Table 1.

List of chemicals used in this study and summary of their effects on P.a. biofilms

Chemical	Mode of action	Effect on elasticity *	Effect on recovery	Effect on viability **
NaCl	osmotic stress inducer, inhibitor of biofilm formation34	NO	NO	NO
KH2PO4	osmotic stress inducer	NO	NO	NO
CaCl2	regulator of alginate gel elasticity35	NO	NO	NO
CuSO4	bactericidal36, inhibitor of normal biofilm growth36	NO	NO	NO
FeCl2	non-metabolizable analog of FeCl3	−	NO	NO
FeCl3	necessary metabolite of bacterial growth37	+++	NO	NO
Al2(SO4)3	trivalent ion, control for Fe(III)	+++	NO	NO
pH	control for pH changes induced by other chemicals	NO	NO	NO
Salicylic acid	quorum sensing inhibitor38	NO	NO	NO
Citric acid	ion chelating agent, putative biofilm removal agent39, antimicrobial agent40, 41	− −	NO	YES
EDTA	ion chelating agent, putative biofilm removal agent39, inhibitor of biofilm formation42	−	NO	NO
EGTA	calcium chelating agent	−	NO	NO
Lactoferrin	iron chelating protein, antimicrobial43	NO	NO	NO
Spermidine	polyelectrolyte	NO	NO	NO
Gentamycin	bactericidal: disrupts protein synthesis	NO	NO	NO
Colistin	bactericidal: disrupts the integrity of bacterial outer membrane	NO	NO	NO
Ofloxacin	bactericidal: disrupts separation of replicated DNA	NO	NO	YES
Amylase	enzyme present in the oral cavity	NO	NO	NO
Ethanol	antimicrobial agent	NO	NO	NO
Triton	detergent	NO	NO	NO
Bleach	antimicrobial agent	NO	NO	YES
Glucose	nutrient	NO	NO	NO
Urea	potential biofilm removal agent39	NO	NO	NO
Xylitol	disrupts biofilm function43	NO	NO	NO
Hexandiol	interferes with hydrophobic interactions	NO	NO	NO

^*chemicals with a weakening effect (reduction of biofilms stiffness by ~90%) are marked with (−); chemicals with a strong weakening effect (reduction of biofilm stiffness by ~99 %) are marked with (− −); chemicals inducing a fortification effect are marked with (+); we only detect very strong fortification effects and those are marked as (+++) accordingly

^**chemicals are defined effective if they reduce bacterial viability by more than 95%