Medical Microbiology - How to be a good pathogen

Portals of entry

Sites through which pathogens gain access to the body

→ ear, respiratory tract, eye, skin (broken), openings, etc.

Some pathogens can be transplacental

Outer layer of skin

packed & dead skin cells = barrier to pathogens

Openings or cuts allow entry

Pathogens & Skin

Some pathogens can burrow into or digest the skin’s outer layers

→ scabies mites, Staphylococcus aureus

Mucous Membranes

Line body cavities open to the environment

Moist, warm environment

Fun fact: Heliobacter pylori can live in the stomach mucosa

Respiratory tract & entry

Most common site of entry - nose, mouth, or eyes

Parenteral route

Artificial portal of entry (entry point created by injury or medical procedures)

Pathogens can be deposited directly into tissues

Pathogens Cross the Placenta

Treponema pallidum (syphilis): abortion, multi-organ birth defects

Toxoplasma gondii: microcephaly, deafness, still birth

Treponema pallidum

=syphilis

Abortion, multi-organ birth defects

Toxoplasma gondii

Microcephaly, deafness, stillbirth

Congenital Rubella Syndrome

Rubella virus (“german measles”) can cross the placenta of non-immune mothers

Cause a variety of birth defects

Prevented via vaccinating our babies

Measle parties/Mump parties

German measles were spread to hopefully encourage resistance to it

Adhesion

Microorganisms attach to cells

Microbes must attach to the host before they can grow and cause disease

If cannot attach, they are removed by body defense (mucus, saliva, urine, etc)

Adhesion factors (block to treat disease)

Specialized structures: hooks, suckers, fimbriae

Attachment proteins = ligands = adhesins

Biofilms → can be adhesion factor

Infection

Invasion of the host by pathogen

Infectious dose = # of agent needed to cause disease

Disease

Pathogen altering normal body functions

= Morbidity

Pathogenicity

Microbe’s ability cause disease

Virulence

Degree of pathogenicity

Virulence factors

traits or structures that help a pathogen infect a host and cause disease

→ adhesion factors, invasion, toxins

Extracellular enzymes

Enzymes secreted by pathogens

What do extracellular enzymes do?

Dissolve structural chemicals in tissues

Example of extracellular enzyme

Hyaluronidase

Why are extracellular enzymes important?

They help pathogens spread through tissues

How do pathogens evade the immune system and become good pathogens?

Avoiding detection and surviving in the hostile environment

Ways pathogens evade the immune system

Antigen masking, antigen mimicry, and antigen variation

What is an antigen?

Anything that provokes an antibody response

What is antigen masking?

A pathogen hides its antigens from the immune system

What is antigen mimicry

A pathogen resembles host molecules to avoid detection

What is antigen variation?

A pathogen changes its antigens to avoid the immune response

What are invasins?

Virulence factors that help pathogens enter host cells

What does Salmonella alter to enter a host cell

Host cell actin

What happens when Salmonella alters actin?

The cell membrane ruffles and engulfs the bacterium

What is membrane ruffling?

Folding of the host cell membrane that helps Salmonella enter the cell

What are antiphagocytic factors

Factors that help bacteria avoid phagocytosis include

What is phagocytosis?

The process where phagocytes engulf and destroy pathogens

What bacterial structure can prevent phagocytosis

A capsule

Why does a capsule help bacteria avoid phagocytosis?

It is made of “self-like” chemicals

How does the slippery nature of a capsule help bacteria?

It makes it harder for phagocytes to engulf them

What are antiphagocytic chemicals

Chemicals that help bacteria survive phagocytosis?

How do some antiphagocytic chemicals help bacteria survive

They prevent fusion of the lysosome and phagosome

What is a leukocidin?

A toxin produced by some bacteria

What do leukocidins do?

They kill phagocytes

Three ways that bacteria can avoid destruction by phagocytes

Capsules, blocking lysosome-phagosome fusion, and producing leukocidins

What are toxins?

Chemicals that harm tissues or trigger damaging host immune responses

What are the two types of toxins?

Exotoxins & endotoxins are

What is an example of an exotoxin?

Botox

What is an example of an endotoxin

LPS (lipopolysaccharide)

How does the host sequester Iron?

Via transferrins in the blood.

→ Keeps iron unavailable from bacteria

What are transferrins?

Proteins in the blood that bind iron

What are siderophores?

Molecules produced by bacteria to obtain iron

They liberate Iron (Fe), and acquire iron (Fe) from the host

Symptoms

Subjective characteristics of disease (nausea)

Signs

Objective manifestations of disease (vomiting)

What happens during the incubation period?

No symptoms; the pathogen is building up steam

Are symptoms present during the incubation period?

No

What happens during the prodromal phase?

Early symptoms appear and the person feels like they may be getting sick

“I think I might be coming down with something”

What happens during the acute phase?

The most severe signs and symptoms occur

Which stage has the most severe signs and symptoms?

The acute phase

What happens during the decline stage?

The immune system begins clearing the pathogens

What happens to the pathogen during the decline stage?

It begins to be eliminated by the immune system

What is convalescence?

The recovery stage of disease

Can a person still be contagious during convalescence?

Yes

What are the five stages of infectious disease in order?

Incubation, prodromal, acute, decline, convalescence

Portals of exit

Sites through which pathogens exit the body

Name the major portals of exit.

Respiratory mucosa, GI mucosa, urogenital tract, skin, parenteral route, ocular route, and otic route

Why do pathogens need a reservoir?

They cannot survive long outside a host

What is a reservoir?

A pathogen holding tank

→ Harbor and maintain pathogens

What are the three types of reservoirs?

Animal, human, and nonliving reservoirs

nonliving reservoir = nonliving environment that harbors a pathogen

Which type of reservoir includes carriers?

Human reservoirs

T/F: Most pathogens can survive for long periods outside a host

False.