Topic 4

the ability to cause disease by overcoming host defenses

Pathogenicity

The degree of pathogenicity

Virulence

Portals of Entry

• Mucous membranes

• Skin

• Parental Route

When it is inhaled it can cause pneumonia

Streptococcus pneumoniae

Streptococcus pneumoniae does not show symptoms if its

swallowed

The virulence of a microbe is often expressed as the infectious dose for 50% of a sample population

ID50

the potency of a toxin is often expressed as lethal dose for 50% of a sample population

LD50

All pathogens have some means of

attachment

Surface molecules on the pathogen that attaches it to the host which bind specifically to surface receptors on cells of host tissues

Adhesins or Ligands

Adhesins or Ligands are located on

glycocalyx or other microbial surface structures

Microbes have the ability to come together in masses, cling to surfaces, and take in and share available nutrients in communities called

Biofilms

The first microbes to attach are usually

bacteria

Once they adhere to the surface, they multiply and secrete a _________ that further attaches the bacteria to each other and to the surface

glycocalyx

Increases the virulence of pathogenic species

Capsules

Capsules prevent the _____________ from adhering to the bacterium

phagocytic cell

Capsules are not the only cause of

virulence

Heat-resistant and acid-resistant protein produces by Streptococcus pyogenes

M protein

M protein are produced by

Streptococcus pyogenes

bacterial enzymes that coagulate (clot) the fibrinogen in blood

Coagulases

a plasma protein produced by the liver, is converted by coagulases into fibrin, the threads that form a blood clot

Fibrinogen

Fibrinogen is converted by coagulases into

fibrin

the thread that forms blood clot

Fibrin

may protect the bacterium from phagocytosis and isolate it from other defenses of the host

Fibrin clot

bacterial enzymes that break down fibrin and thus digest clots formed by the body to isolate the infection

Kinases

Better known kinases is

fibrinolysin

Fibrinolysin is produced by

Streptococcus pyogens

Kinases are used therapeutically to break down blood clots causing

heart attacks

another enzyme secreted by certain bacteria, such as streptococci

Hyaluronidase

a type of polysaccharide that holds together certain cells of the body, particularly cells connective tissue

hydrolyzes hyaluronic acid

Hyaluronidase is involved in __________ of infected wounds

tissue blackening

Help the microorganism spread from its initial site of infection

Hyaluronidase

Hyaluronidase is produced by some

Clostridia

Clostiridia causes

gas gangrene

hyaluronidase may be mixed with a drug promote the ________________ through a body tissue

spread of the drug

Collagenase is produced by several species of

Clostridium

Facilitates the spread of gas gangrene

Collagenase

Enzymes produced by some pathogens that can destroy a class of antibodies called IgA antibodies

IgA proteases

Enzymes produced by some pathogens that can destroy a class of antibodies called

IgA antibodies

As a defense against adherence of pathogens to mucosal surfaces

IgA proteases

Surface proteins produced by microbes which when in contact with the host cell membrane, leads to dramatic changes in the membrane at point of contact

Invasins

Invasins results to disruption in the

cytoskeleton of the host cell