Chapter Summary


  • Identifying a pathogen enables us to:
    • Use appropriate antibiotics, if necessary.
    • Anticipate possible sequelae.
    • Track the spread of the disease.


  • Selective media are used to inhibit growth of one group of organisms while permitting growth of others (such as Gram-positive bacteria versus Gramnegative bacteria). This technique is often used to prevent growth of normal microbiota while permitting growth of pathogens.
  • Differential media exploit the unique biochemical properties of a pathogen to distinguish it from similar-looking nonpathogens.
  • Bacterial species can be identified with biochemical analyses, molecular techniques (for example, PCR), and/or immunological methods (for example, ELISA).
  • Viral diseases are often diagnosed using immunological tests, such as ELISA, that measure the presence of antibody or antigen, or by real-time quantitative PCR.
  • Fluorescent antibody staining can rapidly identify organisms or antigens present in tissues.


  • Special collection precautions must be taken when collecting specimens from abscesses of suspected anaerobic etiology.
  • Common specimens include blood, pus, urine, sputum, throat, stool, and cerebrospinal fluid.
  • Specimens from sites containing normal microbiota must be handled differently than specimens taken from normally sterile body sites.


  • Various levels of protective measures are used in handling potentially infectious biological materials.
  • Category I agents are generally not pathogenic and require the lowest level of containment.
  • Category II agents are pathogenic but not typically transmitted via the respiratory tract. Laminar flow hoods are required.
  • Category III agents are virulent and transmitted by respiratory route. They require laboratories with special ventilation and air-lock doors.
  • Category IV agents are highly virulent and require the use of positive-pressure suits.


  • John Snow founded the discipline of epidemiology.
  • Epidemiology examines factors that determine the distribution and source of disease.
  • Endemic, epidemic, and pandemic are terms for different frequencies of disease in different geographic areas.
  • Finding patient zero (the index case) is important for containing the spread of disease.
  • Molecular approaches using PCR and nucleic acid hybridization are used to identify nonculturable pathogens and to track disease movements.
  • Bioweapons, when they have been used, typically kill few people but incite great fear.
  • The CDC has assembled a list of select agents with bioweapon potential.


  • Emerging diseases can spread quickly around the world as a result of air travel.
  • Modern technology and urban growth have provided opportunities for new diseases to emerge.
  • Multidisciplinary collaboration among ecologists, veterinarians, clinicians, and other scientists is necessary for devising appropriate strategies aimed at disease intervention and epidemic prevention.