Pathogenicity BMS2031 Medical Microbiology PDF

Pathogenicity BMS2031 Organisms Medical Microbiology Dr Clare Miller [email protected] Symptoms 1 The Nature of Infectious Disease Virulence Factors of Infectious Agents – Pathogenicity...

Pathogenicity BMS2031 Organisms Medical Microbiology Dr Clare Miller [email protected] Symptoms 1 The Nature of Infectious Disease Virulence Factors of Infectious Agents – Pathogenicity – Ability of a microorganism to cause disease – Virulence – Degree of pathogenicity – Virulence factors contribute to virulence – Adhesion factors – Biofilms – Extracellular enzymes – Toxins – Antiphagocytic factors 2 © 2012 Pearson Education Inc. Figure 14.8 Relative virulence of some microbial pathogens More virulent Francisella tularensis (rabbit fever) Yersinia pestis (plague) Bordetella pertussis (whooping cough) Pseudomonas aeruginosa (infections of burns) Clostridium difficile (antibiotic-induced colitis) Candida albicans (vaginitis, thrush) Lactobacilli, diphtheroids Less virulent 3 The Nature of Infectious Disease Virulence Factors of Infectious Agents – Extracellular enzymes – Secreted by the pathogen – Dissolve structural chemicals in the body – Help pathogen maintain infection, invade, and avoid body defenses 4 © 2012 Pearson Education Inc. 5 The Nature of Infectious Disease Virulence Factors of Infectious Agents – Toxins – Chemicals that harm tissues or trigger host immune responses that cause damage – Toxemia refers to toxins in the bloodstream that are carried beyond the site of infection – Two types – Exotoxins – Endotoxins 6 © 2012 Pearson Education Inc. 7 The Nature of Infectious Disease Virulence Factors of Infectious Agents – Antiphagocytic factors – Factors prevent phagocytosis by the host’s phagocytic cells – Bacterial capsule – Composed of chemicals not recognized as foreign – Slippery – Antiphagocytic chemicals – Prevent fusion of lysosome and phagocytic vesicles – Leukocidins directly destroy phagocytic white blood cells 8 © 2012 Pearson Education Inc.  Figure 14.9c Some virulence factors: Antiphagocytic factors Phagocytosis blocked by capsule Incomplete phagocytosis Capsule around Capsule around Bacteria bacterium bacterium reproduce Phagocytic vesicle Phagocyte Lysosome Antiphagocytic factors 9 Typical prokaryotic cell Inclusions Ribosome Cytoplasm Nucleoid Flagellum Glycocalyx Cell wall Cytoplasmic membrane 10 Glycocalyces: – Gelatinous, sticky substance surrounding the outside of the cell – Composed of polysaccharides, polypeptides, or both – Capsule Composed of organized repeating units of organic chemicals Firmly attached to cell surface May prevent bacteria from being recognized by host – Slime layer Loosely attached to cell surface Water soluble Sticky layer allows prokaryotes to attach to surfaces 11 Glycocalyces: overview Glycocalyx Glycocalyx (capsule) (slime layer) 12 The Role of Adhesion in Infection – Process by which microorganisms attach themselves to cells – Required to successfully establish colonies within the host – Uses adhesion factors Specialized structures Attachment proteins 13 The adhesion of pathogens to host cells: overview 14 The Role of Adhesion in Infection – Attachment proteins help in adhesion Found on viruses and many bacteria Viral or bacterial ligands bind host cell receptors – Interaction can determine host cell specificity – Changing/blocking a ligand or its receptor can prevent infection – Inability to make attachment proteins or adhesins renders microorganisms avirulent – Some bacterial pathogens attach to each other to form a biofilm 15 Dental plaque 16 Associations and Biofilms – Organisms live in association with different species – Antagonistic relationships – Synergistic relationships – Symbiotic relationships – Biofilms Complex relationships among numerous microorganisms Develop an extracellular matrix – Adheres cells to one another – Allows attachment to a substrate – Sequesters nutrients – May protect individuals in the biofilm Form on surfaces often as a result of quorum sensing Many microorganisms more harmful as part of a biofilm 17 Further reading: Bauman, R. W. (2019). Microbiology with diseases by body system (5th ed.). Pearson. Chapter 14. Microbial biofilms Riddle of Biofilm Resistance Mechanisms of biofilm resista nce to antimicrobial agents Bacterial Biofilms: Developme nt, Dispersal, and Therapeutic Strategies in the Dawn of the Postantibiotic Era Bacterial biofilms: from the Na tural environment to infectiou s diseases https://www.youtube.com/wat ch?v=qZCanCxo0tI https://www.youtube.com/wat 18 ch?v=FeFKAl9KyMg