Microorganisms, Disease Transmission, and Immune Response: Key Concepts in Microbiology

Infection

occurs when microorganisms enter the body and begin multiplying

disease

infection causes damage and symptoms

reservoir

where microorganisms normally live and mulitply

types of reservoirs

soil, water, animals, humans

zoonoses

diseases transmitted from animals to humans

Rabies, lyme disease

examples of zoonoses

human microbiome

the collection of microorganisms living on and inside the body

portal of entry

how pathogens enter the body

respiratory tract

the most common portal of entry

respiratory tract, gastrointestinal tract, urogenital tract, skin, placenta

examples of portals of entry

carrier

someone who has a pathogen but shows no symptoms

fomite

an inanimate object that spreads disease

vector

a living organism that spreads pathogens

zoonosis

disease spread from animals to humans

pathogenicity

ability to cause disease

virulence

degree or severity of disease

capsule, pili/fimbriae, enzymes, toxins, biofilms,

virulence factors that help bacteria cause disease

capsule

prevents phaygocytosis

pili/fimbriae

help bacteria attach

enzymes

break down tissues

toxins

damage host cells

biofilms

protect bacteria

endotoxin (LPS)

found only in Gram-negative bacteria. Releases lipopolysaccharide when bacteria die. causes fever, inflammation, septic shock, and low blood pressure

direct transmission

person to person contact

indirect transmission

spread through something else

innate immunity

present at birth, immediate, non specific, no memory

skin

first line of defense

slows

acidic pH _______ bacteria

mucus membranes

trap microbes; located in the respiratory tract, digestive tract, and reproductive tract

microbiome

normal flora compete with pathogens

lysozyme

chemical defense found in tears, saliva, sweat; breaks down baterial cell walls

stomach acid

chemical defense that has a very low pH and kills many microorganisms

second line of defense

activated if pathogens enter tissues

phagocytosis

cells engulf pathogens

phagocytic cells

neutrophils, macrophages, dendritic cells

neutrophils

first responders

marophages

tissue phagocytes

dendritic cells

phagocytosis, present antigens

signs of inflammation

red, hot, swollen, painful

histamine, vasodilation

_______ causes __________

fever

slows bacterial growth, increases immune activity

opsonization

coats pathogens so phagocytes can recognize them more easily

adaptive immunity

specific, slower first response, has memory, improve after repeated exposure

b cells

produce antibodies

plasma cells

make antibodies

memory b cells

long term immunity

antibodies

also called immunoglobulins; neutralize toxins, prevent attachment, cause agglutination, activate complement, promote opsonization

antigens

anything recognized as foreign (proteins, polysaccharides)

variable region

located at the tips of antibodies, responsible for binding a specific antigen

helper t cells (CD4)

Coordinate immune response, activate B cells, cytotoxic t cells, and macrophages; MHC Class II

cytotoxic t cells (CD8)

destroy infected cells; releases perforin, granzymes, MHC class I

MHC Class I

found on all nucleated cells, recognized by CD8, presents intracellular pathogens

MHC class II

found on antigen-presenting cells only, recognized by CD4, presents extracellular pathogens

Antigen presenting cells (APCs)

macrophages, dendritic cells, b cells; present antigen using MHC II to activate helper t cells

clonal deletion

immature immune cells that attack the body's own tissues are destroyed, preventing autoimmune disease

immune tolerance

immune system learns NOT to attack the body's own cells

autoimmune disease

loss of tolerance causes:

t cells

need antigen presented by MHC molecules, require cell to cell contact

b cells

can recognize free floating antigens, do NOT require MHC to recognize antigen

phenotypic, immunologic, genotypic

methods of identifying bacteria

phenotypic

identification based on observable features (colony appearance, shape, arrangement, gram stain, physiology, biochemical reactions)

gram stain, catalase test, coagulase test, growth on selective media

Examples of phenotypic method

immunologic methods

uses antibodies and antigens (also called serology) detects antibodies, antigens, confirm infections, determine previous exposure

ELISA, agglutination tests

examples of immunologic methods

genotypic methods

Identify organisms by their DNA or RNA (PCR, DNA sequencing)

Aseptic technique, sterile containers, proper transport, proper storage, correct labeling

correct specimen collection

aseptic, contamination

_______ technique prevents _________ from environment, healthcare worker, patient's normal microbiota

Important rules of sampling

only sample the infected site, dont sample surrounding tissue, avoid contaminating normal flora

Sepsis

a medical emergency, microorganisms actively multiply in the bloodstream

saliva

specimen collected by spitting, drooling

sputum

specimen collected by coughing deeply or catheter

urine

specimen collected by catheter, clean catch, dirty catch

clean catch

midstream urine collection

dirty catch

first urine stream collection

swab specimens

urethra, cervix, vagina

skin samples

collected by swab, scalpel scraping

wounds

collected by swab or punch biopsy

sterile needle aspiration

used for blood, cerebrospinal fluid, tissue fluid

Eye, ear, nose, synovial fluid, diseased tissue biopsy

collected by swab

bacteria culture time

18-24 hours

specialized media (enrichment media)

increase growth of bacteria present in very small numbers

selective media

allow only certain bacteria to grow, suppressing unwanted organisms

MacConkey agar, mannitol salt agar

examples of selective media

differential media

differentiate bacteria by biochemical reactions, often shows color changes

blood agar, MacConkey agar, mannitol salt agar

examples of differential media

phenotypic direct examination

fastest way to evaluate specimens (fresh specimens or stained)

Gram stain

Differentiates gram-positive and gram negative

acid fast stain

used for mycobacterium (ex tuberculosis)

KOH preparation

used for fungi; dissolves human cells but leaves fungi cells intact

dichotomous key

a flowchart used to identify bacteria using gram stain, growth characteristics, and biochemical tests (each answer leads to another question until the organism is identified)

disadvantages of phenotypic methods

slow, requires growth, some organisms cannot be cultured, sometimes a cultured organism is only a contaminant

Serology

antigen-antibody reactions tested through serum, urine, CSF, saliva, whole tissues that determine past infection, current infection, immune status, response to vaccination, and disease screening

antibodies, antigen

________ bind only to their matching _________

serology detection

known antigen, unknown antibody OR known antibody, unknown antigen

aggulation tests

Visible clumping that occurs when antibodies bind particles carrying antigens.

aggultination uses

blood typing, bacterial identfication, detection of antibodies, detection of antigens

antibody titers

amount (concentration) of antibdoy in a patient's serum

titer

highest dilution that still shows agglutination

ex: positive at 1:128, negative at 1:256

titer = 1:128

more antibodies present

higher titer =

MRSA

a strain of staphylococcus aureus that is resistant to multiple antibiotics