Vitec Antimicrobial - Mechanism of action

 

Technical summary for 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride

 

A general structure for 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride (TMAQ) is shown as Figure 1.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1:  Structure of 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride

 

Hydrolysis of the oxymethyl groups at the silane end of the molecule are used to covalently bond the TMAQ to a variety of solid matrices [5].  Isquith and colleagues report favourable binding of TMAQ to 28 different surfaces which included cotton fabrics, wood, plastic and ceramics [6].  Large numbers of TMAQ molecules can be bound to a surface because TMAQ molecules will bind with other TMAQ molecules forming polymers of the type shown below as Figure 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2:  Polymerisation of TMAQ on binding to a matrix.  OR are other TMAQ molecules.  Reproduced from Gottenbosa et al. [5]

 

Once bonded, the positively charged nitrogen on the TMAQ molecule confers a net positive charge to the coated surface and the densely-packed fatty acid tails generate a region of hydrophobicity just above the surface [5,7].  Both of these characteristics are important for bacterial kill.  It is widely acknowledged that quaternary ammonium salts in solution can interact with the lipid bilayers of bacterial plasma membranes [8].  However, Isquith and colleagues [6] and Gottenbosa and colleages conclude that immobilized hydrophobic TMAQ molecules still interact with the bacterial membranes.  Both groups speculate that the hydrophobic nature of the fatty acid tails allows membrane insertion and that the highly packed organisation TMAQ tails causes physical membrane disruption, electrolyte leakage and ultimately cell death.  Furthermore, the cytoplasm of all bacterial cells has a net negative charge relative to the environment. Although there exists a high concentration of protons on the external side of bacterial plasma membranes, it is believed that bacterial cells are still attracted towards the positively charged coated surface further promoting cellular lysis.

A powerful advantage of the physical disruption approach exploited by TMAQ is that the mechanism used for cell death minimizes selective pressure on bacterial populations.  Thus the AM is unlikely to cause the development of resistance in target bacteria. 

 

Lay-person’s summary of mechanism of action for 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride

 

In brief, the 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride (TMAQ) is irreversibly bound to the surface of a matrix such as wood or linen and will not diffuse away from the fabric.  TMAQ acts by physically disrupting cells that come in direct contact with the tail of the chemical which extends outwards from the surface to which it is bound.  Direct contact is required to kill a cell and unlike most antimicrobials (AM), the TMAQ chemical is not consumed by the process.  A simplified diagram which attempts to explain how the TMAQ AM works is depicted as Figure 3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3:  Mechanism of action of the 3-(trimethyloxysilyl) propyl dimethyl octa decyl ammonium chloride–based AM. 

 

The AM acts as a “molecular sword” physically piercing any bacterial cells which are in the proximity of the AM tail.  The mechanism is similar to the manner in which a pin physically pierces the skin of a balloon which then ruptures due to a large amount of pressure being applied to a small puncture.