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Mosaic-CLSM Assessment of Bacterial Spatial Distribution in Cosmetic Matrices According to Matrix Viscosity and Bacterial Hydrophobicity

1
Micalis Institute, INRAE, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
2
Laboratoires Clarins, 5 Rue Ampère, 95300 Pontoise, France
*
Author to whom correspondence should be addressed.
Cosmetics 2020, 7(2), 32; https://doi.org/10.3390/cosmetics7020032
Received: 26 March 2020 / Revised: 21 April 2020 / Accepted: 5 May 2020 / Published: 11 May 2020
(This article belongs to the Special Issue Feature Papers in Cosmetics in 2020)
The reliability of the challenge test depends, among other parameters, on the spatial distribution of microorganisms in the matrix. The present study aims to quickly identify factors that are susceptible to impair a uniform distribution of inoculated bacteria in cosmetic matrices in this context. We used mosaic confocal laser scanning microscopy (M-CLSM) to obtain rapid assessment of the impact of the composition and viscosity of cosmetic matrices on S. aureus spatial distribution. Several models of cosmetic matrices were formulated with different concentrations of two thickeners and were inoculated with three S. aureus strains having different levels of hydrophobicity. The spatial distribution of S. aureus in each matrix was evaluated according to the frequency distribution of the fluorescence values of at least 1350 CLSM images. We showed that, whatever the thickener used, an increasingly concentration of thickener results in increasingly bacterial clustered distribution. Moreover, higher bacterial hydrophobicity also resulted in a more clustered spatial distribution. In conclusion, CLSM-based method allows a rapid characterization of bacterial spatial distribution in complex emulsified systems. Both matrix viscosity and bacterial surface hydrophobicity affect the bacterial spatial distribution which can have an impact on the reliability of bacterial enumeration during challenge test. View Full-Text
Keywords: clustered distribution; regular distribution; viscous matrix; thickener; bacterial hydrophobicity; challenge test; CLSM clustered distribution; regular distribution; viscous matrix; thickener; bacterial hydrophobicity; challenge test; CLSM
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Almoughrabie, S.; Ngari, C.; Briandet, R.; Poulet, V.; Dubois-Brissonnet, F. Mosaic-CLSM Assessment of Bacterial Spatial Distribution in Cosmetic Matrices According to Matrix Viscosity and Bacterial Hydrophobicity. Cosmetics 2020, 7, 32.

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