Expert: Christopher Rosch - 1/9/2006

Question
What is gram positive bacteria?

Answer
Hello Vignesh,

a simple means to classify bacteria are staining methods. The Gram staining is one such method, developed some 100 years ago, which allows to differentiate between Gram-positive and Gram-negative bacteria; the first stay colored while the latter don't retain the Gram dye. This staining method can be applied to most bacteria if certain standard protocols are followed:
http://en.wikipedia.org/wiki/Gram_stain

Gram-positive bacteria have thick and complex cell walls as outermost boundary. Gram-negative bacteria have thin walls which are surrounded by another membrane (simply called outer membrane). A simple explanation for the success of Gram staining is that thick cell walls can store more dye than thin cell walls and therefore appear darker.

The taxonomic classification Gram-positive / -negative is historically founded and obsolete in modern bacteriology. Still, the Gram stain is an important test to roughly classify bacteria and is generally the very first test when dealing with unidentified bacteria.

Typical Gram-positive bacteria belong to the bacterial classes..
Bacilli (including Bacillus anthracis, Staphylococcus, Lactobacillus),
Clostridia (including Clostridium botulinum) and
Actinobacteria (including actinomycetes, Frankia, Corynebacterium and streptomycetes).

(Gram-negative bacteria include Escherichia coli, Salmonella and rhizobia.)

Best regards,
Christopher