PCM

• Pathogen: A disease-causing microorganism that can invade our systems and resist defenses by producing capsules or enzymes
• Some bacteria release toxins that can seriously affect health
• A delicate balance exists between our defenses and disease-producing mechanisms of the environment
• Defenses resist the disease-producing capacity, but when overwhelmed, disease results
• After becoming established, an infected subject may recover completely, suffer temporary or permanent damage, or die
• Outcome depends on many factors
• Pathology: Scientific study of disease, dealing with pathogenesis
• Pathogenesis: Manner in which a disease develops, concerned with structural and functional changes brought about by diseases with their final effect on the body
• Infection: Invasion and colonization of the body by microorganisms
• Disease: Occurs when an infection results in deviation from a state of health, an abnormal state where part or all of the body is not properly admired or is not capable of carrying out its normal function
• Few microorganisms are pathogenic, some benefit the host
• Normal microbiota: Microorganisms that establish more or less permanent residence and colonize but do not produce disease under normal conditions
• Estimated that a typical human body harbors around 10^14 bacteria
• Transient microorganisms may be present for several days, weeks, or months, then disappear
• Principal normal microbiota in normal regions of the body have first-in-core features in that specific location of their residence
• Location of the normal microbiota in the human body:

  • Skin
  • Genital tract
  • Mouth
  • Respiratory tract
  • Nose
• • Example: Normal bacteria in the genital region maintain a pH of 3.5-4.5, inhibiting the growth of Candida albicans
  • Disruption of microbiota population can lead to conditions like vaginitis
  • Streptococcus in the mouth produces compounds that prevent the growth of gram-negative bacteria
  • E. coli in the large intestine produces bacteriocins that inhibit the growth of pathogenic bacteria like Salmonella and Shigella
  • Clostridium difficile in the large intestine can cause diseases ranging from mild diarrhea to severe pseudomembranous colitis
• Relations between the normal microbiota and the body:

  • Normal microbiota can benefit the host by preventing the overgrowth of harmful microorganisms through microbial antagonism
  • Microbial antagonism involves competition among microbes
  • Normal microbiota protects the host against colonization by pathogenic microbes by competing for nutrients, producing substances harmful to invading microbes, and affecting conditions like pH and oxygen levels
  • Imbalance between host microbiota and pathogenic microbes can lead to disease
• Types of relationships between normal microbiota and the host:

  • Commensalism: one organism benefits while the other is unaffected
  • Example: Bacteria in the eye contribute to defense and inhibit harmful bacteria growth
  • Mutualism: benefits both organisms
  • Example: Bacteria in the large intestine synthesize vitamin K and B vitamins in exchange for nutrients from the host
  • Opportunistic organisms: potentially pathogenic organisms that cause infection when host defenses are compromised
  • Example: Tooth decay and gum disease caused by bacteria in the normal oral microbiota
• Pathogens carried by some individuals:

  • Salmonella can cause intestinal diseases
  • Adenoviruses cause respiratory diseases
  • Neisseria meningitidis can cause meningitis
  • Streptococcus pneumoniae can cause pneumonia
• Cooperation among microorganisms helps maintain balance in the microbiota and contributes to overall health
• Etiology of infectious diseases:

  • Some diseases, like polio, have well-known etiological agents
  • Others, like chronic fatigue syndrome and Epstein-Barr virus, have unknown etiologies
  • Not all diseases are caused by infectious agents; e.g., hemophilia is inherited, osteoarthritis and diabetes are degenerative diseases
  • We will focus on infectious diseases caused by microorganisms
• Robert Koch's work:

  • German physician who established that microorganisms cause specific diseases
  • In 1877, published papers on anthrax, demonstrating that Bacillus anthracis bacteria were always present in diseased animals but not in healthy ones
  • Conducted experiments by inoculating blood samples from infected animals into healthy ones, which resulted in the disease and death of the healthy animals
  • Repeated experiments with consistent results, showing that anthrax is caused by microorganisms (bacteria)
  • Used the same method to prove Mycobacterium tuberculosis causes tuberculosis
• • Koch's research laid the foundation for studying the etiology of infectious diseases today
• Koch's postulates:

  1. The same pathogen must be present in every case of the disease

  2. The pathogen must be isolated from the diseased host and grown in pure culture

  3. The pathogen from the pure culture must cause the disease when inoculated into a susceptible laboratory animal

  4. The pathogen must be isolated from the inoculated animal and shown to be the original organism causing the disease
• Robert Koch played a major role in establishing that microorganisms caused specific diseases
• Koch demonstrated that Bacillus anthracis bacteria were always present in the blood of animals with anthrax
• Koch's experimental requirements for determining the etiology of infectious diseases are known as Koch's postulates
• Koch's postulates:

  • The same pathogen must be present in every case of the disease
  • The pathogen must be isolated from the diseased host and grown in pure culture
  • The pathogen from the pure culture must cause the disease when inoculated into a susceptible laboratory animal
  • The pathogen must be isolated from the inoculated animal and shown to be the original organism causing the disease
• Diseases can be classified based on how they behave within a population
• Communicable diseases spread from one host to another, directly or indirectly
• Non-communicable diseases are caused by microorganisms that normally inhabit the body or by microorganisms introduced into the body from outside sources
• The occurrence of a disease can be described in terms of its incidence, prevalence, and frequency
• Incidence is the fraction of a population contracting the disease during a specific period
• Prevalence is the fraction of the population having the disease at a specific time
• Sporadic diseases occur only occasionally, endemic diseases are constantly present in a population, epidemic diseases affect many people in a short period, and pandemic diseases occur worldwide
• Emerging infectious diseases are new or changing diseases that challenge public health officials
• Factors contributing to emerging infectious diseases include changes in pathogens, host susceptibility, and ecological factors
• Diseases can be classified based on their severity or duration
• Acute diseases develop rapidly but last a short time, chronic diseases develop slowly and are continuous or recurrent, subacute diseases are intermediate, and latent diseases have inactive causative agents that become active later