Med201 Bacterial interaction.pdf

Interactions between bacteria & humans (infections: types, transmission, sources) Dr.Asma Sawan Asisstant Professor Department of Microbiology Iman Abdulrahman University ‫أ‪ .‬االنتقال من مصادر خارجية أو من‬ ‫أفراد مصابني ‪ -‬عندما يتم نقل العامل‬ ‫املمرض من مصادر خارجية‪ ،‬مثل الطيور‬ ‫أو الحيوا...

Interactions between bacteria & humans (infections: types, transmission, sources) Dr.Asma Sawan Asisstant Professor Department of Microbiology Iman Abdulrahman University ‫أ‪ .‬االنتقال من مصادر خارجية أو من‬ ‫أفراد مصابني ‪ -‬عندما يتم نقل العامل‬ ‫املمرض من مصادر خارجية‪ ،‬مثل الطيور‬ ‫أو الحيوانات املصابة‪ ،‬أو عندما ينتقل بني‬ ‫األفراد املصابني‪ ،‬مثل اإلنسان إلى‬ ‫اإلنسان‪.‬‬ ‫ب‪ .‬دخول العامل املمرض إلى جسم‬ ‫اإلنسان ‪ -‬بعد االنتقال‪ ،‬يدخل العامل‬ ‫املمرض إلى جسم اإلنسان عبر مسالك‬ ‫التنفس‪ ،‬أو الجهاز الهضمي‪ ،‬أو عن‬ ‫طريق الجروح أو الكدمات في الجلد‪.‬‬ ‫ج‪ .‬التغلب على الدفاعات املضيفة ‪ -‬بمجرد‬ ‫دخول العامل املمرض إلى الجسم‪ ،‬يحاول‬ ‫التغلب على نظام الدفاع الطبيعي للجسم‪،‬‬ ‫مثل جهاز املناعة‪ ،‬ليتمكن من البقاء‬ ‫والتكاثر‪.‬‬ ‫د‪ .‬التكاثر والتوزيع داخل الجسم ‪ -‬بعد‬ ‫‪Objectives‬‬ ‫)‪Interactions between bacteria and humans (Infections‬‬ ‫‪1. The infection process‬‬ ‫‪2. Different types of Infections‬‬ ‫‪3. Sites of entry and exit‬‬ ‫‪4. Different sources and modes of transmission of infection‬‬ ‫‪5. Vertical and horizontal transmission‬‬ ‫‪6. The ‘iceberg’ concept of infectious disease.‬‬ The Infection Process (1) How Do Bacteria Cause Disease? A. Transmission from exogenous sources or infected individuals – epidemiology B. Entry into human body C. Overcome host defenses D. Multiply and disseminate within the body ➢ Adhere to host surfaces ➢ Invade host cells E. Cause cell and tissue damage F. Spread to other members of population J The Infection Process (2) A.Transmission of Infectious Diseases y The Infection Process (2) Can Normal Flora cause Disease? Yes ➠Opportunistic infections • Bacteria inhabit a wide variety of different niches on human body ✓ ✓ ✓ ✓ Skin Respiratory tract Gastrointestinal tract Urinogenital tract • Normally these bacteria do not cause disease • BUT – they can cause disease (opportunistic infections) if: ✓ they gain entry to the body cavity ✓ there is a change in the ecological niche ✓ the host is immunosuppressed B.Entry Into the Human Body 2 Mims’ Model of the Human Body • Our body is a closed system and has openings to the outside environment through which microbes can get access to our bodies Figure 13.1 Body surfaces as sites of microbial infection and shedding C.Overcome Host Defenses Physical and Chemical Barriers Innate immune responses Adaptive immune responses ✓ ✓ ✓ ✓ ✓ High salt, fatty acids (skin) Acid (stomach) Mucous + cilia (LRT), peristalsis (GIT) Soluble mediators eg. Lysozyme E ✓ Complement ✓ Phagocytosis Y ✓ Antibodies ✓ Cell-mediated immunity (cytotoxic Tcells) D. Multiply and disseminate within the body (Colonisation of the Host) • Colonisation of the host is the process whereby pathogens establish themselves within the host a) They need to adhere to host surfaces b) Multiply to outcompete the normal flora if present Establishing A Connection Between Microorganisms And Disease • Koch's postulates: 1. Association of microbe with disease lesions 2. Isolation of bacterium in pure culture 3. Isolated bacterium must cause disease in humans/animals 4. Re-isolation of same bacterium from infected animal Koch’s Postulates Limitations of Koch’s Postulates: 1. 2. 3. 4. No host factors taken into account (asymptomatic carrier) Emphasis on ability to culture organism Organism can lose virulence in lab Requires animal model (have Koch's postulates ever been tested in humans?) 5. Disease may not require organism to infect host (eg. Toxins), although this is rare Definition of Terms ➢Pathogen : An organism able to cause disease ➢Pathogenesis : The process whereby an organism causes disease (the ability) ➢ Virulence : The quantitative ability of an organism to cause disease (the power) ➢Virulence factor : are the properties of a pathogens that allow them to cause disease (eg. Toxins or proteins that modulate immunity). ➢The genes that encode virulence factors may be carried on mobile genetic elements (plasmids, transposons, or bacteriophages) ➢Or found on large pathogenicity islands on bacterial chromosomes The ‘iceberg’ concept of infectious disease. Classical Bacterial Diseases Disease Bacterial Agent Tetanus Clostridium tetani Plaque Yersinia pestis Cholera Vibrio cholerae Gas Gamgrene Clostridium perfringens Tuberculosis Mycobacterium tuberculosis Dysentery Shigella spp. Typhoid Fever Salmonella typhi