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. 2023 Dec 9;13(1):21807.
doi: 10.1038/s41598-023-49005-4.

Staphylococcus epidermidis is a safer surrogate of Staphylococcus aureus in testing bacterial filtration efficiency of face masks

Silvia Chiera #  1 , Francesca Bosco #  2 , Chiara Mollea  3 , Amelia Piscitello  4 , Rajandrea Sethi  4 , Giandomenico Nollo  1 , Iole Caola  5 , Francesco Tessarolo  1
Affiliations

Staphylococcus epidermidis is a safer surrogate of Staphylococcus aureus in testing bacterial filtration efficiency of face masks

Silvia Chiera et al. Sci Rep. .

Abstract

Face masks play a role in reducing the spread of airborne pathogens, providing that they have a good filtration performance, are correctly fitted and maintained. Bacterial Filtration Efficiency (BFE) is a key indicator for evaluating filtration performance according to both European and US standards, requiring the use of Staphylococcus aureus loaded aerosol. However, the generation and handling of a Biohazard group 2 bacterium aerosol require a careful management of the biological risk and pose limitations to the accessibility to this method. To mitigate these drawbacks, we investigated the use of S. epidermidis ATCC 12228, a Biohazard group 1 bacterium, as surrogate in BFE test. To this end, tests with the surrogate strain were performed to tune the method. Then, three face mask models, representative for both surgical and community masks, were tested according to the standard method and then using an aerosolized suspension of S. epidermidis. BFE% values were calculated for each mask model and tested microorganisms. Results showed that BFE test can be performed using the S. epidermidis instead of S. aureus, preserving results validity and turnaround time, but reducing residual risk for laboratory operators.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Calibration curve, correlating bacterial concentration (CFU/mL) to OD600 for a bacterial suspension obtained from the dilution in peptone water (PW) of a 24 h culture of S. epidermidis in Tryptone soy broth (TSB) at 37 °C.
Figure 2
Figure 2
BFE (%) values collected from the three mask models (five replicated measurements each) using S. aureus and S. epidermidis.
Figure 3
Figure 3
Spectral filtration performance (BFEi) for the two types of bacterial strains: S. aureus (blue) and S. epidermidis (orange). Data of each tested mask model (B, C, D) is presented in a separate graph. Experimental values N = 5, *p-value < 0.05.
Figure 4
Figure 4
BFE test rig set up used to tune the BFE test method using S. epidermidis .
See this image and copyright information in PMC

References

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