Antibacterial activity of MgAg1% sticks

Ag⁺ has an important antimicrobial effect (BRETT, 2006). This effect depends on the superficial contact between Ag⁺ and the enzymatic systems of the respiratory chain with altered DNA synthesis (BRETT, 2006; HIDALGO and DOMINGUEZ 1998).

Nevertheless, Ag ions continue to be used as antibacterial agents. They constitute excellent bacteriostatic or bactericidal agents, the main advantage of which is their activity against Gram-negative bacilli (particularly Pseudomonas spp. and Proteus spp.). Their antimicrobial power and their non-accidental exposure to Ag⁺ is increasing their use in drugs, dental amalgams, and covered catheters. Since toxicity of Ag⁺ ions is poorly characterized, different aspects of cellular toxicity mechanisms produced by this antiseptic in cultured human fibroblasts were studied further (LIEDBERG and LUNDEBERG, 1898; HOLLINGER, 1996).

AgNO₃ greatly inhibits the growth of bacteria. Ag⁺ can be effective against a wide range of microorganisms, including aerobic, anaerobic, negative and

Gram-Discussion

positive bacteria, yeast, fungi, and viruses. The antimicrobial effect of Ag⁺ can be explained by various mechanisms. Ag⁺ interferes with the respiratory chain in the cytochromes of microbacteria; additionally, Ag ions also interfere with components of the microbial electron transport system, bind DNA, and inhibit DNA replication (LOK et al., 2006; LANSDOWN, 2002) and that was discussed before in literature review.

The soluble form of Ag⁺ is the most toxic to bacteria (TILTON and ROSENBERG, 1978; TREVORS, 1987) and Ag⁺ toxicity can be reduced by precipitation of the metal by phosphates, sulphides and chloride ions (TREVORS, 1987).

Our results showed that the number of the bacterial colonies (E. coli and S. aureus) incubated with the supernatants of degradation of MgAg1% in NaCl, decreased 5 times compared to the control, when cultivated on petri dishes. The measured amount of silver which induced the antibacterial effect was 0.2-0.3 mmol/l as measured before after 15 days of incubation. Furthermore, the preliminary results of bouillion dilution test showed antibacterial effect of the degrading supernatants (MgAg1% sticks incubated in NaCl) the on the growth of bacterial colonies (E. coli and S. aureus).

Interestingly, another study by STARODUB and TREVORS (1989) stated that E. coli strain R1 cultures treated with AgNO3 concentrations of 1, 0.5 and 0.3 mM, did not have an extended lag phase, but the final cell biomass was slightly reduced in the presence of any of AgNO3 concentrations. Strain Rl was capable of growth in the presence of 0.1 mM AgNO3, but not at 0.5 or 1.0 mM, even when the incubation period was extended to 48 h.

In addition, we could observe that cells grown in the presence of AgNO3 were capable of binding more Ag⁺. Ag⁺ is not an essential metal and it is unlikely that there is a specific energy dependent transport system for it, but Ag⁺ could enter cells via a transport system for an essential metal.

Moreover, the results we obtained from BRT-MRL screening test was clear that Geobacillus stearothermophilus shift brilliant black colour to yellow or colourless at concentrations equal or below 0.003 mmol/l of AgNO3 solution, which indicates that concentrations of AgNO₃ solution starting from 1 up to 0.01 mmol/l has antibacterial effect. Moreover, different volume of degradation medium of MgAg1% shifted the

Discussion

blue colour to yellow or colourless at volume equal or above 3 ml, which indicates the presence of antibacterial effect at 1 and 3 ml volume of degradation medium of MgAg1%.

Quite interestingly, the measured Ag⁺ amounts at 1 and 3 ml volume were about 0.02-1 mmol/l. Surprisingly, these amounts of Ag⁺ are the same amounts which had antibacterial effect, when the bacteria were treated with different concentrations of AgNO3 solution.

JANSEN et al. (1994) and SCHIERHOLZ et al. (1998) stated that the effect of Ag ions is continuous and long lasting due to the oligodynamic effect of elementary Ag⁺. Moreover, BOWSWALD et al. (1999) and OLSON et al. (2002) stated that the ability of many bacteria to produce a biofilm is reduced and the likelihood of bacterial colonization is decreased when Ag⁺ is introduced. This result supports our idea that MgAg 1% sticks may have antibacterial effects. That is why our idea could be attractive for further applications and interesting for other investigation.

Hopfully, our study could be a useful aid for the treatment of mastitis. MgAg1% sticks would share in the treatment of mastitis at dry off period alone or combined with some antibiotics depending on the concentration of Ag⁺. As a result, we can help in saving some of the economical losses (vet. costs, labour costs, antibiotics costs and intreferring with the manufacturing of dairy products) and culling rates, when mastitis appeared. In addition, protecting the animal wealh and providing a safer human consumption

Finally, our hypothesis was confirmed, namely that MgAg1% alloys are of a good biocompatibility action, did not have any cytotoxic effect on primary mammry cell cultures, while MgAg1% alloys had a slight cytotoxic effect on murine cell lines at high concentrations, or affect the metabolic activities and did not enhance the production of some inflammatory mediators. In addition to its ability to be degraded, however, the solubility of Ag⁺ was known to be poor and at the end the most valuable knowledge is about the antibacterial effect of the alloy which makes it of interest to use it in wider applications for treating mastitis in dry off period, whether to be used in some drugs or as ancillary treatment.

Discussion