What is an endolysin

It is an enzyme used by certain viruses called bacteriophages. These are viruses that infect . Endolysins dissolve a part of the bacterial cell wall called the , an essential part of the virus life cycle.

Whoa! What’s a peptidoglycan cell layer

Bacteria have a cell wall which is composed of peptidoglycans which are largely sugars and proteins which form a mesh around the cell. This mesh-like layer gives strength to the cell wall counteracting the pressure from the fluid-like centre of the bacterium. In essence, the cell wall holds the bacterium together.

endolysin

Endolysins dissolve the peptidoglycan cell wall of bacteria and this results in the cell basically disintegrating by rupture through its defective cell wall and the cell therefore dying. Bacteriophages exploit this mechanism because cell rupture results in the release of virus particles from inside the infected bacterium which can then go on to infect other bacterial cells.

Certain types of bacteria, so called gram positive bacteria have more peptidoglycan than gram negative bacteria. In addition, gram negative bacteria have an outer membrane which protects its peptidoglycan layer.

 

 

This outer membrane means that gram negative bacteria are essentially protected from attack by endolysins. However, gram positive bacteria are susceptible.

So these endolysin-containing creams will then kill all gram positive bacteria on the skin?

No. Endolysins are highly specific for certain types of peptidoglycans which essentially limits them to certain species of bacteria. This means that the risk of bacterial resistance developing is reduced. Also, healthy bacteria in the skin (or other organ) microflora can be left unaffected.

 

Are these the new alternative to antibiotics then?

If these endolysins work in clinical practice, they would certainly be far more desirable than broad-spectrum antibiotics which kill all sensitive organisms during treatment.

Their potential use in the control of food-borne pathogens in food safety, in veterinary medicine in bovine mastitis, plant agriculture and treatment of gram positive bacterial infections in mice have all been investigated.

So should we use these creams ?

The main worry with the use of endolysins administered orally or intravenously is that there are potential risks such as an immune reaction to the endolysin itself or to the bacterial cell proteins that would be released after bacterial cell rupture.

It is thought that endolysins applied as creams may avoid or reduce these risks but with the absence of robust clinical trials, it is difficult to recommend them at all, especially as patients tell me that a 100ml tube of the cream is rather pricey and beyond the reach of many in the population.

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