Procedure & Assessment
BioLabTests offers the absorption inoculation method using the bacterial species Staphylococcus aureus and Escherichia coli. The method involves growing the bacteria in a liquid culture medium and then suspending them in nutrient broth that affords bacteria the potential to grow during testing.
Controls are always used to validate growth results of test bacteria and validate the test. Test specimens are aseptically inoculated with the bacterial suspensions in triplicate (3 control specimens and 3 testing fabric specimens), ensuring that the inoculum is directly pipetted onto the fabrics and not touching the surface or the cap of the vials.
Three of the control specimens and three of the antibacterial testing specimens are used for zero time after inoculation and the remaining six specimens are used for the contact time after 18h to 24 h incubation.
Therefore, immediately after the inoculation, a neutralising medium (Soybean-Casein Digest Broth with Lecithin & Polysorbate 80 or SCDLP) is added into each of the six vials containing control and antibacterial testing specimens to determine initial microbial concentrations at zero time. The vials are shaken, plated onto nutrient agar medium (Plate Count Agar or PCA) and the plates are incubated at 37°C for 24h.
Additional inoculated control and test fabrics are incubated at 37°C for 18h to 24h in sealed containers. After incubation, SCDLP medium is added into each, shaken, plated onto PCA plates and the plates are incubated at 37°C for 24h.
The colony forming units are then counted and the reduction of microorganisms relative to initial concentrations and the control fabrics is calculated. The results are generally reproducible and the method runs triplicate experimentation, which increases the precision of individual tests and overall experimental accuracy. It is also possible to modify the method to suit a client’s specific needs.