Ethanol and Isopropyl Alcohol Exposure Increases Biofilm Formation in Staphylococcus aureus and Staphylococcus epidermidis.
BACKGROUND
Alcohols, including ethanol and isopropyl alcohol, are used in clinical practice for disinfection and infection prevention. Recent studies, however, demonstrate that alcohols may enhance biofilm production in Staphylococci.


METHODS
We quantified biofilm formation in the presence of ethanol and isopropyl alcohol in six different, well-characterized strains of Staphylococcus epidermidis and Staphylococcus aureus. After 24 h of biofilm development, each strain was exposed to normal saline (NS), ethanol, or isopropyl alcohol (40%, 60%, 80% and 95%) for additional 24 h incubation. Adherent biofilms were stained and optical density was determined. Viability of strains was also determined after alcohol exposure.


RESULTS
Ethanol increased biofilm formation in all six strains compared to normal saline (p < 0.05). There was increased biofilm formation with increasing ethanol concentration. Isopropyl alcohol also increased biofilm formation with increasing alcohol concentration in all six strains (p < 0.01 vs NS). The slime-negative, chemical mutant strain of S. epidermidis increased biofilm formation after exposure to both alcohols, likely reverting back its primary phenotype through modulation of the intercellular adhesin repressor. All strains demonstrated viability after exposure to each alcohol concentration, though viability was decreased.


CONCLUSIONS
Ethanol and isopropyl alcohol exposure increases biofilm formation of S. aureus and S. epidermidis at concentrations used in clinical settings. Ethanol and isopropyl alcohol did not eradicate viable Staphylococci from formed biofilm.
Department of Pharmacy Practice, University of Rhode Island, 7 Greenhouse Road, Kingston, RI, 02881, USA.
Megan K
MK
Luther
Sarah
S
Bilida
Leonard A
LA
Mermel
Kerry L
KL
LaPlante