Experiment on the Antimicrobial Effectiveness of Montmorillonite Clays

Despite having a great immune system, we, humans, cannot still fight dangerous pathogens such as bacteria or fungi and our contemporary civilization is still dependant on other various means of coping with them; thus we rely on modern-day technology to sustain this need. In this research, we pursue the study of experimental montmorillonite clays (also known as MMT) and their antimicrobial effectiveness, in an effort to combat or at least keep the pathogens at bay.

Since MMT clays were shown to absorb heavy metal ions such as silver, copper, and zinc, thus acting as carriers, consequently the resulting clays were transformed in efficient antimicrobial fighters, mainly because metal ions aforementioned have been used for sterilizing actions since centuries.

MMT-AgNO3 turned out to be extremely efficient against pathogenic bacteria such as E. coli and S. aureus. This combo displayed 99% efficacy against bacterial growth mentioned above, as well as an extraordinary blood and tissue biocompatibility by manifesting low cytotoxicity and low hemolytic activity [1].

Moreover, by adding different-sized silver nanoparticles in MMT, the antimicrobial activity against gram-positive (ie S. aureus) and gram-negative bacteria (ie E. coli and K. pneumoniae) was studied, resulting in higher efficacy with the modification in size of Ag nanoparticles by case [2].

In addition, it was observed that positively charged ions of silver (Ag+) can attract the membrane of Gram-negative bacteria to the surface of the experimental MMT clay, thus destroying the bacteria efficiently [3].

The use of silver loaded montmorillonites (Ag-MMT) was also shown to improve the shelf life of fresh fruit salads by inhibiting the microbial growth. It also improved the sensorial qualities of the fresh-cut fruit samples stored in an active packaging based on Ag-MMT coating by leading to longer and better preservation, thus representing a viable solution for the packaging industry against the fast decaying of fresh fruits [4].

Likewise, researches noted that Ag-MMT had a slow-release property, besides the already-known antibacterial efficiency, thus making it a great low-cost material for different purposes, whether it would be medical or food-related industry [5].

Even though silver sulfadiazine (AgSD) is known for its cytotoxicity towards fibroblasts and keratinocytes by delaying the healing of the wounds, the negative effects are greatly reduced when it is combined with montmorillonite and chitosan nanocomposites, thus maintaining the antimicrobial effectiveness of AgSD against S. aureus, S. pyogenes, E. coli, and P. aeruginosa [6].

A strong antimicrobial effect was noted when Zn2+-Ce3+ were added to MMT, thus demonstrating a great efficacy in combating a wide spectrum of harmful pathogens like E. coli, S. aureus, C. albicans, and Mucor, due to the synergistic effect of Zn and Ce [7].

Active bio-films based on chitosan, glycerol, and MMT-CuO exhibited significant antimicrobial activity against foodborne pathogenic bacteria S. aureus, B. cereus, E. coli, and P. aeruginosa with 99% effectiveness. By adding a 3% concentration of MMT-CuO to chitosan films, an increment in tensile strength and elongation rate was observed, while the water vapor permeability and oxygen permeability decreased. Due to these characteristics, chitosan-MMT-CuO films would constitute a promising novelty in the food packaging industry [8]. These characteristics were also mentioned by Wang et al. [9] who found that MMT nano-form clay was found to enhance the thermal stability and also the sturdiness and elastic modulus of the polymer matrices, the benefic effect being directly proportional to the added quantity.

Moreover, MMT-Cu(II) demonstrated its efficacy in vitro against E. coli and S. choleraesuis by inhibiting their growth, more specifically by damaging the bacterial cell wall, by causing bacterial enzyme leakage and by inhibiting the bacterial respiratory metabolism. These promising results could lead to new non-toxic antibiotic alternatives that can act against dangerous pathogens found in the gastrointestinal tract of animals destined for human consumption such as pigs [10].

It was also remarked the antibacterial potential of chlorhexidine acetate-montmorillonite (CA-MMT) on S. aureus and P. aeruginosa by strongly inhibiting their growth and it was concluded that MMT clays can act as potential drug delivery carriers with controlled-releasing properties [11]. CA-MMT organo-clay displayed potent antimicrobial activity that can last up to one year. The antibacterial activity was enhanced as the CA loading increased thus making it suitable for the creation of novel antibacterial materials [12].

Likewise, the efficacy of Curcumin loaded MMT was demonstrated against S. mutans by preventing the bacterial proliferation to take place on experimental dental models [13]. It was also shown that MMT clays can be successfully used as reinforcing dental fillers, therefore making them a great solution as adhesives between dentin and restorative resin [14].

Clay minerals have been bringing important benefits to people and society. Montmorillonite, an important mineral-clay type, has been gaining recent interest in being used in polymer matrices, due to its versatile characteristics – especially the one about being a carrier for those materials possessing antimicrobial properties.