Chapter 7: Microscopic Examination

purulence

pus, or the condition of containing or discharging pus

gram postive bacteria

purple

-thick peptidoglycan wall

Gram-negative bacteria

pink/red

-thin peptidoglycan wall

smears from swabs

-Don't use swab from inoculated media

-Collect two swabs

-Don't rub swab on slide

-Roll back and forth

smears from thick liquids or semisolids

such as feces

-swab immersed in the specimen for several seconds

-thin spread of material on the slide

Smears from thick, granular, or mucoid materials

-Two-slide technique

-Place slide on top of other slide and pull slides away from each other

smears from thin fluids

-dropped, not spread

-done on well-marked area

cytocentrifugation

mechanical process in which centrifugal force is used in a machine to deposit cells on a glass slide for staining and viewing

Protein stains

gram-negative

cytocentrifuge technique

1. small aliquots of fluid are placed in the cytocentrifuge holders

2. material is spun for 10 minutes

3. slide is removed; if deposit of cells is too heavy, a portion of the cellular deposition can be smeared

4. the sediment is fixed and decontaminated in 70% alcohol for 5 minutes

simple stains

one dye is used; reveals shape, size, and arrangement

-directed toward coloring the forms and shapes present

differential stains

directed toward coloring specific components of the elements present

probe-mediated stains

are directed specifically at identification of an organism

Wright-Giemsa stain

visualizes bacteria, yeasts, parasites, and viral inclusions

Leifson stain

flagella

Methylene blue stain

metachromatic granules

-Corynebacterium diphtheriae

Acid-fast stains

differential stain used to identify acid-fast organisms such as members of the genus Mycobacterium

Ziehl-Neelsen stain

Use to stain Acid-fast bacteria

-sediments for mycobacteria

-partial acid-fastness of Nocardia spp.

Fluorochrome stain

preferred acid-fast stain

-sediments for mycobacteria

Kinyoun stain

This stain is a modified Ziehl-Neelson stain, with no heating step

-for Crytosporidium and Cyclospora parasites in stool specimens

Calcofluor white stain

A fluorochrome that stains chitin found in the cell wall of fungi. Viewed under UV light. Fungi appear white to blue.

-for bronchoalveolar fungi and some parasitic cysts

-differentiates them from background materials of similar morphology

gross examination

Viewing specimens with the naked eye

-eyes, magnifying glass, and dissecting microscope

bright-field microscope

most widely used; specimen is darker than surrounding field; used for live and preserved stained specimens

dark-field microscope

brightly illuminated specimens surrounded by dark field; used for live and unstained specimens

phase-contrast microscope

light microscope that enhances contrast; useful in examining living, unstained cells

fluorescence microscope

Instrument used to visualize a specimen that has been labeled with a fluorescent dye

electron microscope

microscope that forms an image by focusing beams of electrons onto a specimen

transmission electron microscope

An electron microscope used to study the internal structure of thin sections of cells

scanning electron microscope

An electron microscope used to study the fine details of cell surfaces

Background material: amorphous debris

Debris without form or shape that is made up of necrotic tissue or cells, protein fluids, or mucus

Background material: black particulate debris

smoke inhalation, crack cocaine

Background material: Charcot-Leyden crystals

Bronchial asthma (eosinophil membranes)

Background material: Epithelials with contaminating bacteria

passage of specimen through contaminated area during collection

Background material: Curschmann's spirals present (sputum)

Bronchospasm, obstruction, asthma

Background material: Epithelial cells

epithelial surface involved or adjacent to collection site

Background material: Intracellular organisms

inferred association in infection

Background material: Local material

reflection of collection site

Background material: mononuclear cells present

chronic inflammation

Background material: mononuclear cells

blood cells that have a single, round nucleus, such as lymphocytes and monocytes

Background material: mucus

irritation of glandular surface

Background material: purulence

acute inflammation, exudation

Background material: red blood cells

trauma, hemorrhage

colony-forming units

A number of separable cells on the surface of a semisolid agar medium that create a visible colony.

monomicrobial

infection caused by a single species

polymicrobial

infection caused by multiple species

Direct smear examination of clinical samples is a rapid means to identify presumptively the etiologic agents of infectious disease. (True or False)

True

The presence of an infectious disease process can be assessed on a direct smear based on which of the following?

a. the presence of numerous inflammatory cells

b. the morphology of the bacteria present

c. gram stain reaction of bacteria present

d. the presence of numerous epithelial cells

A. the presence of numerous inflammatory cells

Which of the following stains may be used for direct smear examination?

a. gram stain

b. acid-fast stain

c. wright or giemsa stain

d. calcofluor white stain

e. all of the above

E. all of the above

Which of the following stains is best used to detect mycobacterial organisms in clinical samples?

a. gram

b. giemsa

c. acid-fast

d. india ink

C. acid-fast

Calcofluor white is a colorless dye that binds with which of the following structures?

a. cell wall containing mycolic acid

b. chitin

c. peptidoglycan layer

d. metachromatic granules

B. chitin

chitin

Polysaccharide found in arthropod exoskeletons and fungal cell walls.

Cytocentrifugation is an excellent method for which of the following types of samples?

a. heavily contaminated

b. nonviscous fluids

c. thick purulent material

d. filled with mucus

B. nonviscous fluids

A monobacterial type of infection can be immediately suspected based on the direct microscopic examination of the clinical sample. (True or False)

True

In a Wright-Giemsa-stained smear, bacteria would appear as which of the following colors?

a. red

b. blue

c. purple

d. orange

B. blue