Chap 1

• Purpose of Clinical Microbiology

  To isolate and identify pathogenic microorganisms
• Microbiology Lab Provides


  • Direct smears and stains
  • Cultures
  • Molecular analysis
  • Serological testing
  • Antimicrobial susceptibility testing
• Historical classification


  • Based on observable properties such as morphology, biochemical characteristics and antigenic relationships
  • Phenotypical classification then replaced with system based on genetic homology
• Genetic homology


  Classification based on DNA base composition and ratio
• Nucleic acid sequence analysis

  Uses the order of bases along the DNA or RNA sequence and determines similar sequence between two organisms
• When identifying microorganisms, the key features are outlined based on genotypic characteristics, including genes and nucleic acids and phenotypic characteristics including genes and nucleic acids and phenotypic characteristics which is observable
• Species


  Most basic taxonomic group encompasses bacterial strains with common genetic, physiologic, and phenotypic characteristics
• Subspecies


  Subgroups within the species
• Biotypes, subtypes or strains or genotypes

  Microorganisms that share specific minor characteristics
• Genus


  Different species with many important features in common
• Binomial System of Nomenclature

  • Two names - genus and species
  • From Latin and Greek language
  • Genus name is always capitalized
  • Accepted abbreviation include uppercase form of the first letter of the genus with a period
• Infection


  The entrance and multiplication of microorganism in or on a host
• Infectious disease


  An infection with functional and structural harm to host usually accompanied by signs and symptoms
• Pathogen


  Microorganism including bacteria, virus, fungi, and parasites that is capable causing infectious disease
• Stages of infectious disease

  • Incubation period
  • Prodromal period
  • Period of illness
  • Period of decline
  • Period of convalescence
• Symbiotic Relationships


  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  Organisms which live in or on the body of a host, do no harm in this association, but conversely do no good either
• Mutualism


  Both member benefit from the relationship
• Parasitism


  Live in or on the body of the host and do it harm
• Opportunistic pathogens


  Commensals which can trigger disease if allowed to exceed small population sizes
• Modes of Transmission-Routes of Infection

  • Direct transmission
  • Indirect transmission
• Host Defence Mechanisms


  • Innate immunity or natural
  • Acquired immunity
  • Phagocytosis
• Toxins


  • Exotoxin
  • Endotoxin
• Exotoxin


  Protein, soluble & diffusible, heat labile, specific pharmacological action, high immunogenicity, inactivated to form toxoids
• Endotoxin


  Lipopolysaccharide, part of cell wall, heat stable, non-specific, low immunogenicity, do not form toxoid, induce fever
• Robert Hooke observed fruiting structures of molds in 1665 and was the first to describe microorganisms
• Antoni van Leeuwenhoek was the first to describe bacteria in 1676
• Louis Pasteur disproved spontaneous generation
• Robert Koch developed a set of postulates to prove that a specific microorganism causes a specific disease
• Koch's Postulates


  • The suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals
  • The suspected organism should be grown in pure culture
  • Cells from a pure culture of the suspected organism should cause disease in a healthy animal
  • The organism should be reisolated and shown to be the same as the original