Module 10 - Disease Principles & Pathogenicity

Infection

presence and growth of a microbe in/on the host; may be asymptomatic

Disease

tissue damage or dysfunction that produces signs/symptoms (can be infectious or non-infectious)

Resident microbes

microbes loving in/on body

includes bac, fungi, protozoa, and viruses

healthy individuals often carry potential opportunists at low abundance

Microbiota diversity

1/3 common among humans, 2/3 unique to person

Microbiome

all genomes and genes of microbes in your body

What does microbiota do for you?

• digest certain foods

• produce some vitamins

• stimulates development of certain tissues (intestinal microvilli, lymph tissue)

• combats opportunistic pathogens

Dysbiosis

imbalance of body’s microbial community

Low microbe diversity

low good bacteria = high pathogenic bacteria

Dysbiosis has been linked to

• obesity

• allergies/immune disorders

• cancer

• inflammatory bowel disease

• anxiety

• autism

• parkinson’s disease

Initial colonization

fetuses are seeded with normal microbiota upon birth, important for healthy full-term pregnancies & health new borns

C-sectio births and microbiota

results in early dysbiosis, vaginal seeding is used by taking bac from the mothers vagina to the baby

Continued colonization

done through breast milk and is critical for maintaining a healthy get microbiome

Breast milk

conatins human milk oligosaccharides (HMOs) not digestible by babies

Pathogen

microbe whose relationship with host results in infection and disease

Pathogenicity

organisms potential to cause infection or disease, qualitative measures

True pathogens

cause disease in healthy people

Opportunistic pathogens

causes disease in hosts with compromised immune defenses, non-normal body part

Virulence

relative severity of the disease, quantitative measure

Virulence factors

structures, products, or capabilities allowing pathogen to cause infection

Infectious dose (ID)

number of microbes required for infection; fewer bacteria = no infection, varies between microbes

The progress of infection

1) entry, 2) attaching to the host, 3) surviving host defense, 4) causing disease, 5) vacating the host

Portal of entry

route taken by microbe to start infection, broken skin, GI tract, respiratory tract, urogenital system (STD), pregnancy, and birth

Exogenous infection

originate outside the body, environment, another person, animal

Endogenous infection

caused by resident biota, microorg in a non-normal site

Adhesion

microbes gain foothold in host tissues, binding of specific host and pathogen molecules, then invades body compartments

Phagocytes

white blood cells, engulf and destroy pathogens (=phagocytosis)

Antiphagocytic factors

virulence factor used by pathogens to avoid WBC, some pathogens survive inside WBCs

Leukocidins

kill phagocytes, antiphagocytic factor

Slime layer or capsule

hinders WBCs, antiphagocytic factor

Direct virulence factors

toxins and enzymes

Extracellular enzymes (exoenzymes)

secreted by pathogenic organisms, break down and damage tissues, dissolve defense barriers allowing spread to deeper tissues

Indirect virulence factors

host’s excessive or inappropriate immune response and causes many cases of microbial disease

What are pathogenicity and disease a result of?

interplay between microbe and host response

Vacating the host

transmission which includes normal body processes and vectors

Normal body processes

respiration and saliva, skin scales, feces, urogenital tract, blood

Vectors

blood-feeding animals, ticks, fleas, mosquitos