
indicator media cause certain bacteria to change colour
how do cell counts measure the growth of bacteria?
- bacteria and s.c fungi can be counted using haemocytometer
- dead cells stain blue from the trypan blue stain
- count the bacterial cells in each 4 sets of 16 squares and take a mean
- pre calibrated haemocytometer, to allow number of microorganisms in a standard volume of broth to be calculated
what does it mean if something is turbid?
opaque/cloudy/thick with suspended matter, in the context of water
- as turbidity increases, transmission of light decreases and absorbance increases.
how do optical methods (turbidity) show and measure the growth of bacteria?
As the number of bacterial cells in a culture increases, it becomes more cloudy or turbid
- turbid solutions absorb more light - LIGHT PASSING THROUGH MEASURED BY COLORIMETER - show how many microorganisms are present
- calibration curve produced by growing a control culture and taking samples at regular tie intervals
- turbidity and cell count (with haemocytometer) measured for each sample - relationship between turbidity and num. of cells present
how can dilution plating be used to measure the growth of bacteria?
- finds total viable cell count
- use assumption that each colony grows from a single microorganism
- eg. 30 patches of mycelia means that there were 30 fungal cells on plat when inoculated.
- solid mass of microbes is present after culturing
0 this is done by diluting the original culture in stages until a point is reached when the colonies can be counted - each colony assumed to come from one cell (refer to picture in sia’s notes)
how can the area and mass of fungi be used to measure the growth of culture?
- measure diameter of patches of mycelium
- used to compare growth rate in different conditions
what is the lag phase
microorganisms adapting to their environment and reproduction rate increases slowly
what is the log phase
microorganisms grow at their maximum rate, as long as there are SUFFICIENT RESOURCES
what is stationary phase?
death rate = reproduction rate (due to buildup of waste products and lack of nutrients).
what is death phase
deaths exceed new cell population as conditions continue to worsen
what are the different types of mediums ?
broth cultures, agar and selective media
what is a medium ?
mediums can favour the growth of one organism by controlling the nutrients or adding growth inhibitors
different methods of measuring growth of bacterial culture
cell counts, dilution plating, mass and optical methods
different phases of bacterial growth curve?
lag phase, log phase, stationary phase and death phase
how can bacteria enter the body
- cuts on skin/eyes
droplets through nose/mouth - reproductive tract
- can be through direct contact or by a vector (exterior organism)
what can bacteria do as pathogens?
can be :
- agents of infection
- invading and destroying host tissues
- producing toxins
what is an exotoxin and how do they cause damage?
(gram pos and neg bacteria)
- exotoxins proteins are released from their cytoplasm
- An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism.
example of exotoxin
- how they cause disease
- gram pos or neg
- where is it found on body
- pathogenic effect
- how is it treated
staphylococcus (S.aureus)
- only cause disease if they get into tissue due to another disease, or if the person is immunocompromised
- gram positive bacteria
- found on the skin
- can cause skin and joint infections, infections of membranes around the heart, toxic shock syndrome, bacterial meningitis if it has access to the brain.
- treated with antibiotics, but becoming increasingly resistant –> cause death rapidly
what is an endotoxin and how do they cause damage?
(gram neg bacteria)
- endotoxins are a part of the cell’s surface membrane
- they initiate a host inflammatory response to Gram-negative bacterial infection (fever esc).
example of endotoxin
- pathogenic effect
salmonella ( gram negative bacteria)
- invades the intestine lining - endotoxins cause inflammation
- cells no longer reabsorb water
what is invasion of host tissue?
The response of the host cell to this invasion causes the symptoms
Linked to the production of exotoxins and endotoxins in the cell walls
how is TB spread?
Spread by droplet infection - the immunocompromised are more at risk
how does a primary infection of invasion of host cell work? (of tubercolosis)
- bacteria invade the lung cells and multiply. cause NO SYMPTOMS
- localised inflammation –> mass of tissue (tubercule)
- The immune system usually then controls the bacteria and the inflammation dies down
how is Tb adapted to avoid the immune system?
Can remain dormant and protected from macrophage enzymes, until the person’s immune system is weakened, then it can cause serious lung damage (symptoms like coughing up blood)
- this will all allow some bacteria to survive this.
what are antibiotics and what do they do?
- chemicals that target differences in structure/biochemistry between bacterial and mammalian cells
- destroy or inhibit reproduction of bacterial cells.
what is a bactericidal antibiotic?
directly destroys bacterial cells (kills)
what is a bacteriostatic antibiotic?
inhibit growth and reproduction of bacteria
how do bacteria become resistance to antibiotics?
- mutations common in bacteria because they divide so rapidly (can create a difference in structure or biochemistry)
- meaning that the bacterium is no longer affected by antibiotics (eg. penicillinase)
example of bacterial infection which is resistant to antibiotics and how do they come about?
- MRSA
- resistance to antibiotics results in antibiotic resistance bacterial infections in hospitals
how to control the spread of antibiotic resistant infections?
- new patients screened at arrival, isolated and treated if they are infected - prevented spread of bacteria
- antibiotic only used when needed ant the entire course of antibiotics is completed
- hygiene - wash with alcohol based antibacterial gells and wearing suitable clothes
all to minimise the transmission of resistant bacteria
why should antibiotic courses be completed?
ensure that bacteria are destroyed and minimise the selection pressure on bacteria to prevent resistant strains from forming
describe the evolutionary race (natural selection behind antibiotic resistance
- in a population of bacteria, there are random mutations that cause antibiotic resistance, and then these bacteria will be resistant to antibiotics
- there will be a competition for resources (eg. co2) - better adapted ones will survive for longer
- non-resistant bacteria will die
- the resistant bacteria will reproduce and eventually all population will have antibiotic resistance.
what is a macrophage?
- derived from monocytes, in the leukocytes (WBC) in the blood (4%)
- monocytes migrate to tissues - become macrophages (now macrophages in tussues)
- good capacity of ingesting pathogens (can renew their lysosomes).
- They accumulate at the site of infection.
what is a neutrophil?
- granulocytes, in leukocytes in blood (70%)
- each one can only digest a few pathogens before it dies - cannot renew lysosomes
- accumulate at the sight of infection
why is it difficult to control endemic diseases?
- Widespread
- Hard to remove all sources of infection, particularly with 2 hosts
- Large numbers - expensive
control measures of endemic disease (specific to malaria)?
- Prevent bites - insect repellants, mosquito nets with insecticide, screens over windows and doors
-Control mosquito numbers - avoid stagnant water and sewage, introduce predators, pesticides
ethical implications of controlling endemic disease (specific to malaria) ?
- Safety of vaccines - reservations (some people might want it, while others will not)
- Difficult to obtain informed consent
where education on health is poor - spraying mosquitoes with insecticides will affect other organisms
social implications of controlling endemic disease (specific to malaria) ?
- vaccines needed to become accepted
- Social changes to reduce infection are difficult to bring about
- People may need to change customs (eg. sleeping under a mosquito net)
economic implications of controlling endemic disease (specific to malaria) ?
Treatment, control and prevention is very expensive
Many of the affected countries are poor
Where to place resources - in these countries, issues such as malnutrition are also prevalent
what is the definition of a pathogen
microorganisms that cause diseases
what is agglutination (by antibodies)
clumping microorganisms together - makes phagocytosis easier
what is lysis (by antibodies)
bursting of bacterial cell
what is opsonisation (by antibodies)
making an antigen/pathogen easily detectable/ recognised by phagocytes
what is precipitation (by antibodies)
soluble toxin made inactive
what is neutralisation (by antibodies)
bind to bacterial toxin and neutralise
what are HCAI’s
healthcare associated infections
