Topic 6- microbiology and pathogens

Question 1

define aseptic technique

Answer 1

a way of working , designed to prevent contamination from other microorganisms

Question 2

describe how you would carry out aseptic technique

Answer 2

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

Question 3

explain the differences between ; broth, agar and selective medium

Answer 3

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)

Question 4

bacteria invade and destroy host tissue by producing toxins. (this incapacitates organism/immune system)

explain exotoxins

Answer 4

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

Question 5

bacteria invade and destroy host tissue by producing toxins. (this incapacitates organism/immune system)

explain endotoxins

Answer 5

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

Question 6

explain the difference between bacteriostatic and bactericidal antibiotics

Answer 6

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)

Question 7

influenza

Answer 7

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

Question 8

stem rust fungus

Answer 8

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

Question 9

explain social, economic and ethical considerations for the control of the endemic malaria

Answer 9

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

Question 10

define endemic

Answer 10

Widespread disease in one particular area/region

Question 11

malaria

Answer 11

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)

Question 12

physical barriers

Answer 12

Skin has keratin

Stomach acid

Gut and skin flora (pathogens have to compete for food and space)

Question 13

non-specific immune response

Answer 13

Kills anything foreign

Size of response = size of infection

Inflammation, fever, phagocytosis

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Question 14

specific immune response- cell mediated response

Answer 14

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

Question 15

explain how the structures of erythrocytes and monocytes are related to their functions

Answer 15

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

Question 16

specific immune response - humoural response

Answer 16

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

Question 17

what are the different typed of vaccines you can get?

Answer 17

live (living pathogens)
dead (killed pathogens)
attenuated (weakened pathogens)
toxoids (toxins made harmless)
DNA
edible vaccines

Question 18

blood taken from a patient may have an unusually high proportion of eosinophils - why?

Answer 18

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

Question 19

why would people infected with staphylococcus present symptoms quicker than those infected with salmonella?

Answer 19

staphylococcus produces exotoxins whereas salmonella produces endotoxins.

endotoxins are produced much later, takes longer

Question 20

describe techniques microbiologists could use to prove what food poisoning was caused by?

Answer 20

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

Question 21

on nutrient agar plates , if an antibiotic is not effective , what will the outcome be?

Answer 21

there will be no clear zone (zone of inhibition)

Question 22

why may a sample tube be sealed?

Answer 22

prevent microorganisms entering

maintain conditions (e.g humidity)

Question 23

name the property of cells that may allow them to develop new shoots

Answer 23

totipotency

Question 24

describe how bacteria should be added to a petri dish.

Answer 24

use sterile equipment

uniform spreading e.g lawn spreading

Question 25

why may a lid of a petri dish be secured with tape?

Answer 25

prevent microorganisms entering and contaminating the dish

allow for aerobic conditions, reducing the growth of harmful anaerobic bacteria.

Question 26

how would you calculate the mean diameter of a zone of inhibition if it was not circular?

Answer 26

record several measurements
divide that number by the number of measurements.

Question 27

why is it good safety practice to incubate bacteria at a temperature BELOW 37 degrees?

Answer 27

37 degrees is the human body temp

encourages more rapid growth of potentially dangerous bacteria.