The effects of contact time and concentration on bactericidal efficacy of three disinfectants on hard non-porous surfaces

Mr Peter Teska1, Dr Haley Oliver2, Dr Yingying Hong2

1Diversey Care – Sealed Air Corp, Charlotte, United States

2Purdue University, West Lafayette, United States

This study investigated the influence of contact time and concentration on bactericidal efficacy of three disinfectants, on stainless steel surfaces using EPA procedure MB-25-02. Efficacy was measured at six contact times (1, 2, 3, 4, 5, and 10 min) at label concentrations and at eight concentrations (25%, 50%, 75%, 100%, 125%, 150%, 175%, and 200% of label concentration) with 5 min contact time.

We found that decreases in contact time or concentration did not result in immediate reduction of bactericidal efficacy, but all three disinfectants were less bactericidal at significantly lower than label use concentrations. AHP at 1 min, sodium hypochlorite at 1 min, and Quat at 1 to 4 min contact times resulted in 15.7% to 76.3% reductions of Staphylococcus aureus, which were significantly lower than 100% reduction at label contact times (Padj<0.01). Similarly, AHP at 25% and 50% concentrations, sodium hypochlorite at 25% concentration, and Quat at 25% and 50% concentrations were significantly less bactericidal, resulting in 40.9% to 67.5% reductions of Staphylococcus aureus compared to 89.4% to 100% reductions at label concentrations (Padj<0.01). Quat was also less bactericidal against Pseudomonas aeruginosa at lower than label contact time (1 to 5 min) and concentrations (25% and 50%).

Overall, the bactericidal efficacy of sodium hypochlorite was most tolerant to the decreases of contact times and concentrations, followed closely by AHP, while Quat was most affected.  In practice, changes in label use directions could result in sub-optimal disinfections and should be made cautiously.


Peter Teska currently works for Sealed Air’s Diversey Care division as the Global Infection Prevention Application Expert. In his role he provides customer support on Infection Prevention issues related to environmental hygiene, writes technical literature and documents, presents at Infection Prevention events, monitors the scientific literature related to environmental hygiene, provides technical support to the portfolio teams in development of innovations, and provides training to Diversey’s employees and customers. He has worked as a supplier to the Healthcare industry for 20+ years, having worked in a range of technical and product marketing roles in his career.

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