Exam 3 - Chapter 25

Bacteremia

The presence of bacteria in the bloodstream

Septicemia

Bloodborne systemic infection

Septicemia may lead to…

massive inflammation, septic shock, and death

Process of microbial pathogenesis

1. Exposure to pathogens

2. Adherence to skin or mucosa

3. Invasion through epithelium

4. Multiplication, growth, and production of virulence factors and toxins

5. Toxicity (local or systemic) OR invasiveness and further growth at original and distant sites

6. Tissue or systemic damage

Adhesins

Glycoproteins or lipoproteins found on the pathogen’s surface that enable it to bind to host cells

What is microbial adherence facilitated by?

Many different receptors coating both the pathogen and tissues where the bacteria or virus binds

Adherence structures for pathogen attachment

• Fimbriae

• Pili

• Flagella

• Adhesins

The bacterial capsule can act as a…

facilitator of pathogen attachment

Examples of bacteria that use capsule for pathogen attachment

• B. anthracis

• Enteropathogenic E. coli

Pathogenicity

Genetic capacity of a pathogen to cause disease

Virulence

Relative ability of a pathogen to cause disease

Virulence factors

Toxic or destructive substances produced by the pathogen that directly or indirectly enhance invasiveness and host damage by facilitating and promoting infection

Virulence can be estimated from…

experimental studies of the LD50 (lethal dose 50)

LD50

The amount of an agent that kills 50% of the animals in a test group

Virulence in Salmonella

Pathogenicity islands and plasmids

Attenuation

Decrease or loss of virulence

What happens to virulence when pathogens are kept in laboratory culture rather than isolated from diseased animals?

Virulence often decreases or may be completely lost

Why are attenuated strains of pathogens valuable to clinical medicine?

They are often used for the production of viral vaccines

Attenuation of virulence in vaccine production

• Isolate yellow fever virus from diseased patient

• Multiple passages of virus in Rhesus macaques

• Multiple passages of virus in mouse embryos

• Multiple passages of virus in chicken embryos

• Final preparation of attenuated vaccine in fertilized chicken eggs

• Administration of vaccine to susceptible individual to elicit immune response without disease symptoms

Pathogen-host interaction is dependent upon…

both the host and the pathogen

_________ can predispose individuals to develop diseases

Certain medical procedures or underlying conditions

______ affect nearly 2 million people each year

Nosocomial infections

Nosocomial infections

healthcare-associated infections

Infections with viruses, like HIV, have what effect?

weaken the immune system

Opportunistic infections

Infections caused by organisms that don’t cause disease in healthy hosts

Characteristics of exotoxins

• Protein based

• Heat sensitive

Tissue destroying enzymes

• Hyaluronidase

• Coagulase

• Streptokinase

Hyaluronidase

Breaks down host tissues

Coagulase and streptokinase both…

manipulate clotting

Coagulase

forms clots

Streptokinase

Breaks down clots

Proteins released from the pathogen cell as it grows

• Cytolytic toxins

• AB toxins

• Superantigen toxins

Activity of botulinum toxin

Blocks release of acetylcholine, which inhibits muscle contraction

Activity of tetanus toxin

Binds to inhibitory interneurons, preventing release of glycine, which would stop acetylcholine from inducing muscle contraction, therefore preventing relaxation of the muscle.

Endotoxins

Toxic lipopolysaccharides (LPS) found in the cell walls of most gram negative bacteria

Characteristics of endotoxins

• Not proteins

• Heat stable

• Not release by live bacteria