Silver Hydrosol Info


Case Study: Inhibition of Staphylococcus Aureus by various silver products (III)

June 2001: Natural-Immunogenics Corp.


The purpose of this study was to compare and contrast the inhibition of various types of silvers on both normal and antibiotic resistant strains of Staphylococcus aureus ("Staph"). This was accomplished by inoculating healthy Staph with silver on standard YT plates, then placing them in a 37° C incubator overnight.

Materials and Methods.

Each 95mm sterile polystyrene plate was filled with 5mm of YT media consisting of 0.5% sodium chloride, 0.6% yeast extract, 0.8% tryptone and 2% agar. A small 3 mm scrape of Staph was re-suspended in sterile 18 MW lab water and diluted. To each 1 mL dilution of staph cells, 100ul of each silver was added and then left to sit for 7 minutes. After the appointed time, five 10µl spots of each diluted strain containing silver were arranged on a YT plate.

  • The YT media was autoclaved and poured into sterile plates and allowed to dry.
  • Two strains of Staph received from the New York Hospital of Queens.
    1. B14192 – wildtype/ normal strain - Renamed S-1
    2. B14310 – antibiotic resistant (MRSA) - Renamed S-2
  • An optical density (O.D590) of 0.135 was achieved by using a 3 mm scrape of both S-1 and S-2, which were re-suspended in 1250µl of lab pure water. Then a 10:1 dilution series was performed on each strain.
  • Silver was added to each dilution of S-1 and S-2; the cultures were then agitated and allowed to sit until spotted onto the YT plate. The exposure time of each dilution to the silver was seven minutes. This protocol was repeated for each of the four different silver materials.
  • Four different types of colloidal silver were used:

    1. Sovereign Silver (SS)

    ppm = 10.06
    pH = 6.73

    Clear in color

    2. Colloidal Silver (XX4A)

    a. ppm = 30.00
    b. pH = 6.54
    Yellow in color

    3. Silver Nitrate (AgNO3)

    a. ppm = 10.00
    b. pH = 2.35
    Clear in color

    4. Colloidal Silver (XX7D)

    a. ppm = 10, 100, and 200
    b. pH = 7.73
    Very dark amber in color
  • Positive control plate -No colloidal silver added to S-1 or S-2 cultures
    Negative control plate -No Staph or silver added to check for contamination
  • Plates then placed in a 37°C incubator overnight.


Qualitative results can easily be seen on each plate. The positive control for S-1 grew out 4.5 spots, represented by (++++½) and the positive control for S-2 grew out 4.5 spots when colloidal silver was not present (++++½). A (-) represents no Staph grew on the plate. The effectiveness of the silver products for each company can be compared by the number of spots or +’s seen in the graph.

Inhibition of Staph

  S-1 S-2
+ control ++++½ ++++½
Sovereign Silver ½ -
XX4A ++½ ++½
AgNO3 ++++½ ++++½
XX7D 10 ppm ++++½ ++++½
XX7D 100 ppm +++ +++
XX7D 200 ppm ++ +

Results of inhibition with various silver products at 7 Minutes

  S-1 S-2


In this experiment Sovereign Silver (SS) almost totally eradicated the bacteria, while XX4A at 30ppm and XX7D at 100 ppm and 200 ppm were only partially effective. Silver nitrate and XX7D at 10 ppm appear to be only marginally effective at inhibiting the growth of Staphylococcus aureus.