Microbiology Lecture 3 - PDF

General Microbiology and Immunology Lecture 3 : Virulence factors , Bacterial Growth and Growth Requirements Dr./ Shimaa Mohamed Ali Sphinx University  Virulence Factors Invasi Adherence ve Factors Factor...

General Microbiology and Immunology Lecture 3 : Virulence factors , Bacterial Growth and Growth Requirements Dr./ Shimaa Mohamed Ali Sphinx University  Virulence Factors Invasi Adherence ve Factors Factor s Extracellular Ability to Toxin Antiphagocytic Enzymes Survive Production Intracellular Exotoxins Endotoxins  I. Adherence Factors  These are aggregates of interactive bacteria attached to each other and encased in an exo-polysaccharide matrix, forming a slimy coat on solid surfaces. Bacteria in biofilms are protected from the immune mechanisms of the host and are resistant to antibiotics.  II. Invasive factors This is the ability to invade tissues, multiply and spread rapidly causing the inflammatory process. This may be partly due to the: A. Antiphagocytic action of certain surface components that protect the bacteria from phagocytosis and destruction, e.g.  The capsule of many organisms e.g. Pneumococci.  The "M" proteins found on the  B. Extracellular Enzymes These are substances produced by some bacteria that help the spread, invasion and establishment of microorganisms into the tissues, these include: C. Ability to Survive Intracellular: Some organisms use several mechanisms to allow them to survive and grow intracellular multiply inside phagocytic cells escaping intracellular killing by phagocytic cells e.g. M. tuberculosis which survive by inhibiting phagosome- lysosome fusion.  D. Toxin Production Toxins are bacterial products which have a direct harmful action on tissue cells. They fall into two groups:  1. Exotoxins They are protein toxins secreted by living bacteria and diffuse freely into the surrounding medium i.e. extracellular toxins. The production of most exotoxins is controlled by genes in plasmids or bacteriophages rather than by chromosomal genes. Toxins are specific in action and can be sub- classified according to the organs affected as: Neurotoxins interfere with normal nerve impulses. e.g. Botulinum Toxin Enterotoxins effect cells lining the G.I. Tract. e.g. Cholera toxin Cytotoxins Inhibition of protein synthesis and kill cells  2. Endotoxins These are lipid toxins integral part of the cell wall of Gram-negative bacteria (e.g. E. coli) from which they are liberated when the cell dies and disintegrates. The toxicity of the endotoxin is associated with the lipid A fraction of LPS which is apart of chromosomal genes. Endotoxins are the most important cause of endotoxic or septic shock (fever, hypotension, disseminated intravascular coagulation) and sometimes death due to massive organ failure.  Property Exotoxins Endotoxins Produced by Gram +ve bacteria mainly Gram -ve bacteria only Extrachromosomal Ex. Plasmid, Location of genes Bacterial chromosome bacteriophages Composition Proteins Lipid A fraction of LPS Specific they are classified into: Action neurotoxins, enterotoxins, or Non-specific toxic effects cytotoxins. Fever No Yes Heat stability Labile, destroyed at 60°C Stable at 100°C for 1 hr. Toxicity Strong Weak Immunogenicity Strong Weak Conversion to Yes No toxoid  Toxoid = Exotoxin + formalin nontoxigenic but antigenic Question G.R……? Sometimes, treating a patient who has a gram negative infection with antibiotics can worsen the patient’s condition. Answer because all the bacteria are lysed, releasing large quantities of endotoxin ( non specific and not have a toxoid ).  Pathogenicity of Microorganisms Definitions Pathogenic microorganism (Pathogen) is that capable of causing disease. Opportunistic pathogen is that unable to cause disease in healthy immune-competent people but can infect people whose defenses have been impaired (immune-compromised‫)ضعف المناعة‬. These opportunists are frequent members of the body's normal flora. Virulence is a quantitative measure of the pathogenicity and is measured by the number of the organisms required to cause disease (the infectious dose of bacteria).  1. Transmission from an external source into the portal of entry. 2. Evasion(overcome) of host Stages of primary defenses such as skin. 3. Adherence of microorganism to bacterial host cells. pathogenesis 4. Colonization by growth of the bacteria at the site of adherence. 5. Diseases symptoms caused by toxin production or invasion and inflammation. 6. Evasion (overcome) of host secondary defenses. 7. Progression or resolution of the disease.  Bacterial Growth : 1. Mother or parent cell doubles in size. 2. Divides into two daughter cells similar in genetic character Bacterial to the mother cell. Growth and so, Cell Division Microbial growth is defined as the increase in the number of cells, which occurs by cell division (Binary fission) Binary Fission Thin section of the bacterium Staphylococcus, undergoing binary fission  The generation (doubling) time It is the time required by the bacteria to double its number. It varies from one species to another. It may range from, as little as 20 minutes for the rapid growing E. coli, to more than 24 hours for the slow growing M. tuberculosis.  Phases of Growth If a small inoculum of an actively growing culture is inoculated into a limited volume of fresh liquid medium, the subsequent four phases of growth can be detected: 1. The lag phase 2. The logarithmic phase 3. The stationary phase The Lag Phase Organisms do not increase significantly in number They are metabolically active Grow in size, synthesize enzymes, and incorporate molecules from medium Produce large quantities of energy in the form of ATP The lag phase corresponds the incubation period. The Logarithmic (Exponential)Phase Organisms have adapted to a growth medium. Growth occurs at an exponential (log) rate. The organisms divide at their most rapid rate. In vivo, the logarithmic is analogous to phase of invasion. Bacterial Growth Curve Bacterial Growth Requirements 1. Gaseous Requirement of A. Bacteria Oxygen:  For most organisms, an adequate supply of oxygen enhances metabolism and growth. The oxygen acts as the hydrogen acceptor in the final steps of energy production.  The use of oxygen generates 2 toxic molecules, hydrogen peroxide (H2O2) and the free radical superoxide (O2¯), so in the presence of oxygen the bacteria require 2 enzymes (to eliminate these toxic products): Superoxide dismutase (SOD) Catalase B. Carbon dioxide (CO2): Most bacteria require minute quantities as that present in air. Certain species of bacteria (e.g. the pathogenic Neisseria) require higher concentrations (5-20%), which should be included in the atmosphere surrounding the culture. 2. Nutritional Requirement of Bacteria Bacteria, like all cells, require nutrients for maintenance of their metabolism and for cell division. Two nutritional groups can be distinguished; autotrophs and heterotrophs. Bacterial nutrients which are used for their growth and multiplication in the laboratory is known as culture media. Fastidious organisms are those which require unusually complex nutrients added to the growth media. 3. Moisture Water is essential for bacterial growth as it acts as a vehicle for food transmission. Drying may affect some types of bacteria while others can resist drying for different periods (spores resist dryness for long durations, while delicate bacteria as gonococcus resist dryness only for few hours).  All the processes of growth depend on chemical reaction. The rate of these 4. chemical reactions is influenced by Temperature temperature. bacteria can be classified according to their ability for growth at different degree of temperature as follows: The optimum temperature: It is the temperature of incubation which allows for most rapid growth during a short period of time (12-24 h.). This optimum temperature differs from one species to another. Temperature below the optimum will stop or retard the growth of the bacteria. For this purpose, cooling is used as a method for preserving bacterial strains. When bacteria are later exposed to a favorable temperature for their growth, multiplication will start again. 6. Light Most bacteria are injured by diffuse day light and are killed within few hours by direct sunlight. The action of day light and sunlight is due to the presence of ultraviolet rays bacteria Some which hasmust a bactericidal be exposed action. to a source of light since it is their source of energy. These types of bacteria are saprophytic and known as photosynthetic autotrophic organisms. 7. Bacterial Bi-products Bacterial reproduction causes release of many bi-products: Acids are the most important bi-products due to their action on changing the PH of media. Pigments which may be used for identification of bacteria. There are 2 types of pigments: Toxins which can be used for production of vaccines against the dangerous effect of these microorganisms (toxoid). Protein breakdown products: Some other types of bacteria have proteolytic activity on media containing proteins with production of substances as indole, H2S, NH3 and Co2. Fat breakdown products: Many bacteria are able to decompose fats into glycerol and fatty acids and then to simpler material. The degree by which organism can act on proteins, fats and ferment carbohydrates can be used as a basis for identification and typing of different microorganism (Biotyping). Thank You