Last Years Bacterial Structure

8/8/2019 Last Years Bacterial Structure

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Genetic SizeGenetic SizeDNDN A (Haploid) A (Haploid)ORGANISMORGANISM (base pairs x 10(base pairs x 10 66 ) GENES) GENES

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Eukaryote HumanEukaryote Human 2,850 202,850 20 -- 25,00025,000

EukaryoteEukaryote Saccharomyces Saccharomyces cerevisiae cerevisiae 12.1 5,88512.1 5,885

GramGram--negativenegative Escherichia Escherichia coli coli 4.6 4,2884.6 4,288BacillusBacillus

GramGram--negativenegative Haemophilus influenzae Haemophilus influenzae 1.8 1,7431.8 1,743

BacillusBacillus

Cell wallCell wall--lackinglacking Mycoplasma genitalium Mycoplasma genitalium 0.58 4700.58 470BacteriumBacterium

Virus Poxvirus (vaccinia) Virus Poxvirus (vaccinia) 0.190.19 250250


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Bacterial ShapeBacterial Shape


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CapsuleCapsule Negative StainNegative Stain


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Multiple FlagellaMultiple Flagella Salmonella enteritidis Salmonella enteritidis


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Flagellar RotorFlagellar Rotor -- GramGram--Negative CellNegative Cell


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Flagellar Rotation and MotilityFlagellar Rotation and Motility

Counterclockwise RotationCounterclockwise RotationBacteria Swim in a StraightBacteria Swim in a StraightLine (A & C)Line (A & C)

Clockwise RotationClockwise RotationBacteria Tumble in aBacteria Tumble in aRandom Fashion (B & D)Random Fashion (B & D)

Control of the Extent of Control of the Extent of Swimming and TumblingSwimming and Tumbling

Enables ChemotaxisEnables Chemotaxis


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The Sex Pilus inThe Sex Pilus in E. coli E. coli Enables aEnables a

Male Cell to Attach to a Female Cell Male Cell to Attach to a Female Cell


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ConjugationConjugation

A) Attachment to Female Cell via Sex Pilus A) Attachment to Female Cell via Sex Pilus

B) CellB) Cell--Cell Apposition Enabling DNA TransferCell Apposition Enabling DNA Transfer


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Bacillus Species: GramBacillus Species: Gram -- PositivePositive


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E. Coli E. Coli : Gram: Gram -- NegativeNegative


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Gram StainGram Stain


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GramGram--positivepositive

((Staphylococcus aureus Staphylococcus aureus ))


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GramGram--negative (negative ( Escherichia coli Escherichia coli ))


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Comparison of G+ and GComparison of G+ and G -- Cell WallsCell Walls

G+

G-


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Comparison of G+ and GComparison of G+ and G -- Cell WallsCell Walls

G THICK PEPTIDOGLYCANG THICK PEPTIDOGLYCAN


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G+: THICK PEPTIDOGLYCANG+: THICK PEPTIDOGLYCAN~ 40 Layers (20~ 40 Layers (20 --80 nm)80 nm)

contains:contains:TEICHOIC ACIDTEICHOIC ACIDLIPOTEICHOIC ACIDLIPOTEICHOIC ACID

GG-- : THIN PEPTIDOGLYCAN: THIN PEPTIDOGLYCAN11 -- 2 Layers (22 Layers (2 --5 nm)5 nm)

PERIPLASMIC SPACEPERIPLASMIC SPACEOUTER MEMBRANEOUTER MEMBRANE

Lipid Bilayer (10Lipid Bilayer (10--30 nm)30 nm)

contains:contains:LIPOPOLYSACCHARIDELIPOPOLYSACCHARIDE

(LPS)(LPS)

HYDROPHILIC PORESHYDROPHILIC PORES(Porins)(Porins)


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GramGram -- Positive Cell WallPositive Cell Wall


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GramGram -- Negative Cell WallNegative Cell Wall


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Comparison of GComparison of G -- and G+ Peptidoglycanand G+ Peptidoglycan

NAMNAM--LL-- Alanine Alanine --DD--isoGlutamateisoGlutamate Muramyl dipeptide or MDPMuramyl dipeptide or MDP Highly conserved in G+ and GHighly conserved in G+ and G -- peptidoglycanspeptidoglycans iso = peptide bond viaiso = peptide bond via --carboxyl groupcarboxyl groupThird amino acid contains a freeThird amino acid contains a free NHNH22

Typically LTypically L--Lysine in G+Lysine in G+ Typically Diaminopimelic acid (DAP) in GTypically Diaminopimelic acid (DAP) in G--Crosslink Crosslink Typically direct in GTypically direct in G -- Typically a short peptide in Gram+Typically a short peptide in Gram+

Penicillins and cephalosporins inhibit thePenicillins and cephalosporins inhibit thecrosslinking step in both G+ and Gcrosslinking step in both G+ and G -- bacteriabacteria

C i f GC i f G d G P id ld G P id l


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Comparison of GComparison of G -- and G+ Peptidoglycanand G+ Peptidoglycan


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DiaminoacidsDiaminoacids in Peptidoglycanin Peptidoglycan33 rdrd Position of PentapeptidePosition of Pentapeptide Enables CrosslinkingEnables Crosslinking


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Teichoic AcidsTeichoic Acids


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GramGram -- Positive Cell WallPositive Cell Wall


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LIPOPOLYSACCHARIDE (LPS) = ENDOTOXIN - Restrictedto Gram- bacteria ; major component of cell wall; anchored in

the outer leaflet of the outer membrane by LIPID A.

O-ANTIGEN : 3 - 7 sugar polysaccharide unit, repeated 50 100 times. A major antigenic determinant

Example: E. coli serotype O157:H7

LIPID A: responsible for ENDOTOXIN activity

LPS (E d t i ) i iti t t i


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LPS (Endotoxin) initiates many systemiceffects of Gram-negative infections

1. INFLAMMATION - LPS activates

complement and has additional effects oninnate immunity

2. FEVER (PYROGENICITY ) - at moderatesystemic LPS levels

3. LETHAL TOXICITY - at high systemicLPS levels Hypotension, Shock, Death


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E. Coli E. Coli Lipid A is Lipid A is hexahexa --acyl acyl

Li id A d E d iLi id A d E d i


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Lipid A structures and EndotoxinLipid A structures and Endotoxin

activity vary between bacterial speciesactivity vary between bacterial species

Maximal endotoxin activity occurs with Maximal endotoxin activity occurs with hexahexa --acylacylLPSsLPSs, which contain an, which contain an E. coli E. coli - - like lipid A: 6 fattylike lipid A: 6 fattyacyl chains attached toacyl chains attached to diphosphoryldiphosphoryl diglucosaminediglucosamineThe number, length and position of the acyl chains,The number, length and position of the acyl chains,

and the phosphorylation state, affects activityand the phosphorylation state, affects activityThe periodontal pathogenThe periodontal pathogen Porphyromonas Porphyromonas gingivalis gingivalis (Pg)(Pg) produces triproduces tri --, tetra, tetra -- and pentaand penta --acylated lipid Aacylated lipid A

the relative amount of each species is growththe relative amount of each species is growthdependent and affects the inflammatory responsedependent and affects the inflammatory responseto this organismto this organism


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ENDOTOXIN (LPS) is a heat stable toxinDo not confuse with

EXOTOXINS , which are proteins andgenerally are heat labile

ENTEROTOXINS , which are exotoxins that

cause an enteritis (diarrhea, vomiting)

GG N ti C ll W llN g ti C ll W ll


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GramGram -- Negative Cell WallNegative Cell Wall

Th NTh N T i f B t i l Li t i iT i f B t i l Li t i i


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The NThe N -- Terminus of Bacterial Lipoprotein isTerminus of Bacterial Lipoprotein isTriacylTriacyl -- or Diacylor Diacyl -- CysteineCysteine

This structure is absent from EukaryotesThis structure is absent from Eukaryotes

FA= Fatty AcidFA= Fatty Acid


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PEPTIDOGLYCANPEPTIDOGLYCAN -- DEFICIENT FORMSDEFICIENT FORMS

MycoplasmaMycoplasma :: a genus with no genesa genus with no genesfor the cell wallfor the cell wall

L Phase BacteriaL Phase Bacteria :: naturally occurringnaturally occurringwallwall--less variants of cell wallless variants of cell wall --containingcontainingspecies; can regain cell wall; mayspecies; can regain cell wall; maycontribute to some treatment failurecontribute to some treatment failure

L for Lister Institute, where discoveredL for Lister Institute, where discovered


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ACID ACID -- FAST BACTERIAFAST BACTERIA

Stained with a dye (e.g., the red dyeStained with a dye (e.g., the red dyecarbolfuchsin) that resists decolorizationcarbolfuchsin) that resists decolorization

with acidwith acid -- alcohol solutionsalcohol solutions

Members of the genusMembers of the genus Mycobacterium Mycobacterium (e.g.,(e.g., M. tuberculosis M. tuberculosis ;; M. leprae M. leprae ) are) arestrongly acidstrongly acid -- fastfast Acid Acid -- fast staining results from largefast staining results from large

amounts of amounts of MYCOLIC ACIDSMYCOLIC ACIDS andand

mycolic acidmycolic acid -- esters in the cell wallesters in the cell wall


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Acid Acid -- Fast Cell WallFast Cell Wall

Though Gram+, the acidThough Gram+, the acid --fast cell wall hasfast cell wall hasan outer membrane as well as porinsan outer membrane as well as porins

like the Glike the G -- cell wallcell wallThe inner leaflet of the outer membraneThe inner leaflet of the outer membrane

contains mycolic acids linked tocontains mycolic acids linked toarabinogalactan, (arabinogalactan, ( Arabinose)n Arabinose)n --(Galactose)n(Galactose)n , which is covalently linked to, which is covalently linked topeptidoglycanpeptidoglycanThe outer leaflet also contains mycolicThe outer leaflet also contains mycolicacid structuresacid structures


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A Model of the Mycobacterial Cell Wall A Model of the Mycobacterial Cell Wall A = Arabinose; G = galactose A = Arabinose; G = galactose


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Mycolic AcidsMycolic Acids

High molecular weight (60High molecular weight (60 --90 carbon atoms),90 carbon atoms),branchedbranched --chain, very hydrophobic, fatty acidschain, very hydrophobic, fatty acidsthat are responsible forthat are responsible for Acid Acid--Fast StainingFast Staining ,,

Virulence Virulence andand HighHigh--StabilityStability of Mycobacteriaof MycobacteriaShorter homologs occur in other generaShorter homologs occur in other genera Corynobacterium Corynobacterium :: corynomycoliccorynomycolic acids (22acids (22 --36 carbons)36 carbons) Nocardia Nocardia :: nocardomycolicnocardomycolic acids (44acids (44 --60 carbons)60 carbons)

A idAcid F t St i d L h N d f AIDS P ti tFast Stained L mph Node from an AIDS Patient:


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Acid Acid--Fast Stained Lymph Node from an AIDS Patient:Fast Stained Lymph Node from an AIDS Patient:Mycobacterium Mycobacterium Avium Avium - - intracellulare intracellulare in Macrophagesin Macrophages

E dE d


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EndosporesEndosporesCertain bacteria can differentiate into a dormant,Certain bacteria can differentiate into a dormant,heatheat --stable formstable form EndosporesEndospores

Endospores are a means of survival andEndospores are a means of survival anddissemination, not reproductiondissemination, not reproduction

The endospore formers of clinical interest areThe endospore formers of clinical interest arefound in two genera of G+ bacillifound in two genera of G+ bacilli

Clostridium Clostridium -- anaerobes that includeanaerobes that includeC.C. botulinum botulinum -- causes botulismcauses botulismC. tetani C. tetani causes tetanuscauses tetanus

Bacillus Bacillus aerobes/facultative anaerobes that includeaerobes/facultative anaerobes that includeB. anthracis B. anthracis causes anthraxcauses anthrax

E d C i dE d C i d


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Endospores ContinuedEndospores ContinuedEndospores are like seedsEndospores are like seeds no metabolic properties,no metabolic properties, very low water contentvery low water content -- thus, very refractilethus, very refractile stable for long periods of timestable for long periods of time -- years, decadesyears, decadesEndospores are resistant toEndospores are resistant to heatheat desiccationdesiccation

pH extremespH extremes chemical agentschemical agents radiationradiation

These resistance traits are associated withThese resistance traits are associated with the low water content of the core (which contains the DNA,the low water content of the core (which contains the DNA,

ribosomes, etc.)ribosomes, etc.)

SS--S bonded keratinS bonded keratin --like proteins in the spore coatlike proteins in the spore coat


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SporulationSporulation


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Spores Are RefractileSpores Are Refractile

BacillusBacillus

ClostridiumClostridium

Importance of the Cell Envelope inImportance of the Cell Envelope in


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p pp pBacterial InfectionBacterial Infection

Antigenic Antigenic

Antiphagocytic Antiphagocytic

Source of adhesins: many bacteriaSource of adhesins: many bacteria

Site of action of cell wall antimicrobial agents: e.g., peniciSite of action of cell wall antimicrobial agents: e.g., penici llinsllins

Many components (e.g., LPS, polysaccharides, teichoic acids)Many components (e.g., LPS, polysaccharides, teichoic acids)activate complementactivate complement

Many components (e.g., LPS,Many components (e.g., LPS, lipoteichoiclipoteichoic acid, lipoproteins,acid, lipoproteins,peptidoglycan,peptidoglycan, flagellarflagellar protein) stimulate additional elementsprotein) stimulate additional elementsof the innate immune responseof the innate immune response such componentssuch components arearePathogenPathogen -- Associated Molecular Patterns (PAMPs) Associated Molecular Patterns (PAMPs)

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Last Years Bacterial Structure