Principles Of Identification

Microbiologists use various methods to identify organisms cultivated from patient specimens. Although many of the principles and issues about bacterial identification discussed in this chapter are generally applicable to most

Colony form

Punctlform (pinpoint)





Rat Raised Convex


Entire (smooth) Irregular

Figure 7-11 Colony morphologic features and descriptive terms for commonly encountered bacterial colonies.

clinically relevant bacteria, specific information regarding particular organism groups is covered in the appropriate chapters in Part HI.

The importance of accurate bacterial identification cannot be overstated because identity is central to diagnostic bacteriology issues, including:

  • Determining the clinical significance of a particular pathogen (e.g., is the isolate a pathogen or a contaminant?)
  • Guiding physician care of the patient
  • Determining whether laboratory testing for detection of antimicrobial resistance is warranted
  • Determining the type of antimicrobial therapy that is appropriate
  • Determining whether the antimicrobial susceptibility profiles are unusual or aberrant for a particular bacterial species
  • Determining whether the infecting organism is a risk for other patients in the hospital, the public; or laboratory workers (i.e., is the organism one that may pose problems for infection control, public health, or laboratory safety?)

The identification of a bacterial isolate requires analysis of information gathered from laboratory tests that provide characteristic profiles of bacteria. The tests and the order in which they are used for organism identification are often referred to as an identification scheme. Identification schemes can be classified into one of two categories: (1) those that are based on genotypic characteristics of bacteria and (2) those that are based on phenotypic characteristics. Certain schemes rely on both genotypic and phenotypic characteristics. Additionally, some tests, such as the Gram stain, are an integral part of many schemes used for identifying a wide variety of bacteria, whereas other tests may only be used in the identification scheme for a single species such as the fluorescent antibody test for identification of Legionella pneumophila.

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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