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Microbial Mechanism of Pathogenicity

Microbial Mechanism of Pathogenicity. OUT LINES. MICROBIAL GROWTH MICROBIAL GENETICS PATHOGENIC PROPERITIES OF MICROBES CHAIN OF INFECTION. Objectives:. At the end of this lecture the students will be able to: Understand microbial growth Describe microbial genetics

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Microbial Mechanism of Pathogenicity

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  1. Microbial Mechanism of Pathogenicity

  2. microbiology team/ 3rd level students 1439-1440 OUT LINES • MICROBIAL GROWTH • MICROBIAL GENETICS • PATHOGENIC PROPERITIES OF MICROBES • CHAIN OF INFECTION

  3. microbiology team/ 3rd level students 1439-1440 Objectives: • At the end of this lecture the students will be able to: • Understand microbial growth • Describe microbial genetics • Differentiate between pathogenic properties of versus, fungi, helminthes and algae • Enumerate the elements of infection cycle • Predict & practice how infection cycle can be broken and infection can be prevented

  4. Microbial Growth microbiology team/ 3rd level students 1439-1440

  5. microbiology team/ 3rd level students 1439-1440 1- Microbial Growth It refers to an increase in cell number, not in cell size. There are basic requirements needed for bacterial growth which are both physical & chemical .

  6. microbiology team/ 3rd level students 1439-1440 A- Physical requirements of M.Growth • Temperature • On the basis of preferred temperature ranges ,microbes are classified into : • Psychrophiles (cold- loving microbes ) • Example of disease caused by psychrophilesare dysentery, diarrhea, meningitis, sepsis, food poisoning, urinary tractinfections, and gastrointestinal infections. • Mesophiles (moderate –temperature loving microbes) • Common types: staphylococcus aureus, salmonella and listeria. • Thermophiles (heat –loving microbes ) • Can be the cause of meningitis, endocarditis, and septicemia.

  7. microbiology team/ 3rd level students 1439-1440 Temperature ……cont,. • The minimum growth temperature is the lowest temperature at which (microbes) will grow • The optimum growth temperature is the temperature at which microbes grows best . • The maximum growth temperature is the highest temperature at which growth is possible .

  8. microbiology team/ 3rd level students 1439-1440 A- Physical requirements • pH Most bacteria prefer neutral pH (6.5-7.5). Molds and yeast grow in wider pH range, but prefer pH between 5 and 6. 4 Acidity inhibits most microbial growth and is used frequently for food preservation (e.g.: pickling). Alkalinityinhibits microbial growth, but not commonly used for food preservation.

  9. microbiology team/ 3rd level students 1439-1440 A- Physical requirements Organisms can be classified as: • A.Acidophiles : “Acid loving”. Grow at very low pH (0.1 to 5.4) Lactobacillus produces lactic acid, tolerates mild acidity. • B.Neutrophiles : Grow at pH 5.4 to 8.5. Includes most human pathogens. • C.Alkaliphiles : “Alkali loving”. Grow at alkaline or high pH (7 to 12 or higher) Vibrio cholera

  10. microbiology team/ 3rd level students 1439-1440 A- Physical requirement • Osmotic Pressure : Cells are formed of 80 to 90% water. • Hypertonic solutions: High osmotic pressure removes water from cell, causing shrinkage of cell membrane (plasmolysis). Used to control spoilage and microbial growth. • Hypotonic solutions: Low osmotic pressure causes water to enter the cell. In most cases cell wall prevents excessive entry of water. Microbe may lyse or burst if cell wall is weak

  11. microbiology team/ 3rd level students 1439-1440 Isotonic ,Hypotonic & Hypertonic Solution Plasmolysis

  12. microbiology team/ 3rd level students 1439-1440

  13. microbiology team/ 3rd level students 1439-1440 B- Chemical requirements of Mic. Growth • 1- Carbon: Makes up 50% of dry weight of cell • 2- Nitrogen, Sulfur, and Phosphorus: A . Nitrogen: Makes up 14% of dry cell weight. Used to form amino acids, DNA, and RNA B. Sulfur: Used to form proteins and some vitamins (thiamin and biotin). C. Phosphorus: Used to form DNA, RNA, ATP, and phospholipids. 3- Other Elements: Potassium, magnesium, and calcium are often required as enzyme cofactors. 4. Trace Elements: . Many are used as enzyme cofactors. Commonly found in tap water. as Iron , Copper & Zinc

  14. microbiology team/ 3rd level students 1439-1440 B- Chemical requirements of Mic. Growth • 5. Oxygen: • Organisms that use molecular oxygen (O2 ), produce more energy from nutrients than anaerobes. We can classify microorganism based on their oxygen requirements to: • A. Obligate Aerobes: Require oxygen to live. Disadvantage : Oxygen dissolves poorly in water. Example: Pseudomonas, common nosocomial pathogen • B. Facultative Anaerobes: Can use oxygen, but can grow in its absence. Have complex set of enzymes. Examples: E. coli, Staphylococcus, yeasts, and many intestinal bacteria. • C. Obligate Anaerobes: Can not use oxygen and are harmed by the presence of oxygen. Examples: Clostridium bacteria that cause tetanus and botulism.

  15. microbiology team/ 3rd level students 1439-1440 B- Chemical requirements of Mic. Growth • D .AerotolerantAnaerobes: • Can’t use oxygen, but tolerate its presence. Example:Lactobacillus carries out fermentation regardless of oxygen presence. • E. Microaerophiles: Require oxygen, but at low concentrations.. Example: Campylobacter.

  16. microbiology team/ 3rd level students 1439-1440 Culture Media • Culture Medium: Nutrient material prepared for microbial growth in the laboratory. Requirements: • Must be sterile • Contain appropriate nutrients • Must be incubated at appropriate temperature Culture: Microbes that grow and multiply in or on a culture medium

  17. microbiology team/ 3rd level students 1439-1440 Bacterial Growth: Binary Fission

  18. microbiology team/ 3rd level students 1439-1440 Phases of Mic.Growth • Four phases of Bacterial Growth: • 1. Lag Phase: • Period of adjustment to new conditions. • Little or no cell division occurs, population size doesn’t increase. • Phase of intense metabolic activity, in which individual organisms grow in size. • May last from one hour to several days.

  19. microbiology team/ 3rd level students 1439-1440 Phases of Mic.Growth • 2. Log Phase: • Cells begin to divide and generation time reaches a constant minimum. • Period of most rapid growth. Number of cells produced > Number of cells dying • Cells are at highest metabolic activity. • Cells are most susceptible to adverse environmental factors at this stage as radiation & antibiotics

  20. microbiology team/ 3rd level students 1439-1440 Phases of Mic.Growth • 3. Stationary Phase: • Population size begins to stabilize. Number of cells produced = Number of cells dying • Overall cell number does not increase. • Cell division begins to slow down. • Factors that slow down microbial growth: • • Accumulation of toxic waste materials • • Acidic pH of media • • Limited nutrients • • Insufficient oxygen supply

  21. microbiology team/ 3rd level students 1439-1440 Phases of Mic.Growth • 4. Death or Decline Phase: • Population size begins to decrease. Number of cells dying > Number of cells produced • Cell number decreases at a logarithmic rate. • Cells lose their ability to divide. • A few cells may remain alive for a long period of time

  22. Microbial Genetics microbiology team/ 3rd level students 1439-1440

  23. microbiology team/ 3rd level students 1439-1440 Microbial Genetics • Is the science of heredity; includes the study of genes, how they carry information, how they are replicated & how they are expressed

  24. microbiology team/ 3rd level students 1439-1440 Related terminologies • Gene: it is the unit of heredity. It is a segment of DNA that carries, in its nucleotide sequence, information for specific biochemical or physiologic property. • Phenotype: All the heritable physical characters of the organism (Eye colour in humans, resistance to antibiotic in bacteria ….. etc.) • Genotype: It means the information in the DNA that control the phenotype.

  25. microbiology team/ 3rd level students 1439-1440 Microbial Genetics • Structure and function of genetic material : 1- DNA : Deoxyribonucleic acid contains the genetic instructions for the development and function of living things 2- RNA: Ribonucleic acid 3- Nucleotides composed of : • Phosphate group • Pentose sugar • Nitrogenous base

  26. microbiology team/ 3rd level students 1439-1440 Genetic Materials

  27. microbiology team/ 3rd level students 1439-1440 Molecules of Genetics • The main molecules of genetics are called nucleic acids. • All the genetic information are stored as a sequence of bases through nucleic acids mainly in DNA and in RNA in some RNA viruses.

  28. microbiology team/ 3rd level students 1439-1440 Structure of DNA • DNA (Deoxyribonucleic acid serves as organism’s genetic material. • It is divided into functional units (genes). • Most of DNA is double stranded. • The two strands held together by hydrogen bonds between A and T or G and C • It consists of non- identical, complementary base sequence

  29. microbiology team/ 3rd level students 1439-1440 Nucleotide The basic structure of DNA molecules is the Nucleotide

  30. microbiology team/ 3rd level students 1439-1440 Structure of RNA RNA (Ribonucleic acid): • Structurally similar to DNA except: • Most of RNAs are single stranded. • Sugar is ribose instead of deoxyribose. • Uracil base instead of thymine base

  31. microbiology team/ 3rd level students 1439-1440 Differentiation between DNA & RNA RNA functionally differ from DNA in which : • Some of RNAs are used as messenger molecules (mRNA) to transfer information from DNA to protein • Some of RNA as a part of ribosomes (rRNA ). • Some are adaptor molecules(tRNA) Few RNA only acts as a genetic material like DNA

  32. microbiology team/ 3rd level students 1439-1440 Function of DNA in Microbiology • I- Replication : which means that one DNA molecule gives two DNA molecules each one consists of one strand from the original DNA and the other strand is newly formed one • II- Gene expression (protein synthesis):The mechanism by which the sequence of nucleotides in a gene determines the sequence of amino acids in a protein occurs in the following steps: • A.Transcription • B. Translation • C. post-translationalprocesses

  33. microbiology team/ 3rd level students 1439-1440 Transcription • The process by which a ssRNA (single stranded RNA) is formed by RNA- polymerase using DNA as a template, this RNA is called mRNA (messenger RNA).

  34. microbiology team/ 3rd level students 1439-1440 PATHOGENIC PROPERITIES OF MICROBES

  35. microbiology team/ 3rd level students 1439-1440 MICROBIAL PATHOGENICITY • Factors that Influence the degree of Pathogenicity and the Progression of Infection and Disease include: • 1- Host factors: Age, sex, ethnicity, nutrition (diet), hormonal status; personal hygiene and immune status; Underlying disease or medical condition; Antibiotic or drug usage; Presence of foreign object (e.g., splinter, catheter, sutures, etc.); Innate differences between hosts • 2- Microbial factors: Bacterial virulence factors; Inoculum size (dosage) External factors (e.g., crowding; seasonal variations; hygiene, sanitation and public health; food processing, storage and preparation; etc.

  36. microbiology team/ 3rd level students 1439-1440 MICROBIAL PATHOGENICITY To cause disease a pathogen must: •  Gain access to the host.  Adhere to host tissues. •  Penetrate or evade host defenses. •  Damage the host, either directly or accumulation of microbial wastes

  37. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Virus • Viruses have mechanisms to evade host defenses. viruses grow inside host cells to hide from immune defense. • Kill immune cells e.g. HIV. • Cytopathic effects: - The visible effects of viral infection on host cell. Some effects will kill the cell and some will just change the cells. • Viruses stop DNA, RNA and/or protein synthesis e.g. Herpes virus block mitosis.

  38. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Virus • Lysosomal autolysis of host cells e.g. Influenza: bronchiolar epithelium. • Production of inclusion bodies (visible viral parts inside the cell) can identify a particular virus e.g. Rabies virus: Negri bodies. • Syncytium formation (neighboring cells fuse together) e.g. Varicella Zoster virus. • Change in cell function e.g. Measles, production of interferon by host cell (triggers host immune response), induce antigenic changes on host cell surface (triggers destruction of infected cell by host immune response)

  39. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Fungi • They produce toxins causing allergies or disease e.g. -chronic sinusitis. • Stachybotrys: headaches, vomiting, mental disturbance. Invasive systemic mycosis in immune compromised patients e.g. Candida. • Mushrooms: mycotoxins may be hallucinogenic or deadly effect.

  40. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Protozoa • They can grow inside host cells causing lysis e.g. Malaria (Plasmodium) • They use host cells as food source and produce wastes that cause disease.

  41. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Algae • It produces neurotoxin substances e.g. shellfish poisoning

  42. microbiology team/ 3rd level students 1439-1440 Pathogenic Properties of Helminths 1- Cellular damage evokes symptoms2- Use host tissue for their own growth3- Produce large parasitic masses4- Presence of parasite interferes with host function5- Parasite's metabolic waste can cause symptoms

  43. microbiology team/ 3rd level students 1439-1440 CHAIN OF INFECTION

  44. microbiology team/ 3rd level students 1439-1440 introduction • The standard model of infectious disease causation. • It has 3 corners (vertices). • Agent:A microbe that causes disease. • Host:An organism that harbors disease. • Environment:External factors that allows disease transmission.

  45. microbiology team/ 3rd level students 1439-1440

  46. microbiology team/ 3rd level students 1439-1440 Dynamics of transmission Communicable diseases are transmitted from the reservoir/source of infection to susceptible host through .

  47. microbiology team/ 3rd level students 1439-1440 I. Source or reservoir • These are natural habitat of infectious agents in which an infectious agent normally lives and multiplies. • Examples are; • Human reservoirs • Animal reservoirs (zoonotic diseases) • Reservoir in non-living things.

  48. 1. Human reservoirs • Type: • Incubatory • Convalescent • healthy Cases Carriers • Primary case • Index case • Secondary cases • Portal of exit: • Urinary • Intestinal • Respiratory • others • According to spectrum of disease: • Clinical cases • (Mild/severe-typical/atypical) • Sub-clinical cases • Latent infection cases • Duration: • Temporary • Chronic microbiology team/ 3rd level students 1439-1440

  49. microbiology team/ 3rd level students 1439-1440 2. Animal reservoirs (zoonotic diseases) • Infection disease that are transmissible under natural conditions from vertebrate animals to man, e.g. rabies, plague, bovine tuberculosis etc.

  50. microbiology team/ 3rd level students 1439-1440 3. Reservoir in non-living things • Soil and inanimate matter can also act as reservoir of infection. E.g. soil may harbor agents that causes tetanus, anthrax etc.

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