Scientific and practical significance of extended microbiological analysis of floating suspensions (biofilms) in packaged natural mineral table drinking water

Introduction. The problem of biofilms in drinking water supply systems is well-studied; however, their presence in bottled water requires additional attention.

The aim of the study was to assess the microbiological composition and potential risk of transparent suspensions (sediment) found in bottled natural mineral table non-carbonated drinking water.

Materials and methods. A comprehensive sanitary-microbiological study of the water was conducted. The standard analysis for compliance with the requirements of TR EAEU 044/2017 included the determination of standardized indicators (TVC, Coliform bacteria, E. coli, P. aeruginosa, enterococci) according to GOST 34786–2021. For the analysis of suspensions, there were used methods of concentrating large volumes of water (1 and 3 dm³) by centrifugation and membrane filtration followed by inoculation onto nutrient media (Nutrient Agar, Endo Agar, Sabouraud Agar, Brolacin agar, MRS agar) by the direct method and via thioglycolate enrichment broth. Species identification of all grown colonies was performed using time-of-flight mass spectrometry (MALDI-TOF MS). Additional studies for coliphages and parasitological objects were also conducted.

Results. A standard analysis of two hundred fifty cm³ of water did not detect E. coli, coliform bacteria (BGKP), or other regulated pathogens. An excess of the standard for total microbial count (TMC) at 22 °C by a factor of 2 (289 CFU/cm³) was recorded; however, according to TR EAEU 044/2017, this test was not required in this case. After concentrating 1 and 3 dm³ of water, diverse microorganisms were identified in the suspended solids, including Escherichia coli, Kocuria rhizophila, Micrococcus luteus, Aquabacterium parvum, Microbacterium testaceum, as well as the fungi Aspergillus fumigatus and Syncephalastrum racemosum. Coliphages and parasitic objects were not detected.

Limitations. The study was conducted once on one batch of bottled natural mineral drinking water. It is necessary to conduct a series of similar studies on biofilms of a different composition to confirm the correctness of the developed tactics.

Conclusion. The results demonstrate that standard control methods based on the analysis of small volumes (up to 250 cm³) may be insufficient to detect microbiological contamination present as local aggregates (suspensions or biofilms) in bottled water. The detection of E. coli after concentration indicates fecal contamination and a potential epidemiological risk. The obtained data justify the need to develop and implement extended control protocols, including the concentration of representative water volumes and use of enrichment media, to ensure the safety of packaged drinking water.

Compliance with ethical standards. The study does not require the conclusion of the Biomedical Ethics Committee.

Contribution:
Alekseeva A.V. – study concept and design, writing the text, collecting material and processing data, editing, approval of the final version of the article, responsibility for the integrity of all parts of the article;
Zagaynova A.V. – study concept and design, editing;
Rakhmanin Yu.A., Rusakov N.V. – editing, approval of the final version of the article;
Kurbatova I.V., Kravchenko K.S. – collecting material and processing data.

Conflict of interest. The authors declare no conflict of interest.

Funding. The study had no sponsorship.

Received: June 6, 2025 / Revised: November 27, 2025 / Accepted: December 2, 2025 / Published: January 15, 2026

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