Host microbe interaction

it includes the information's about host and pathogens. mechanism of defense and pathogenesis. and their interactions.

1. H ost Microbe I nteraction Fathima Hameed

2. Outlines Host microbe interaction Types of pathogen Infectious disease defense mechanisms Mechanism of pathogenesis Microbial interactions

3. What is host microbe interaction? The host pathogen interaction is defined as how microbes / viruses sustain themselves within host organisms on a molecular, cellular/ population level. It refer to disease causing microorganisms although they may not cause illness in all hosts. Host: any organism that harbors another organisms or particle(virus/prion).

4. Pathogen 1 st pathogens observed by scientists was Vibrio cholera , described by Filippo Pacini in 1854 . Pathogens- bacteria, fungi, protozoa, helminths and viruses . These organisms are classified based on its mode of transmission. It includes, food borne, air borne, water borne, blood borne, vector borne. Bacteria- Staph. aureus & C. botulinum Virus- HIV & Hepatitis B Fungi- Aspergillus

5. Types of pathogens Primary pathogen: cause disease upon infection, not normally associated with host. Yersinia pestis , Influenza virus Opportunistic pathogens: cause disease under some circumstances, sometimes members of normal flora. pseudomonas, candida albicans

6. Bacteria: These one cell organism are responsible for illness such as strept throat, urinary tract infection and tuberculosis. Viruses: Smaller than bacteria,viruses cause a multitude of diseases ranging from the common cold to AIDS. Fungi: Many skin diseases, such as ringwarm and athlets foot, are caused by fungi. Other types of fungi can infect your lungs or nervous system. Parasites : Malaria is caused by a tiny parasite that is transmitted by a mosquito bite. Other parasites may be transmitted to humans from animal feces.

7. Infectious diseases Several different factors influence a microorganism’s relationship to it’s host and level of severity. These includes; 1.pathogenecity 2.virulence 3.infectivity 4.transmissibility

8. Pathogenecity : The ability to produce disease in a host organism. Virulence: The degree of pathogenicity of a microorganisms. Virulence for a pathogen include a pathogen’s genetic, biochemical or structural features. Infectivity: The level at which a microorganism is able to infect or invade a host. Transmissibilty : the measure of microorganisms ability to spread from one host to the next.

9. The body’s normal flora The body contains two types of narmal flora; 1.resident flora(survive for extended periods) 2.transient flora(temporary) Normal flora help to provide defenses against invading pathogens by covering adherence sites, producing compounds toxic to other organisms, and preventing pathogens from consuming available nutrients. For disease to occur there must be a change in the body’s environment, which, in turn, allows the pathogen to overcome the normal flora. This can occur through a change in the pH of the body or elimination of normal flora due to antibiotics.

10. Host defenses A microorganisms will not be able to invade unless it overcomes an animal’s or individual’s host defenses. Specific host defenses may include: Skin and mucosal secretions Non specific local responses.( eg.,pH ) Non specific inflammatory responses Specific immune responses( eg ., lymphocytes)

11. Pathogen defenses Pathogen contain virulence factors that promote disease formation and provide the opportunity for a microbe to infect and cause disease. The greater the virulence, the more likely disease will occur. Such factors include: Ability of a pathogen to adhere to a host Ability of a pathogen to colonize(overcome) a host Ability of a pathogen to evade host defenses

12. Mechanisms of pathogenesis Pathogenesis is the method by which a disease can develop. This can occur through food borne intoxication where the causative agent produces toxins in the body ( eg ., botulism). Another route is the colonization of an invadig pathogen on the host surface, which allows the pathogen to increase in numbers and produce toxins that are damaging to the host’s cells( eg ., vibrio and corynebacterium ). The relationship between a host and pathogen is dynamic. Production of disease occurs through a process of steps.

13. 1.Transmission Contact transmission vehicle/ fomite transmission Vector borne transmission

14. Contact transmission Direct: person to person,through direct physical contact (skin to skin/body fluids) eg ; STD’s & cold sores. Indirect: pathogens or agents transferred via intermediate item, organisms etc, to susceptible hosts.

15. Vehicle or fomite transmission Airborne: pathogen suspended in droplets or dust; can remain in air for hours to days. eg , cold virus travels in droplets when person sneezes & talks. Vehicle borne: pathogen transmitted from source to susceptible individual via intermediate object( fomite ). eg , contaminated medical equipment. Food or water borne: pathogen transmitted to susceptible individual via or food /water. intoxication: chemical or toxin causes body malfunction.Eg , lead & botulism. infection: ingestion of pathogenic organism that grows in GI tract. Eg , V.cholerae transmitted in water sources, E.coli in hamburger.

16. Vector borne transmission pathogen transmitted to susceptible individual via animal or insect. Mechanical transmission:(external) use a host for transport. eg , fly landing on food at picnic after it picked up some E.coli . Biological transmission:(internal) carried inside vector; use vector part of life cycle. eg , malaria parasite Plasmodium in blood ingested by Anopheles mosquito after bite.

17. Mechanism of microbial pathogenecity

18. 2. Adherence Pathogen gained to the body attachment(adherence) pathogenecity microbe ligands + host receptor

19. 3.Invasion microbes invade the host produce bacteremia (i.e., presence of bacteria in the bloodstream) viremia (presence of a virus in the bloostream ) microbes are exposed to many barriers after penetration can multiply without competition.

20. 4.colonization Multiplication of pathogenic organisms toxins produced & overcome the normal flora pathogens usually colonize in host tissue host begins to show signs of septicemia(blood infection where bacteria are producing reproducing) minimal number of microbes to establish infection require larger no. of pathogens to cause disease(10-100 for shigella and 1,000,000 for salmonella)

21. 5.Evasion of host defenses Intracellular pathogens that live inside a host cell Avoid phagocyte recognition by producing capsules prevents phagocytosis Producing membrane damaging toxins which can kill phagocytes Interfere with complement activation Survive in the phagocytes

22. 6. Toxigenicity Microbes produce toxins, which are poisonous substances that produce toxemia within a host. 3 types of toxins are produced to cause damage; Exotoxins - proteins secreted by pathogens that cause damage to the host eg , botulinum toxin, tetanus toxin, hemolysin (ruptures red blood cells). Endotoxins - toxic substances that are released when a cell is killed ( lipopolysaccharides ). Exoenzymes - enzymes that function outside the host cells or tissues. 1.coagulase- forms a fibrin clot that ‘hides’ the microbe from phagocytosis 2. hyaluronidase - breaks connective tissues down 3. fibrinase - breakdown blood clots to allow pathogens to continue spreading.

23. 7.Exiting the host A pathogen must exit the body. This occurs various routes. Include, sneezing, coughing, diarrhea, coitus, pus, blood & insect bites. 8. Survival outside the host A pathogen must be able to survive in the environment long enough to be transmitted to another host.

24. Microbial interaction An association between two species (“living together’’). Sometimes beneficial and sometimes harmful. One organism can be located on the surface of another organism as an ‘ ectobiont’ or located within another organism as ‘ endobiont ’. these may be positive and negative such as, Positive- mutualism, proto cooperation, commensalism. Negative- parasitism, predation, competition, amensalism .

25. Possitive relationship Mutualism: the relationship in which each organism in interaction gets benefits from association. eg , lichens. Protocooperation : it is a relationship in which organism in association is mutually benefited with each other. eg , interaction between N2 fixing bacteria and cellulolytic bacteria such as cellulomonas . Commensalism: it is a relationship in which one organism in the association is benefited while other organism (host)of the association is neither benefited nor harmed. eg , association of nitrosomona s (host) and nitrobacter ( commensal ) in nitrification.

26. Negative relationship Parasitism: one population (parasites) get benefitted and derive its nutrition from other population (host) in the association which is harmed. Long period of contact may be physical or metabolic. some parasite lives outside of host cell, known as ectoparasite while other parasite lives inside of host cell, known as endoparasites . Eg , viruses. Predation: one organism (predator) engulf or attack other organism(prey). short duration and normally results in death of prey.eg, protozoan- bacteria in soil.

27. Competition: microbial population in which both the population are adversely affected with respect to their survival and growth. It occurs when both population uses same resources such as same space or same nutrition. One will win the competition and the other one is eliminated. Eg , competition between Paramecium cadatum and Paramecium aurelia . Amensalism : one microbial population produces substances that is inhibitory to other population then this inter population relationship is known as amensalism or antagonism. The 1 st population which produces inhibitory substances are unaffected while other population get inhibited. This chemical inhibition is known as antibiosis. Eg , fatty acids produced by skin normal flora.

28. References: www.google.com www.onlinebiologynotes.com en.m.wikipedia.org

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