Why Chemical Disinfection Alone May Not Remove Biofilm

The 2026 Journal of Applied Microbiology study

A study published in the Journal of Applied Microbiology on 21 January 2026 (Hou et al., doi 10.1093/jambio/lxag023) grew Salmonella Typhimurium and Staphylococcus aureus biofilms on stainless steel and PVC coupons, two materials common in food-processing plant, and treated them with water, 50 mg/L sodium hypochlorite, 50 mg/L chlorine dioxide, or each sanitiser combined with microbubbles.

The combinations outperformed the sanitisers alone by an additional five to six log reductions. After ten minutes, the hypochlorite–microbubble combination reduced Salmonella on stainless steel to below the detection limit; the chlorine dioxide–microbubble combination reduced it to about 2.6 log CFU per coupon. Residual populations were consistently higher on PVC than on stainless steel, and Salmonella was harder to remove than S. aureus on both materials. Scanning electron microscopy showed no biofilm remaining on coupons treated with the hypochlorite–microbubble combination, whereas biofilm remained on coupons treated with hypochlorite alone or water alone. Staining for extracellular material confirmed that the microbubble combination removed the most matrix.

Kill, reduction and removal are different endpoints

The result that matters most for practice is the microscopy: chemical treatment alone could reduce viable counts while leaving the structure of the biofilm on the surface. Surviving matrix and embedded cells provide a foothold for regrowth and can shield organisms from the next treatment. This is why laboratory endpoints such as inhibition, log reduction and eradication should not be read as interchangeable.

Microbubbles add physical action: shear at the surface and disruption of the matrix, which improves access for the oxidant. The general lesson is not specific to microbubbles. Mechanical cleaning, flow, flushing and surface condition all contribute to whether a biofilm is removed rather than merely damaged, which is why hygiene programmes separate cleaning from disinfection.

What this study does and does not establish

It establishes that, for two food-borne organisms on two materials in the laboratory, adding microbubbles to a 50 mg/L sanitiser produced substantially greater inactivation and visibly more complete biofilm removal than the sanitiser alone, and that surface material affected the outcome. It supports the principle that disinfection chemistry is one component of biofilm control alongside physical removal.

It does not establish that chlorine dioxide is ineffective against biofilm, nor that microbubbles are required. The biofilms were young, single-species laboratory cultures; the sanitiser concentrations and contact times were fixed by the experimental design; and the most complete removal in this study was reported for the hypochlorite–microbubble combination, not for chlorine dioxide. The chlorine dioxide was a laboratory solution; ChloroKlean products were not tested. Findings on food-contact surfaces do not transfer to pipework, cooling systems or spa plumbing without separate evidence.

Evidence and uncertainty

Published biofilm studies are valuable for understanding mechanisms, but their conditions may not match a particular installation. Species, surfaces, deposits and operating conditions should be recorded when interpreting evidence.

For safety-critical systems, decisions should be documented through the relevant risk assessment and management plan.

Choosing the next question

A useful next step is to identify what is known, what is inferred and what needs verification. This avoids treating a general reference as a site diagnosis.

Where a product is considered, confirm the intended use, lawful GB BPR route and label directions independently of this educational guide.

A 2026 mechanistic reminder: dispersed cells are not eliminated cells

Park and Sauer's 2026 Journal of Bacteriology study examined induced dispersion of laboratory Pseudomonas aeruginosa PAO1 biofilms, using mutants and fluorescent microscopy/reporters to follow the chemosensory protein BdlA, the phosphodiesterase DipA, cyclic di-GMP signalling and flagellar gene expression. After a dispersion cue, BdlA clustered and moved to the flagellated pole, interacting with DipA; the linked drop in cyclic di-GMP and rise in fliC expression help explain the shift from attached to motile cells. The paper investigated how cells leave a biofilm, not whether a disinfectant destroys them.

For real systems, it is important not to confuse disruption or sloughing with complete removal and inactivation. Physical cleaning and controlled flushing can remove loosened material, but the route for handling flushed water, residual treatment and follow-up verification must be selected for the specific system and its risk assessment. These are operational implications, not interventions or outcomes established by the P. aeruginosa experiments. Check both accessible surfaces and appropriately selected water sampling points over time rather than treating a temporary decline in attached biomass as proof of eradication.

Where the site programme includes a disinfectant residual, confirm delivery at representative and distal points using the correct measurement method for that chemical and the limits in the label and written scheme. Do not raise a dose simply because material has dispersed, or assume that a bulk-water residual proves cells in deposits have been inactivated. Plan post-treatment water and surface checks, record flushing and sampling timing, and review later results for regrowth or ongoing shedding. No universal residual, sampling interval or treatment endpoint can be taken from this mechanistic paper.

The mechanistic study did not test chlorine dioxide, ChloroKlean, mixed-species operational pipe biofilms or any validated field cleaning regime. It gives no product dose or efficacy claim. The authors report NIH funding (1R01AI150761), state that funders had no role in the study or publication decision, and declare no conflict of interest. This evidence complements, but does not change, the separate food-surface disinfection and microbubble findings above.

Use this sequence to frame investigation and control; it is not a dosing protocol.

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