Pathogen virulence factors and evolution

How do pathogens enter the body?

• cutaneously through skin/wound or a vector

• mucosal

What are the mucosal routes of pathogen entry into the body?

• ocular

• respiratory

• oral

• urogenital/rectal

What is the first line of defense against pathogens and some examples?

• stops pathogen entry and adhesion

• physical - skin, hair, eyelashes, urination, mucus membranes

• chemical - low pH, Iga, lysozynes

• biological - microbiome in gut

What is the second line of defense against pathogens?

• inside of body after pathogen enters

• prevents pathogen establishment/infection

• innate and adpative immune system

What is the innate immune system?

• 2nd line of defense

• white blood cells

  • engulf pathogens, lysozymes, etc

  • release cytokines

What is the adaptive immune system?

• 2nd line of defense

• B and T cells

  • remember pathogens

  • produce antibodies

How does the body respond to viruses vs bacteria?

• respond differently

• different complement factors and cytokines released

What is unique about viruses?

• only DNA or RNA, not both

• no organelles or ribosomes

• no cell wall

• no flagella

• need a host to reproduce

What are some diseases caused by viruses?

• flu

• measles

• HIV

What is a bacteriophage?

viruses that infect bacteria/archaea

What are the actions of virulence factors?

• adhesion

• invasion

• colonization/infection

• immune evasion

• persistence/replication

• want to attach or evade host immune defense

• causes toxicity/harm to cells

What is a virulence factor?

something that makes an organism pathogenic and gives it a survival edge in the host

What are some possible outcomes of viral replication to a host’s cells?

• cell death

• persistence/latency (ex. HIV)

• cell proliferation

• malignant transformation (cancer)

What are some diseases caused by bacteria?

• typhoid

• tuberculosis

• strep throat

What virulence strategies do bacteria use?

• release exotoxins

• release endotoxins

• fimbriae for adherence

• cytoxin

• antibiotic resistance from plasmids from other bacteria/virus

What is an exotoxin?

• toxic protein secreted by a bacterium

• ex. cytotoxin, enterotoxin (diarrhea)

Why are fungal infections hard to treat?

fungi are more similar to humans, so medication may impact human cells as well

What are some diseases caused by fungi?

• histoplasmosis

• valley fever

• athletes foot

• ringworm

What unique strategies do fungi use for dispersal?

hyphae and spores when in mold state

Describe fungi at a broad level

• eukaryotes

• unicellular/multicellular

• DNA and RNA

• ribosomes

What virulence strategies do fungi use?

• morphological transition between yeast, hyphae, and spores depending on what survives best in host vs environment

• thermotolerance - survive hotter temps in host

• adhesion

• secrete exoenzymes that digest human tissue

• secrete toxins

• immune evasion

• cell wall for robustness

What are some diseases caused by protozoans?

• malaria

• chagas disease

• giardiasis

Describe protozoans at a broad level

• eukaryotes

• unicellular

• DNA and RNA

• organelles

• some have complex lifestyles and life stages

What are virulence strategies of protozoans?

• surface proteins to evade host immune system

• adhesive factors to attach to host cells

• proteins/enzymes to prevent death (ex. destroy machrophages)

What are challenges infectious agents face when jumping to a new type of host (spillover)?

• must contact novel host

• must successfully infect - needs new virulence factors for host cell receptor binding, entering cells, replicating, escaping host immune response, etc.

• sufficien transmission

Why do infectious agents develop virulence factors?

to persist and replicate in host

How can symptoms be involved in pathogen transmission?

can help spread disease; ex. sneezing and coughing

What limits pathogen transmission rates?

• host mortality

• pathogen replication and spread speed

• host immunity

How can viruses evolve?

• mix with an established virus in a bridge host

• multiple viruses from different sources mix in a bridge host

What is an endotoxin?

• found in membrane of gram-neg bacteria

• causes fever

What is an enterotoxin?

exotoxin that causes vomiting/diarrhea

Why is adhesion important for pathogens?

• prevents pathogen from being physically removed from host cell

• helps pathogen colonize host tissue

What are fimbriae?

bacterial structures that help bacteria adhere to host cells

What is recombination?

• when gene fragments from parental viruses recomnbine and form a hybrid virus

• small changes occur

What is reassortment?

• when entire gene segments from parental viruses are exchanged to form a hybrid virus

• causes big changes, potentially antigenic shift

• only in segmented viruses like influenza

How can bacteria evolve?

• mutations

• modification of a gene function

• acquisition of new genes (horizontal gene transfer) via transformation, transduction, or conjugation

What are the types of horizontal gene transfer bacteria can undergo?

• transformation

• transduction

• conjugation

Describe transformation

• when bacteria pick up bacterial DNA fragments

• can be from dead bacteria or membrane-bound DNA bud cells from a living cell

• occurs between similar species of bacteria

Describe transduction

• when bacteriophage transfer DNA between bacteria

• DNA then incorporated into bacterial genome

Describe conjugation

• when competent Donor bacteria physically trasnfers DNA to recipient cell

• type of sexual reproduction

• transfers plasmid

What is a plasmid?

• small, circular piece of DNA separate from a bacterium’s main chromosome

• often carries useful genes, like antibiotic-resistance genes.

Why is bacterial horizontal gene transfer medically significant

• transduction can carry dangerous genes between bacteria in the same family

• conjugation is a common method of acquiring antiobiotic resistance

Which horizontal gene-transfer method uses free DNA?

transformation

Which horizontal gene-transfer uses a bacteriophage?

transduction