Biology 260: Review for Final

Biology 260: Review for Final

Microorganisms

• Bacteria: unicellular prokaryotic organisms; extremely diverse, adapted to essentially all habitats

• Fungi: unicellular or multicellular eukaryotic organisms

• Protozoa: unicellular eukaryotic organisms• Algae: unicellular or multicellular eukaryotic

organisms

Viruses

• Protein coat = capsid + nucleic acid– DNA (ds or ss) or RNA (ss)

• Not living organisms• Not a true cell• No cell membrane

– Enveloped viruses have a “stolen membrane” that they acquire when budding out of an infected cell

• No nucleus

Cell type Cell wall? Cell membrane?

Bacteria Prokaryotic Yes Yes

Fungi Eukaryotic Yes Yes

Protozoa Eukaryotic No Yes

Algae Eukaryotic Yes Yes

Cell type DNA Organelles Nucleus Cell membrane

Ribosomes

Prokaryotic Double stranded

No No Yes 70s (50s + 30s)

Eukaryotic Double stranded

Yes Yes Yes 80s (60s + 40s)

Bacterial Structures

Cell Wall Gram-positive

Thick layer of peptidoglycanTeichoic acids

Cell WallGram-negative

Thin layer of peptidoglycanOuter membrane - additional membrane barrier

Lipopolysaccharide (LPS)

O antigen

Core polysaccharide

Lipid A

Cytoplasmic membrane

•Defines the boundary of the cell

•Transport proteins function as selective gates (selectively permeable)

• Control entrance/expulsion of antimicrobial drugs

•Receptors provide a sensor system

•Semi-permeable; excludes all but water, gases, and some small hydrophobic molecules

•Phospholipid bilayer, embedded with proteins•Fluid mosaic model

Electron transport chain - Series of proteins that eject protons from the cell, creating an electrochemical gradient

Proton motive force is used to fuel:• Synthesis of ATP (the cell’s energy currency)• Rotation of flagella (motility)• One form of active transport across the membrane

Cytoplasmic membrane

Electron transport chain

Internal structures: Ribosomes

Unique molecules in bacteria can be used as targets for chemotherapy

• Cell wall: peptidoglycan, techoic acid• Ribosomes• Unique biosynthetic pathways

Bacterial growth & metabolism

• Binary fission• Growth = increase in #• Generation time: time it takes to double the

population• Pathogens with a short generation time cause

rapidly progressive disease (i.e. Vibrio cholera)• Pathogens with a long generation time cause

chronic, slowly progressive disease (i.e. Mycobacterium tuberculosis)

Growth = increase in #

• Many of our drugs are most effective against growing bacteria – – Interrupt cell wall synthesis– Interrupt/block replication– Interrupt/block translation– Interfere with biosynthetic pathways

Primary and Secondary metabolites

Requirements for bacterial growth

• Environmental factors that influence– Temperature, pH, osmotic pressure, oxygen

• Nutritional factors– Carbon, nitrogen, sulfur, and phosphorous– Trace elements: iron

Chemical control: choosing the right germicidal chemical

• What is your goal?– What type or organism are you targeting?– What environment are you treating?– sterility vs. disinfection; level of disinfection required dictates potency of

chemical required• Toxicity: risk-benefit analysis• Activity in presence of organic material: most are diminished or

inactivated• Sensitivity of the material to be treated• Residue: toxic or corrosive vs residual desired antimicrobial effect• Cost and availability• Storage and stability: concentrate vs stock solution• Environmental risk: antimicrobials in the environment

Innate immune system

• 1st line defenses: skin, mucosal barriers, secretions - antimicrobials (lysozyme), iron-binding proteins (transferrin)

• Complement system• Granulocytes (neutrophils, eosinophils, mast

cells), monocytes/macrophages, dendritic cells

Antimicrobial substances

• Produced by animals:– Lysozyme– Peroxidase enzymes– Lactoferrin– Transferrin– Defensins

• Produced by your microbiota:– Fatty acids– Colicins– Lactic acid

Immune Defenses

• Sensory systems:– Pattern recognition receptors

• Toll-like receptors• NOD-like receptors• RIG-like receptors

– Complement system• Alternative pathway• Classical pathway• Lectin pathway

The Complement System• Central feature = splitting of C3 → C3a & C3b• Enzyme that splits C3 = C3 convertase• C3 also spontaneously degenerates to form C3a & C3b at

a constant rate• Alternative pathway: C3b binds to foreign cell surface

receptors → formation of C3 convertase • Lectin pathway: pattern recognition receptors = mannose

binding lectins (MBLs): bind to mannose molecules on microbial surface → formation of C3 convertase

• Classical pathway: antibody binds antigen = antigen-antibody complex → formation of C3 convertase (adaptive immune response)

Leukocytes

• Phagocytes: macrophages & neutrophils• Antigen presenting cells• Natural killer cells

The Acute Inflammatory Response

• Calor = heat: increased blood flow to site• Rumor = redness: increased blood flow• Tumor = swelling: fluid and cells accumulate• Dolor = pain: pressure + chemical mediators• Functio laesa = loss of function: many possible

causes . . .

The acute inflammatory response

Leukocytes have to get out of the blood vessels: recruitment

The Adaptive Immune Response

• Primary response• Secondary response• Humoral immunity:

– B cells, plasma cells, antibodies: target extracellular pathogens

• Cell-mediated immunity– T cells, dendritic cells – antigen is inside a cell

Overview of the Adaptive Immune Response

Lymphocytes

• CD4 = T helper lymphocytes– Activate B cells, macrophages and cytotoxic T cells– Memory T cells

• CD8 = Cytotoxic T lymphocytes• B cells

– Naïve– Activated– Mature = plasma cell (no longer a dividing cell)– Memory B cells

How are B cells activated?

What can happen when antibody binds antigen?

MHC

• MHC class II molecules– Expressed by antigen-presenting cells– Used to present exogenous (non-self) antigen

• MHC class I molecules– Expressed on the surface of all cells – Used to present endogenous (self) antigen– Allows recognition and elimination of infected cells

– viruses, intracellular bacteria

Helper T cells recognize MHC Class II

Cytotoxic T cells recognize MHC Class I markers

What determines outcome of infection?• Host defenses: functional immune system? Age?• Predisposing infection or other disease? Injury?• Pathogenicity of organism – virulence factors; evasion

or invasion tactics?• Infectious dose – very large numbers of an organism

that is not very virulent will still be able to establish infection; some organisms are so virulent that only a few organisms are required to establish an infection

Colonization

• 2 possible outcomes:– Symbiosis– Infection

• Infection:– Subclinical vs infectious

disease– Primary vs secondary

infection– Opportunist vs primary

pathogen

Establishing infection

• Adherence– Pili, capsules, cell wall

components – binding to receptors on host cells

• Colonization– Compete for iron,

nutrients– Resist opsonization– Resist resident’s

antimicrobials• Secretion systems

Exploitation of antigen sampling processes

Avoiding host defenses

• Hide in cells• Avoid complement-

mediated killing• Avoid phagocytosis• Survive in phagocytes• Avoid antibodies

Disease: damage to host

• Damage caused by bacterial exotoxins– Proteins synthesized by

bacteria– Highly specific

interactions with host cells

– Highly immunogenic• Toxoids• Antitoxin

Diseases caused by exotoxins• Neurotoxins

– Botulism– Tetanus

• Entereotoxins– Cholera– Traveler’s diarrhea

• Cytotoxins– Anthrax– Pertussus (whooping cough)– Diptheria– Hemolytic uremic syndrome– Dystentery

• Membrane-damaging toxins:– Gas gangrene– Strep throat– Abscesses

• Superantigens– Some foodborne

intoxications– Toxic shock syndromes

CholeraEtiologic agent: Vibrio

choleraeToxin: cholera toxinToxin type: A-B toxinCell type with receptor:

human enterocytes

Mechanisms of antimicrobial drugs

• Inhibition of cell wall synthesis• Inhibition of protein synthesis• Inhibition of nucleic acid synthesis• Inhibition of biosynthetic pathways • Disruption of cell membrane integrity

Mechanisms of acquired drug resistance

• Destruction or inactivation of the drug: drug inactivation enzymes

• Alteration of target molecule (mutation)

• Decreased uptake: alteration of porins

• Increased elimination: efflux pumps

Acquiring resistance

• Spontaneous mutation• Gene transfer

– R plasmids

Genetics review

Replication: duplication of the genome prior to cell division

Gene expression: decoding of DNA in order to synthesize gene products (proteins):

Transcription: DNA →RNATranslation: RNA → protein

Enzymes necessary for DNA replication

• Primase: synthesizes the RNA primer• DNA Polymerase: synthesize 5’→3’• DNA gyrase: releases tension during uncoiling of

circular DNA**target of quinolones and aminocoumarins**

• DNA ligase: seals the gaps between Okazaki fragments (forms covalent bonds)

• Helicase: “unzips” 2 strands of DNA

ESBL producers are resistant to all β-lactam drugs:

• Penicillins• Cephalosporins• Carbapenems• Vancomycin• Bacitracin

Emerging drug resistance

• MRSA: Methicillin-resistant Staphylococcus aureus

• Drug-resistant Mycobacterium tuberculosis• ESBL producers (enterobacteria,

enterococccus)• Vancomycin-resistant enterococcus

Antimicrobial resistance & antimicrobial stewardship

• Remember the 4 D’s:– Right Drug– Right Dose– De-escalation to pathogen-targeted therapy– Right Duration

Vectors

• biological vector a vector in whose body the infecting organism develops or multiplies before becoming infective to the recipient individual.

• mechanical vector a vector which transmits an infective organism from one host to another but which is not essential to the life cycle of the parasite.

• Normal microbiota– Protection– Training of the immune system

• Fermentation: beer, wine, cheese, yoghurt, bread, pickled foods