biology topic 6

Why are aseptic techniques important?

to make an uncontaminated culture so results are reliable

aseptic techniques

sterilsation

3 multiple choice options

how to culture microorganisms pt 1

transfer bacteria to an agar plate using sterile onoculating loop

how to culture microorganisms pt 2

tape lid and incubate

do not incubate above 25

spread plate

distribute microorganisms evenly with a sterile spreader

streak plate

obtain single colonies by building layers of culture on at least 3 seperate streaks

types of nutrient medium

liquid broth

solid agar

selective medium

advantages of using broth medium

can provide anoxic and oxic conditions helps identify mircobes

can grow large volume of bacteria

advantages of using agar

obtain single discrete colony for study

lag phase

Bacteria adapt to new environment; synthesise enzymes and molecules needed for growth;

log phase

population size doubles after each division

stationary phase

reproduction rate equals death tate so population size is at maximum

death phase

die due to buildup of toxic waste or lack of nutrients

methods of estimating growth of culture

cell count

turbidity measurement

dilution plating

conducting cell count pt 1

The sample of broth is diluted 1:1 with trypan blue , which stains dead cells blue

conducting cell count pt 2

use calibrated haemocytometer with volume of 0.1 count cells in square and get mean

conducting cell count pt 3

number of bacterial cells = number counted x 10*4 per cm3

advantages and disadvantages of using cell count

only counts living cells

slow

expensive

margin for human error

process of dilution plating pt 1

grow colony from single microorganism

process of dilution plating pt 2

serial dillution with distilled water to see single colonies

process of dilution plating pt 3

prepare plate and count colonies

process of dilution plating pt 4

number of cells = number of colonies x dilution factor

Turbidity

• Measure absorbance of culture using a colorimeter or spectrophotometer.

• More cells = more turbid = higher absorbance.

Turbidity Advantages and Disadvantages

Advantage: rapid, non-destructive, continuous monitoring possible.
Disadvantage: counts dead AND live cells; not accurate at very low or very high densities; requires calibration curve.

why are bacteria considered agents of infection

produce exotoxins

endotoxins on surface trigger immune response

invade and destroy host tissue

salmonella

• gram negative bacterium

• lipolysaccharide outer membrane

• endotoxins

• released when the bacterial cell dies and lyses

• Cause fever / inflammation

staphylococcus

secretes exotoxins that embed in host cell membrane so contents leak

secreated by living bacteria

protease toxins

mycobacterium tuberculosis pt 1

inflammatory response, infects phagocytes in lungs

mycobacterium tuberculosis pt 2

infected phagocytes are sealed so bacteria remain dormant

mycobacterium tuberculosis pt 3

When the immune system becomes weakened, the bacteria become acive again, and slowly destroy the lung tissue, Leads to breathing problems, coughing, weight loss, and fever

Difference between Endo toxins and Exotoxins

penicillin

bactericidal antibiotic

prevents formation of peptidoglycan cell wall so osmotic lysis occurs

tetracycline

bacteriostatic antibiotic prevents protein synthesis by stopping tRNA from attaching inhibiting growth

causes of antibiotic resistance

random genetic mutation confers resistance

reproduce and pass allele to offspring

directional selection results in resistance strain

causes of antigen variability pt 1

random genetic mutation changes DNA base sequence

diff sequence of condons on mRNA

causes of antigen variability pt 2

diff primary structure of antigen so H bonds ionic bonds and disulfide bridges form in diff places causing diff shape in tertiary structre of antigen

how does antigen variability affect incidence of disease

memory cells no longer complementary to antigen so individual is no longs immune

hard to develop vaccine containing all antigen types

why is it hard to control spead of antibiotic resistance bacteria

horizontal conjunction transfers plasmids between bacteria rapidly

endemic

disease occurs routinely in geographical area

epidemic

temporary rapid increase in disease in geographical area

how is influenzavirus transmitted

droplet infection

direct contact

zoonotic infection

contact with fomites

mode of infection of influenza

injects RNA into epithelial cells

RNA hijacks cells to produce new virions

cell lysis releases virions

how is influenza treated

antiviral medicaton

antibiotics for secondary infections

painkillers for management

how is stem rust fungus transmitted

windbourne spores

host crops leave infection in soil

mode of infection of stem rust fungus pt 1

presence of water lets spores germinate and produce hyphae that enter through stomata

mode of infection of stem rust fungus pt 2

cellulase digest plant cells so fungus can get nutrients as it grows into mycelium and surronds tissues

effect of stem rust fungus

depletes nutrients

weakens stem

plants lose control of transpiration rates
therefore less photosynthesis,pustules on epidermis which eventually burst to release more

name of malarial parasite

plasmodium singled celled protozoan

mode of transmission of malaria

female anopheles mosquito acts as vector and transfers parasite while feeding

parasite reproduces in red blood cells in liver

how is endemic malaria controlled

preventing mostiquito bites

controlling mosquito numbers

drug treatment

ethical and social implications of controlling malaria

treatments must be evidence based

difficulty in getting informed consent

using insectidies kills other organisms

social and economic implications of controlling endemic malaria

expensive to implement

money could be spent on other issues

preventative measures require change of customs

practical issues of controlling malaria

widespread endemic

2 hosts involved

antigen variability

parasite enters host cell sheilding it from immune response

what is an antigen

molecule that can stimulate immune response

glycoprotein glycolipid or polysaccharide

enables identifcation of cells

process of inflammation

vessel damaged

blood flow and permeability of blood vessels increase

white blood cells and plasma move to infected tissue

2 types of white blood cell involved in phagocytosis

neutrophils

macrophages

how does phagocytosis destroy pathogens pt 1

phagocyte engulfs pathogen via endocytosis to form a phagosome

how does phagocytosis destroy pathogens pt 2

phagosome fuses with lysosome

how does phagocytosis destroy pathogens pt 3

lysozymes digest pathogen

role of antigen presenting cells APCS

macrophage displays antigen from pathogen on surface

allowed recognition by t helper cells

non specific immune responses

inflammation and phagocytosis

immediate

specific immune responses

B and T lymphocytes

time lag

2 types of specific immune responses

cell mediated

humoral

process of cell mediated response pt 1

complementary t helper cells bind to foreign antigen on APC

process of cell mediated response pt 2 a

rapid mitosis of T helper cells to become memory cells or trigger humoral response

process of cell mediated response pt 2 b

clonal expansion of T killer cells to secrete enzymes to destroy infected cells

process of humoral response pt 1

complementary t helper lymphocytes bind to foreign antigen on antigen presenting T cells

process of humoral response pt 2

release cytokines that stimulate rapid mitosis of complementary B lymphocytes

process of humoral response pt 3

B cells differentiate into plasma cells

process of humoral response pt 4

plasma cells secrete antibodies with complementary varible region to antigen

antibodies

protein from plasma cells

two light chains held by disulfide bridges 2 longer heavy chains

tertiary structure complementary to antigen

how do antibodies lead to destruction of a pathogen pt 1

antigen antibody complex cause agglutination

activation of complement

opsonisation

precipitation

neutralisation

opsonisation

marks microbes for phagocytoes

precipitation/ neutralisation

makes toxins insoluble

what are memory cells

specialised T helper and B cells produced from primary immune response

undegoes mitosis if encounters same pathogen

secondary immune response

faster rate of antibody production

higher conc of antibodies

pathogen usually destroyed before symptoms

passive and active immunity

involve antibodies

can be natural or artifical

passive natural

antibodies in breast milk

passive artifical

anti vemon

active natural

humoral response

active artifical

vaccination

principles of vaccination pt 1

contains dead or inactive pathogen or antigen

principles of vaccination pt 2

triggers primary immune response

principles of vaccination pt 3

memory cells made remain in bloodstream so secondary response is fast