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Diagnostics

Gram Staining Positive Bacteria

1 year, 6 months ago

3183  0
Posted on Mar 29, 2018, 9 p.m.

Gram positive bacteria are cells that display a purple colour in Gram staining procedure, which cell wall structure includes teichoic acids and a thick peptidoglycan layer. Gram staining was developed in the 1800s and was one of the first laboratory techniques taught to help classify microorganisms based on cell wall structural differences to distinguish between Gram negative and positive bacterias.

 

Gram staining distinguish cells into Gram negative and positive bacteria by providing a colour contrast. Addition of crystal violet stain to a bacterial smear is done to begin the process which is followed by applying iodine to a form a complex that fixes to crystal violet stain within the cells. Positive CV ions compose crystal violet which penetrate the cell wall and membranes of both Gram bacterias, addition of either acetone or alcohol will achieve decolourization, counterstaining is produced with application of another stain such as safranin, with the differences between colour stains serving to distinguish between negative and positive Gram bacteria as a result of their different cell wall structures. Gram negative bacteria will not retain crystal violet stain as the decolorization step disintegrates their outer membrane, whereas red/pink colour which indicates Gram negative bacteria is achieved as a result of the addition of the counterstain. Crystal violet stain is retained by Gram positive bacteria which is indicated by purple coloration which counterstain will not effect because it is a lighter colour.

 

Gram positive bacteria cell wall structure consists of periplasmic space enclosed between a thick peptidoglycan layer and the plasma membrane, which in comparison to Gram negative bacteria the periplasmic space is smaller in volume and cell was is thicker, with the cell wall being composed of several peptidoglycan layers, highly cross linked peptide chains, and a structure based on glycan backbone. Presence of teichoic acids within cell walls are specific characteristics of Gram positive bacteria, which are anionic polyol phosphate polymers that serve to provide rigidity to cell walls by way of anchoring to plasma membrane or through covalent attachment to peptidoglycan. Anionic polymers have similar functions to outer membranes of Gram negative proteins by mediating interactions, acting as scaffold for extracytoplasmic enzymes, and influencing permeability during cell wall growth.

 

Gram positive bacteria lack in an outer membrane making them more susceptible to treatment with antibiotics, but certain bacterial strains can display antimicrobial resistance. MRSA is an example of a common Gram positive pathogen that is resistance to B-lactam antimicrobials including penicillin, of which are prescribed as first line therapy for staphylococcal infections because of efficacy; resistance to these drugs requires a second line of agents which can complicate treatments and have negative impacts on patient outcomes.

 

Effectiveness of antibiotics on Gram positive bacteria is decreased due to antimicrobial resistance to mechanisms such as B-lactamase production and modifications to target site of the antibiotic. Genetic determinants of antibiotic resistance are transmitted between bacteria via vertical and horizontal transfer with several genes being capable of being inserted in an integron leading to build up of resistance to multiple antimicrobials. Strategies for therapeutic treatment of MRSA and other resistant bacteria include combination treatment with nonconventional drugs and development of new drugs, and higher antibiotic dosages.

 

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