Introduction in Diagnostic Bacteriology

• Culture techniques such as streak plates, deep inoculation and pour plates allow isolation of distinct bacterial colonies from mixed cultures.
• Microbiology is the study of certain nonliving entities as well as certain living organisms
• Microbes are said to be ubiquitous, meaning they are found everywhere
• • Parasites: subdivided into single-celled organisms (protozoa) or multi-celled organisms (worms and bugs)
• Microbes are subdivided into four groups:

  • Viruses: very simple microbes, consisting of nucleic acid, a few proteins, and (in some) a lipid envelope, completely dependent on the cells they infect for their survival and replication
  • Bacteria: with both RNA and DNA, metabolic machinery for self-replication, and a complex cell wall structure (ASEXUAL), prokaryotic - simple unicellular organisms
  • Fungi: subdivided into single-celled organisms (yeasts) or multi-celled organisms (molds), with a few medically important members existing in both forms (dimorphic fungi)
• Pathogens are disease-causing microorganisms such as bacteria, fungi, protozoans, and viruses
• True Pathogen refers to an organism that will cause disease in a healthy host
• Opportunistic Pathogens refer to organisms that will cause disease in an immunocompromised host
• Pathogenicity refers to the ability of an organism to cause disease in a host organism
• Virulence refers to the degree of pathogenicity; the power by which a pathogen can cause severe disease
• Pathogenic determinants/virulence factors refer to any genetic, biochemical, or structural features that enable a pathogen to cause disease in a host organism
• Endogenous Infection arises from colonizing flora
• Infection refers to the entry, invasion, and multiplication of pathogens in or on the host body system, resulting in subsequent tissue injury and progression to overt disease
• Exogenous Infection arises from invading pathogens from the external environment
• Acute Infection has a rapid/sudden onset of signs and symptoms, usually severe to fatal that may lead to death
• Chronic Infection has a gradual onset of signs and symptoms, usually mild to moderate that may progress to long-standing infection
• Disease is an altered health state in an infected host
• Infectious Disease is an illness caused by a pathogen that invades body tissues and causes damage
• Communicable Disease is an infectious disease capable of spreading from person to person
• Symptoms refer to any subjective evidence of disease, usually perceived by the patient such as headache, dizziness, etc.
• Signs refer to readily observable evidence of disease, usually physical manifestations such as rashes, bleeding, etc.
• Normal Flora are bacteria in or on different sites of the body that usually do not harm the host unless the host defense is compromised
• Colonization refers to the establishment of a substantial number of microorganisms usually in the skin or mucosa but there is no penetration of tissues
• Anton van Leeuwenhoek was the first person to see live bacteria and protozoa, known as the "Father of Microbiology" and "Father of Bacteriology"
• Louis Pasteur demonstrated that different types of microbes produce different fermentation products, introduced the terms "aerobes" and "anaerobes", and developed vaccines to prevent diseases like chicken cholera, anthrax, and swine erysipelas
• Robert Koch made significant contributions to the germ theory of disease, discovered spores in B. anthracis, developed methods of fixing, staining, and photographing bacteria, and discovered the bacteria that causes tuberculosis and cholera
• John Tyndall provided initial evidence that some microbes in dust and air have high heat resistance, and Ferdinand Cohn clarified reasons why heat might fail to eliminate all microorganisms, establishing the concept of "sterile" as completely free of all life forms and virus particles
• Dr. Oliver Wendell Holmes observed fewer infections in mothers who gave birth at home, Dr. Ignaz Semmelweis showed infections in the maternity ward were due to physicians coming from the autopsy room, and Joseph Lister introduced aseptic techniques to reduce microbes in medical settings and prevent wound infections
• Careers in Microbiology include Bacteriologist, Phycologists, Protozoologists, Mycologist, Virologists, Cell Biologists, and genetic engineers who transfer genetic material from one cell type to another
• The Gram stain differentiates between gram-positive and gram-negative bacteria by using crystal violet dye and iodine solution.
• Microscopic examination involves observing bacterial colonies under a light microscope at low power magnification (LP) and higher power magnification (HP).
• Microbiology:

  • Study of certain nonliving entities as well as certain living organisms
  • Microbes are ubiquitous, meaning they are found everywhere
  • Microbes are subdivided into four groups:
  • Viruses: very simple microbes, consisting of nucleic acid, a few proteins, and a lipid envelope
  • Bacteria: with both RNA and DNA, metabolic machinery for self-replication, and a complex cell wall structure (ASEXUAL)
  • Fungi: subdivided into single-celled organisms (yeasts) or multi-celled organisms (molds)
• • Protozoa: subdivided into single-celled organisms (protozoa) or multi-celled organisms (worms and bugs)
• Pathogens:

  • Disease-causing microorganisms such as bacteria, fungi, protozoans, and viruses
  • Types of pathogens:
  • True Pathogen: causes disease in a healthy host
  • Opportunistic Pathogens: cause disease in an immunocompromised host
  • Pathogenicity: ability of an organism to cause disease
  • Virulence: degree of pathogenicity; the power by which a pathogen can cause severe disease
  • Pathogenic determinants/virulence factors: genetic, biochemical, or structural features that enable a pathogen to cause disease
• Infection:

  • Refers to the entry, invasion, and multiplication of pathogens in or on the host body system
  • Types of infection:
  • Endogenous Infection: arising from colonizing flora
  • Exogenous Infection: arising from invading pathogens from the external environment
  • Acute Infection: rapid/sudden onset of severe symptoms
  • Chronic Infection: gradual onset of mild to moderate symptoms
• Disease:

  • Altered health state in an infected host
  • Infectious Disease: illness caused by a pathogen invading body tissues and causing damage
  • Communicable Disease: capable of spreading from person to person
  • Symptoms: subjective evidence of disease
  • Signs: observable evidence of disease
• Normal Flora:

  • Bacteria in or on different sites of the body that usually do not harm the host unless the host defense is compromised
  • Synonyms: Indigenous Flora, Resident Flora, Normal Microbiota
  • Colonization: establishment of a substantial number of microorganisms without tissue penetration
• Earliest Known Infectious Diseases:

  • First recorded epidemic
  • Epidemics of plague, smallpox, rabies, anthrax, dysentery, etc.
  • Treponema pallidum first appearance in Europe in 1493
• Pioneers in the Science of Microbiology:

  • Anton van Leeuwenhoek: first to see live bacteria and protozoa
  • Louis Pasteur: demonstrated different microbe fermentation products, introduced aerobes and anaerobes, developed vaccines
  • Robert Koch: significant contributions to the germ theory of disease, discovered spores in B. anthracis and bacteria causing tuberculosis and cholera
• Careers in Microbiology:

  • Bacteriologist: specializes in the study of bacteria
  • Phycologists (algologists): study algae
  • Protozoologists: study protozoa
  • Mycologist: study fungi
  • Virologists and cell biologists: study viruses, genetic engineers