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Microbes and Human Diseases

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Presentation on theme: "Microbes and Human Diseases"— Presentation transcript:

1 Microbes and Human Diseases
Microbial Mechanisms of Pathogenicity How microorganisms enter a host How microorganisms penetrate host defenses How microorganisms damage host cells

2 Microbial Mechanisms of Pathogenicity
Pathogenicity = is the ability of a pathogen to produce a disease by overcoming the defenses of the host Virulence = is the degree of Pathogenicity Incubation period = is the period between the entry of the microbe till the appearance of disease symptoms

3 Microbial Mechanisms of Pathogenicity
To cause disease , most pathogens must Enter the host Adhere to host tissues Penetrate or evade host defenses Damage the host tissues Exit from the host

4 Portals of entry Mucous membranes , conjunctiva , skin
Respiratory tract (inhalation) (Common cold ,pneumonia ,tuberculosis ,influenza ,measles) Gastrointestinal tract(food ,water, fingers) (poliomyelitis ,hepatitis A ,typhoid fever ,amoebic dysentery ,cholera ,giardiasis) Genitourinary tract (sexually transmitted diseases) (HIV ,genital warts ,chlamydia ,herpes ,syphilis ,gonorrhea)

5 Portals of entry Skin Intact skin = important defense
Hair follicles ,sweat gland ducts ,larvae of the hookworm ,fungi Inoculation through the skin & mucous membranes (injury) Bites = rabies Injection =malaria Wound Parenteral route

6 Adhere to host tissues Adhesins or ligands == Surface projections on a pathogen = glycoproteins or lipoproteins = associated with fimbriae Adhere to complementary receptors on host cells = mannose

7 How pathogen penetrate host defenses
Capsules =some bacteria make glycocalyx material that forms capsules around their cell wall This increase the virulence of species ==prevent bacteria from being phagocytized Streptococcus pneumoniae

8 How pathogen penetrate host defenses
Cell wall components = some bacteria contain chemical substances that contribute to virulence Streptococcus pyogenes =produce a heat-resistant & acid-resistant protein = M-protein =present in cell surface & fimbriae =increase the virulence M-protein mediates attachment of the bacteria to epithelial cells of the host & helps them resist phagocytosis by WBC

9 How pathogen penetrate host defenses
Mycobacterium tuberculosis can even multiply inside phagocytes waxy lipid = mycolic acid Mycolic acid increase virulence by resisting digestion by phagocytes

10 How pathogen penetrate host defenses
Enzymes = the virulence of some bacteria is thought to be aided by the production of extracellular enzymes =exoenzymes ==can digest materials between cells or digest blood clot

11 How pathogen penetrate host defenses
Coagulases = enzymes that coagulate (clot) the fibrinogen in blood Staphylococcus (some members) protect the bacteria from phagocytosis

12 How pathogen penetrate host defenses
Other enzymes Kinases Fibrinolysin Streptokinase collagenase IgA proteases = destroy IgA = antibody in mucosal surfaces Neisseria gonorrhaeae Neisseria meningitidis

13 How pathogen penetrate host defenses
Antigenic variation =some pathogen alter their surface antigens Adaptive immunity = acquired = specific defensive response of the body to an infection or to antigen In the presence of antigen the body produces protein called antibody = bind to antigen and inactivate or destroy them

14 How pathogen penetrate host defenses
by the time the body mounts an immune response against a pathogen When the pathogen has altered its antigens and is unaffected by the antibodies Neisseria gonorrhoeae Influenza virus

15 Penetration into the host cell cytoskeleton
Cytoskeleton =protein filaments (microfilaments ,intermediate filaments & microtubules) that present in the cytoplasm of eukaryotic cells that provide support & movement

16 Penetration into the host cell cytoskeleton
** when microbes attach host cell by adhesins **this triggers signals in the host cell that activate factors that can result in the entrance of bacteria **this mechanism is provided by the host cell cytoskeleton

17 How bacterial pathogen damage host cell
Pathogen can damage host cell in four basic ways: ## by using the host`s nutrients ## by causing direct damage ## by producing toxins ## by inducing hypersensitivity

18 How bacterial pathogen damage host cell
Using the host cell nutrients siderophores =protein secreted by some bacteria in order to obtain free iron !!-iron is required for the growth of pathogenic bacteria !!-in human body the concentration of free iron is low = most of it is bound to iron transport protein (transferrin , ferritin & hemoglobin) **** = bacteria secrete siderophores in order to obtain free iron

19 How bacterial pathogen damage host cell
Direct damage=pathogens metabolized & multiply inside the host cell by using nutrients & produce waste products=destroyed = rupture the microbe released & spread to other tissues in greater number

20 How bacterial pathogen damage host cell
The production of toxins = poisonous substance produced by bacteria Toxemia = the presence of toxins in the blood Toxigenicity = the ability to produce toxins

21 How bacterial pathogen damage host cell
Toxins=are primary factor contributing to the pathogenic bacteria =when transported by blood or lymph can cause serious & some times fatal effects fever cardiovascular disturbances diarrhea & shock

22 How bacterial pathogen damage host cell
Toxins = can inhibit protein synthesis destroy blood cells = = vessels & disrupt the nervous system by causing spasms Exotoxins & Endotoxins

23 How bacterial pathogen damage host cell
Exotoxins = are proteins = Gram positive & Gram negative bacteria ====produced inside bacteria as a part of their growth & metabolism & are secreted into the surrounding medium or released following lysis

24 How bacterial pathogen damage host cell
Exotoxins = are soluble in body fluids = they can easily diffuse into the blood = are rapidly transported through the body Botulism

25 How bacterial pathogen damage host cell
Antitoxins = antibody to toxins = provide immunity to exotoxins Toxoid = altered exotoxin = exotoxins are inactivated by heat or by formaldehyde , iodine or other chemicals they no longer cause disease but can still stimulate the body to produce antibody (antitoxins) tetanus vaccine

26 How bacterial pathogen damage host cell
Types of exotoxins +++A-B toxins +++membrane-disrupting toxins +++superantigens A-B toxins=polypeptides = inhibits protein synthesis & kill the host cell Diphtheria toxin

27 How bacterial pathogen damage host cell
membrane-disrupting toxins =cause lysis of host cells by disrupting their plasma membranes Staphylococcus aureus = hemolysin Destroy RBC

28 How bacterial pathogen damage host cell
Streptococci = hemolysin Streptolysins Streptolysin O (SLO) =is inactivated by atmospheric O2 Streptolysin S (SLS) =is stable in an O2 environment Lysis of RBC & WBC

29 How bacterial pathogen damage host cell
Superantigens =bacterial proteins = antigen that activate immune system ===electing a large immune response=====large amount of proteins (cytokines) ==== give rise to a number of symptoms *fever *diarrhea *nausea *vomiting *some time shock & even death Staphylococcal toxins ==food poisoning ==toxic shock syndrome

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31 How bacterial pathogen damage host cell
Endotoxins = are lipopolysaccharides **the lipid A component of the cell wall of Gram negative bacteria ## are part of the outer portion of the cell wall **are released when Gram negative bacteria die & their cell walls undergo lysis

32 How bacterial pathogen damage host cell
Antibiotics used to treat diseases caused by Gram negative bacteria can lyses the bacterial cell ===this reaction releases endotoxin ====lead to an immediate worsening of the symptoms

33 Pyrogenic response caused by endotoxin == when gm –ve bacteria ingested by phagocytes – degradation & the release of toxin ==the endotoxin cause the macrophages to produce a cytokine = interleukin-1 ==carried via the blood to hypothalamus=a temp control center in the brain ==prostaglandins released = reset the thermostat = high temp = fever

34 How bacterial pathogen damage host cell
Shock = any life-threatening decrease in blood pressure Septic shock = shock caused by bacteria Endotoxic shock = Gram negative bacteria endotoxin

35 How bacterial pathogen damage host cell
Phagocytosis of Gram negative bacteria Phagocytes ---secrete polypeptide (tumor necrosis factor) bind to many tissues in the body & alter the metabolism Damage blood capillaries –their permeability drop in blood pressure

36 How bacterial pathogen damage host cell
Salmonella typhi == typhoid Proteus spp == urinary tract infection == wound infection Neisseria meningitidis == meningitis

37 exotoxins Naming – according to the system that can be affected
Neurotoxins = nervous system Hepatotoxins = liver Nephrotoxins = urinary tract

38 exotoxins Diphtheria toxin Tetanus toxin Vibrio toxin
According to the disease Diphtheria toxin Tetanus toxin Vibrio toxin

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40 Pathogenic properties of viruses
**viruses evade destruction by the host s immune response by: ---viruses can penetrate and grow inside of host cell ---viruses have specific attachment sites for receptors on their target cells CD4 for HIV

41 Pathogenic properties of viruses
Cytopathic effects of viruses (CPE) = destruction , killing & death of host cells **stop mitosis = cytocidal **inclusion bodies =viral parts ,nucleic acid or proteins in the cytoplasm or in the nucleus Negri bodies=rabies

42 Pathogenic properties of viruses
**syncytium=giant cell **decrease immunity= measles **interferon production **chromosomal changes & contact inhibition = oncogen =cancer causing genes =transformation = malignant cell

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44 Pathogenic properties of fungi
Symptoms of fungal infections can be caused by : Capsules Toxins =inhibit protein synthesis Ingestion of toxins cause headaches , vomiting nausea Allergic responses = molds growing in homes

45 Pathogenic properties of protozoa & helminths
Symptoms of protozoan & helminthic can be caused by **damage to host tissue **the metabolic waste products of the parasite **some protozoan change their surface antigen while growing in a host thus avoiding destruction by the host antibodies

46 Portals of exit Pathogens have preferred portal of entry , they also have definite portals of exit **respiratory tract = coughing ,sneezing **gastrointestinal tract =saliva , feces **genitourinary tract = genital secretions

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48 Mechanisms of Pathogenicity
Microbial entry Penetration of host defenses Damage of the host Microbial exit

49 Microbes and Human Diseases
Normal Microbiota Biofilms Infectious diseases Emerging Infectious diseases

50 Biofilms Masses of microbes & their extracellular products attach to living & non living surfaces == biofilms Dental plaque on teeth Algae on walls of swimming pools Scum accumulates on shower doors Biofilms provide attachment & resistance to antimicrobial agents

51 Biofilms Microbes adhere to particular surface that is typically moist & contain organic matter Microbes multiply & secrete a glycocalyx glycocalyx = enzyme produced by bacteria convert glucose into sticky polysaccharide glycocalyx

52 Normal microbiota = normal flora
Pathology = is the science of diseases Etiology = the causes of the disease Pathogenesis & Pathogenicity Virulence Infection = invasion or colonization of the body by pathogenic microorganism = the presence of a particular type of microorganism in a part of the body where it is not normally found E.coli = normally in intestine ** urinary tract infection

53 Normal microbiota = normal flora
disease = an abnormal state in the body , in which part or all of the body is not properly adjusted , or incapable of performing normal functions ====any change from a state of health Infectious disease = caused by a microbe

54 Normal microbiota = normal flora
Microorganisms -----few are pathogenic -----some are benefit Humans are generally free of microbes in utero Microbes being colonization in & on the surface of the body soon after birth

55 Normal microbiota = normal flora
The first contact is during delivery Lactobacilli ==become the predominant organism in the newborn E.coli == acquired from foods begin to inhibit large intestine & remain there throughout life

56 Normal microbiota = normal flora
14 The number of bacteria on the body =1x10 13 The number of body cells =1x10 Bacteria which are establish permanent residence inside or on the body without producing disease is called === normal microbiota or normal flora Transient microbiota ==present for various periods & then disappear

57 Normal microbiota = normal flora
There are many factors that determine the distribution & composition of the normal microbiota Nutrients Physical & chemical factors Defenses of the host Mechanical factors

58 Normal microbiota = normal flora
Nutrients== bacteria can colonize only those body sites that can supply the appropriate nutrients Nutrients may be derived from secretary products of cells Body fluids Dead cells food in gastrointestinal tract

59 Normal microbiota = normal flora
Physical & chemical factors === temperature pH, O2 , CO2 Defenses=immune response=variety of molecules & activated cells that kill microbes or inhibit their growth or prevent adhesion & neutralize toxins

60 Normal microbiota = normal flora
Mechanical factors=may affect colonization by normal flora e.g. Chewing action of the teeth remove microorganism attachment G.I.T. – flow of saliva & digestive secretions R.T –mucus membrane

61 Normal microbiota = normal flora
Other factors that also affect the normal microbiota Age Nutritional status Diet Health status Disability Climate\geography Personal hygiene Life style

62 Relationship between the normal microbiota and the host
Microbial antagonism ===competitive exclusion ====normal microbiota prevent pathogen from colonization === protect the host By----- Competing for nutrients Producing harmful substance affecting the growth of the pathogen

63 Relationship between the normal microbiota and the host
e.g. Lactobacilli & the yeast Candida albicans Vagina pH 4 E.coli in the intestine produce bacteriocins , that inhibit the growth of salmonella & shigella

64 Relationship between the normal microbiota and the host
Symbiosis==the relation between normal microbiota &the host ==means living together

65 Relationship between the normal microbiota and the host
commensalism One of the organism is benefited &the other is unaffected Corynebacteria- eye---mycobacteria-ear no apparent benefit or harm to the host mutualism Both are benefits E.coli in intestine synthesize vitamins K ?& some B vitamins parasitism One organism Is benefited by deriving nutrients at the expense of the other disease

66 Relationship between the normal microbiota and the host
Probiotics==are live culture application to exert beneficial effect Microbes produce CD4 --- HIV The relationship (symbiosis) can change under certain condition

67 Opportunistic microorganisms
==microorganisms that do not cause disease under normal conditions but cause disease under special conditions ***the symbiotic relationship can be changed

68 Opportunistic microorganisms
e.g. E.coli=harmless as long as it remains in the large intestine – but if it gains access to other body sites it may cause disease Urinary bladder===urinary tract infection Lung===pulmonary infection Spinal cord===meningitis Wounds===abscesses Opportunistic pathogen

69 Opportunistic microorganisms
AIDS is often accompanied by a common opportunistic infections Because AIDS patients immune system is suppressed

70 Second Term Exam. Good Luck


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