Influence of possible disinfectant transfer on Staphylococcus aureus plate counts after agar contact sampling

Our plain-English summary of Influence of possible disinfectant transfer on Staphylococcus aureus plate counts after agar contact sampling, by B. Brummer (Applied and Environmental Microbiology, 1976).

The study

• Author: B. Brummer
• Journal: Applied and Environmental Microbiology
• Published: 1976;32(1):80-4
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos-vinyl tile floor panels were mopped with three types of chemical disinfectant product, as well as after contact, with the untreated control panel were prepared according to the manufacturer's label instructions. Similar floor panels were inoculated artificially with Staphylococcus aureus. RODAC (replicate organism detection and counting) surface sampling plates were pressed to the disinfectant-treated panels or to the untreated control panel and then immediately pressed to sampling sites on the artificially inoculated floor panels. Plate counts were determined after contact with panels treated with each type of disinfectant, product, as well as after contact with the untreated control panel. Results indicate that disinfectant residues on environmental surfaces do not alter the average plate counts obtained by RODAC samplings.

In plain English

This laboratory study tested whether disinfectant left on floors could make a common bacteria-sampling method undercount bacteria. It did not study asbestos exposure or health. Asbestos-vinyl floor tiles were only the surface used to build eight test floor panels. Three panels were mopped with a phenolic, a quaternary ammonium, or an iodine-based (iodophor) disinfectant. One panel was left untreated, and four were coated with Staphylococcus aureus bacteria. RODAC agar plates containing neutralizers were pressed onto 64 sites on each treated or untreated panel, then onto an inoculated panel. This was repeated in three experiments. Plates from the untreated control averaged 53, 176 and 60 colonies in the three experiments. Plates from the disinfectant panels averaged between 50 and 191. The author described counts as generally higher after disinfectant contact, most so for the quaternary product. The author concluded that the residues were adequately neutralized and did not alter the validity of RODAC sampling. The author cautioned that simulated results must be extrapolated to real use very cautiously.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory experiment using simulated floor panels, repeated three times
• Who was studied: No people were studied. The study used eight simulated floor panels, each made of four 1-foot squares of asbestos-vinyl floor tile on plywood with 64 sampling sites, and a disinfectant-resistant strain of Staphylococcus aureus (ATCC 6835).
• Exposure: Residues of three disinfectant products, each diluted to the manufacturer's recommended concentration: a phenolic preparation (One-Stroke Vesphene), a quaternary ammonium chloride formulation (A-33 Liquid), and a nonionic-iodine complex (Wescodyne). Asbestos was not an exposure studied; asbestos-vinyl tile was only the test surface.
• Main results:
  • Untreated control panel: average colonies for 64 plates were 53 ± 15.4 (experiment 1), 176 ± 60.7 (experiment 2) and 60 ± 39.9 (experiment 3).
  • Phenolic-treated panel: average colonies for 64 plates were 60 ± 18.0, 188 ± 46.5 and 50 (standard deviation 18.8) in experiments 1 to 3.
  • Quaternary-treated panel: average colonies for 64 plates were 75 ± 22.5, 191 ± 47.1 and 58 ± 23.1 in experiments 1 to 3.
  • Iodophor-treated panel: average colonies for 64 plates were 71 ± 23.1, 160 ± 42.1 and 63 ± 20.3 in experiments 1 to 3.
  • The author stated that plate counts were generally higher after contact with disinfectant-treated panels than with the untreated control, with the greatest difference for the quaternary formulation. The author attributed this probably to the detergent properties of that formulation breaking up clusters of bacteria.
• The authors' conclusion: The author concluded that disinfectant residues picked up on RODAC plates containing the neutralizers lecithin and Polysorbate 80 (Letheen) are adequately neutralized and do not alter the validity of RODAC sampling.
• Limitations the authors state:
  • The author stated that results from simulated in-use tests must be extrapolated to actual in-use conditions very cautiously.
  • The amount of disinfectant residue transferred from the floor could not be measured.

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