Micropara Lecture 3

• Symbiosis means “to live together”
• • Commensalism:


  A relationship between two organisms where one receives a benefit or benefits from the other and the other is not affected.
• • Mutualism


  • A relationship which two organisms of different species exist in which each individual benefits from the activity of the other
• •Parasitism


  A relationship between two organisms where one is usually harmed and the other gets benefits from the relationship.
• Normal flora” or “ Indigenous microbiota


  • Organism that reside or colonize the body’s surfaces or deep layers, without normally causing disease.
• Resident microbiota


  Most commensal bacteria remain part of a host's normal microbiota throughout life.
• Transient microbiota


  This refers to a brief period of inactivity or absence in the body, often characterized by competition, immune system, or physiological changes.
• Role of resident microbiota

  Commensals maintain health, aid in nutrient absorption, provide defense against pathogens, degrade toxins, and contribute to immune system maturation.
• Normal flora can overpopulate or move into areas of the body where they do not normally occur.• Invasive medical procedures
• •When the balance of normal microbes is disrupted.• A person takes broad spectrum antibiotics.
• Contamination


  The mere presence of microbes in or on the body
• Infection


  When organism evades body’s external defenses, multiplies, and becomes established in the body
• An infection may cause no symptoms “Asymptomatic” and be subclinical, or it may cause symptoms “Symptomatic” and be clinically apparent.
• PORTALS OF ENTRY


  Any point/site at which organisms can enter the body.
• Skin


  Covered with many types of microorganism
• Covered with many types of microorganism

  To prevent pathogens from entering, line open body cavities and provide a moist, warm environment
• Mucous membranes


  •Respiratory tract•Gastrointestinal tract•Genitourinary tract
• The Respiratory Tract


  •Most favorable to pathogens •Facilitates entry through breathing
• The Gastrointestinal Tract


  • Open to the outside world. • A leading portal of exit for pathogens in feces.
• Urinary and reproductive tracts


  • Diseases of the reproductive tract are usually sexually transmitted
• The Parenteral Route


  Movement of organisms past the barrier of the skin that requires a break in the barrier.• Injections• Insect bites• Animal bites
• A pathogen must find a way to stay in the host if it is to establish the focus of the infection.
• Adherence (adhesion, attachment)


  which pathogens stick to the surfaces ofhost cells.
• The Role of Adhesion in Infection• Microorganisms attach themselves to cells(process)
• •Fimbriae


  enable the bacteria to bind to specific receptor structures and thereby to colonize specific surfaces.
• •Glycocalyx


  covering that surrounds the cell membranes of some bacteria, epithelia, and other cells.
• •M Protein – Streptococcus pyogenes


  The virulence factor on the surface plays various roles in streptococcal infection, including resistance to phagocytosis, adherence to epidermal keratinocytes, microcolony formation, and invasion of epithelial cells.
• Opa proteins


  outer membrane proteins that mediate tight interaction of these pathogens with human cells.
• AVOIDING, EVADING, OR COMPROMISING HOSTDEFENSES (DEFEAT THE HOST DEFENSES)


  Pathogenic bacteria have built-in passive defenses, such as capsules and cell wall components, and active defenses, which involve attacking the host's defenses, primarily through enzymes.
• Capsule (Passive) Defenses


  Pathogens can encapsulate themselves, covering their entire surface in a slimy capsule, to protect against phagocytosis, preventing phagocytes from adhering to the bacterium's surface.
• Cell Wall (Passive) Defenses

  Bacteria use wall components to increase virulence against host defenses, such as M proteins in Streptococcus pyogenes and mycolic acid in Mycobacterium tuberculosis.
• Enzyme (Active) Defenses

  Leukocidins, hemolysins, coagulase, kinases, and hyaluronidase are enzymes that destroy white blood cells, disrupt host cell membranes, cause fibrin clot formation, break down connective tissue, and allow infections to spread.
• DAMAGING THE HOST


  Infection damage can be categorized into two parts: damage due to bacteria, by-product of host response, and direct or indirect damage directly attributed to the pathogen.
• Direct damage


  Is the obvious destruction of host cells and tissues and is usually localized to the site of the infection
• Indirect damage


  seen in most serious infections and is much more dangerous to the host because it involves systemic disease
• Microbial Toxins


  • Promote infection and disease by directly damaging host tissues and by disabling the immune system.
• Exotoxins


  Proteins produced inside pathogenic bacteria
• Endotoxins


  part of outer membrane of cell wall, and liberated when bacteria die and the cell wall breaks apart
• TYPES OF EXOTOXIN

  • Type I- • Superantigens• Cause intense immune response. •Type II • Membrane-disrupting toxins• Damage host cell membranes. •Type III • A-B Toxins( Protein complexes secreted by bacteria)
• Endotoxins• LPS: Lipopolysaccharide/Lipoglycans• Not produce by the bacteria• Part of the cell wall (outer membrane)• Only Present in Gm- bacteria