| In microbiology, the visualization of bacteria at the | | | | granulomatous lymphadenitis, pneumonitis, pharyngitis, |
| microscopic level is facilitated by the use of stains, | | | | skin infections, and endocarditis. The Firmicutes have |
| which react with components present in some cells | | | | a low G+C content in contrast to the Actinobacteria. |
| but not others. This technique is used to classify | | | | Firmicutes can be cocci or rod-shaped forms. Many |
| bacteria as either Gram-positive or Gram-negative | | | | produce endospores. They are found in various |
| depending on their colour following a specific staining | | | | environments and some are important pathogens, for |
| procedure originally developed by Hans Christian | | | | example Bacillus, Listeria, Staphylococcus, and |
| Gram. Gram-positive bacteria appear dark blue or | | | | Streptococcus. |
| violet due to the crystal violet stain following the | | | | In contrast, strains of Lactobacillus are important for |
| Gram stain procedure; Gram-negative bacteria, which | | | | health and live Lactobacillus bacteria are constituents |
| cannot retain the crystal violet stain, appear red or | | | | of many probiotics. Lactic acid bacteria (LAB) such as |
| pink due to the counterstain. Gram-positive bacteria | | | | Lactobacillus and Bifidobacterium are probiotics that |
| retain the crystal violet due to the amount of | | | | have numerous potential therapeutic properties |
| peptidoglycan in the cell wall. | | | | including anti-inflammatory and anti-cancer activities. |
| Gram-positive bacteria are divided into two main | | | | Lactococcus is an important organism in the food |
| groups: the Actinobacteria and the Firmicutes. The | | | | industry and is used to produce cheese and yoghurts |
| Actinobacteria have a high G+C ratio and include | | | | and other fermented foods. Strains of Clostridium are |
| common soil bacteria and some pathogens, such as | | | | being considered as a means of selectively targeting |
| Mycobacterium and Corynebacterium. Strains of | | | | and destroying cancer cells especially for the |
| Mycobacterium can cause tuberculosis and leprosy. | | | | treatment of solid tumors. |
| Strains of Corynebacterium can cause diphtheria, | | | | |