In-Store Cosmetic Testers Harbour Resistant Bacteria: A Pilot Survey of Microbial Contamination and Antimicrobial...

Cosmetic testers in community pharmacies may act as a source of microbial transmission, but their microbiological safety remains poorly characterised. This study assessed microbial contamination of 42 cosmetic testers (eight product categories) from community pharmacies in northern Portugal using culture-based methods, identification and Kirby-Bauer disk diffusion. We characterised the antimicrobial susceptibility of the recovered isolates. Microbial growth was detected in 25/42 testers (59.5%), with polymicrobial contamination in 16.7% of samples. Out of the 25 positive growth products, 33 characterised bacterial isolates were yielded. Staphylococcus sp. predominated (22/33; 66.7%), followed by Pseudomonas sp. (4/33; 12.1%), Streptococcus sp. (3/33; 9.1%), Acinetobacter sp. (2/33; 6.1%) and Bacillus sp. (2/33; 6.1%). Among categories represented by more than one tester, anti-ageing products showed the highest proportion of microbial growth (7/8; 87.5%), followed by sunscreens (10/16; 62.5%). Overall, 12/33 bacterial isolates (36.4%) met the study-defined operational multidrug-resistance criterion, all of which were Staphylococcus sp. (12/22; 54.5%). These findings demonstrate that viable bacteria exhibiting phenotypic antimicrobial resistance can be recovered from in-use cosmetic testers in community pharmacies and support further investigation of their microbiological and antimicrobial-resistance characteristics. This reinforces that pharmacy cosmetic testers may harbour a diverse, and often multidrug-resistant, microbial population of clinical relevance, supporting the need for strengthened tester hygiene and control practices.