Gram-positive bacteria are a group of bacteria that have a thick cell wall composed primarily of a substance called peptidoglycan. This thick peptidoglycan layer retains a stain called crystal violet during the Gram staining procedure, making Gram-positive bacteria appear purple or blue when viewed under a microscope.
Gram-positive bacteria generally lack an outer lipid membrane, which is present in Gram-negative bacteria. Due to the absence of this outer membrane, Gram-positive bacteria are more susceptible to certain antibiotics that target cell wall synthesis, such as penicillin.
Gram-positive bacteria encompass a wide range of genera and species, including well-known pathogens such as Staphylococcus aureus, Streptococcus pyogenes, and Clostridium difficile, as well as beneficial bacteria like Lactobacillus and Bacillus species used in probiotics and industrial applications.
The classification into Gram-positive or Gram-negative bacteria is a fundamental characteristic used in microbiology and has implications for bacterial identification, antibiotic susceptibility testing, and understanding bacterial physiology and pathogenesis.