Ensure you use a pencil as many inks are removed by the reagents used in the staining procedure.Ģ. Label a clean glass microscope slide with your sample identification. Gram stain procedure - Preparing a sampleġ. This is because the wall structure affects the cell’s ability to retain the crystal violet stain used in the Gram staining procedure which can then be visualized under a light microscope. The two key features that lead to the differing visualization properties of Gram positive and Gram negative species are the thickness of the peptidoglycan layer and presence or absence of the outer lipid membrane. The diagram below illustrates the differences in the structure of Gram positive and Gram negative bacteria. Teichoic and lipoteichoic acids not presentĭifference in structure of Gram positive vs Gram negative bacteria Gram positive bacteriaĭistinctive purple appearance after gram stainingīacteria include all staphylococci, all streptococci and some listeria speciesīacteria include enterobacter species, salmonella species and pseudomonas species Gram negative bacteria have a much thinner peptidoglycan cell wall, but in addition they have an outer membrane containing lipopolysaccharides surrounding the cell and are consequently termed diderms. Gram positive bacteria are surrounded by a single thick peptidoglycan cell wall and are therefore termed monoderms. One such useful classification – if a bacterium is Gram positive or Gram negative - is based on the structure of bacterial cell walls.
Depending on the characteristic being studied, bacterial species may be broken down into broad groups, but taken together this information can narrow the possible identities greatly.
This includes characteristics like their shape (bacilli vs cocci for example), growth in particular nutrients and preference for high or low oxygen environments. But even without getting into the molecular nitty gritty, there are phenotypic differences between groups of bacteria that can be used to differentiate them. 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. Download a pdf version of the article hereīeing 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.
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