Mod 11 Host-pathogen Relationships

7/28/2019 Mod 11 Host-pathogen Relationships

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HOST-PATHOGEN

RELATIONSHIPS


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SYMBIOSIS

Relationship in whichany organism spendsa portion/all of its

life physicallyassociated with anorganism of a

different species.

Ectosymbiotic

Endosymbiotic


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SYMBIOSIS

Commensalism

Mutualism

Parasitism


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COMMENSALISM

Eg: Clown fish (commensal) &anemone (host)

Commensal relies on host forfood & shelter

Doesnt depend on hostsmetabolism

Commensal able to survivewithout host


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MUTUALISM

Eg: Boxer crab & anemone

Metabolically dependent oneach other


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PARASITISM

Eg: isopod (ectoparasite) &fish (host)

Parasite lives @ the expenseof its host may be harmful(pathogen)


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PARASITISM

Parasite lives @ theexpense of its host

harmful (pathogen)


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MICROFLORA

Different species associated with particulartissues

Symbiotic relationships:MutualistsCommensals

May become pathogenic opportunistic


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MICROFLORA

1013 cells & 1014 bacteria

105-6

105-7

10910


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MICROFLORA

Germfree or gnotobiotic


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MICROFLORA

Germfree or gnotobiotic


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MICROFLORA

Colon


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MICROFLORA

Acquire microflora immediatelyafter birth

Factors influencing composition:

babies diet:

breast milk Gram +ve

bottles Gram ve

type of tissues environment

must adhere to cells

produce bacteriocins


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DISTRIBUTION OF

MICROFLORA

Resist mechanical removal

supply of nutrients, water, pH &suitable temp

initially aerobes & facultative

anaerobes

then anaerobes

can cause dental caries &

periodontal disease

anaerobes abcesses


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DISTRIBUTION OF

MICROFLORA

Oropharynx

Staphylococci, -haemolytic streps, Neisseriae,

diphtheroids

few anaerobes


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DISTRIBUTION OF

MICROFLORA

transient & resident

different groups in different skin areas

associate with oil & sweat glands

epidermis not easily colonised by transients:periodic drying

slightly acidic

secretions

sweatinhibitory substances of residents

Staphylococci in most areas

Gram-negs only in moist areas (perineum, axilla & toe webs)


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DISTRIBUTION OF

MICROFLORA

Conjunctiva

controlled by lysozyme (tears)Staphylococci, Streptococci,

Neisseriae, Diphtheroids

Moraxellae


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DISTRIBUTION OF

MICROFLORA


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DISTRIBUTION OF

MICROFLORA

Nose

Staphylococci, DiphtheroidsNasopharynx

S pneumoniae, N meningitidis,

H influenzae


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DISTRIBUTION OF

MICROFLORA

Nails:

similar to skin

also fungi eg Aspergillus, Penicillium, Cladosporium


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DISTRIBUTION OF

MICROFLORA

Lower Respiratory Tract:

Sterile mucous productionphagocytic alveolar

macrophageslysozyme in mucous


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DISTRIBUTION OF

MICROFLORA

Upper Respiratory Tract:

S. aureus,S. epidermidisS. viridansE. faecalis

H. influenzaeMoraxella


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DISTRIBUTION OF

MICROFLORA

Urogenital Tract:Upper tract - sterile


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DISTRIBUTION OF

MICROFLORA

Urethra:

few microbes

S. epidermidis,

diphtheroids & Enterococci

Urine is sterile


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DISTRIBUTION OF

MICROFLORA

Vagina:

varies

determined by age, pH &

hormones


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DISTRIBUTION OF

MICROFLORA

Vagina: < 1 month

pH 5

lactobacilli


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DISTRIBUTION OF

MICROFLORA

Vagina: girls

pH 7

S. epidermidis,

Streptococci, E. coli


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INFECTION BY MICROFLORA

Urogenital Tract:

Upper tract - sterile


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THE PROCESS OF INFECTION

Infectious disease any change from the bodys

healthy state in which a part of / the entire body

is incapable of carrying out its normal functions

presence of a pathogen / its products.


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THE PROCESS OF INFECTION

Pathogenicity the ability of the microbe to cause disease.

Pathogenesis mechanism of infection

or

mechanism by means of which disease develops.


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FACTORS CONTRIBUTING TO

INFECTION

No of pathogenic organisms present.

Virulence of the organism

State of ones immune system (Resistance level)


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FACTORS CONTRIBUTING TO

INFECTION

Endogenous disease caused by own microflora

Exogenous disease caused by bacteria from the

environment / another person / animal


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VIRULENCE

Virulence degree / intensity of pathogenesis

Determined by:

invasivenessInfectivity

pathogenic potential


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VIRULENCE


Determined by:

invasiveness ability of the microbes tospread to adjacent / other tissues.

Infectivity



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VIRULENCE


Determined by:

Invasiveness

Infectivity the ability of the microbe to

establish a focal point of infection.



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VIRULENCE


Determined by:

InvasivenessInfectivity the ability of the microbe to

establish a focal point of infection.

Pathogenic potential degree to which the

microbe causes morbid symptoms


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VIRULENCE

Pathogenic potential is determined by:

toxigenicity ability of the microbe to

produce toxins which will damage thehost & cause disease.


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VIRULENCE

Disease may also becaused by:

hypersensitivity

reactions to bacteria.

Autoimmunity due to

bacteria having similar

antigens to host tissue.


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VIRULENCE FACTORS

Factors produces by microbes which enable them

to cause disease.

Not all strains of bacteria are virulent.

Those that are virulent possess virulence factors.


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VIRULENCE FACTORS

4 groups:

adherence & colonisation factors

invasion factors

capsules / other surface componentsToxins & siderophores


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TOXINS

Metabolic products of bacteria

Toxemia / septicemia presence of toxins in the blood

Types:

EndotoxinsExotoxins


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TOXINS

Endotoxins heat-stable toxins found in cell wall of bacteria i.e LPS in

gram-negative bacteria.


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TOXINS

Endotoxins released when bacterium lyses / multiplies

cause a series of reactions in the body


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TOXINS

Exotoxins:soluble, heat labile proteins secreted by bacteria

produced by gram +ve & -ve bacteria

Effects:

inhibit protein synthesis

inhibit nerve synapse function

disrupt membrane transportdamage plasma membrane

act as superantigens


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TOXINS

Effects:inhibit protein synthesis


disrupt membrane transport

damage plasma membraneact as superantigens

botulinum toxin


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TOXINS

Effects:inhibit protein synthesis


disrupt membrane transport

damage plasma membraneact as superantigens

Tetanus toxin


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SIDEROPHORES

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Mod 11 Host-pathogen Relationships