Introduction
Monitoring bioburden in pharmaceutical, food, hospital settings is crucial for internal control. It serves to validate cleanliness, investigate hospital outbreaks and food contamination, verify baseline surface contamination, and detect individual microorganisms. The use of a kit that enables sample collection, sample preservation, and inactivation of residual disinfectants on surfaces would simplify and standardize monitoring activities. Study aims to assess the performance of the SRK® (Copan Italia, Brescia) in maintaining a panel of bacteria and fungi and its ability to inactivate sanitizing agents.
Methods
1 ml tube of SRK was inoculated with a bacterial suspension (10-120 CFU). For each of 27 targets, 1 tube was prepared for T0, and three tubes for T24 hours (h) stored at room temperature (RT, 22-25°C), T24h and T48h refrigerated (5°C), respectively. 100 µl were plated on suitable agar plates to verify that the originally load was maintained (T0±30%). Concerning the inactivation tests, serial dilutions (1:1 to 1:10000) of disinfectants belonging to five different antimicrobial families were prepared (Oxidizing compounds, Quaternary ammonium compounds, Biguanides, Alcohols and mix of Phenolic). 100μl of each dilution were added to 1 ml of SRK medium and 1 ml of water, as control, already inoculated with 100μl of the previous suspensions prepared. After 24h of incubation at RT, the maximum neutralizing concentration was evaluated, expressed in part per million (ppm).
Results
Overall, target microorganisms were recovered from every experimental setting within the predetermined limits. An average value (± standard deviation) of 112 ± 26 CFU was used as inoculum concentration. The percentage rate of increase/decrease compared to T0 ranged from 22% to -14.6%, 22.7% to -19%, and 25.3% to -26.4% for T24h and T48h at 5°C, and T24h at RT, respectively. Furthermore, SRK medium has demonstrated the ability to neutralize the tested classes of disinfectants. The microbial suspensions inoculated in water, in the presence of the disinfectant, did not exhibit growth on the agar plates.
Conclusion
SRK® can preserve a broad range of microorganisms for up to 48h. The inactivating capacity of the medium allows overcoming potential biases related to the growth inhibition caused by environmental disinfectants.