Agents of Disease

what is an infectious disease

A disease caused by a pathogenic microorganism that can be transmitted from one individual to another

wha are some examples of pathogenic microorganisms

bacterium, virus, parasite, fungi

What is the difference between infectious and contagious disease

Infectious Disease: invasions of the body by pathogens

Contagious Disease: pathogens that can spread from one person to another

Name the sequence of how pathogens cause disease

Exposure

Adherence

Invasion

Evasion of defences

Cell and tissue damage

Exit

How can the exposure stage take place

entry of pathogens through eyes, skin, eyes or inhalation into lungs

Can the body stop adherence of pathogens

Yes via reflexes like sneezing or coughing

Do pathogens have adaptations to combat the struggle of adherance

Yes like flagella and fimbria

What is the most common way of exit of a pathogen

the same way it came in eg. pathogens inhaled may be transmitted out via coughing

What is a virulence factor

ability of an organism to infect a host and causes disease- for example use of flagella or cillia

What do groups can we divide bacteria into

coccus and bacillus

What is the shape of coccus bacteria

orbs like berries

What is the shape of bacillus bacteria

rods/staffs

What is a coccobacillus

part way between a coccus bacteria and a bacilli bacteria

Why is it useful to know bacterial morphology

to identify what diseases animals have in practice

structure of gram positive bacteria

has a thick outer cell wall made of peptidoglycan

what does peptidoglycan enable to cell to do

survive in dry environments and prevent the bacteria from drying out

structure of gram-negative bacteria

no cell wall only an outer cell membrane

what does the structure of Gram-negative bacteria allow it to do

live in very wet and humid enviroments

Why is the cell membrane so important to bacteria

They don’t have any membrane-bound organelles, so all metabolic processes need to occur in the structures within the cell membrane

what structures are found in the membrane of Gram-negative bacteria

lipopolysaccharides (LPS)

what is the purpose of LPSs

they trigger the immune system to recognise the bacteria- more specifically, it is the lipid A that causes the immune system to become most responsive

what is another name for the LPSs

endotoxins

What is endotoxemia

condition where a large amount of endotoxins are released into the bloodstream

What is endotoxemia caused by

gram-negative bacteria and the LPS found on their cell membrane

how can we identify bacteria types in the lab

The Gram Stain

explain the gram stain process for gram POSITIVE bacteria

-crystal violet added which fixes purple dye into cell wall of Gram-positive bacteria

-alcohol used to wash the sample

-because the dye is fixed gram POSITIVE remain purple

explain the gram stain process for gram NEGATIVE bacteria

-crystal violet added

-alchol washes out dye as it isnt fixed in cell wall (has no cell wall)

-dilute fuchsin turns Gram-negative bacteria pink

Once a sample has undergone the gram stain what colour is everything

Gram POSITIVE: purple

Gram NEGATIVE: pink

What are flagella

structures that come out of bacterial membrane allowing them to move around

How are flagella advantageous to bacteria

they can move around and evade host immune systems, can also move towards things like nutrients and conditions that can help them to survive

What are fimbria

small hair like structures surrounding the cell

Why are fimbria adventageous

can use them to stick to the host- helping evade the eviction stage of infection

what are the 4 categories of bacteria in terms of how they deal with oxygen conditions

Obligate aerobes

Obligate anaerobes

Facultative anaerobe

Microaerophilic

What are obligate aerobes

bacteria that require oxegen

What are obligate anaerobes

bacteria that require anaerobic conditions

Oxygen is toxic to them

What are facultative anaerobes

prefer to be in an environment with O2 but can survive in anaerobic conditions

What are microaerophilic

need o2 but too high a concentration is toxic to them

What category of bacteria is most pathogenic in terms of o2 requirements

facultative anaerobes because they can survive in all environments