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Similar to Microbial pathogenicity Dr.Ashna Ajimsha
Microbial pathogenicity Dr.Ashna Ajimsha
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- 3. ■ Saprophytes -Free living - live on dead or decaying matter, incapable of multiplying on living tissue -some (B.subtilis) infect devitalised tissue ■ Parasites - Establish themselves and multiply in the host Pathogens - Capable of producing disease in host Commensals - Harmony with host without causing disease -Normal flora ■ Opportunistic pathogens- Causes disease in immunocompromised peoople
- 4. ■ Infection- Processin which pathogenic organism enters, establishes itself, multiplies & invades the Anatomical barrier of the host causing disease ■ Infectious disease- infection + clinical manifestations ■ Colonization- The pathogenic organism enters, establishes itself, multiplies but does not invade the Anatomical barrier of the host- no disease, no immune response ■ Infestation- parasites of Macroscopic size. E.g. Parasitic worms in the intestine & arthropods
- 5. TYPES OF INFECTIOUSDISEASES ■ Localised/generalised ■ Superficial/deep ■ Bacteremia – circulation of bacteria in blood ■ Septicemia – bacteria circulate and multiply in the blood causing high swinging type of fever ■ Pyemia – pyogenic bacteria produce septicemia with multiple abscesses in internal organs
- 6. Classification of infections ■Primary infection – initial infection ■ Reinfection – subsequent infection with same parasite ■ Secondary infection – new parasite, pre-existing infectious disease ■ Focal infection – localised sites E.g. Appendix , tonsils ■ Cross-infection – new infection from another host or another source ■ Nosocomial infection/hospital acquired/ healthcare associated infection – cross-infection in hospitals ■ Iatrogenic infection – physician induced due to therapeutic/investigative/diagnostic cause
- 7. ■ Inapparent infection/subclinicalinfection - clinical effects not apparent ■ Symptomatic/apparent infection- -Acute-Short period -Chronic- long period ■ Atypical infection – characteristic clinical manifestations not apparent ■ Latent infection –dormant or hidden form, can reactivate later
- 8. Epidemiological patterns ofinfection ■ Endemic disease - constantly present in a particular area. E.g. typhoid in India ■ Epidemic disease - involves many people in an area at the same time. E.g. Influenza in cold countries ■ Pandemic disease - epidemic that spreads through many areas of the world. E.g. Cholera,plague ■ Sporadic disease -irregular intervals in few places, scattered or isolated
- 9. Sources and Reservoirsof infection ■ Source Person/animal/object from which a micro organism is transmitted to the host ■ Reservoir -Natural habitat in which the organism lives & multiplies -Person/animal/arthropod/plant/soil/substance
- 10. Human reservoir ■ Communicablediseases-Diseases that can be spread from 1 person to another ■ Cases/ patients- Persons in a given population identified as having disease ■ Carriers-persons/animals who harbour the infectious agent ---Healthy carrier – harbours the pathogen, but never suffered from the disease. E.g. Polio, Cholera ---Convalescent carrier – recovered from disease and continues to harbour the pathogen ---Incubatory carrier- shed organism during the incubation period of the disease. E.g. Measles, mumps, diphtheria, pertussis
- 11. Depending on duration ---Temporarycarrier – less than six months ---Chronic carrier – several years Depending on source ---Contact carrier – acquires pathogen from carrier ---Paradoxical carrier – acquires pathogen from another carrier
- 12. Animal Reservoir ■ Reservoirhost – maintain the parasite in nature ■ Zoonoses – diseases transmitted from animals to human beings ■ Amplifier host -Vertebrate reservoir in which organism multiplies exponentially E.g. Pigs in Japanese B encephalitis
- 14. SOIL AND WATER •Spores of tetanus • Geophilic dermatophytes • Aquatic vectors – cyclops • Anthrax
- 15. Modes of transmission CONTACT -Contagiousdisease – direct contact -indirect contact – fomites INHALATION Respiratory infections – droplet nuclei (1-10µm)-Travel long, infect any person.E.g. TB, Chickenpox - Droplet/dust transmission->10µm-Travel short distances, settle down on objects. E.g. Influenza, RSV
- 16. INGESTION ■ Waterborne-Cholera ■ Foodborne-Foodpoisoning ■ Fingerborne-Dysentery INOCULATION ■ Deep wounds - tetanus ■ Dog bite – Rabies ■ Unsterile needles – iatrogenic – HIV, Hepatitis C
- 17. INSECTS ■ Mechanical vectors Carrymicro organisms , transmit them to eatables, no multiplication ■ Biological vectors Pathogen multiplies in the body of the vector, undergoing part of their developmental cycle in it.E.g.Culex mosquito in filariasis ■ Extrinsic incubation period Time taken for the vector to become infective after entry of pathogen into the vector
- 18. VERTICAL TRANSMISSION ■ Transplacentaltransmission abortion/miscarriage/still birth/ congenital malformations- TERATOGENIC INFECTIONS E.g. TORCH infections ■ Transmission via birth canal Group B Streptococcus, HBV, HCV, HIV, N.gonorrhoeae, C. trachomatis, Listeria
- 19. MECHANISM OF MICROBIALPATHOGENICITY ■ Pathogenicity – ability of a microbial species to produce disease ■ Virulence – ability of a strain of microorganism to produce disease, relative degree of Pathogenicity ■ Exaltation – enhancement of virulence ■ Attenuation – reduction of virulence
- 21. Factors affecting bacterialpathogenicity ■ Route of transmission of infection -Streptococci – any route -Vibrio- only oral route ■ Infective dose of the organism -Minimum inoculum size capable of initiating infection -Low infective dose-Shigella, Cryptosporidium oocysts -Large infective dose-Vibrio, Salmonella, E.coli -Depends on virulence, age & immunity of organism, gastric acidity
- 22. Adhesion ■ Adhesion –attachment of bacteria to body surfaces ■ Specific reaction between surface receptors on host cells and adhesive structures (ligands) on the surface of bacteria ■ Adhesins – organised structures – fimbrae, pili or colonising factors/ non pilus adhesins/Biofilm formation
- 24. BIOFILMS ■ Well organisedmicrocolonies of bacteria enclosed in self-produced extracellular polymer matrices known glycocalyx ■ Types - Monomicrobial and polymicrobial ■ Free floating bacteria come in contact with medical devices and attach to them with pili
- 25. INVASION o Spreading lesions– Streptococci o Localised lesions – Staphylococci o Lack invasiveness, but cause fatal disease by producing toxins- Clostridium tetani Important virulence factors -VMA/IPA in Shigella (virulence marker Ag/invasion plasmid Ag) -Enzymes-Coagulase, Streptokinase, Hyaluronidase, IgA protease
- 27. Anti phagocytic factors 1)Capsule- polysaccharide/ polypeptide 2) Cell wall proteins- protein M in Streptococcus & Protein A in Staphylococcus 3) Cytotoxins- Hemolysins & leucocidin- lyse and damage RBCs and WBCs
- 28. Intracellular survival Facultative intracellularorganisms Obligate intracellular organisms Bacteria Salmonella typhi,Brucella , Meningococci,Yersinia,Mycobact.TB Mycobact leprae,Rickettsia,Chlamydia,Coxiella burnetii All viruses Fungi Histoplasma capsulatum,Cryptococcus neoformans Pneumocystis jirovecii Parasites Lishmania,Trypanosoma,Plasmodium,Babesia, ptosporidium,Toxoplasma
- 29. Toxins Feature Endotoxins Exotoxins NatureLipopolysaccharides Proteins Source Cell wall of GNB GNB & GPB – diffuse into surrounding medium Released by Cell lysis Secretion Heat stability Stable Labile, destroyed @ 600 C MOA IL-1,IL- Enzyme like action Effect Non specific Specific action on particular Tissue affinity No Yes Fatal dose Large More potent, small doses fatal Antigenicity Poor Highly antigenic Neutralization by Antibodies Ineffective Yes Vaccine NA Available
- 30. BIOLOGICAL ACTIVITY OF ENDOTOXIN S Pyrogenicity Activation of complement Leucocytosis Macrophageinhibition Lethal action Intravascular coagulation Inhibition of glucose and stimulation of B lymphocytes Interferon release Depression of blood pressure Leucopenia Stimulation of B lymphocytes Induction of prostaglandin synthesis
- 33. PLASMIDS ■ Enterotoxin producedby E.coli and S.aureus ■ Multiple drug resistance (R) plasmids BACTERIOPHAGES ■ Toxin producing beta of tox + corynephages