Host-Parasite Interaction 2022-2023 PDF

Host-Parasite interaction •By: •Dr. Shadi A. Zakai (PhD) •Assistant Professor and Molecular Microbiology Scientist •Department of Medical Microbiology and Parasitology •Faculty of Medicine •King Abdulaziz University Objectives • At the end of the lecture the student will be able to : • Define: Sa...

Host-Parasite interaction •By: •Dr. Shadi A. Zakai (PhD) •Assistant Professor and Molecular Microbiology Scientist •Department of Medical Microbiology and Parasitology •Faculty of Medicine •King Abdulaziz University Objectives • At the end of the lecture the student will be able to : • Define: Saprophytes, Parasites, Normal Flora (Commensal), Infection, Opportunistic Infection, Virulence Factors. • Discuss normal flora of the human body, areas colonized, their importance, and the potential for infection. • Discuss virulence factors produced by microorganisms that cause infection. • Differentiate between bacterial endotoxins & exotoxins. • List specific and non-specific host resistance. Introduction • You are all disgusting • Daily we • Ingest thousands of microorganisms on the food we eat • Inhale hundreds of thousands of microorganisms in the air we breath • Have microorganisms stick to us wherever we go • Don’t bother washing, ever again • microorganisms colonize warm, moist, nutrient rich environment (I.E.; the human body) • usually, they live as normal flora • in some cases, they can overcome the bodies defenses, and cause disease • organisms that can cause any noticeable damage, invade tissue, or produce toxins are called pathogens Terminology* Normal flora Bacteria and fungi that are PERMANENT RESIDENTs of certain body sites. Commensals: organisms that benefit from a host without causing damage. Colonization Acquisition of a new organism to a site in the body Symbiosis Two or more organisms co-exist in close physical association Often used synonymously with “mutualism” Symbiosis Mutualism • Both organisms benefit from symbiosis Neutralism • Neither organism derives benefit or harm Commensalism • One organism benefits, the other derives neither benefit nor harm Parasitism • One organism (parasite) benefits at the expense of the other (host) Mutualism • In this type of relationship, both partners benefit • E. coli synthesizes vitamin K in the intestine • in exchange the large intestine provides nutrients necessary for survival of the microorganisms Commensalism • One organism is benefited and the other is unaffected by this type of relationship • Many of the microorganisms that make up our normal flora inhabit places like the eyes, ears, and external genitalia • these bacteria live on secretions and sloughed off cells • they bring no benefit to the host and yet the microorganisms benefit greatly from the environment they inhabit Parasitism • One organism benefits at the expense of the other • All pathogens are parasites Terminology of Infectious Diseases Term Definition Infectious dose Number of microbes needed to establish infection (some are less contagious than others, so they need larger number of pathogens to establish disease) Signs Symptoms Pathogenicity Virulence Virulence factors Capacity of bacteria to cause disease by overcoming the host defenses. Degree of pathogenicity Substances or features of a microorganism that help it infect and cause disease Localized infection Invading microorganisms are limited to a small area (e.g. abscesses) Systemic infection Infectious agent spreads throughout the body by blood or lymph (e.g. measles) objective changes that are observable and measurable (swelling, fever, paralysis) subjective effects experienced by patient (pain or nausea) Terminology of Infectious Diseases Term Definition Stages of disease the time between the initial infection and the first appearance of incubation illness any signs or symptoms signs and symptoms of the disease are experienced convalescence person regains strength and the body returns to its prediseased state Terminology of Infectious Diseases Term Definition Types of infectious diseases Rapid onset, short duration (Influenza) Acute Chronic Latent Develops slowly, lasts longer (Hepatitis B virus) Causative agent is never completely eliminated, Remains inactive in the body, but can be reactivated if immune system is weak (Shingles ‫)الحزام الناري‬ Normal Flora • Microorganisms that colonize a host without causing disease • Benefits: • Synthesis and excretion of vitamins • Prevention of colonization by pathogens • Antagonistic reactions to other bacteria • Simulation of the production of natural antibodies • ***The normal bacterial microorganisms of the adult human vagina maintain the pH at about 3.4 – 4.5 • The presence of this normal flora inhibits the overgrowth of Candida albicans, yeast Normal Flora Harmful effects: • When the balance between normal flora and pathogens is upset, disease can result • Bacterial synergism (cross-feeding) • Competition of nutrients • Low-grade toxemia • Source of endogenous disease • Transmission to susceptible host Normal Flora Harmful effects: • When the balance between normal flora and pathogens is upset, disease can result • Bacterial synergism (crossfeeding) • Competition of nutrients • Low-grade toxemia • Source of endogenous disease • Transmission to susceptible host Non-sterile and sterile body sites Non-sterile sites Sterile sites Have normal flora No normal flora Non-sterile sites • Exposed to the environment • Directly • Indirectly • No mechanism in place to maintain sterility Sterile sites Sterility maintained by surface cleaning Open to the environment Sterility maintained by barriers that allow unidirectional flow Adjacent to non-sterile sites Sterility maintained by physical separation from non-sterile sites Closed cavities Normal flora of the skin • The skin flora found in superficial layers of the epidermis and the upper parts of the hair follicles • The high moisture content of the axilla, groin, and areas between the allows growth of high number of bacterial cells • Normal flora can enter bloodstream by needle, catheter, causing systematic diseases. Normal flora of the respiratory tract • Huge amount found in • Nose • Throat • Oral cavity • Lower resp. tract; hardly any. Dental caries & Normal flora • Dental plaque, is material adhering to the teeth, consists of bacterial cells (60-70% the volume of the plaque), salivary polymers, and bacterial extracellular products. • The dominant bacterial species in dental plaque are • Streptococcus sanguis • Streptococcus mutans • Dental caries is a bacterial infection that causes demineralization and destruction of the hard tissues of the teeth (enamel, dentin and cementum). Normal flora of the intestinal tract • Stomach: low number of bacteria (low pH) • Small intestine • Colon: the main location of bacteria in the body. • 20% of feces contain bacteria • 1011/g • 90% of fecal flora are ANAEROBIC • Antibiotics reduces the amount of persisting flora in the intestine, allowing other pathogens to overgrow and cause colitis. Normal flora of the genitourinary tract • Lactobacilli, a major vaginal flora that produces acid ! maintain low pH. • If suppressed by antibiotics ! overgrowth of C. albicans. • newborns may get infected during passage Principle of infectious diseases • Pathogenicity is the ability of a microorganism to cause disease by overcoming the host defenses • This can be accomplished with • Primary pathogen: microorganism capable of causing disease in a healthy host • Opportunistic pathogen: is only capable of causing disease when the immune system is overcome, or the organism is introduced to an unusual location • opportunistic organisms can be part of the normal flora or found in the environment Endogenous • Normal Flora Source of infection Exogenous • Humans: An infected person can either be a case or a carrier • Animal: zoonotic disease is one that is transferred from animal to human. • Environmental: Dust ! Tetanus Entrance Spread Exit Horizontal: by skin or mucous membranes (oral, respiratory, droplets, sexual direct contact, and injection (by syringe, blood transfusion, insects, and arthropods) • Vertical : (mother to fetus) -Trans-placental - Trans-vaginal - Trans-mammary (through breastfeeding) Same way of entry •Direct continuity • Blood • Lymphatic • Neural (on nerves) (Entrance from mouth ! Exit with stool) (Entrance from blood !Exit from blood) (Entrance from nose ! Exit from nose) Mechanisms of bacterial pathogenicity Two broad mechanisms of Pathogenicity • 1. Invasiveness is the ability to invade tissues. It encompasses mechanisms for: • colonization (adherence and initial multiplication) • production of extracellular substances which facilitate invasion (invasins) • ability to bypass or overcome host defense mechanisms. • 2. Toxigenesis is the ability to produce toxins. • Exotoxins • endotoxins. Mechanisms of bacterial pathogenicity (Invasiveness) Colonization: the establishment of the pathogen at the appropriate portal of entry Adherence of bacteria to eukaryotic cell: e.g. pilli (adhesive hair-like organelles on the bacterial surface) Mechanisms of bacterial pathogenicity (Invasiveness) Invasion: production of (invasins) bacterial extracellular substances that break down primary or secondary defenses of the body •Spreading Factors bacterial enzymes that affect the physical properties of tissue matrices and intercellular spaces, thereby promoting the spread of the pathogen. E.g.: •Hyaluronidase. •Collagenase •Hemolysis and/or Leucolysis •Phospholipases •Hemolysins Mechanisms of bacterial pathogenicity (Invasiveness) Evasion of host defenses: Some pathogenic bacteria are inherently able to resist the bactericidal components of host tissues. Mechanisms of bacterial pathogenicity (Toxigenesis) Two types of bacterial toxins • ENDOTOXINS (lipopolysaccharides) associated with the cell walls of Gram-negative bacteria. • EXOTOXINS (proteins) released into the extracellular environment of pathogenic bacteria. Direct Host Damage ❑Toxins are produced by the invading pathogen cause direct damage to the host which results in disease ❑Toxins capable of causing damage include ❑Exotoxins ❑Endotoxins Bacillus anthraxis produces an exotoxin Exotoxoins • a protein toxin released from a living cell • mostly found in Gram + cells • Secreted by the bacteria or released following lysis • Soluble in body fluids which makes them easily diffused into blood and then are rapidly transported throughout the body • exotoxins are highly specific • Among the most lethal substances known to man • 0.1 gram of the exotoxin produced from Clostridium botulinum can kill the entire population of the KSA, close to 30 million people Endotoxins Are lipopolysaccharides (LPS) found in the lipid portion of the outer wall of Gram –ve bacteria • endotoxins are released when Gram –ve bacteria die and the cell wall undergoes lysis • antibiotics that are used to treat Gram –ve diseases can lyse the bacterial cells, releasing the endotoxin • this can lead to an immediate worsening of the symptoms • these symptoms usually improve as the endotoxins break down Properties of Exotoxins and Endotoxins. Bacteria Diffusability Nature Effect of Heat Antigenicity Toxicity Specificity Toxoid Form Exotoxins Endotoxins Gram-positive Gram-negatives Released in medium Remains with Cell wall Protein LPS Labile Stable High Weak Strong Weak High Low Yes No Non-specific Resistance (Natural /Innate) • Skin. Physical barrier. Sebaceous glands produce sweat with lysozyme. Host Resistance to Infection • Respiratory Tract. Ciliated cells and Mucous produced. Nasal hairs. Reflex of coughing. • Gastrointestinal Tract. Normal flora in mouth and stomach. Acid and enzymes produced in stomach. • Genital Tract. Stratified epithelium (in vagina). Acid produced by lactobacilli. • Conjunctiva. Reflex of blinking. Tears act to clear (washing) and have lysozyme. • Phagocytic system. Polymorphs and macrophages. Specific Resistance. Host Resistance to Infection • must be induced or turned on by host exposure to a pathogen • Directed against specific microbes. • Humoral antibodies. • Cell Mediated Immunity. Acquired immunity.