Lecture 7 Host-Pathogen Interactions I PDF

Department of Microbiology and Biotechnology Host-Pathogen Interaction (I) Dr. Mohamed El-Azizi Lecture 7 Murray Medical Microbiology Chapter 9: 83-...

Department of Microbiology and Biotechnology Host-Pathogen Interaction (I) Dr. Mohamed El-Azizi Lecture 7 Murray Medical Microbiology Chapter 9: 83-86  Learning Outcomes (Los) By the end of this lecture the students will be able to: 1. Define the terms, infection, disease and colonization 2. Recognize the role of normal flora in the human body. 3. Recognize the relation between bacterial pathogenicity and host immunity 4. Differentiate pathogenic bacteria from opportunists. 5. Analyze given clinical cases related to bacterial infections to diagnose and recommend ideal ways of intervention. 6. Apply the concept of host-pathogen relationship in patient counseling. 7. Differentiate between nosocomial and community-acquired infection in patient setting. 2 Text book: Patrick Murray et al. Medical Microbiology, 5th ed. 2007 10 copies are available in the library 1. Log to www.studentconsult.com (from the university) User name: (Available in the library) Password: A. You can browse the book text, images and animations. B. You can download them to your flash drive (as pages) C. Unfortunately, you are not allowed to use the username and password at home 3  Bacteria: the Good, the Bad & the Ugly Good bacteria: - non pathogenic, produce antibiotics, dairy products and other valuable industrial products Bad bacteria: - Cause illness with low or no mortality in healthy individuals - e.g. Most disease-causing bacteria such as Staphylococcus aureus, Shigella Ugly bacteria: - Cause high mortality in untreated healthy individuals - e.g. Bacillus anthracis, Vibrio cholera, Clostridium tetani 4  Classification of Bacteria Bacteria Normal Flora Pathogenic Non-Pathogenic (Symbiosis) Overt Pathogen Opportunistic Mutualistic Commensal/ Host and bacteria benefit They coexist with host each other without harm or benefit They cause diseases when reaching Opportunistic unprotected sterile sites (e.g., blood, tissues). 5  Definitio Disease ns Damage caused by presence of microorganisms or their products. Why symptoms? As of presence of microorganism. How can bacteria cause diseases? 1. Presence of the microorganism stimulates host immune/ inflammatory response (damage) 2. Proliferation of the organism (damage) 3. Damage by microbial products: degradative enzymes, by- products (acids & gases), and toxins 6 4. Absorb proteins or a.a by degradation of tissues  Definitio Infection ns A. In any site of the body: - Infection means presence of microorganism (other than normal flora) without referring to a disease. - Not all infections lead to disease (no symptoms) - Many bacteria can cause infection but can’t proceed to cause disease B. In a patient (symptoms) - Infection always means disease caused by presence of a (in a patient) microorganism. INFECTION ALWAYS MEANS DISEASE 7  Colonization (c) vs Colonization Disease (d) Presence of microorganisms without disease at that point. Usually, there’s no need for antibiotics. - Presence of the microorganism doesn't interfere with normal body function - This term applies to surfaces only, i.e., the blood cannot be colonized. Colonization Proliferation Disease (pathogenic, or non (Damag pathogenic e) bacteria, Non replicating, on non sterile surfaces) 8  Colonization vs Infection e.g. if a person has Methicillin-resistant Staphylococcus aureus (MRSA) in his nose, but has no symptoms, his nose is said to be colonized. As soon as symptoms appear (e.g., an inflamed hair follicle with pus and pain), his nose is said to have disease (infected) - Colonization usually doesn’t required intervention with antibiotics - Disease requires treatment with antibiotics 9  Colonization vs Disease Sometimes colonization should be handled as it is a disease and treated with antibiotics: 1. The site being colonized is normally sterile e.g colonization of the lung with Pseudomonas aeruginosa in cystic fibrosis 2. The site is not normally sterile but colonized with specific pathogens e.g colonization of the anterior urethra with Chlamydia trachomatis, or Neisseria gonorrhoeae (sexual transmitted disease STD) Indicator of STD 10  Colonization vs Disease Changing the status of bacteria from colonization to disease: 1. When bacteria reach unprotected sterile area e.g. E. coli (normal flora) if there is ulcer in colon 2. Available route of entry to colonizing pathogens e.g. Staphylococcus aureus on wounded skin 3. Immune status of the host being colonized e.g. in immunocompromised patients 4. Virulence factors of the colonizing pathogens e.g. encapsulated vs non capsulated strains of 11 bacteria  Microbial Exposure Outcomes 1. The organism transiently colonizes the person. 2. The organism permanently colonizes the person. 3. The organism produce disease.  Organisms that colonize humans (transient or permanently) do not interfere with normal body functions.  Disease occurs when the interaction between microbe and human leads to a damage to the human host  Not all infections lead to disease because of the 12 A 20-year old female has recurrent dermatitis every a while.At the time a swap was taken from her skin, there was no symptoms at all but the cultural medium showed colonies of MRSA. Two weeks later, she had dermatitis again and the culture medium showed MRSA again. What is the causative agent of the symptoms? A. MRSA from the air. B. Bacteria other than MRSA. C. MRSA colonizes her skin and it is responsible for the infection. D. None of the above 13  Overt Pathogens vs Opportunists Carrier A person colonized with a pathogen (no disease) which may act as source (reservoir) of infection for other individuals. Pathogen Any organism that has the potential to cause disease Overt pathogens They have a high probability of causing disease in an otherwise healthy host e.g. Mycobacterium tuberculosis (tuberculosis), Neisseria gonorrhoeae (gonorrhea), Neisseria meningitides 14  Pathogens vs Opportunists Opportunistic pathogens They have a low probability of causing disease and usually require a debilitated or compromised host  Most human infections are caused by opportunistic microorganisms.  If a patient's immune system is defective, that patient is more susceptible to disease caused by opportunistic pathogens.  e.g. Pseudomonas aeruginosa, Staphylococcus aureus. 15  Pathogens vs Opportunists Five healthy individuals and one immunocompromised person were exposed to spores of Aspergillus niger, a fungus normally inhabits the environment around us. Few weeks later, the immunocompromised person developed fungal pneumonia. Aspergillus niger is considered as…….. A. Overt pathogenic B. Normal flora C. Commensal organism D. Opportunist E. All of the above except A 16  Pathogens vs Opportunists A group of 3 friends were admitted to the hospital and diagnosed for typhoid fever caused by Salmonella typhi. They ate fresh vegetable from the salad bar of a famous restaurant. In this case, Salmonella typhi is considered as…… A. Normal flora that invades their blood. B. Opportunist C. Overt pathogen D. Commensal E. All of the above 17  Factors Affecting Susceptibility to infection 1. Bacterial infective dose e.g., less than 200 cells of Shigella to cause shigellosis e.g., 108 cells of Vibrio cholerae to cause cholera 2. Bacterial strain - Virulent vs avirulent strains, highly virulent vs moderate or low virulent strains 3. Host factors. e.g. > 105 cells of Salmonella are necessary for gastroenteritis to become established in a healthy 1 neutra 8  Normal Flora Microorganism that frequently found on or within the body of healthy persons They may cause disease under the certain conditions (when reaching unprotected sterile sites) Infections caused by normal flora are called endogenous infections. Infections caused by bacteria other than the normal flora are called exogenous infections 19  Normal Flora Colonized sites (with normal flora) 1. gastrointestinal (GI) tract 2. upper respiratory tract 3. distal genitourinary tract 4. skin Normally sterile sites 5. Blood 6. CSF 7. interstitial fluid and spaces 8. Lymph 9. Organs e.g. brain, heart etc. 20  Normal Flora Example of sterile site in the human body A. Liver B. Brain C. Kidney D. Oral cavity E. All of the above except D 21  Normal Flora A blood sample taken from immunocompromised patient showed colonies of Pseudomonas aeruginosa on cetrimide agar plate. Taking that into consideration, which of the following is true… A. Blood can be colonized by Pseudomonas aeruginosa and there is no need for treatment. B. Existence of any bacteria in the blood must be considered as disease C. Blood harbors many types of bacterial flora. D. Existence of bacteria in blood doesn’t mean infection 22  Normal Flora- Protective effectsMutualism by normal flora 1. Stimulating the immune system e.g. Formation of antibodies against flora that cross- react with pathogens. 2. Exclusion of pathogens from colonized surfaces. 3. Depletion of nutrients essential for growth of pathogenic bacteria 23  Normal Flora- Benefits 4. Fermentation of sugar leading to pH drop which is not suitable for many pathogenic bacteria e.g. Fermentation of glycogen by lactobacillus in the vagina to lactic acid (healthy vagina pH is 4±0.5) prevent STD pathogens 5. Production of vitamin K 6. Digestion of food 7. Secretion of antimicrobial substances. 24  Norma Flora- Fetus: Sterile Sources Newborns : They get their bacterial flora from their mother and the environment. Adults: - Microbial flora is in a continual state of flux -In adults, microbial flora are affected by many factors: 1. age 2. diet, 3. hormonal state, 4. health 25 5. personal hygiene  Factors Affecting Normal Flora Environment e.g. Hospitalization: Replacement of colonized avirulent bacteria with virulent one Nosocomial infections - It is infections acquired from hospitals and usually becomes evident 48 hours (i.e., the typical incubation period) or more after admission. Community-acquired infections Infections (other than nosocomial )acquired from the community 26  Factors Affecting Normal Flora Health of the host e.g. Broad spectrum antibiotics: Inhibit commensal flora and flourish pathogenic one e.g. Candida oral thrush Candida oral thrush 27  Normal Flora- Sit Examples Flor e a Ski e.g. Staphylococcus aureus, Staphylococcus epidermidis n Stomac e.g. Helicobacter h pylori. -H. pylori is a cause of gastritis and ulcerative disease. Large More microbes are present in the large intestin intestine than anywhere else in the human e body. - e.g. E. coli and Bacteroides fragilis 28  Normal Flora- Sit Sites Flor e a genitourina -Anterior urethra ry system -Urinary bladder can be transiently colonized with bacteria migrating upstream from the urethra, -These should be cleared rapidly by the flushing action of voided urine (Fimbriae ????)* 29  Pathogenic Pathogenicity Bacteria Denotes the ability of the microorganism to cause infection. Virulence Denotes the degree of pathogenicity Virulence factors Genetic traits that enhance the ability of bacteria to cause disease. e.g. Capsule, fimbriae, glycocalyx 1. Enter the Virulence host enable bacteria to: factors 2. Spread (+/-) 3. Multiply 4. Evade host defenses. 5. Damage host tissues 6. Transmit to a new host 3 0 Explain the following “bacterial normal flora play important role in antibody formation against ABO blood antigens” e.g. Person with blood group B has anti A antibodies 3 1