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Categorising bacteria in purple and pink

When confronted with a new bacteria there are a series of simple tests that can be carried out to give a rough idea of the properties of the bacteria you are dealing with. One of the simplest and most useful tests is known as "Gram staining" which is a process of staining cells either purple or pink depending on the properties of their cell walls. It was discovered by Christian Gram who wasn't initially trying to find a test for bacteria, he just wanted to make them visible.

Gram staining colours the bacteria either purple, in which case they are referred to as "Gram positive," or pink which are known as "Gram negative". Although Christian Gram didn't realise it at the time, this different…

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Gram Positive vs Gram Negative

Being able to differentiate bacterial species is important for a host of reasons, from diagnosing infection or checking food safety, to identifying which species it is that gives a cheese it’s fantastic character. Bacterial species, and even specific strains can be differentiated using a number of molecular techniques such as PCR, quantitative PCR, genome sequencing and mass spectrometry. But even without getting into the molecular nitty gritty, there are phenotypic differences between groups of bacteria that can be used to differentiate them.

Gram Positive vs Gram Negative Bacteria

Here is a look at the differences between Gram positive and Gram negative bacteria and why telling them apart is important.

Gram Positive vs Gram Negative Bacteria and the Fight Against HAIs

Gram-positive bacteria, those species with peptidoglycan outer layers, are easier to kill - their thick peptidoglycan layer absorbs antibiotics and cleaning products easily. In contrast, their many-membraned cousins resist this intrusion with their multi-layered structure. Therefore, infection prevention techniques must ensure that they can breach the thick peptidoglycan layer of the Gram-positive bacteria but also get through the many layers of the Gram-negative bacteria. However thin their peptidoglycan layer, Gram-negative bacteria are protected from certain physical assaults because they do not absorb foreign materials that surround it (including Gram's purple dye). Imagine a spacecraft with a series of airlocks. Any intruder would have to make their way through these airlocks before entering the ship. Such is the case with gram-negative bacteria. Their additional membrane allows them to control what reaches the inner airlock, enabling them to sequester or even remove threats in that space between the membranes (periplasmic space) before it reaches the cell itself.

Gram-Positive vs Gram-Negative Bacteria- 31 Differences with Examples

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Gram-Positive vs. Gram-Negative Bacteria

The major structural difference between Gram-positive and Gram-negative bacteria is the thickness of peptidoglycan and the presence of the outer membrane. Gram-negative bacteria have a thin peptidoglycan layer covered by an outer lipid-containing membrane (lipopolysaccharide layer), whereas Gram-positive bacteria have thick peptidoglycan and no outer membrane.