Bacterial Pathogenicity Lecture Notes PDF

BACTERIAL PATHOGENICITY DR. MERVAT ABDEL-BASSER TOHAMY  Important Definitions  Infection: is the invasion or colonization of the body by pathogenic microorganisms; most of infections end without occurrence of pathological changes and manifestation which is called subclinical, sile...

BACTERIAL PATHOGENICITY DR. MERVAT ABDEL-BASSER TOHAMY  Important Definitions  Infection: is the invasion or colonization of the body by pathogenic microorganisms; most of infections end without occurrence of pathological changes and manifestation which is called subclinical, silent or abortive infections.  Disease: A process by which the organism enters into a relationship with the host with occurrence of pathological changes and appearance of clinical manifestations. N.B.: Not all infections will proceed to be diseases but all diseases are originally infections.  Pathogenicity: The ability of a bacterial species to produce disease.  Virulence: is the degree of pathogenicity (that is determined by virulence factor) Dr.Azza Abdulazim  Classification of bacteria according to their Relationship to host Saprophytic Parasitic bacteria bacteria live freely in nature live in or on a living host Pathogenic Commensals (flora) Opportunistic Always cause Never cause May or may not a disease a disease cause a disease Opportunistic bacteria potentially pathogenic Opportunistic bacteria cause diseases in following condition: 1-In immunocompromised patients 2- Change their normal habitat Dr.Azza Abdulazim  Stages of the Infectious Process 1. Source of infection 2. Mode of transmission 3. Portal of entry (mucous membranes, skin, parenteral route). 4. Portal of exit (urine, stool, blood, secretions) Source of infection - Exogenous or Endogenous (By Normal flora) - Hospital(nosocomial) , Community , environment - man (case or carrier), animal Dr.Azza Abdulazim  Mode of transmission of infections : - 1- Contacts Direct Indirect (contaminated objects. 2- Droplet 3- Air borne During cough, Sneezing formed from the evaporation of respiratory droplets Droplet large in size , travel short Droplet Nuclei small in size, carrry by distance air for long distance e.g influenza tuberculosis 3- Ingestion 4- Vector borne (mosquitoes). 5- Blood borne: (sharp injuries or needle sticks).  Virulence Factors of Bacteria Structures or products that enable the organism to cause disease. Virulence Factors may be: 1. Adherence factors: Enable the bacteria to attach to the host surface:  fimbriae or glycocalyx (Glycocalyx of Staph & Streptococci adhere the organism strongly to heart valves.  Pili or fimbriae as present in E. coli that allow it to attach to urinary tract epithelium. Dr.Azza Abdulazim  2- Invasion Factors Enzymes:  Catalase of staphylococci  Leukocidin which destroy PMNL & macrophages.  IgA protease which degrades IgA.  Deoxyribonuclease that breaks down DNA. 3- Antiphagocytic factors:  Capsule (e.g. Strept. Pneumoniae)  Cell wall proteins of Gram+ve cocci as A protein in Staph and M protein in Strept pyogenes  Coagulase enzyme of Staphylococci.  Biofilm: A biofilm is an assembly of surface-associated microbial cells that is enclosed in an extracellular polymeric substance matrix. Dr.Azza Abdulazim  Biofilms Biofilms are sticky, surface-attached agglomerations of bacteria that are embedded in an extracellular matrix and provide protection from antibiotics and phagocytosis. Biofilms may comprise an increased number of so-called “persister” cells, Its formation occurs on a three-step process, involving attachment (in which bacteria adhere to a surface) and subsequent maturation (when a 3D structure evolves). Finally detachment occurs and moves to a new location where the biofilm becomes extended (e.g S. epidermidis)  5- Toxin production: Bacterial toxins are either: exotoxins or endotoxins Dr.Azza Abdulazim  Comparison between Exotoxin & Endotoxin Exotoxins Endotoxins Source Secreted by living Part of the cell wall organisms both Gram-positive of Gram-negative organisms. (mainly) and Gram-negative Liberated upon cell Disintegration or death Examples C. diphtheriae E. coli endotoxin Coding genes Chromosome, Plasmids or Chromosome Bacteriophages Antigenicity Highly antigenic Poorly antigenic Nature Protein LPS (lipid A) Heat stability Unstable Stable Detoxification Can be converted into toxoid Can not be converted into toxoid Specificity Every toxin has specific action Non-specific in action (all give fever and septic shock) Toxicity Highdulazim Low Toxoid: detoxified toxin obtained by treatment of exotoxin with formalin to remove its toxicity and retain its antigenicity. It can be used for immunization. Dr.Azza Abdulazim