Agricultural Microbiology Lecture 10 Slides PDF

MICR20010 Agricultural Microbiology Dr. Tadhg Ó Cróinín Assessments Practical accounts for 30% 15% on the two Practical reports to be submitted online after the practicals. Note these include write ups on practicals as well as online material. 15% on the Practical Exam online to...

MICR20010 Agricultural Microbiology Dr. Tadhg Ó Cróinín Assessments Practical accounts for 30% 15% on the two Practical reports to be submitted online after the practicals. Note these include write ups on practicals as well as online material. 15% on the Practical Exam online to be held Friday Nov 22nd 2-3pm. 70% on an end of term MCQ exam in the RDS. Microbiology The study of microorganisms. Bacteria/Viruses which cause disease Bacteria which help – antibiotics, probiotics Biotech Industry Why is Microbiology Important? Industrial Microbiology Food and Beverage Industry Health Industry Environmental Microbiology Bacteria and their role in the ecosystem Pollution and Bioremediation Clinical Microbiology Developing vaccines, antibiotics new treatments Diagnostics MICR20010 - remaining lectures Lecture 10 – Microorganisms and Disease Lecture 11 – The Immune System Lecture 12 - Pathogenic Bacteria Lecture 13 – Pathogenic Fungi and Viruses Lecture 14 – Antibiotic Resistant Microorganisms Lecture 15 – Microbiology in the Food Industry – The Fungi Lecture 16 – Microbiology in the Food Industry - Fermentations Lecture 17 – The Nitrogen Cycle Microorganisms and Disease Microorganisms play a variety of different roles in disease and we have complex relationships with these organisms. Mutualism Beneficial associations – bacteria providing vitamin precursors in gut Commensalism Passive associations – non pathogenic Staphylococci Parasitism Microorganism causes harm – pathogenic bacteria Key is understanding the relationship How do we prove a pathogen Koch’s postulates 1. The m/o must be present in the diseased and not in a healthy animal 2. M/O must be cultivated in pure culture 3. Pure culture inoculated into 2nd animaldisease 4. Pure culture from 2nd animal should be same as 1st. Koch’s Postulates What about exceptions?  Some pathogens difficult to culture.  Some diseases are caused by combinations of  Pathogens  Physical, environmental  Genetic factors  Animal models and ethics: inoculation of healthy susceptible host not always possible (the postulate could never be fully applied to HIV) Virulence Factors A key differential in pathogens is the presence of virulence factors which help the organisms cause disease. Evolution allows these toxins to often be host specific Toxins which have very specific targets Adhesins which recognise specific receptors Other less so – Endotoxins (e.g. LPS) Virulence factors can thus define host specificity  Extracellular Enzymes Secretion of enzymes allows microorganisms to alter their environment Avoiding the Immune system– Some blood borne pathogens have the ability to secrete coagulase which leads to coagulation allowing microorganisms to form clots which in turn can provide a physical hiding place from the immune system. Leukocidins can be used to destroy white blood cells. Catalase can be used to protect from reactive oxygen species in the Macrophage  Toxins  Exotoxins 1. Cytotoxins: kills or affects the functions of host cells 2. Neurotoxins: interferes with nerve cells 3. Enterotoxins: affects cells lining gut tract (clostridia, pathogenic strains of S.aureus and E.coli) Cytotoxins Neurotoxins Clostridum botulinum and Clostridium tetanii secrete extremely potent neurotoxins which lead to two very different forms of fatal paralysis Related toxins Botulinum toxin inhibits the release of acetylcholine which stimulates contraction therefore leading to relaxation Tetanus toxin inhibits the release of Glycine which induces relaxation of a contracted muscle which thus leads to contraction. Tetanus not a food poisoning toxin! Enterotoxins Clostridium perfringens secretes an enterotoxin which can induce gastroentertis on its own Inoculation with the toxin alone has the same effect as inoculating with the bacteria Virulence vs Colonization factors A virulence factor is directly involved in causing disease Toxins etc A colonization factor may be necessary for disease to progress but is not directly involved Adhesins and flagella for motility Clostridium perfringens entertoxin (CPE) clearly a virulence factor Endotoxins Primarily found in Gram negative organisms Key is the constituents of the Outer membrane Lipopolysaccharide (LPS) Released on cell death or through membrane blebbing but has dramatic effect on Immune system Anti-phagocytic factors  Capsules: many are made of chemicals found in body : no immune responses made  Anti-phagocytic compounds: some m/o make compounds that prevent fusion of lysosomes with phagocytic vesicles… (Neisseria gonorrhea)  Previously mentioned enzymes such as catalase Immune Evasion Phagocytosis blocked by capsule Surviving phagocytosis How is disease transmitted Microorganisms do not simply appear They can be already present and taking advantage of a change in environment – Opportunistic pathogens S. aureus commonly found on skin but pathogenic in blood infections C. difficile takes advantage of antibiotic treatments changing microbiome How are organisms transmitted - epidemiology Modes of Transmission A. Contact transmission Direct contact-person to person Indirect contact-needles, toothbrushes Droplet transmission- spread via droplet nuclei B. Vehicle transmission Air, drinking water, food C. Vector transmission Biological and mechanical Basic protections from infection Skin: barrier…tight layer of packed cells…entrance through cuts Mucous membranes: that line the body cavities open to the outside world (nose etc..) To infect: adherence of parasite to cells to allow for establishment of colonies Adaptive immunity Acquired immunity Develops from birth, as we encounter various pathogens Antigens trigger specific response Components of bacterial cells Cell walls, capsules Flagella Proteins (internal + external) Toxins Food may have antigens that provoke allergic reactions What are Antigens? Properties of antigens Antigens recognised by antigenic determinants (epitopes) >5-100KDa better than smaller antigens Proteins, glycoproteins etc…