bac path 4.ppt file/bacterial pathogenesis by shyamal.pdf · necrosis factor or tnfα.. at low...

Bacterial PathogenesisBacterial Pathogenesis

Dr Shyamal Kr Paul Associate. ProfessorMicrobiology, MMC

12/30/201312/30/2013 11Dr. Shyamal Kumar Paul, Bacterial Dr. Shyamal Kumar Paul, Bacterial

PathogenesisPathogenesis

PATHOGENICITY & VIRULENCEPATHOGENICITY & VIRULENCE

�� PathogenicityPathogenicity –– the ability to cause disease by the ability to cause disease by overcoming the defenses of the hostovercoming the defenses of the host

�� VirulenceVirulence –– is a quantitative measure of the is a quantitative measure of the pathogenicitypathogenicity

�� Virulence factors Virulence factors –– AnyAny microbial product or strategy that contributes to disease . These . These

includeinclude-- adhesion,adhesion, toxin production,toxin production,

anyany microbial product or strategy

that contributes to disease resistance toresistance to

antibioticsantibiotics, , ability to invade host tissues,ability to invade host tissues,

enhanced intracellular survival and growthenhanced intracellular survival and growth1212//3030//20132013 22

Dr. Shyamal Kumar Paul, Bacterial Dr. Shyamal Kumar Paul, Bacterial PathogenesisPathogenesis

How to distinguish infection How to distinguish infection from colonization ~from colonization ~

colonization disease = infection

vs.vs.

colonization by normal flora disease ≠ infection

colonization of an infectious agent no disease =asymptomatic carrier



Asymptomatic colonization by Asymptomatic colonization by pathogenic bacteriapathogenic bacteria

Streptococcus pyogenes …. 20-30% - nasopharynx(strep throat / rheumatic fever / “flesh-eating dis ease”/ scarlet fever)

Streptococcus pneumoniae .. .. 20-50% - nasopharynx(pneumonia / septicemia / meningitis / ear infectio ns)

Group B streptococci . … >24% of females - vaginal(neonatal septicemia / pneumonia / meningitis)

(pneumonia / septicemia / meningitis / ear infectio ns)

Staphylococcus aureus …. >40% - anterior nares(hospital infections, septicemia, pneumonia)

12/30/2013 4Dr. Shyamal Kumar Paul, Bacterial Pathogenesis

PORTALS OF ENTRYPORTALS OF ENTRY�� ToTo causecause disease,disease, mostmost pathogenicpathogenic bacteriabacteria mustmust

gaingain accessaccess toto thethe hosthost

�� OrganismsOrganisms mustmust alsoalso bebe ableable toto evade,evade,compromisecompromise oror taketake advantageadvantage ofof aa compromisedcompromisedinnateinnate immuneimmune systemsystem includingincluding thethe primaryprimarybarriersbarriers ofof skinskin andand mucusmucus membranesmembranesbarriersbarriers ofof skinskin andand mucusmucus membranesmembranes

�� AnyAny compromisecompromise inin thesethese barriersbarriers (cuts,(cuts, ulcers,ulcers,surgicalsurgical procedures,procedures, catheters,catheters, etc)etc) maymay allowallowbacteriabacteria entranceentrance intointo thethe hosthost

�� NormalNormal skinskin flora,flora, includingincluding StaphylococcusStaphylococcus aureusaureusandand StaphylococcusStaphylococcus epidermidisepidermidis,, cancan enterenterthroughthrough thesethese compromisedcompromised barriersbarriers andand establishestablishanan infectioninfection12/30/201312/30/2013 55


PORTALS OF ENTRYPORTALS OF ENTRY

�� May enter through the mucus membranes of May enter through the mucus membranes of the respiratory tract, gastrointestinal tract and the respiratory tract, gastrointestinal tract and urogenital tracturogenital tract

�� the innate immune system also is comprised of the innate immune system also is comprised of mucus and cilia in the upper respiratory tract, mucus and cilia in the upper respiratory tract, mucus and cilia in the upper respiratory tract, mucus and cilia in the upper respiratory tract, acid pH and bile in the GI tract, lysozyme in acid pH and bile in the GI tract, lysozyme in tears and mucustears and mucus

�� Bacteria that can withstand the stomach acid Bacteria that can withstand the stomach acid and cause disease include and cause disease include Vibrio choleraeVibrio cholerae, , Salmonella typhiSalmonella typhi and and Campylobcter jejuniCampylobcter jejuni



PORTALS OF ENTRYPORTALS OF ENTRY

�� Many pathogens have Many pathogens have preferred portals of preferred portals of entryentry that are necessary for disease that are necessary for disease productionproduction

�� If they gain entrance via another portal, If they gain entrance via another portal, disease may not occurdisease may not occurdisease may not occurdisease may not occur

–– Bacillus anthracis Bacillus anthracis can initiate disease from more can initiate disease from more than one portal of entry (skin inoculation, GI, than one portal of entry (skin inoculation, GI, respiratory)respiratory)



NUMBERS OF INVADING BACTERIANUMBERS OF INVADING BACTERIA

�� Generally speaking, entry of only a few or very Generally speaking, entry of only a few or very small number of bacteria into the body will not small number of bacteria into the body will not result in infection. They will be overcome by result in infection. They will be overcome by host defenseshost defenses

�� One virulence factor is the number of bacteria One virulence factor is the number of bacteria �� One virulence factor is the number of bacteria One virulence factor is the number of bacteria required to institute an infection. This is called required to institute an infection. This is called the IDthe ID5050 or infectious dose for 50% of a sample or infectious dose for 50% of a sample populationpopulation

–– Less than 100 Less than 100 ShigellaShigella organisms are required to organisms are required to induce dysentery whereas 10induce dysentery whereas 1066 –– 101099 SalmonellaSalmonellaorganisms are required for an infectionorganisms are required for an infection



Virulence of pathogenic bacterial12/30/201312/30/2013 99


ADHERENCE AND INVASIONADHERENCE AND INVASION�� Most pathogenic bacteria have some Most pathogenic bacteria have some

mechanism of adherence for target cells mechanism of adherence for target cells

�� Adherence is accomplished by Adherence is accomplished by adhesinsadhesins on the on the organism binding with some degree of organism binding with some degree of specificity to receptors on the target cellsspecificity to receptors on the target cells

�� Most adhesins are either glycoproteins or Most adhesins are either glycoproteins or lipoproteins and the receptors on target cells lipoproteins and the receptors on target cells are usually some form of sugar such as are usually some form of sugar such as mannosemannose

�� Gram negative bacteria have adhesins located Gram negative bacteria have adhesins located at the ends of pili.at the ends of pili.

1212//3030//20132013 1010Dr. Shyamal Kumar Paul, Bacterial Dr. Shyamal Kumar Paul, Bacterial


ADHERENCE AND INVASIONADHERENCE AND INVASION�� The term The term pilipili ((piluspilus) is also used to describe ) is also used to describe

these projections for the tubethese projections for the tube--like projections like projections that transfer genetic material from one that transfer genetic material from one bacterium to another in conjugationbacterium to another in conjugation

�� Gram positive organisms use other structures Gram positive organisms use other structures for adhesins (lipoproteins, etc). for adhesins (lipoproteins, etc). Streptococcus Streptococcus for adhesins (lipoproteins, etc). for adhesins (lipoproteins, etc). Streptococcus Streptococcus pyogenespyogenes uses lipoteichoic acid to bind to uses lipoteichoic acid to bind to epithelial cellsepithelial cells

�� Once attached to target cells, many bacteria Once attached to target cells, many bacteria can then invade the cellcan then invade the cell



ADHERENCE AND INVASIONADHERENCE AND INVASION�� Not all bacteria are invasive. Invasive Not all bacteria are invasive. Invasive

organisms attach and enter host cells by a organisms attach and enter host cells by a number of mechanisms:number of mechanisms:

–– Production of surface proteins called Production of surface proteins called invasinsinvasins that that rearrange host cell actin filamentsrearrange host cell actin filaments

–– Production of enzymes: Production of enzymes: –– Production of enzymes: Production of enzymes:

�� collagenasecollagenase --breaks down collagen in connective tissuebreaks down collagen in connective tissue

�� hyaluronidasehyaluronidase -- breaks down hyaluronic acid that holds breaks down hyaluronic acid that holds cells togethercells together

�� CoagulaseCoagulase -- converts fibrinogen to fibrin producing a converts fibrinogen to fibrin producing a clot (may be protective against phagocytes)clot (may be protective against phagocytes)

�� KinasesKinases -- can break down clots decreasing the isolation can break down clots decreasing the isolation of bacteria in clots (spreading effect)of bacteria in clots (spreading effect)



TISSUE DAMAGETISSUE DAMAGE�� Most of the enzymes cause tissue destruction. Most of the enzymes cause tissue destruction.

Others include:Others include:

–– DNAaseDNAase

–– LipaseLipase

–– PhospholipasePhospholipase

–– ProteasesProteases–– ProteasesProteases

�� Toxin production Toxin production –– toxins are bacterial toxins are bacterial products produced by certain microorganisms. products produced by certain microorganisms. They are byproducts of bacterial growth that They are byproducts of bacterial growth that are poisonous to host cells. Basically, there are are poisonous to host cells. Basically, there are

exotoxins and endotoxinsexotoxins and endotoxins12/30/201312/30/2013 1313


TISSUE DAMAGETISSUE DAMAGE�� Exotoxins are generally released while the Exotoxins are generally released while the

bacterium is actively growing but may also be bacterium is actively growing but may also be released when the organism diesreleased when the organism dies

�� May be produced by both gram positive and May be produced by both gram positive and gram negative bacteriagram negative bacteriagram negative bacteriagram negative bacteria

�� Are protein in nature and many are enzymes Are protein in nature and many are enzymes that catalyze certain biochemical reactions. that catalyze certain biochemical reactions.

�� The genes for most exotoxins are carried on The genes for most exotoxins are carried on bacterial plasmids or bacteriophagesbacterial plasmids or bacteriophages



TISSUE DAMAGETISSUE DAMAGE�� Exotoxins are typically soluble in body fluids Exotoxins are typically soluble in body fluids

and can easily diffuse into the blood where and can easily diffuse into the blood where they are rapidly transported systemicallythey are rapidly transported systemically

�� Many exotoxins are composed of A and B Many exotoxins are composed of A and B subunit and are called Asubunit and are called A--B toxinsB toxins

–– The A subunit is the active or enzymatic component The A subunit is the active or enzymatic component –– The A subunit is the active or enzymatic component The A subunit is the active or enzymatic component

–– The B subunit is the binding component The B subunit is the binding component

–– When the AWhen the A--B toxin is released from the bacterium, B toxin is released from the bacterium, the B subunit binds to a surface receptor on the the B subunit binds to a surface receptor on the host cellhost cell

–– Following binding, the toxin is transported across Following binding, the toxin is transported across the plasma membrane where the two subunits the plasma membrane where the two subunits separate. The A subunit then exerts its enzy activityseparate. The A subunit then exerts its enzy activity



TISSUE DAMAGETISSUE DAMAGE�� Representative exotoxins:Representative exotoxins:

–– Diphtheria toxin Diphtheria toxin –– inhibits protein synthesis inhibits protein synthesis

–– Erythrogenic toxins Erythrogenic toxins ––Streptococcus pyogenes Streptococcus pyogenes produces that damage plasma membranes of produces that damage plasma membranes of capillaries in the skin producing a red rashcapillaries in the skin producing a red rash

–– Botulinum toxin Botulinum toxin –– neurotoxin that inhibits neurotoxin that inhibits –– Botulinum toxin Botulinum toxin –– neurotoxin that inhibits neurotoxin that inhibits acetylcholine LDacetylcholine LD5050 for the botulism toxin is for the botulism toxin is 10 10 nanograms/kg or nanograms/kg or 00..00001 00001 mg/kg mg/kg

–– Tetanus toxin Tetanus toxin –– neurotoxin that inhibits the neurotoxin that inhibits the relaxation pathway resulting in uncontrollable relaxation pathway resulting in uncontrollable muscle contractionsmuscle contractions

–– Vibrio enterotoxin Vibrio enterotoxin –– toxin increases intracellular toxin increases intracellular cAMP resulting in prolonged hypersecretion of water cAMP resulting in prolonged hypersecretion of water and electrolytesand electrolytes



TISSUE DAMAGETISSUE DAMAGE�� Superantigens are a type of exotoxin that can Superantigens are a type of exotoxin that can

bind to the outside of the T cell receptor and bind to the outside of the T cell receptor and the major histocompatability complex receptor the major histocompatability complex receptor on antigenon antigen--presenting cells.presenting cells.

�� This binding is not specific for a particular T cell This binding is not specific for a particular T cell and can result in production of large quantities and can result in production of large quantities and can result in production of large quantities and can result in production of large quantities of cytokines including interleukin 1 and tumor of cytokines including interleukin 1 and tumor necrosis factor leading to systemic necrosis factor leading to systemic inflammatory responsesinflammatory responses

�� Examples are staphylococcal toxic shock Examples are staphylococcal toxic shock syndrome toxin, enterotoxins and erythrogenic syndrome toxin, enterotoxins and erythrogenic toxinstoxins1212//3030//20132013 2222


TISSUE DAMAGETISSUE DAMAGE�� EndotoxinEndotoxin is an integral part of the outer is an integral part of the outer

leaflet of the leaflet of the gram negative gram negative cell wall. Also cell wall. Also called lipopolysaccharide or LPScalled lipopolysaccharide or LPS

�� The actual toxic component of endotoxin is The actual toxic component of endotoxin is lipid Alipid A

�� Endotoxin is released as gram negative bacteria Endotoxin is released as gram negative bacteria �� Endotoxin is released as gram negative bacteria Endotoxin is released as gram negative bacteria lyselyse

�� Are lipopolysaccharides and relatively resistant Are lipopolysaccharides and relatively resistant to heat. Exotoxins are readily denatured by to heat. Exotoxins are readily denatured by heatheat



TISSUE DAMAGETISSUE DAMAGE�� Endotoxin is one of many molecular patterns on Endotoxin is one of many molecular patterns on

bacteria termed bacteria termed pathogenpathogen--associated associated molecular patternsmolecular patterns or PAMPsor PAMPs

�� Upon release, endotoxin binds receptors (tollUpon release, endotoxin binds receptors (toll--like receptors or TLRs) on various cells like receptors or TLRs) on various cells including macrophages and B lymphocytesincluding macrophages and B lymphocytesincluding macrophages and B lymphocytesincluding macrophages and B lymphocytes

�� This binding leads to the stimulation of various This binding leads to the stimulation of various cytokines including the procytokines including the pro--inflammatory inflammatory cytokines Interleukin or ILcytokines Interleukin or IL--1, IL1, IL--6 and Tumor 6 and Tumor Necrosis factor or TNFNecrosis factor or TNFαα. .

�� At low concentrations inflammatory and At low concentrations inflammatory and immune responses occurimmune responses occur1212//3030//20132013 2626


TISSUE DAMAGETISSUE DAMAGE�� At higher concentrations, endotoxin can induce At higher concentrations, endotoxin can induce

what is known as gram negative shock, septic what is known as gram negative shock, septic shock or endotoxic shockshock or endotoxic shock

�� Due to activation of the complement pathway with Due to activation of the complement pathway with the production of C3a and C5a (anaphylotoxins)the production of C3a and C5a (anaphylotoxins)

�� These anaphylotoxins, along with inflammatory These anaphylotoxins, along with inflammatory cytokines can lead to fluid loss from the cytokines can lead to fluid loss from the These anaphylotoxins, along with inflammatory These anaphylotoxins, along with inflammatory cytokines can lead to fluid loss from the cytokines can lead to fluid loss from the vasculature and result in hypotension and shockvasculature and result in hypotension and shock

�� Fever also results as ILFever also results as IL--1 and TNF1 and TNFαα stimulate the stimulate the hypothalamus to adjust body temperaturehypothalamus to adjust body temperature

�� Disseminated intravascular coagulation (DIC) can Disseminated intravascular coagulation (DIC) can also result from activation of the clotting also result from activation of the clotting mechanismmechanism12/30/201312/30/2013 2727


Endotoxin

(especially lipid A))

Activates

macrophages

Activates

complement

Activates

Hageman fatcor

IL-1

Fever

TNF

Fever and hypotension

Nitric oxide

hypotension

C3a

Hypotension Edema

C5a

Neutrophil chemotaxis

Coagulation cascade

DIC



The different between indotoxin and The different between indotoxin and exotoxinexotoxin

kindskinds exotoxinexotoxin indotoxinindotoxin

sourcesource GG ++99ve)ve) oror aa fewfew GG –– (ve)(ve) GG –– (ve)(ve)

componcomponentent

proteinprotein LPSLPS

entent

stebilitystebility ShortShort ofof goodgood、、160160℃℃ 22--4h 4h

destroyeddestroyed

virulencvirulencee

strongstrong weakweak

antigenicantigenicityity

strongstrong weakweak



MECHANISMS OF EVADING HOST MECHANISMS OF EVADING HOST DEFENSESDEFENSES

�� Capsules Capsules –– the chemical nature of the capsule the chemical nature of the capsule appears to prevent phagocytic cells from appears to prevent phagocytic cells from adhering to the organismadhering to the organism

–– Capsules are often polysaccharide in nature but Capsules are often polysaccharide in nature but may be amino acid (may be amino acid (Bacillus anthracisBacillus anthracis))may be amino acid (may be amino acid (Bacillus anthracisBacillus anthracis))

�� Cell wall componentsCell wall components

–– M protein in M protein in Streptococcus pyogenesStreptococcus pyogenes –– mediates mediates attachment and inhibits phagocytosisattachment and inhibits phagocytosis

�� Intracellular growthIntracellular growth

–– Neisseria gonorrhoeaeNeisseria gonorrhoeae

–– Mycobacterium tuberculosis Mycobacterium tuberculosis –– mycolic acidmycolic acid12/30/201312/30/2013 3131Dr. Shyamal Kumar Paul, Bacterial Dr. Shyamal Kumar Paul, Bacterial


MECHANISMS OF EVADING HOST MECHANISMS OF EVADING HOST DEFENSESDEFENSES

�� Antigenic variation occurs when the organism Antigenic variation occurs when the organism has the genetic ability to produce different has the genetic ability to produce different structural compositions for a particular bacterial structural compositions for a particular bacterial structure which is recognized as an antigen by structure which is recognized as an antigen by the immune systemthe immune systemthe immune systemthe immune system

�� An example is An example is Neisseria gonorrhoeae Neisseria gonorrhoeae with with multiple copies of the gene that codes for Opa multiple copies of the gene that codes for Opa protein (a protein that mediates binding of the protein (a protein that mediates binding of the organism with cellsorganism with cells



Generalized infection Generalized infection

�� BacteremiaBacteremia

oo Definition: a transitory disease in which bacteria Definition: a transitory disease in which bacteria present in the blood are usually cleared from the present in the blood are usually cleared from the vascular system with no harmful effects. vascular system with no harmful effects. vascular system with no harmful effects. vascular system with no harmful effects.

�� SepticemiaSepticemia

oo DefinitionDefinition:: aa diseasedisease inin whichwhich thethe bloodblood servesserves asas aasitesite ofof bacterialbacterial multiplicationmultiplication asas wellwell asas aa meansmeans ofoftransfertransfer ofof thethe infectiousinfectious agentagent fromfrom oneone sitesite totoanotheranother..



��ToxemiaToxemiaoo DefinitionDefinition:: thethe presencepresence ofof microbialmicrobial

toxinstoxins inin thethe bloodblood

��PyemiaPyemiaoo DefinitionDefinition:: thethe presencepresence ofof pyogenicpyogenic

bacteriabacteria inin thethe bloodblood asas theythey areare beingbeingspreadspread fromfrom oneone sitesite toto anotheranother inin thethebodybody



毒

素

血液

毒

素

toxin

toxin

special toxic symptom

局

部

病

灶

局

部

病

灶

pathogenic bacterium can

Defense function↓↓

毒素毒素毒素毒素毒素毒素toxin

Organism is seriously dadamaged,

Local lesion

symptom

e.g.tetanus

Toxemia

bacterium can grow in blood

BacteremiaBacteremia

seriously dadamaged, toxic symptom all over the body。

Septicemia


blood

局

部

病

灶

局

部

病

灶

毒素toxin

毒

素

毒

素

toxin

When Pyosis bacteria

New pyosis focus of infection

Pyosepticemia

When Pyosis bacteria cause Septicemia，multiple pyosis focus of infection will happen.e.g. staphylococci aureus


Host resistance mechanisms Host resistance mechanisms

�� Nonspecific host defenses Nonspecific host defenses

�� Anatomical defenses Anatomical defenses

oo Skin and mucosal membrane Skin and mucosal membrane

Mechanical barriersMechanical barriersMechanical barriersMechanical barriers

Secretions Secretions

Normal floraNormal flora



oo BloodBlood--brain barrier brain barrier

oo Placenta barrierPlacenta barrier

�� Cellular defenses:Cellular defenses: the reticuloendothelial the reticuloendothelial �� Cellular defenses:Cellular defenses: the reticuloendothelial the reticuloendothelial

system system

��Molecular defenses:Molecular defenses: complements, lysozymes, complements, lysozymes,

etc etc



Innate immunityInnate immunity

Skin & mucous membranesSkin & mucous membranes

Intact skinIntact skin

Fatty acids sebaceous glandsFatty acids sebaceous glandsFatty acids sebaceous glandsFatty acids sebaceous glands

Mucous membrane of respiratory tract Mucous membrane of respiratory tract

1.1. ciliary action ciliary action 2.2. traps many microorganismstraps many microorganismsLysozymeLysozyme

Normal floraNormal flora



Innate immunityInnate immunity

Inflammatory response & phagocytosisInflammatory response & phagocytosis

(early host responses to bacteria infection)(early host responses to bacteria infection)

Bacteria infectionBacteria infection→→vasoactive factors vasoactive factors →→Bacteria infectionBacteria infection→→vasoactive factors vasoactive factors →→

the increased permeability the increased permeability

Chemokines Chemokines →→ Neutrophils and Neutrophils and

macrophagesmacrophages



Host resistance mechanismsHost resistance mechanisms

�� Specific host of defenses Specific host of defenses

�� Humoral immunity: antibodyHumoral immunity: antibody--mediated immunity mediated immunity

�� Cellular immunity: cellCellular immunity: cell--mediated immunity mediated immunity

Inflammatory response & phagocytosis



Host defences



Acquired immunityAcquired immunity

Humoral immunityHumoral immunity

antibody to aggressinantibody to aggressin

antibody to toxinantibody to toxin

CellCell--mediated immunitymediated immunityCellCell--mediated immunitymediated immunity

T cells T cells

lymphokines (IFNlymphokines (IFN-- γγ))

macrophages macrophages



bac path 4.ppt file/bacterial pathogenesis by shyamal.pdf · necrosis factor or tnfα.. at low...

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