Role of Special Histochemical Stains in Staining ... - Dako

Silver Stains (Warthin Starry Stain, Dieterle, Steiner Stains)
Utility of the Stains: Silver stains are very sensitive for the staining of
bacteria and therefore most useful for bacteria which do not stain or
stain weakly with the Grams and Giemsa stains. Although they can be
used to stain almost any bacteria, they are tricky to perform and are
therefore reserved for visualizing spirochetes, legionella, bartonella
and H. pylori.
Principles of Staining: Spirochetes and other bacteria can bind
silver ions from solution but cannot reduce the bound silver. The slide
is first incubated in a silver nitrate solution for half an hour and then
“developed” with hydroquinone which reduces the bound silver to a
visible metallic form. The bacteria stain dark-brown to black while the
background is yellow (Fig. 6).
Auramine O- Rhodamine B Stain
The auramine O-rhodamine B stain is highly specific and sensitive for
mycobateria. It also stains dead and dying bacteria not stained by the
acid-fast stains. The mycobacteria take up the dye and show a reddishyellow
fluorescence when examined under a fluorescence microscope.
Summary
Histochemical stains available for demonstrating microorganisms
include Giemsa stain, Grams stain, carbol fuschin acid-alcohol stain
and a variety of silver stains such as Warthin-Starry, Dieterle and Steiner
stains. The Gram stain allows classification of bacteria into Grampositive
and Gram-negative bacteria. The acid-alcohol stain allows
classification of bacilli into acid-fast and non-acid-fast bacilli. These are
both clinically useful classifications. The silver stains are very sensitive
and help to visualize difficult-to-stain bacteria. Most protozoans are
stained by the Giemsa stain.
Glossary
Bacteria are unicellular organisms that do not contain a nucleus or other membrane-bound
organelles. Most bacteria have a rigid cell wall composed of peptidoglycan. Although there
are exceptions, bacteria come in 3 basic shapes: round (cocci), rod-like (bacilli) and spiral
(spirochetes). Bacteria cause a variety of infections in various organs.
Bartonella is a Gram-negative bacillus which causes cat-scratch disease. The bacilli are
transmitted to humans by cat-bite or cat-scratch.
Chlamydia are Gram-negative bacteria which are unusual because they do not have typical
bacterial cell walls. They are obligate intracellular parasites which means that they can
only survive within cells. Chlamydia cause sexually transmitted diseases and pneumonia
in humans.
Helicobacter pylori is a Gram-negative bacteria which causes inflammation (gastritis) and
ulcers of the stomach. The name derives from the Greek “helix” for spiral and “pylorus” for
the distal end of the stomach.
Legionella is a Gram-negative bacillus so named because it caused an outbreak of
pneumonia in people attending a 1976 convention of the American Legion in Philadelphia.
The organism was unknown till then and was subsequently named Legionella. It causes
pneumonia.
Mycobacteria are bacilli that have a thick and waxy (Latin, myco = wax) cell wall composed
of a lipid called mycolic acid. This cell wall is responsible for the hardiness of this organism
as well as for its staining characteristics. The waxy cell wall is hydrophobic and resists
staining with aqueous stains like the Gram and Giemsa stains. It also resists decolorisation
once stained. Mycobacteria causes tuberculosis, leprosy and infections in patients
with AIDS.
Protozoa (Greek, proton = first; zoa = animal) are unicellular organisms that have a
membrane-bound nucleus and other complex membrane-bound organelles.
Rickettsia are Gram-negative bacteria that like Chlamydia lack typical cell walls and are
obligate intracellular parasites. The rickettsial diseases are primary diseases of animals
(zoonosis) such as the deer which are transmitted to humans by bites of insects like fleas
and ticks. Rickettsial diseases include typhus fever and Rocky Mountain Spotty Fever.
Spirochetes are long Gram-negative bacilli with tightly-coiled helical shapes. Spirochetes
cause syphilis, leptospirosis and Lyme’s disease.
Connection 2010 | 91