infection and microbial pathogenecity (host microbe

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infection and microbial pathogenecity (host microbe
INFECTION AND MICROBIAL
PATHOGENECITY
(HOST MICROBE RELATION AND
DISEASE PROCESS)
Infection and Immunity involve the
interaction between the host and infecting
organisms
Based on their relationship
Micro Organisms
Saprophytes
- Free living organism
found in soil, water, air
- Depend on dead and
organic matters
- Incapable of multiplying
in the tissue
- B.subtilis infect devitalized
host
Parasites
- Can establish and
multiply in host
Commensals
Pathogenic capable of
producing disease
Symbiosis is an association between 2 species (Living
together)
Spectrum of Associations:
Mutualism (Benefit each other E. Coli synthesize Vit
B12 of Vit K
Commensalism (Neither benefit
parasitize on the skin surface
nor
harm)
Parasitism (One benefits but other is harmed)
E.coli causing UTI.
CONTAMINATION, INFECTION,
INFESTATION
Contamination: Micro-organism are present in
inanimate object, surface of the skin and mucus
membrane (lodgement)
Infection: Invasion and multiplication in or on host
tissue
Infestation: Presence of large parasites or arthropodes
(lice) in or on the surface of the body
CHARACTERISTIC OF INFECTION
Acute disease: Symptoms develop rapidly and runs
quickly
Chronic disease: Symptoms develop slowly and
disappears slowly
Sub acute: Intermediate between Acute and chronic
Latent infection: Symptoms appear/reappear long
after infection
Primary infection: Initial infection with a parasite in
host
Sec. infection: Infection by a new parasite in a host
whose resistance is lowered by pre-existing infection
Re – infection: Subsequent infection by the same
organism in the same host
Local infection: Confined to small part of the body
(Boils, abscess)
Focal infection: Confined infection from where
pathogen travel other region of the body (abscessed
tooth, infected sinuses)
Cross infection: Pt have one disease. A new infection
is set up from another host or ext. source
Nosocomial infection: Cross infection in a hospital
Iatrogenic infection: Physician induced infection
(By investigative of therapatic procedure)
Endogenous infection: Infection from Internal
sources
Exogenous infection: Infection from hosts own body
Inapparent infection: Infection fail to produce full
set of symptoms
Atypical infection: Typical or characteristic clinical
manifestation of the disease not present
Mixed infection: Infection by 2 or more pathogens
Super infection: Sec infection that is usually caused
by agent resistant to the treatment of Pr infection
Septicemia: Presence and multiplication of
pathogens in blood
Bacteremia: Presence but not multiplication of
bacteria
Viremia: Presence of viruses in blood
Toxemia: Presence of toxins in blood
Sapremia: Presence of metabolic products of
saprophytes.
SOURCE OF INFECTIONS
Human Being
Commonest source from Human being
From patient or from carrier
Carrier: Harbors the organism but do not suffer
- Healthy carrier: Never suffered
- Convalescent Carrier: Recovered but harbor
- Temporary Carrier: Harbors < 6 months
- Chronic Carrier: Harbors for several months or rest of
life
- Contact Carrier: Got the organism from Pt
- Paradoxical Carrier: Got the organism from carrier
ANIMALS: May be source of infection without suffering
Zoonosis: Transmission of infections from animals to man
Bacterial: Plague from rats, Brucellosis and Tuberculosis
from cows, anthrax from sheep, leptospirosis from rats etc.
Viral: Rabies from Dog, J-E from Pig etc.
Parasitic: Hydatid disease ( Dog), tape worm infection
(cattle and swine)
Fungal: Ring worms (cats, dogs) histoplasmosis (bird)
INSECTS
Mosquito's, ticks, flies
Vectors: Transmit Pathogens
Biological: Pathogens multiply and undergo developmental
life cycle (Malaria, Filaria, Kala- azar)
Mechanical: Transmits pathogen mechanically
(house fly carry amoebic cyst, giardia cyst etc.)
SOIL AND WATER
Soil  Spores of tetanus and Gas gangrene bacilli,
Histoplasma capsulatum etc.
Water  V. Cholerae, Hepatitis ‘A’, ‘E’ etc.
Contaminated materials: Food poisoning (S. aureus, E.
Coli etc.) pre-existed infection of meat, milk etc.
(S.typhimurium, myc bovis)
METHODS OF TRANSMISSION
Contact Transmission
Transmission by Vehicle
Transmission by Vectors
Contact Transmission
Direct contact:
- Horizontal transmission by shaking hands, kissing, touching
(genitals- herpes, etc.)
- Sexual contact (syphilis, gonorrhoea etc.)
- Faeco – oral (unwashed heads)
Vertical transmission:
- Mother to offspring across placenta, milk.
Indirect contact: fomites, nonliving objects
Droplet infection: (Through coughs, sneezes) particles
inhaled or airborne.
TRANSMISSION BY VEHICLES
Water-Borne:
- Water contaminated with stools - polio, HVA, HVE
- V. Cholera, shigella, campylobacter etc.
Air Borne:
- Mainly transmission from soil, water, plants and animals.
- Dust particles harboring pathogens (Staphylococci,
Streptococci, Bacterial and Fungal spores.
- Hospitalized patients are at a great risk.
Food Borne:
- Unsanitarily cooked, refrigerated food.
Gastroenteritis (botulinum toxin, aflatoxin salmonellosis,
listeriosis, HVA & HVE etc.
TRANSMISSION BY VECTORS
Mechanical vectors: flies (Amoebiasis, giardiasis,
shigellosis etc.
Biological vectors: (Malaria, Filaria, kala-azar, plague,
chagas disease etc.
MICROBIAL PATHOGENICITY
Pathogenecity
refers to the ability of microbial to produce
disease or tissue injury
Virulence
There is a minor difference
Pathogenecity  Capacity to produce disease
Myc tuberculosis  Always pathogenic
Staph epidermidis  Rarely pathogenic
Virulence:
- Intensity of the disease produced vary among different
microbial species
- Virulence varies among members of the same species
- Organisms freshly discharged are more virulent.
MICROBIAL VIRULERCE FACTORS
Adhesion
Invasiveness
Toxigenicity
Enzymes and other bacteria
Inhibition of phagocytosis
Escape from host Immune response
Acquisition of Nutrients from host.
ADHESION
Must adhere to cell surface other wise will be swept
away by the mucus of other BF
Adhesins are protein or glycoprotein found on pili
(fimbrae) or capsule (receptors)
First step in the pathogenesis of many infectious
diseases
Adhesion allows the organism to colonize
INVASSIVENESS
It is as active process
It is central to the infectious process
Some bacteria (Strepto, pneumo) release digestive
enzymes that allow them to invade
Bacteria use a subs called cadherin
TOXIGENECITY
Properties
Chem. nature
Loc. in cell
Heat stability
Extraction
Exotoxins
Protein
Endotoxins
LPS (Lipid) A
Extracellularly secreted
Bound to cell wall.
into the medium
Released upon death
Unstable, denatured
Heat stable, withstand
above 60oC
above 60oC
Can be separated
Obtained only by
cell lysis
Pharmacological
prop
(filtration) specific
Non specific
Tissue affinity
Sp. tissue affinity
Toxicity,
high, active in very
low, active in large
minute dose
dose
Highly antigenic
Weakly antigenic
can be toxoided
can not be toxided
Immunogenicity
Bacterial source
GM+ve bact (mostly)
No tissue affinity
GM-ve Bact.
Some GM-ve bact
(vibrio EPTC)
Fever Production
Little or no fever
High fever
(IL-1,TNF-)
Control
Extra chrom. genes
Chromosomal,
(Plasmids)
genus
Enzymes and other Bacterial products
Enzymes
Bacteria
Coagulase
Staph aureus
Mode of action
Deposition of fibrin on the
surface which prevents
phagocytosis
Hyaluronidase
Str. pyogenes
Spreading factor
Collaginase and
Cl. Perfringens
facilitate spread of gas
Lecithinase
gangrene
Haemolysin and
Staph aureus,
Cytocidin
Str.pyogenes,
Kills RBC and WBC
Cl.perfringenes
Streptokinase
Str. Pyogenes
Dissolve the clot and
spread infection
Inhibition of Phagocytosis
Inhibition of chemotaxis
Inhibition of attachment of phagocytes
Anti phagocytic subs
Inhibition of Lysosome fusion
Resistance to killing in phagolysosomes
Escape from phagolysosome into cytoplasm
ESCAPE FROM HOST IMM.RESPONSE
Antigenic variation
- Trypanosomes, Malaria, Influenza virus, HIV, Borrelia sp.
(Modify surface Ag)
- Sch. Mansoni (Incorporate host Ag)
Super antigens
Reduction in expression of Ags
- Persistent viral infection
(Paramyxo, Areno, Retro virus etc.)
Immunosuppression
Antibody cleavage (Proteases cleave human Ig A)

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