Micriobio chapter 15

Pathogenicity

Ability of a microbe to cause disease

Virulence

Degree or severity of disease caused by a microbe

Pathogenicity vs Virulence

Pathogenicity is whether it can cause disease while virulence is how severe the disease is

Portals of entry

Ways microbes enter the body including mucous membranes skin and parenteral routes

Mucous membranes entry

Microbes enter through respiratory or gastrointestinal tracts

Skin entry

Microbes enter through breaks in the skin such as cuts or wounds

Parenteral route

Direct entry into tissues through injections bites or surgery

Preferred portal of entry

Most microbes infect best through a specific route

ID50

Number of microbes required to infect 50 percent of a population

LD50

Amount of toxin required to kill 50 percent of a population

Low ID50 or LD50 meaning

Lower values indicate higher virulence and greater danger

Adherence

Process by which microbes attach to host cells to begin infection

Adhesins

Molecules on microbes that bind to host cell receptors

Glycocalyx

Sticky coating that helps bacteria attach to surfaces such as teeth

Fimbriae

Hair like structures used by bacteria to attach to host cells

Viral spikes

Structures that allow viruses to bind to specific host receptors

Capsule

Outer layer around bacteria that prevents phagocytosis

M protein

Cell wall component that helps bacteria resist immune attack

Mycolic acid

Waxy lipid that protects bacteria from digestion

Coagulase

Enzyme that forms clots to protect bacteria from immune cells

Kinases

Enzymes that break down clots to allow bacterial spread

Hyaluronidase

Enzyme that breaks down connective tissue between cells

Collagenase

Enzyme that breaks down collagen to allow invasion

IgA protease

Enzyme that destroys IgA antibodies

Enzymes role in infection

Help bacteria invade spread and evade immune responses

Antigenic variation

Process where microbes change surface proteins to avoid immune detection

Effect of antigenic variation

Allows reinfection and makes immunity difficult

Examples of antigenic variation

Influenza virus and Neisseria gonorrhoeae

Invasins

Proteins that allow bacteria to enter host cells by altering the cytoskeleton

Intracellular survival

Ability of microbes to live inside host cells and avoid destruction

Phagosome escape

Microbes escape from phagosome before lysosome fusion

Prevention of lysosome fusion

Microbes block fusion to survive inside immune cells

Biofilms

Communities of microbes attached to surfaces and surrounded by protective slime

EPS in biofilms

Extracellular polymeric substance that protects bacteria

Biofilm importance

Increases resistance to antibiotics and immune system

Example of biofilm

Dental plaque

Siderophores

Molecules that bind and steal iron from the host

Importance of iron

Iron is essential for bacterial growth and metabolism

Direct damage by microbes

Damage caused by using nutrients producing waste reproducing and bursting host cells

Toxins

Poisonous substances produced by microbes that damage host tissues

Toxigenicity

Ability of a microorganism to produce toxins

Toxemia

Presence of toxins in the bloodstream

Intoxication

Disease caused by toxins without microbial growth

Exotoxins

Proteins secreted by bacteria that are highly specific and potent

Exotoxin properties

Soluble specific and often highly lethal

A B toxin

Exotoxin with A active component and B binding component

A component of A B toxin

Part that damages host cells

B component of A B toxin

Part that allows toxin to enter cells

Example of A B toxin

Diphtheria toxin

Membrane disrupting toxins

Toxins that destroy cell membranes and cause cell death

Hemolysins

Toxins that destroy red blood cells

Leukocidins

Toxins that destroy white blood cells

Superantigens

Toxins that overstimulate immune system causing massive cytokine release

Effects of superantigens

Fever shock and possible death

Endotoxins

Lipid A component of gram negative bacteria released when cells die

Source of endotoxin

Lipopolysaccharide of gram negative bacteria

Effects of endotoxin

Fever inflammation clotting problems and shock

Endotoxin vs exotoxin

Endotoxins are less specific but still harmful while exotoxins are highly specific and potent

Fever mechanism

Cytokines released by macrophages signal hypothalamus to raise body temperature

IL 1 and TNF

Cytokines that trigger fever response

Plasmids

Extra DNA that carries genes for toxins resistance and virulence

Virulence plasmids

Plasmids that increase pathogenicity of microbes

R plasmids

Plasmids that provide antibiotic resistance

Lysogenic conversion

Viral DNA insertion into bacteria changing its traits

Viral cytopathic effects

Visible changes in host cells caused by viral infection

Syncytium formation

Fusion of infected cells into one large cell

Inclusion bodies

Structures formed inside infected cells during viral infection

Cytokine storm

Excessive immune response caused by some viral infections

Fungi pathogenicity

Caused by toxins allergic responses and tissue damage

Aflatoxin

Carcinogenic toxin produced by fungi

Candida infection

Fungal infection caused by Candida species

Protozoa pathogenicity

Caused by cell destruction intracellular growth and antigenic variation

Giardia

Protozoa that damages intestinal cells

Toxoplasma

Protozoa that can live inside host cells

Portals of exit

Ways pathogens leave the body to spread infection

Respiratory exit

Pathogens leave through coughing and sneezing

Gastrointestinal exit

Pathogens leave through feces and saliva

Genitourinary exit

Pathogens leave through urine and secretions

Skin exit

Pathogens leave through wounds

Blood exit

Pathogens leave through needles or insect bites

High yield concepts

Pathogenicity virulence ID50 LD50 adherence biofilms antigenic variation exotoxins endotoxins and immune evasion strategies