11 Facts About Gram-positive bacteria

In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.

Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope.

Conversely, gram-negative Gram-positive bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells, making the cell wall more porous and incapable of retaining the crystal violet stain.

Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall.

All gram-positive bacteria are bounded by a single-unit lipid membrane, and, in general, they contain a thick layer of peptidoglycan responsible for retaining the Gram stain.

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In contrast to gram-positive bacteria, all typical gram-negative bacteria are bounded by a cytoplasmic membrane and an outer cell membrane; they contain only a thin layer of peptidoglycan between these membranes.

In general, gram-positive bacteria are monoderms and have a single lipid bilayer whereas gram-negative bacteria are diderms and have two bilayers.

The spore-forming Gram-positive bacteria can again be divided based on their respiration: Bacillus is a facultative anaerobe, while Clostridium is an obligate anaerobe.

Gram-positive bacteria are capable of causing serious and sometimes fatal infections in newborn infants.

Novel species of clinically relevant gram-positive bacteria include Catabacter hongkongensis, which is an emerging pathogen belonging to Bacillota.

Transformation among gram-positive bacteria has been studied in medically important species such as Streptococcus pneumoniae, Streptococcus mutans, Staphylococcus aureus and Streptococcus sanguinis and in gram-positive soil bacterium Bacillus subtilis, Bacillus cereus.