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Influence of Dead Cells Killed by Industrial Biocides (BAC and DBNPA) on Biofilm Formation

by Ana C. Barros, Diogo A. C. Narciso, Luis F. Melo and Ana Pereira

Antibiotics 2024, 13(2), 140; https://doi.org/10.3390/antibiotics13020140 - 31 Jan 2024

Cited by 5 | Viewed by 4095

Industrial biocides aim to keep water systems microbiologically controlled and to minimize biofouling. However, the resulting dead cells are usually not removed from the water streams and can influence the growth of the remaining live cells in planktonic and sessile states. This study aims to understand the effect of dead Pseudomonas fluorescens cells killed by industrial biocides—benzalkonium chloride (BAC) and 2,2-dibromo-3-nitrilopropionamide (DBNPA)—on biofilm formation. Additionally, the effect of different dead/live cell ratios (50.00% and 99.99%) was studied. The inoculum was recirculated in a Parallel Plate Flow Cell (PPFC). The overall results indicate that dead cells greatly affect biofilm properties. Inoculum with DBNPA–dead cells led to more active (higher ATP content and metabolic activity) and thicker biofilm layers in comparison to BAC–dead cells, which seems to be linked to the mechanism of action by which the cells were killed. Furthermore, higher dead cell ratios (99.99%) in the inoculum led to more active (higher culturability, metabolic activity and ATP content) and cohesive/compact and uniformly distributed biofilms in comparison with the 50.00% dead cell ratio. The design of future disinfection strategies must consider the contribution of dead cells to the biofilm build-up, as they might negatively affect water system operations. Full article

(This article belongs to the Special Issue Biofilm Formation and Control)

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21 pages, 1845 KB

Open AccessArticle

Biocides with Controlled Degradation for Environmentally Friendly and Cost-Effective Fecal Sludge Management

by Nataliya Loiko, Oleg Kanunnikov, Ksenia Tereshkina, Timofei Pankratov, Svetlana Belova, Ekaterina Botchkova, Anastasia Vishnyakova and Yuriy Litti

Biology 2023, 12(1), 45; https://doi.org/10.3390/biology12010045 - 26 Dec 2022

Cited by 7 | Viewed by 5419

Abstract

Didecyldimethylammonium chloride (DDAC) and polyhexamethylene guanidine (PHMG) exhibit high antimicrobial activity and are widely used as biocidal agents in chemical toilet additives for the management of fecal sludge (FS). Disposal of such biocide-treated FS to a wastewater treatment plant (WWTP) is a major environmental problem. It is possible to reduce environmental damage through the use of biocidal agents, which easily decompose after performing their main biocidal functions. In this work, it is proposed to use the fact of a gradual increase in pH of FS from the initial 7.5 to 9.0–10.0 due to the decomposition of urea. Six biocidal compounds were selected that are capable of rapidly degrading in an alkaline environment and one that naturally degrades upon prolonged incubation. Four of them: bronopol (30 mg/L), DBNPA (500 mg/L), Sharomix (500 mg/L), and sodium percarbonate (6000 mg/L) have shown promise for environmentally friendly management of FS. In selected dosage, they successfully reduced microbial activity under both aerobic and anaerobic conditions and are cost-effective. After 10 days of incubation, degradation of the biocide occurred as measured by biological oxygen demand (BOD₅) in biocide-treated FS. Such FS can be discharged to WWTP without severe damage to the activated sludge process, the need for dilution and additional procedures to neutralize toxicity. Full article

(This article belongs to the Section Microbiology)

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13 pages, 2969 KB

Open AccessArticle

Pseudomonas fluorescens Cells’ Recovery after Exposure to BAC and DBNPA Biocides

by Ana C. Barros, Luis F. Melo and Ana Pereira

Antibiotics 2022, 11(8), 1042; https://doi.org/10.3390/antibiotics11081042 - 2 Aug 2022

Cited by 8 | Viewed by 2988

Abstract

A proper assessment of the effects of biocides on bacterial cells is key to the prevention of antimicrobial resistance and the implementation of suitable biocidal programmes. It is particularly relevant regarding the ability of dead-labelled cells to recover their functional processes once the biocide is removed. In the present work, we studied how Pseudomonas fluorescens cells previously exposed to different concentrations of BAC (benzalkonium chloride) and DBNPA (2,2-Dibromo-3-nitrilopropionamide) behave upon the restoration of optimum growth conditions. The following indicators were evaluated: culturability, membrane integrity, metabolic activity (resazurin), cellular energy (ATP), and cell structure and morphology (transmission electron microscopy (TEM)). The results demonstrated that cells previously labelled as ‘dead’ recovered to a greater extent in all indicators. Only cells previously exposed to BAC at 160 mg/L (concentration above the MBC) showed significant reductions on all the evaluated indicators. However, the obtained values were much higher than the ‘death’ thresholds found for the autoclaved cells. This suggests that cells exposed to this concentration take more time to rebuild their functional processes. The recovery of DBNPA-treated cells did not seem to be related to the biocide concentration. Finally, a reflection on what kind of cells were able to recover (remaining cells below the detection limit and/or dormant cells) is also presented. Full article

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