Diagnosing Infections

1
Chapter 17

• Diagnosing Infections

2
Survey of Microbial Disease

• Methods of identifying unknown microbes fall into
  three categories
• phenotypic - observable microscopic and
  macroscopic characteristics (morphology) as well
  as bacterial physiology or biochemistry
• genotypic genetic make up. Data can produce a
  unique profile of each bacterium. Being used as
  a sole resource for identifying bacteria
• immunological serology (analysis of blood)
  antibody-antigen reactions

3
Phenotypic Methods

• Microscopic morphology fresh or stained
  microorganisms from specimen shape, size, stain
  reaction, cell structures
• Macroscopic morphology colony appearance
  texture, size, shape, pigment, growth
  requirements
• Physiological/biochemical characteristics
  detection of presence or absence of particular
  enzymes or metabolic pathways
• Chemical analysis analyze specific chemical
  composition cell wall peptides, cell membrane
  lipids

4
Genotypic Methods

• Assess genetic make-up
• Culture is not necessary
• Precise, automated methods, quick results

5
Immunological Methods

• Specific antibodies are used to detect antigens

6
Specimen Collection and Laboratory Methods

• Sampling body sites or fluids for suspected
  infectious agent
• Results depend on specimen collection, handling,
  transport and storage
• Aseptic procedures should be used

7
Insert figure 17.1 Sampling sites
8
(No Transcript)
9
(No Transcript)
10
Phenotypic Methods

• Observation
• macroscopic - cultivation colony appearance,
  growth requirements, appropriate media
• microscopic - differential and special stains
  Gram, AFB, fluorescent antibody stains
• Direct antigen/antibody testing
• Biochemical testing physiological reactions to
  nutrients as evidence of the absence or presence
  of enzymes

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15

• It is important to consider whether microbe
  recovered and identified is actually causing the
  disease or simply normal flora

16
Genotypic Methods

• DNA analysis
• assess the proportion of G C nucleotides
  relative to A T content
• determine DNA or ribosomal RNA sequences using
  probes and polymerase chain reactions

17
(No Transcript)
18
Immunological Methods

• Serology attempts to detect signs of infection
  in a patient by identifying specific antibodies
  in vitro
• Visible reactions include precipitates, color
  changes, or the release of radioactivity
• Tests can be used to identify and to determine
  the amount of antibody in serum titer

19
(No Transcript)
20
Agglutination and Precipitation Reactions

• Agglutination testing antibody cross links
  whole-cell antigens, forming complexes that
  settle out and form visible clumps
• blood typing, some bacterial and viral diseases
• Precipitation tests soluble antigen is made
  insoluble by an antibody
• syphilis
• Western blot immunoelectrophoresis separates
  antigens into bands
• HIV

21
(No Transcript)
22
Insert figure 17.10 Cellular\molecular view
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
Complement Fixation

• Detect antibodies that fix complement and lyse
  target cells
• antigen, antibody, complement, and sensitized
  sheep RBCs
• if complement is fixed by the Ag-Ab, the RBCs
  will not be lysed

27
(No Transcript)
28
Immunoassays

• Extremely sensitive to detect trace antigens and
  antibodies
• Radioimmunoassay (RIA) antigens and antibodies
  labeled with radioactive isotopes
• Enzyme-linked immunosorbent assay (ELISA)
  enzyme-antibody complex produces a colored
  product when an enzyme-substrate reaction occurs

29
(No Transcript)
30
(No Transcript)
31
Tests That Differentiate T Cells and B Cells

• Used to evaluate immune dysfunctions such as
  those in AIDS, immunodeficiencies, and cancer

32
(No Transcript)
33
In vivo Testing

• Antigens are introduced directly into the body to
  determine the presence or absence of antibodies
• tuberculin skin test, allergy testing

34
Viral Infection diagnosis