BIO-205 Exam 3

innate immunity

* factors that work generically against any foreign substance entering the host
* Involve pattern recognition of specific molecules

First-line defenses in innate immunity

* skin- difficult for microbes to penetrate
* Mucous membranes
* mucociliary escalator
* Antimicrobial substances
* lactoferrin
* Defensins

normal microbiota (flora)

* competitive exclusion of pathogens
* Organisms that typically reside on and in your body
* Distribution of normal microbiota can predispose person to infections
* clostridium difficile in intestine- diarrhea

Cytokines

voices of the cell

Pattern recognition receptors (PRPs)

detect pathogen-associated molecular patterns (PAMPs), see signs of microbial invasion

Toll-like receptors (TLRs)

anchored in membranes of sentinel cells, each recognize a specific danger molecule

NOD-like receptors (NLRs)

* found in cytoplasmic proteins to form an inflammasome
* activates inflammatory response

RIG-like receptors (RLRs)

* found in cytoplasm
* detect viral RNA produce interons

The complement system

* complements activities of adaptive immune system
* a group of interacting serum proteins that provide a nonspecific defense mechanism
* all pathways of complement activation follow the same sequence after C3

Process of phagocytosis

1. chemotaxis
2. recognition and attachment
3. Engulfment
4. Phagosome maturation and phagolysosome formation
5. Destruction and digestion
6. Exocytosis

Four cardinal signs

* heat
* pain
* redness
* swelling- damaging effects of inflammation

Apoptosis

programmed cell death; does not trigger inflammatory response

Fever

* important host defense mechanism
* strong indicator of infectious disease
* temperature raises during infection in response to pyrogens
* Inhibits bacterial growth and speeds up the body’s reaction

Primary response

* takes a week or more to build following first exposure
* adaptive immunity has memory

Pyrogens

endogenous pyrogens- macrophages detect microbial products and produce these cytokines

Exogenous pyrogens- produced by microbes

2 degree response

* stronger response to re-exposure
* Response has molecular specificity

Primary lymphoid organs

bone marrow and thymus

Secondary lymphoid organs

* sites where lymphocytes gather to encounter antigens
* strategically located in the body and facilitate interactions between cells
* organs include
* lymph nodes
* spleen
* tonsils
* adenoids
* appendix

Lymphocytes

* T cells and B cells
* mature when cells have specific receptors proteins on surface
* at this stage the cells are immunocompetent

B lymphocytes or B cells

* bone marrow
* differentiate into plasma cells
* produce Y-shaped proteins called antibodies
* antibodies bind to antigens with high degree specificity
* some B cells form long-lived memory B cells

T lymphocytes

* mature in thymus
* cytotoxic T cells and helper T cells
* both have T-cell receptor (TCR)
* TCR does no recognize free antigen
* antigen must be presented by body’s own cell
* Third subset is regulatory T cell
* prevent immune system from mounting a response against “self” molecules

T-cell receptor (TCR)

* does not interact with free antigen
* only antigen presented by major hist-compatibility complex (MHC) molecules on surface of cell

What do cytotoxic T cells respond to

endogenous antigens presented on MHC class 1 molecules

What do helper T cells respond to

exogenous antigens presented on MHC class 2 molecules

Class 1 MHC proteins

found on al cells in body

Class 2 MHC proteins

found only on a few types of cells such as macrophages, B-cells

Antigen

* comes from antibody generator
* proteins and polysaccharides
* contain multiple antigenic determinants (epitopes)

Immunogen

antigen that elicits an immune response

T-dependent antigen

for most antigens B-cell requires signal from helper T-cell

T-independent antigen

* polysaccharide capsules and flagella
* LPS and molecules with repeating subunits such as carbohydrates- HiB (encapsulated haemophilius influenza)

T antigens

* do not lead to memory response
* if no helper T cells recognize peptides, B cell may become anergic (unresponsive to future exposure of antigen)

Antibody structure

* two identical arms- Fab region (antigen binding)- variable region is unique to each Ab and accounts for specificity
* The stem- Fc region (crystallized)- constant region- allows immune system components to recognize otherwise diverse antibody molecules

What is Ab class based on

constant region of the Ab

IgM

* first Ab to respond to infection
* agglutinated microbes
* only Ab that can be formed by the fetus

IgG

* Dominant Ab in circulation
* only Ab that can cross the placenta
* the antibody of memory

IgA

* found in secretions
* breast milk, mucous, tears, and saliva

IgD

* involved with development and maturation of antibody response

IgE

* antigen binds to two adjacent IgE molecules carried by mast cells and Basophils, cell releases histamine and other inflammatory mediators

Cell mediated immunity is effective against

* eukaryotic pathogens (fungi/parasites)
* virus-infected cells
* transplanted cells
* cancer
* protozoa
* fungi

Humoral immunity effective vs.

* bacteria- flagella, pilli, capsules
* viruses in body fluids
* toxins and other soluble antigens

Natural killer cells

* bind, deliver perforin- and protease- containing granules to cell, initiating apoptosis

Joseph Lister

* applied carbolic acid (phenol) directly onto damaged tissues, where it prevented infections

Approaches to control microorganisms physical and chemical

* physical- heat treatment, irradiation, filtration, and mechanical removal
* chemical- variety of antimicrobial chemicals
* combination of both

Sterilization and sterile item

* the process of killing or removing all of the microorganisms in or on a material
* Sterile item- free of microbes, endospores, and viruses

disinfection, disinfectant, antiseptic

* eliminates most pathogens
* Disinfectants- used on inanimate objects
* Antiseptics- used on living tissues

Pseudomonas species

resistant to and can actually grow in some disinfectants also mycobacterium sps, Endo spore formers- clostridium and bacillus sp., non enveloped viruses

Biocide/germicide

kills microbes

Bacteriostasis

inhibiting, not killing, microbial growth

Daily life approach to control microbes

soap aids in mechanical removal of organisms

Healthcare-associated infections (HAIs)

* nosocomial infections- acquired from hospital settings
* Patients more susceptible to infection

Pasteurization

* brief heating to reduce number of spoilage organisms, destroy pathogens
* commercial canning process destroys the endospores of Clostridium botulinum
* ultra-high-temperature (UHT): shelf-stable boxes juice and milk; known as “ultra-pasteurization”

Moist heat

* irreversible denatures proteins in microbes- bactericidal
* breaks H bonds
* changes shape of enzymes
* boiling- does not sterilize: endospores can survive
* pasteurization
* Autoclave

Autoclave

* sterilization typically at 121 C for 15 minutes at 15 psi
* longer for larger volumes
* prions thought destroyed at 132 C for 1 hour

Autoclave indicators

* tape: contains heat-sensitive indicators turns black at high temp
* biological indicators: heat resistant endospores of Geobacillus stearothermophilus

Dry heat

* not as effective as moist heat
* incineration- a method of dry heat sterilization
* Hot air ovens oxidize cell components to ashes, denature proteins
* flaming laboratory inoculation loop incinerates organisms

Membrane filters

* some materials cannot withstand heat treatment
* filtration retains bacteria
* filtration of fluids used extensively
* Depth filters
* thick porous filtration material
* electrical charges trap cells
* HEPA- high-efficiency particulate air filter used for air

Ionizing radiation

* damages cytoplasmic membranes of G (-ve): Pseudomonas
* High energy gamma-rays
* used to sterilize or pasteurize

Ultraviolet radiation

* destroys microbes directly
* damages DNA (thymine dimer)

Alcohols

* not reliable against endospores, some naked (some enveloped) viruses
* pure alcohol less effective than aqueous solution

Aldehydes

* 2% alkaline glutaraldehyde common sterilant
* immersion for 10-12 hours kills all microbial life
* is very good for use on heat-sensitive medical items
* Formaldehyde
* used to kill bacteria and inactivate viruses for vaccines

Biguanides

* Chlorhexidine most effective
* extensive use as antiseptics

Ethylene oxide

* useful gaseous sterilant
* useful in sterilizing heat-or-moisture-senstive items
* potentially carcinogenic

Halogens

* chlorine: destroys all microorganisms and viruses
* used as disinfectant
* caustic to skin and mucous membranes
* very low levels disinfect drinking water
* cryptosporidium oocysts and Giardia cysts survive
* emergency- add 2 drops of bleach to 1 liter water, 30 mins before drinking
* Iodine- kills vegetative cells, unreliable on endospores

Metal compounds

* silver still used as an antiseptic: creams, bandages
* Silver nitrate eye drops given at birth to prevent Neisseria gonorrhoeae infections
* Compounds of mercury, tin, copper used as preservatives
* Extensive use led to environmental pollution

Ozone

* hydrogen peroxide: effectiveness depends on surface
* inactivated on living tissue: aerobic cells produce enzyme catalase
* breaks down H2O2 to O2, H2O
* More effective on inanimate object
* Peracetic acid: more potent when used in combination with H2O2

Phenolic compounds

* destroy cytoplasmic membranes, denature proteins
* remain effective in presence of detergents and organic contaminants
* Triclosan have been used widely in various lotions and soaps

Quaternary Ammonium Compounds (QUATS)

* cationic detergents
* Disinfection of food preparation surfaces
* most household soups, detergents are anionic
* positive charge of quats attracted to negative charges of microbial cell surface

Preservation of perishable products

* nitrate and nitrite used in processes meats
* stops growth of clostridium botulinum
* higher concentrations give meats pink color
* Shown to be carcinogenic- form nitrosamines

Low-temperature strorage

freezing preserves by stopping all microbial growth

Lyophlization

freeze drying foods

Paul Ehrlich

* searched for “magic bullet” that would kill microbial pathogens without harming human host
* synthesized arsenic compounds to treat syphilis, caused by Treponema palladium
* the 606th tested compound proved effective in lab animals
* arsphenamine named Salvarsan

Chemotherapeutics

* chemicals used to treat disease
* ex. Salverson and protonsils

Antimicrobials

antimicrobial compounds

Antimicrobials

antimicrobial compounds

Alexander Fleming

* 1928 discovered penicllin
* Made by penicillium fungus (mold) that inhibited Staph aureus

Antibiotic

a substance produced by microbes which in small amounts inhibit the growth of other microbes

most antibiotics produced by three genera

* bacillus- bacteria
* Streptomyces- bacteria, more than half of antibiotics
* Penicillium- fungus

Good antibiotics

* have selectivity toxicity- toxic for microbe, not host
* Dont trigger allergic reactions and toxic effects
* soluble in body fluids
* does not induce drug resistance quickly
* doesn’t suppress normal flora
* is broad spectrum active vs. many different pathogens both g (-ve) and G (+ve)

Therapeutic index

* how toxicity of a given drug is expressed
* high therapeutic index is less toxic to pt/ dose used for therapy

Antagonistic

medications interfere with each other

Synergistic

combinations where one medication enhances

Additive

combinations that are neither antagonistic or synergistic

B- lactam antibotics

* have B-lactam ring and high therapeutic index
* competitively inhibit penicilin-binding proteins (PBPs)- catalyze formation of peptide bridges between adjacent glycan strands; disrupt cell wall synthesis

Penicillin

* interfere with synthesis of peptidoglycan in bacterial cell wall
* limitations- only effective against actively growing cells
* Some bacteria synthesize B-lactamase, which breaks critical B-lactam ring-penicillin resistance

Augmentin

* contains amoxicillin and clavulinic acid ( a beta-lactamase inhibitor)

Inhibit protein synthesis

* aminoglycosides, tetracyclines, macrolides
* can exploit differences between prokaryotic and eukaryotic ribosomes

Aminoglycosides

* irreversibly bind to 30S ribosomal subunit causing it to distort and malfunction- bactericidal
* often toxic
* form of tobramycin administered via inhalation to treat lung infections in cystitis fibrosis patients; safer and more effective

Tetracyclin

* reversible bind 30S ribosomal subunit- bacteriostatic
* blocks attachment of tRNA to ribosome- prevents continuation of protein synthesis

Macrolides

* reversible binds to 50S ribosome- prevents continuation of protein synthesis
* Effective against variety of gram + organisms and those responsible for atypical pneumonia
* often drug of choice for patents allergic to penicillin

Inhibit nucleic acid synthesis

* the fluoroquinolones target DNA synthesis by inhibiting topoisomerases
* enzymes that maintain supercoiling of DNA
* DNA gyros breaks, rejoins strands to relieve strain from localized unwinding of DNA; function is essential
* Bactericidal against wide variety of bacteria
* resistance usually due to alteration in DNA gyrase target

Rifamycins

* block prokaryotic RNA polymerase- block invitation of transcription
* effective against many gram + and some gram - as well as membranes of genus mycobacterium
* primarily used to treat tuberculosis and Hansen’s disease as well as preventing meningitis after exposure to N. meningitidis

Sulfonamides

* structurally similar to PAB, so enzyme binds chemicals
* example of competitive inhibition of Folic acid biosynthesis
* Combination of trimethoprim and sulfonamide has synergistic effect

Antibacterials effective against mycobacterium species

* first-line antibiotics given as combination therapy
* Some target unique cell wall of mycobacteria
* isoniazid inhibits mycolic acid synthesis

Minimum inhibitory concentrations

* lowest concentration that prevents growth in vitro
* microbes with MIC between susceptible and resistant are termed intermediate

Minimum inhibitory bactericidal

* lowest concentration that kills 99.9% of cells in vitro; determined from plate count from MIC

Kirby-bauer disk diffusion test

* routinely used to determine susceptibility of bacterial strain to antibiotics
* Size of zone of inhibition determines whether strain is susceptible, intermediate, or resistant
* drug characteristics must be taken into account