Salicylate UV-Filters in Sunscreen Formulations Compromise the Preservative System Efficacy against Pseudomonas aeruginosa and Burkholderia cepacia

Noa Ziklo,Inbal Tzafrir,Regina Shulkin,Paul Salama

doi:10.3390/cosmetics7030063

Abstract

Contamination of personal-care products are a serious health concern and therefore, preservative solutions are necessary for the costumers’ safety. High sun protection factor (SPF) sunscreen formulations are known to be difficult to preserve, due to their high ratio of organic phase containing the UV-filters. Salicylate esters such as octyl salicylate (OS) and homosalate (HS) are among the most common UV-filters currently used in the market, and can undergo hydrolysis by esterase molecules produced by contaminant microorganisms. The hydrolysis product, salicylic acid (SA) can be assimilated by certain bacteria that contain the chorismate pathway, in which its final product is pyochelin, an iron-chelating siderophore. Here, we show that OS and HS can compromise the preservative efficacy against two pathogenic important bacteria, Pseudomonas aeruginosa and Burkholderia cepacia. Challenge tests of formulations containing the UV-filters demonstrated that only bacteria with the chorismate pathway failed to be eradicated by the preservation system. mRNA expression levels of the bacterial pchD gene, which metabolizes SA to produce pyochelin, indicate a significant increase that was in correlation with increasing concentrations of both OS and HS. These data suggest that certain UV-filters can provide a source for bacterial resistance against common preservatives in sunscreen formulations.

Highlights

Preservation of non-sterile personal-care products containing water and organic/inorganic compounds is necessary in order to prevent spoilage by contaminants microorganisms, which subsequently can cause severe health risk for the consumers [1]
When octyl salicylate (OS) and HS were added to the basic cream formulation, the preservative which was previously effective against P. aeruginosa and B. cepacia, failed to eradicate their growth
In this study we have demonstrated the ability of P. aeruginosa and B. cepacia to survive in preserved formulations supplemented with common UV-filters, OS, and HS often found in sunscreen formulations

Summary

Introduction

Preservation of non-sterile personal-care products containing water and organic/inorganic compounds is necessary in order to prevent spoilage by contaminants microorganisms, which subsequently can cause severe health risk for the consumers [1]. Salicylate esters were the first UV-filters used in sunscreen formulations and yet remain highly popular in the market [2]. Such esters as octyl salicylate (OS) and homosalate (HS) can be hydrolyzed to salicylic acid (SA) by esterases molecules, possibly produced by the contaminant microorganisms [3,4]. Some bacterial species such as Pseudomonas aeruginosa and Burkholderia cepacia contains genes for the chorismate biochemical pathway, in which SA is a precursor to produce pyochelin (Figure 1). As part of the pathway, SA can be adenylated at the carboxyl group by PchD (2,3-dihydroxybenzoyl adenylate synthase), which is encoded by the pchD gene, found in both above mentioned bacterial species [5,6,7]

Results

Discussion

Conclusion