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Grouping bacteria by Gram status Bacteria can be divided into two main groups according to the external structure of the bacterial cell: Grampositive and Gram-negative.1 A simple technique called Gram staining identifies Gram-positive bacteria as dark purple and Gram-negative bacteria as pink.2 Gram-positive • Clostridium difficile • Staphylococcus aureus Cell wall Provides the cell with its structure and helps it tolerate adverse conditions. The cell wall is made up of peptidoglycan, a complex mesh of sugars and amino acids.1,3 • Enterococcus spp. • Streptococcus pneumonia Cell membrane Controls what goes in and out of the bacteria. The inner membrane is also where bacteria generate their energy supply.1 Gram-negative • Klebsiella pneumoniae • Escherichia coli • Neisseria gonorrhoeae Cytoplasm Gel-like substance that contains nutrients essential to the functioning of bacteria.1 • Acinetobacter • Pseudomonas aeruginosa • Haemophilus influenzae Plasmid Contains the genetic blueprint of the bacteria.1 Studded with protein pores that can expel antibiotics from the bacteria4 Thick cell wall2,3 No outer membrane2,3 Thin cell wall2,3 Loose outer wall means many substances, including antibiotics, diffuse easily in and out of the cell2 Gram status and resistance Outer membrane that can prevent antibiotics from entering the bacteria5 Antibiotic resistance is a lethal and growing problem. Differences between Gram-positive and Gram-negative bacterial cell walls result in varying susceptibility to the different types of antibiotics.2,5,6 Gram-negative bacteria are generally more dangerous than Gram-positive bacteria. They have developed resistance against nearly all available antibiotic options. They are able to share their genetic material, allowing this resistance to spread more broadly and quickly.6 There is an urgent need to find new antibiotics, especially against Gram-negative bacteria. References 1. 2. 3. 4. 5. 6. Phillips J, et al. The Biology of Disease. 2nd ed. Blackwell Publishing, Oxford, UK: 2001. Medical Microbiology. Available at: http://www.ncbi.nlm.nih.gov/books/NBK7986/#A698. Last accessed March 2016. Gould JL, Keeton WT. Biological Science. Volume 2. 6th ed. W.W. Norton & Company, London, UK: 1996. Murakami S, et al. Nature 2006;443:173–9. Rang HP, et al. Pharmacology. 5th ed. Churchill Livingstone, London, UK: 2003. Centers for Disease Control and Prevention. Available at: http://www.cdc.gov/drugresistance/pdf/ar-threats-2013-508.pdf. Last accessed March 2016.