BACTE PRELIMS

• Microbiology is a branch of biology dealing with the study of living organisms too small to be seen by the naked eye

  
• Medical Microbiology focuses on medically important microorganisms, their role in human disease, and includes diagnosis, treatment, and prevention of infectious diseases
• Diagnostic Bacteriology is a branch of medical microbiology focusing on the laboratory identification of medically important bacteria by phenotypical and genotypical characterization, including antibiotic susceptibility testing
• Microbes are classified into 4 groups: viruses, bacteria, fungi, and parasites
• Pathogens are disease-causing microorganisms, including true pathogens that cause disease in healthy hosts and opportunistic pathogens that cause disease in immunocompromised hosts
• Pathogenicity refers to the ability of an organism to cause disease, while virulence is the degree of pathogenicity
• Infection refers to the entry, invasion, and multiplication of pathogens in or on the host body system, leading to tissue injury and disease
• Types of infections include endogenous and exogenous based on the source of the pathogen, acute and chronic based on clinical onset, and nosocomial and zoonotic based on etiologic agent
• Disease is an altered health state in an infected host, while infectious disease is caused by a pathogen invading body tissues and causing damage
• Communicable diseases are infectious diseases capable of spreading from person to person
• Symptoms are subjective evidence of disease, while signs are observable evidence of disease
• Normal flora are bacteria in or on 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 in the skin or mucosa without tissue penetration
• Pioneers in microbiology include Anton van Leeuwenhoek, Louis Pasteur, and Robert Koch
• Louis Pasteur introduced the terms "aerobes" and "anaerobes," pasteurization, and the germ theory of disease
• Robert Koch discovered the bacteria causing tuberculosis and cholera, and developed methods for fixing, staining, and photographing bacteria
• John Tyndall provided initial evidence of microbes' heat resistance, while Ferdinand Cohn clarified reasons for heat sterilization failures
• Aseptic techniques were developed by Dr. Oliver Wendell Holmes, who observed lower infection rates in home births compared to hospital births
• Koch's postulates are a set of four criteria used to establish a causal relationship between a microorganism and a disease

  
• Koch's postulates were developed by Robert Koch in the late 19th century and are still used today to identify the causes of infectious diseases
• Koch's postulates:

  • The microorganism must be present in every case of the disease
  • The microorganism must be isolated from the host and grown in pure culture
  • The microorganism must cause the disease when introduced into a healthy host
  • The microorganism must be reisolated from the experimentally infected host
• The diagram of the normal flora of a healthy human person shows different types of microbes living on or in the human body, classified into cellular (bacteria, fungi, protozoa) and acellular (viruses, prions) groups

  
• The traditional Whittaker system of classification divides organisms into three domains: Bacteria, Archaea, and Eukarya, with further subdivisions into kingdoms

  
• The growth curve of a bacterial population over time is divided into four phases: lag phase, logarithmic growth phase, stationary phase, and death phase

  
• Growth curve phases:

  • Lag phase: initial phase of growth, bacteria adapt to the environment
  • Logarithmic growth phase: rapid growth, exponential reproduction
  • Stationary phase: population size remains constant
  • Death phase: population decreases as cell deaths exceed new cell production
• The image shows four types of tubes used in microbiology: slant, slant/deep, deep, and broth

  
• The image illustrates the difference between photochromogens and scotochromogens, two types of pigments produced by bacteria

  
• The urea test determines if a bacterium can produce the enzyme urease, indicated by a color change from yellow to pink

  
• The diagram of the normal flora of a healthy human person shows different types of microbes classified into cellular (bacteria, fungi, protozoa) and acellular (viruses, prions) groups

  
• The image depicts a lactose fermentation test used to determine if a bacterium can produce the enzyme urease

  
• Gram-positive cell walls have a very thick protective peptidoglycan (murein) layer and contain teichoic acid and lipoteichoic acid
• Gram-negative cell walls have a thin peptidoglycan layer, a periplasmic space, and an outer membrane with proteins, phospholipids, and lipopolysaccharide (LPS)
• Guiding rules in the Gram stain reaction of medically important bacteria include that all cocci are Gram-positive except Neisseria, Branhamella/Moraxella, Veilonella
• Acid-fast organisms contain a waxy layer of glycolipids and fatty acids, with Mycobacteria being the most commonly encountered acid-fast bacteria
• Koch's postulates include:

  • The microorganism must be present in every case of the disease
  • The microorganism must be isolated from the host and grown in pure culture
  • The microorganism must cause the disease when introduced into a healthy host
  • The microorganism must be reisolated from the experimentally infected host
• The growth curve of a bacterial population over time is divided into 4 phases: lag phase, logarithmic growth phase, stationary phase, and death phase

  
• In the lag phase, bacteria adapt to their new environment without reproducing
• The logarithmic growth phase is characterized by rapid exponential growth of bacteria
• During the stationary phase, the population size remains constant as new cells produced equal the number of cells dying
• In the death phase, the population size decreases as more cells die than new cells are produced