Topic 6- microbiology and pathogens Flashcards
define aseptic technique
a way of working , designed to prevent contamination from other microorganisms
describe how you would carry out aseptic technique
Provide culture with required nutrients in sterile medium.
Inoculate culture- streak or spread plate
Equipment is sterilised in Bunsen burner
Lids replaced as quickly as possible
explain the differences between ; broth, agar and selective medium
agar is solid (jelly)
broth is liquid
(both have nutrients added)
selective medium contains certain nutrients so that only specific bacteria can grow (contains specific selective agent)
bacteria invade and destroy host tissue by producing toxins. (this incapacitates organism/immune system)
explain exotoxins
Excreted by organisms (living cells)
Found in gram positive and negative bacteria
Highly antigenic
Unstable, heat liable at 60 degrees
Highly toxic
Denatured on boiling
No enzymatic activity
Usually binds to specific receptors
Toxoids can be made by treating with formalin
Polypeptide, soluble proteins
e.g staphylococcus
bacteria invade and destroy host tissue by producing toxins. (this incapacitates organism/immune system)
explain endotoxins
Integral part of cell wall
Mostly found in gram negative bacteria
Lipopolysaccharide complex
Relatively stable and heat tolerant
Moderately toxic , rarely fatal
Weakly immunogenic
Toxoids can not be made
Specific receptors not found
Mostly enzymatic activity
On boiling, cannot be denatured
e.g salmonella
explain the difference between bacteriostatic and bactericidal antibiotics
Bactericidal antibiotics – kill bacteria by destroying their cell wall, causing them to burst (e.g penicillin)
Bacteriostatic antibiotics- inhibit growth/reproduction, by stopping photosynthesis so cell division can’t happen. (e.g tetracycline)
influenza
transmission - direct contact/droplets/coughs/sneezes
mode of infection- Effects epithelial cells in lungs
Viral RNA is continually produced – new virus particles
pathogenic effects-Sore throat/Headache/Cough/sneeze /5-7 days
treatment- antivirals
stem rust fungus
transmission- pores from infected plant transported by wind
mode of infection-
Pores germinate on plant due to water producing hyphae
Hyphae enter plant via stomata
Hyphae grows into mycelium
This surrounds all tissues in the plant, producing enzymes
(these digest plant/make fungus absorb needed nutrients)
pathogenic effects- Weakened stem
Less transpiration and photosynthesis
Pustules on epidermis eventually burst, producing more spores
treatment-fungicide
explain social, economic and ethical considerations for the control of the endemic malaria
Ethical: informed consent difficult, spraying mosquitos may harm them, money spent on vaccines could be spent on education/preventing famine
Social: vaccines need to become accepted , social changes to reduce infection are difficult to bring about
Economical: treatment and control is expensive , malnutrition may be more of a threat to human life than malaria
define endemic
Widespread disease in one particular area/region
malaria
transmission:
Vector of female mosquito
mode of infection:
Parasite transmitted from mosquito travels to liver
Infects RBC
Asexually reproduce in erythrocytes – lysis
Malaria bursts out of RBC every 2-3 days
pathogenic effects:
(paroxysm)
Sweating, shaking, liver damage
treatment/control:
Prevent bites using insect repellent/net, water treatment (introduce predators)
physical barriers
Skin has keratin
Stomach acid
Gut and skin flora (pathogens have to compete for food and space)
non-specific immune response
Kills anything foreign
Size of response = size of infection
Inflammation, fever, phagocytosis
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specific immune response- cell mediated response
Relies on lymphocytes produced in bone marrow – B cells ( humoural) and T cell ( cell mediated)
T cells move to thymus gland to mature
Cell mediated response:
Pathogen invades host cell
Antigen attaches to MHC markers and becomes APC (antigen presenting cell)
T killer cells (with complimentary receptors) bind to APC
Cytokines (from T helper) stimulate T killer to divide by mitosis
T killer divides into active T killer and T killer memory cells
Active T killers bind to APCs, secreting chemicals which cause pores to form in cell membrane
Infected cell dies
explain how the structures of erythrocytes and monocytes are related to their functions
erythrocytes have no nucleus to free up space to carry more haemoglobin (to transport oxygen) , monocytes have a nucleus to synthesise proteins.
shape:
erythrocytes are a biconcave shape, increasing SA to allow more absorption of oxygen and are smaller to pass through capillaries.
monocytes can change shape (are larger) to engulf pathogens
specific immune response - humoural response
T helper activation:
Bacteria engulfed by macrophage
Macrophage acts as APC , presenting antigens on MHCs
APC binds to T helper (has complimentary receptor proteins)
T helped is ‘activated’, divides by mitosis into T memory and T helper
effector stage:
Antigens on APCs that are complimentary to receptors on B cells bind and are taken in by endocytosis
B cell acts as APC and presents antigens on MHCs
Activated T helper cell binds to APC to produce cytokines
Cytokines stimulate B cell to divide by mitosis into B memory and B effector
B effector differentiate into plasma cells
Plasma cells synthesis antibodies
Antibodies have an effect – e.g agglutination means antibodies clump antigens together to make phagocytosis easier
T supressor cells stop immune response
what are the different typed of vaccines you can get?
live (living pathogens)
dead (killed pathogens)
attenuated (weakened pathogens)
toxoids (toxins made harmless)
DNA
edible vaccines
blood taken from a patient may have an unusually high proportion of eosinophils - why?
the patient is producing more of these cells, so more is being released into blood stream
because patient has allergic inflammation due to parasitic infection
why would people infected with staphylococcus present symptoms quicker than those infected with salmonella?
staphylococcus produces exotoxins whereas salmonella produces endotoxins.
endotoxins are produced much later, takes longer
describe techniques microbiologists could use to prove what food poisoning was caused by?
take a sample of sick/faeces
look at colonies to see if they have specific characteristic
use gram staining
grow on selective media
use antibodies specific to the suspected bacteria
on nutrient agar plates , if an antibiotic is not effective , what will the outcome be?
there will be no clear zone (zone of inhibition)
why may a sample tube be sealed?
prevent microorganisms entering
maintain conditions (e.g humidity)
name the property of cells that may allow them to develop new shoots
totipotency
describe how bacteria should be added to a petri dish.
use sterile equipment
uniform spreading e.g lawn spreading
