Synergistic bactericidal effects of conventional biocides and phytochemicals for healthcare disinfection.

AIMS: Antimicrobial resistance, particularly in healthcare-associated infections (HAIs), highlights the need for more effective and sustainable disinfection strategies. This study aimed to evaluated the bactericidal effects of two conventional biocides-benzalkonium chloride (BAC) and peracetic acid (PAA)-and two phytochemicals-salicylic acid (SAL) and eugenol (EUG)-against Escherichia coli and Staphylococcus aureus, focusing on potential synergistic interactions.

METHODS AND

RESULTS

Antimicrobial efficacy was assessed through standardized dose- and time-response assays (EN 1276) and kinetic modeling using the Chick-Watson and Weibull equations. BAC and PAA achieved complete bacterial inactivation at 3 mg/L and 1 mg/L, respectively, within 5-15 min, confirming rapid and potent activity. Conversely, SAL and EUG required substantially higher concentrations (500-1700 mg/L) to achieve total loss of culturability. Chick-Watson modeling demonstrated high disinfection rate coefficients for BAC and PAA, while SAL and EUG exhibited markedly lower values. Synergy testing revealed a strong interaction between BAC and EUG, with fractional bactericidal concentration indices of 0.350 for E. coli and 0.309 for S. aureus, whereas other combinations were additive. Weibull modeling further indicated that bacterial tolerance was dependent on compound type and concentration, with S. aureus generally more susceptible than E. coli.

CONCLUSIONS

These findings collectively confirm the enhanced efficacy of selected biocide/phytochemical combinations, allowing lower concentrations and promoting more sustainable antimicrobial practices.