Identification of Bacteria Pathogens

Topics: State highways in Maryland, Washington County, Maryland, Growth medium Pages: 24 (3783 words) Published: September 18, 2012
Identification of Bacterial Pathogens
basic skills in diagnostic bacteriology

Dr.T.V.Rao MD

Dr.T.V.Rao MD


Identification of Microorganisms
• For many students and professionals the most pressing topic in microbiology is how to identify unknown specimens. • Why is this important?

• Labs can grow, isolate and identify most routinely encountered bacteria within 48 hrs of sampling.

• The methods microbiologist use fall into three categories: ♣Phenotypic- morphology (micro and macroscopic) ♣Immunological- serological analysis ♣Genotypic- genetic techniques Dr.T.V.Rao MD


Microbe Identification
• The successful identification of microbe depends on: ♥ Using the proper aseptic techniques. ♥ Correctly obtaining the specimen. ♥ Correctly handling the specimen ♥ Quickly transporting the specimen to the lab. ♥ Once the specimen reaches the lab it is cultured and identified. Dr.T.V.Rao MD 3

Microbe Identification
• Identification measures include:
♣ Microscopy (staining) ♣ growth on enrichment, selective, differential or characteristic media ♣ specimen biochemical test (rapid test methods) ♣ immunological techniques ♣ molecular (genotypic) methods.

• After the microbe is identified for clinical samples it is used in susceptibility tests to find which method of control is most effective. Dr.T.V.Rao MD 4

Microbe Identification

Dr.T.V.Rao MD


Specimen Collection
• Successful identification depends on how the specimen is collected, handled and stored. • It is important that general aseptic procedures be used including sterile sample containers and sampling methods to prevent contamination of the specimen. • E.g. Throat and nasopharyngeal swabs should not touch the cheek, tongue or salvia. • What other precautions must be taken when collecting specimens?

• After collection the specimen must be taken promptly to the lab and stored appropriately (e.g. refrigeration). Dr.T.V.Rao MD 6

Specimen Collection

Dr.T.V.Rao MD


Phenotypic Methods of Identification
• Microbiologists use 5 basic techniques to grow, examine and characterize microorganisms in the lab. • They are called the 5 ‘I’s: inoculation, incubation, isolation, inspection and identification. • Inoculation: to culture microorganisms a tiny sample (inoculum) is introduced into medium (inoculation). • Isolation involves the separating one species from another. Dr.T.V.Rao MD


Phenotypic methods of Identification
• Incubation: once the media is inoculated it is incubated which means putting the culture in a controlled environment (incubation) to allow for multiplication. • After incubation the organisms are inspected and identified phenotypically, immunologically or genetically. Dr.T.V.Rao MD 9

Specimen collection

5 “I” s
inoculation inspection


identification Dr.T.V.Rao MD


Phenotypic Methods
• ‘Old fashioned’ methods via biochemical, serological and morphological are still used to identify many microorganisms. • Phenotypic Methods • Microscopic Morphology include a combination of cell shape, size, Gram stain, acid fast rxn, special structures e.g. endospores, granule and capsule can be used to give an initial putative identification. Dr.T.V.Rao MD 11

Phenotypic Methods
• Macroscopic morphology are traits that can be accessed with the naked eye e.g. appearance of colony including texture, shape, pigment, speed of growth and growth pattern in broth. • Physiology/Biochemical characteristic are traditional mainstay of bacterial identification. • These include enzymes (catalase, oxidase, decarboxylase), fermentation of sugars, capacity to digest or metabolize complex polymers and sensitivity to drugs can be used in identification. Dr.T.V.Rao MD 12

• Magnification
– enhancement of size using ocular and objective lenses.
• Ocular: eyepiece (10X) • Objective: 4X – 100X

– allows for visualization of bacteria, fungi, and parasites, not viruses...
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