Antibacterial Properties of Magnesium Alloy AZ31B: In - vitro Studies using the Biofilm-forming Bacterium Pseudomonas sp.

Abstract

Magnesium (Mg 2+ ) alloys attract the focus of industries such as the telecom and computer industries and medical and household appliances due to their strength and weightlessness. However, magnesium is one of the major cell components of bacteria, which implicates it in microbial attachment and growth. To understand its involvement in bacterial attachment that leads to microbiologically influenced corrosion (MIC), laboratory exposure studies using a magnesium alloy AZ31B were carried out with the biofilm forming bacterium Pseudomonas sp. A high rate of bacterial attachment (calculated using image processing software), viz. 14.33% ± 6.72% and 33.69% ± 10.25%, was observed for 1 and 2 days' exposure, respectively. However, the area of bacterial adhesion had reduced to 2.71% ± 1.36% by the sixth day. The total viable count (TVC) on the surface of the experimental coupons also showed the maximum value on the first day, and reduced to a very low number by the sixth day. The Mg ion concentration in the experimental medium and in the control showed a gradual increase over the time period. The maximum concentrations were 25.5 and 23.5 mg ml m 1 for the control and experimental samples, respectively, by the sixth day. Consequently, the pH also increased to 9.7 and 9.8 in the control and experimental media, respectively. The coupon surface pH also rose to more than 11 by the third day. Magnesium reacts with water, producing magnesium hydroxide, which forms a protective film over the coupon surface in addition to dissolution into the medium. The formation of such a film and the dissolution of Mg elevated the pH of the coupon surface and the medium to the alkaline range. The combined effect of high pH and a high concentration of Mg ion adversely affected the growth and survival of Pseudomonas sp. both in the medium and on the coupon surface resulting in only a modest amount of attachment and very low TVCs by the sixth day. Thus, Mg alloys exhibited antibacterial properties that prevented bacterial attachment and formation of biofilm.