微生物染色(英文)

Role of Special Histochemical Stains in Staining Microorganisms

Rashmil Saxena, BFA, HT(ASCP)CM

Division of Transplantation

Department of Surgery, Indiana University

Indianapolis, IN, USA

M icroorganisms encountered in routine pathology specimens include bacteria, fungi, protozoa and viruses1. Several histochemical stains help to visualize the first three groups of organisms; however, histochemical stains do not offer an advantage over H&E in the visualization of viruses and immunohistochemistry is the preferred method for this purpose. Histochemical stains also help to identify and classify bacteria, fungi and protozoa.

The Giemsa and Gram’s stains help to visualize bacteria as well as classify them on their morphological characteristics. Thus bacteria can be classified into cocci or bacilli and cocci can be further classified into diplococci, staphylococci and streptococci based on their appearances on the Gram and Giemsa stains. The Gram stain also classifies bacteria into Gram-positive and Gram-negative organisms depending upon whether they take up the Gram stain or not; this classification is clinically useful and helps in therapeutic decisions. Some bacteria may not be adequately visualized with the Gram’s and Giemsa stains. Of these, the clinically most significant ones are mycobacteria and spirochetes. Mycobacteria stain with carbol fuschin and resist decolorization with acid-alcohol, leading to their designation as “acid-fast bacilli”. Spirochetes can be stained with a variety of silver stains such as the Warthin-Starry, Dieterle and Steiner stains. Finally, due to the large number of gastrointestinal biopsies in routine practice, a large number of stains are available for visualization of the Gram-negative bacillus, Helicobacter pylori. These include Giemsa, Alcian yellow - toludine blue, Diff-Quik, Genta, and Sayeed stains. A large number of laboratories prefer immunohistochemistry for identification of Helicobacter pylori.

The Giemsa stain highlights several protozoa such as toxoplasma, leishmania, plasmodium, trichomonas, cryptosporidia and giardia. Ameba can be highlighted by the PAS stain due to their large glycogen content. Histochemical stains for fungi are discussed separately in this publication.

Special Stains for Detection of Bacteria

Gram Stain

Utility of the Stain: The Gram stain is used to stain both bacillary and coccal forms of bacteria (Fig. 1). The most basic classification of bacteria consists of dividing them into Gram-positive and Gram negative bacteria based on whether they take up the Gram’s stain or not. Although the exact mechanism of staining is not known, bacteria that have large amounts of peptidoglycan in their walls retain the methyl violet stain, i.e., they are gram positive, whereas those that have more lipids and lipopolysaccharides in their cell walls are Gram-negative. The definite diagnosis of a bacterial species requires culture but the Gram stain provides a good initial indication of the nature of infection.

1 Some microbiologists also include viruses as microorganisms, but others consider these as non-living. Lwoff (1957). “The concept of virus”. J. Gen. Microbiol. 17 (2): 239–53.

T echnical