Calorimetric studies of microbiological systems

Using mass-cultivation and cryogenic storage, aliquots of standardised inocula giving calorimetric power-time outputs with a variability of 2 to 4% were used to test the antimicrobial efficacy of Aquacel-Ag compared with silver nitrate on P. aeruginosa, S. aureus, and a 50:50 mixed culture in both nutrient broth and simulated wound fluid (SWF). Results show that a small amount (1 cm2) of wound dressing containing 3.4x10-4 mol dm-3 of silver is sufficient to both inhibit cell growth within 1-2 hours of contact and to kill all S. aureus (~3.4 cfu mL-1) cells over a 24 hr period and all P. aeruginosa (~3.4x107 cfu mL-1) cells over a 72-h period. A parallel study using solubilised silver nitrate showed that to produced a similar antimicrobial effect, 12 times more silver ions (in the form of silver nitrate) were needed compared with Aquacel-Ag. By determining in Dmax (the minimum inhibitor concentration), Aquacel-Ag in SWF was found to be 1,9-fold more efficient for S. aureus, 2.4-fold more efficient for P. aeruginosa and 3.2-fold more efficient in inhibiting growth of mixed cultures, compared with silver nitrate. Therefore, significantly less silver can be incorporated into the dressing thereby reducing the risk of agrya. Also, using inductively-coupled plasma-optical emission spectroscopy (ICP-OES), the importance of the sustained release of Ag ions is highlighted and is suggested to be a contributing factor to the increased antimicrobial efficacy of Aquacel-Ag in SWF compared to Aquacel-Ag in nutrient broth. A standardised calorimetric output (reproducibility of 93.7%) from S. cerevisiae was used to study the thermodynamics/kinetics of the antimicrobial action of silver nitrate and tea tree oil. The maximum rate of kill was 8.4x107 cfu mL-1 killed per minute for silver nitrate, and 6.5x107 cfu mL-1 killed per minute for tea tree oil; i.e. 23% more quickly for silver nitrate.EThOS - Electronic Theses Online ServiceGBUnited Kingdo