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
Ribosomes
membrane
Prokaryotic Double
stranded
No
No
Yes
70s (50s +
30s)
Eukaryotic
Yes
Yes
Yes
80s (60s +
40s)
Double
stranded
Bacterial Structures
Cell Wall
Gram-positive
Thick layer of peptidoglycan
Teichoic acids
Cell Wall
Gram-negative
Thin layer of peptidoglycan
Outer membrane - additional
membrane barrier
Lipopolysaccharide (LPS)
O antigen
Core polysaccharide
Lipid A
Cytoplasmic membrane
•Defines the boundary of the cell
•Semi-permeable; excludes all
but water, gases, and some
small hydrophobic molecules
•Transport proteins function as
selective gates (selectively permeable)
•Control entrance/expulsion of
antimicrobial drugs
•Receptors provide a sensor system
•Phospholipid bilayer, embedded with proteins
•Fluid mosaic model
Cytoplasmic membrane
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
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), ironbinding proteins (transferrin)
• Complement system
• Granulocytes (neutrophils, eosinophils, mast
cells), monocytes/macrophages, dendritic
cells
Antimicrobial • Produced by animals:
– Lysozyme
substances
– 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 complementmediated 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
Cholera
Etiologic agent: Vibrio
cholerae
Toxin: cholera toxin
Toxin type: A-B toxin
Cell 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 →RNA
Translation: 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 βlactam 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