Abstract Aims Legionella pneumophila (Lp), a human pathogen, has been detected in windscreen wiper fluid reservoirs (WWFRs) where commercial screen washes (CSWs) are commonly added. Limited information is available on CSWs against planktonic Lp; however, responses of sessile Lp and planktonic Lp pre‐acclimated in nutrient‐limited water to CSWs remain unknown. This study thus investigates the antibacterial effects of CSWs on sessile and starved planktonic Lp, in comparison with unstarved Lp. Methods and Results Lp biofilms were produced on glass and WWFR materials of high‐density polyethylene (HDPE) and polypropylene (PP). Planktonic Lp with and without acclimation in tap water were prepared. Log reductions in cell counts averaged 0.4–5.0 for 10 brands of CSWs against sessile Lp and 1.0–3.9 and 0.9–4.9, respectively, against starved and unstarved planktonic Lp for five CSWs. Both biofilm formation and acclimation in tap water enhanced Lp resistance to CSWs. Significantly different log‐reduction values among CSW brands were observed for sessile Lp on HDPE and planktonic Lp regardless of acclimation (p < 0.05). Conclusions Biofilm formation, starvation acclimation and CSW brand are crucial factors influencing Lp response to CSWs. Significance and Impact of Study This study advances the knowledge of Lp reaction in anthropogenic water systems with CSWs.
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