Major structural features of bacteria (general)
- cell wall 2. characteristic shape 3. characteristic cell surface structures 4. 70S Ribosome 5. Nucleoid
Functions of external cell wall
- resisting osmotic lysis 2. maintaing cell shape
General structure of peptidoglycan layer
polymer w/repeating units of hexose sugars (GlcNAc & MurNAc) linked to tetrapeptide chains w/bacteria-specific amin acids (meso-DAP, D-glutamic acid, & D-alanine); peptidoglycan chains cross-link
Gram-negative vs. Gram-positive peptidoglycan layer
1.Gram-negative=thin, sparsely cross-linked 2. Gram-positive=thick, cross-linked++, w/teichoic acids
Composition of OM of gram-negative bacteria
lipid bilayer=lipopolysaccharide (LPS) + lipoproteins (covalent link to peptidoglycan) + porins + phospholipids
Function of OM of gram-negative bacteria
- barrier to entry of some anitbiotics 2. protects against detergents/toxins
LPS of gram-negative bacteria structure
LPS=Lipid A (endotoxin component) + core poly sacc + oligosaccarachide (O antigen)
Teichoic acid structure
TA=repeating polyglycerol-P or polyribitol-P backbone w/some substitutes covalently linked to peptidoglycan
Capsule structure and fxn
- outer surface layer of complex polysaccharides 2. enhance virulence by resisting phagocytosis
Flagella structure and fxn
- appendages originating in cytoplasmic membrane, composed of cytoskeleton elements. 2. molitily/chemotaxis
Pili structure and fxn
- protein, hair-like structure on surface 2. adherence to surfaces and tissues 3. sex pili–>bacterial conjugation
Cytoplasmic membrane structure and fxn
- lipid bilayer=phospholipids+proteins 2. physiological barrier btwn inside and outside of cell 3. selective permeability 4. electron transport system 5. transport metabolites 6. biosynthesis 7. DNA replication 8. flagellar rotation
Nucleoid structure
- distinct region of cytoplasm=location of tightly coild DNA; no nuclear membrane
Types of DNA present in bacteria
- Chromosome=double-stranded, circular DNA 2. Plasmid=extra-chromosomal, self-replicationg DNA, often encode virulence factors
Bacteriophage definition
viruses that infect bacteria; genomes may incorporate into bacterial chromosome; change in phenotype=”phage conversion”
Phases of bacterial growth (4)
- lag phase 2. exponential phase 3. stationary phase 4. death phase
Characteristics of lag phase
incolum=period of physiologic adjustment; establish enzymes/intracell enviro for growth on new medium
Characteristics of exponential phase
growth rate proportional to cell number/mass; generation time=doubling time (time required to double cell number/mass)
Characteristics of stationary phase
essential nutrients consumed and toxic metabolites acumulate; cell growth slows or stops; most bacteria in nature
Characteristics of death phase
number of viable bacteria decrease over time; autolysis occures
Minimal requirements for bacterial growth
- certain inorganic ions 2. carbon source 3. energy source
heterotrophic bacteria definition
bacteria that require organic carbon source (most bacterial pathogens)
autotrophic bacteria definition
bacteria that obtain carbon exclusively from CO2
fastidious bacteria definition
lacking in one+ biosynthetic pathways; require growth factors
Strict Aerobic bacteria (1. Aerobic growth? 2. Anerobic growth? 3. Example)
- (Requires O2; cannot ferment) 3. mycobacterim tuberculosis
Strict Anaerobic bacteria (1. Aerobic growth?2. Anerobic growth? 3. Example)
- (Killed by O2; ferments) 3. Clostrium or Bacteroides sp
Aeritolerant anaerobic bacteria (1. Aerobic growth? 2. Anerobic growth? 3. Example)
- (Ferments w/ or w/out O2 present) 3. Streptococcus pyogenes
Facultative Anaerobic bacteria (1. Aerobic growth?2. Anerobic growth? 3. Example)
- (Respires w/O2, Ferments w/out) 3. E. Coli or Staphylococcus aureus
Microaerophilic bacteria (1. Aerobic growth?2. Anerobic growth? 3. Example)
- ++ (Grows best at low O2, can grow some w/ or w/out O2) 3. Campylobacter jejuni
2 types of “energy currency” in cells
- ATP 2. electrochemical gradients/proton motive force
Fermentation definition
organic compounds=electron donors and acceptors; no net oxidation of substrates
Respiration definition
generation of ATP through electron transport w/O2 as final electron acceptor
Selective toxicity definition
selective inhibiton of microbial growth at drug concentrations tolerated by the host; principle on which antimicrobials work
Major categories of antimicrobial targets (5)
- Cell wall-active antimicrobials 2. Outer/cytoplasmic membrane-active antimicrobials 3. Inhibition of protein synthesis 4. Inhibition of nucleic acid synthesis 5. Metabolic inhibitory antimicrobials
Antibiotics w/cell wall target
- B-lactams (penicillins, cepalosporins) 2. Vancomycin 3. Cycloserine
Antibiotics w/cytoplasmic membrane target
Polymyxins
Antibiotics w/protein synthesis target
- Aminoglycosidase (streptomycin, kanamycin, etc.) 2. Tetracyclines 3. Chloramphenicol 4. Macrolides & Lincomycins
Antibiotics w/DNA synthesis target
- Quinolones 2. Rifampicin
Antibiotics w/metabolic target
- Sulfonamides 2. Trimethoprim 3. Isoniazid 4. Metronidazole
Sulfonamide target/action
strucutral analog of p-aminobenzoic acid –> inhibits folic acid synthesis –> inhibits nucleic acid synthesis
Trimethoprim target/action
inhibits dihydrofolate reductase –> inhibits folic acid synthesis –> inhibits nucleic acid synthesis
Isoniazid target/action
inhibits lipid synthesis in mycobacteria
Metronidazole target/action
interferes w/anaerobic metabolism
anaerobic respiration definition
ATP generation via electron transport w/inorganic substrates as terminal electron acceptors
