Dd - Bacterial Structure, Function And Growth

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major structural features of bacteria

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-rigid cell wall made up of peptidoglycans (wall resists internal osmotic pressure. resist antimicrobial agents)
-cytoplasmic membrane underneath the cell wall/peptidoglycan layer.
-bacterial chromosome with NO nuclear membrane
-ribosomes (but no membrane bound organelles)
-sometimes have capsule
-flagellae
-pili
-cytosol

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peptidoglycans

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above the cytoplasmic membrane

-mesh of cross-linked hexose sugars
-resist osmotic lysis
-unique to bacteria

lots of peptidoglycans in gram positive bacteria

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cytoplasmic membrane

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• Semipermeable lipid bilayer; impermeable to most hydrophilic compounds and all charged particles.
• Electron transport chain to generate ATP is located in this membrane-- effectively uses proton gradient across the cytoplasmic membrane to drive ATP generation (very much like mitochondria in eukaryotes).
• Membrane contains a variety of transporters to transport vital compounds.

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what is the cytoplasmic membrane permeable to

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semipermeable

impermeable to hydrophilic and all charged particles

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Plasmids:

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non-chromosomal, self-replicating DNA molecules (much smaller than entire bacterial chromosome).

Generally contain specialized genes that are not necessary for survival of the bacteria-- these genes often contain virulence factors and resistance factors to antibiotics.
 This is important. Plasmids are modular elements, interchangeable between bacteria, that confer drug resistance and virulent effects on the host. Sort of "plug and play" action here.

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Bacteriophages:

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viruses that infect bacteria.

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Temperate phages:

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integrate viral DNA into bacterial DNA (like retroviruses in eukaryotes).

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Phage conversion:

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phage-mediated change in the phenotype (virulence, resistance, etc) of a bacterium.

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shape of bacteria is dependent upon

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intracellular cytoskeletal elements

-FtsZ
-MreB
-CreS

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FtsZ

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 FtsZ: prokaryotic analogue to eukaryotic tubulin. Aids in cell division.

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MreB:

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analogue to ACTIN. Influences elongation of Bacillus vs. Coccus.

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CreS:

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analogue to INTERMEDIATE FILAMENTS Influences specific 'curving' of shape (ie spirillum vs. bacillus).

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capsule

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layer of polysaccharides.
hinders phagocytosis

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flagella rotated counterclockwise,

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promotes directed motion or swimming;

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flagella rotated clockwise

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promotes being more or less stationary ('tumbling')

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cytosol of bacteria

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no compartmental barriers between bacterial DNA and riboosomes.

mRNA transcribed and translated in same place without transport mechanism

prokaryotes --> polycistronic mRNA - multiple encoded genes (one mRNA makes many different proteins)

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gram negative cell wall

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-two layers of cell wall surr. cytoplasmic membrane (periplasmic space)
--peptidoglycan inner layer
--outer layer

-LPS chains off of outer layer (toxic in the host)
-porin in outer layer = transmembrane channels

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gram positive cell wall

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ONE cell wall layer (peptidoglycan rich) surrounding cytoplasmic membrane

-lots of cross linking of peptidoglycan layers
--mediated by teichoic acid and lipoteichoic acid

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teichoic acid and lipoteichoic acid

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mediate cross linking of peptidoglycan layers in gram positive bacterial cell walls. serve as scaffolds.

immersed in peptidoglycan layer = teichoic acid

anchored to lipid cytoplasmic membrane is the lipoteichoic acid

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how are bacteria classified according to nutritional requirements

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heterotrophic

autotrophic

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Heterotrophic:

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require organic compounds in media for carbon source.

 Fastidious: require growth factors (ions, nucleic acids, etc) in media.

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autotrophic

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get carbon from CO2 alone

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• indifferent bacteria

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does not use oxygen (always use anaerobic fermentation), but do not find O2 toxic.

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• facultative bacteria

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use oxygen, if present, with oxidative metabolism, but use anaerobic fermention in the absence of oxygen.

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• microaerophilic bacteria

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grow best at very low concentrations of oxygen, but can survive without it.

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o Energy currency: ATP and "PMF" (proton motive force).

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ATP is energy stored in a molecule; PMF is energy stored as a proton gradient across the bacterial membrane. PMF is what drives flagellar rotation and some transport mechanisms.
o Bacteria require reducing agents for electron transport (NADH, etc).
o Fermentation: anaerobic.
• Organic compounds serve as both the donators and acceptors of electrons. No net oxidation or reduction.
o Respiration: aerobic.
• Organic compounds donate electrons and are oxidized; oxygen (less commonly nitrate or nitrite) accepts electrons and are reduced.

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sporulation

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spores = special cells produced by bacteria
-clostridium and bacillus

devel when C, N and PO4 limited

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which bacteria produce spores

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bacillus

clostridium

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sporulation

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bacteria can become highly resistant and dehydrated/no metabolic activity

can convert back to vegetative state --> germinate

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cell wall antimicrobials

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-beta lactams
-vancomycin
-cycloserine

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beta lactams

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penicillin, cephalosporins

inhibit final transpeptidatoin reactoin in cross linking of peptidoglyhcan

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vancomycin

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inhibits utilization of lipid inked intermediate at an intermediate step in peptidoglycan synthesis.

elongation of peptidoglycan chain

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cycloserine

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inhibits alanin racemase

prevents formation of muramyl pentapeptide (early intermediate in peptidoglycan synthesis)

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outer and cytoplasmic membrane active antimicrobials

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polymyxins --
cationic surfactants that disrupt bacterial outer and cytoplasmic membranes.

less active on mammalian cell membranes

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inhibitors of protein sythesis at the ribosomal level

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selective toxicity is due to differences between bacterial and mammalian ribosomes

-aminoglycosides
-tetracyclines
-chloramphenicol
-macrolides

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aminoglycosides

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(including streptomycin, kanamycin, gentamicin, neomycin, tobramycin, amikacin, et)

bind to specific target proteins in teh 30S ribosomal subunit and inhibit protein synthesis

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tetracyclines

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reversibly bind to the 30S ribosomal subunit and inhibit binding of aminoacyl tRNA

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bacterial ribosomes vs eukaryotic ribosomes

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bacterial ribosomes (50+30S = 70S)

eukaryotic ribosomes (60 S + 40S = 80S)

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eukaryotic mitochondrial ribosomes are similar to ____ ribosomes

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bacterial ribosomes

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cycloserine

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inhibits alanine racemase, prevents formation of muramyl pentapeptide

**cell wall active antimicrobial**

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polymyxins

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cationic surfactants that disrupt bacterial outer and cytoplasmic membranes.

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tetracycline

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reversibly binds tto the 30S ribosomal subunit and inhibits binding of aminoacyl tRNA

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chloramphenicol

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binds reverwibly to teh 50S ribosomal subunit and inhibits peptidyl transferase and peptide bond formation

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macrolides

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e.g. erythromycin bind to the 23S ribosomal RNA of the 50S subunit and inhibits peptidyl transferase

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lincomycins

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such as lincomycin and clindamycin

bind to the 23S riboomal RNA of the 50 S subunit and inhibits peptidyl transferase

**similar to the macrolides**

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inhibitors of nucleic acid synthesis

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-quinolones
-rifampicin

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quinolones

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inhibit DNA gyrase and topoisomaerase and interfere with DNA replication

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rifampicin

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inhibits RNA polymerase and interferes with initiation and transcription

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metabolic inhibitory antimicrobials

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-sulfonamides
-trimethoprim
-isoniazid
-metroidazole

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sulfonamides

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analog of p-aminoobenzoidc acid (PABA)
sulfonamides inhibit formation of folic acid by competing with PABA. prevents nucleic acid synthesis

slective b/c only bacteria , not th ehost, phas enzymes to make folic acid

humans get folic acid from bacteria

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trimethoprim

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interferes with folate metabolism by inhibiting dihydrofolate reducatase

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isoniazid

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inhibits lipid synthesis (mycolic acid syntheis) in mycobacteria

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metronidazole

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interfere with anaerobic metabolism

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Frank pathogens

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can cause disease in immunonormal hosts (anthrax, plague).

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Opportunistic pathogens

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can cause disease in immunocompromised hosts but not usually in normal hosts (Pseudomonas aeruginosa).
 Notice that many normal human flora are opportunistic pathogens.

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pseudomonas aeruginosa is what type of pathogen

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opportunistic

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kochs postulate (microbe shown to cause specific disease)

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(1) Must show that microbes are present in characteristic lesions of disease.

(2) Microbes must be isolated and grown in pure culture.

(3) Injection of isolated and grown microbes into undiseased animals must cause the original disease to appear.

(4) The same microbes must appear in the lesions on the new animal

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cholera

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non-invasive bacteria

adheres to SI
secretes toxins
toxins cause diarrhea

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pneumoccocal pneumonia

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multiplies extracellularly b/c has anti-phagocytic capsule
grows
causes tissue damage in the lung

host produces antibodies that coat its capsule and cause it to be destroyed

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TB

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multiplies intracellularly
invades macrophhages and replicate inside its vacuoles

host defends via T-cell mediated response --> + affected macrophages to develop internal granules that kill microbes

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rheumatic fever

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typical immune response

after streptococcal infection

autoimmune response

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spreading factors

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-hyaluronidase
-elastase
-collagenase

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inhibits spread of microbe

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coagulase (promotes deposition of fibrin and helps to localize infection)

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aggressins

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microbial prodcuts tha tdamage the host

e.g. microbial toxins and some enzymes

surface components of microbes

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impedins

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microbial products that block host defenses

e.g. antiphagocytic capsules and leukotoxins

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aggressins and impedins

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surface compnenets of microbes

can be secreted into the microbial culture medium

can be injected by the microbe into target cell

vaccines use these