Photoinduced bactericidal activity of TiO<Subscript>2</Subscript> films

A decrease in CFU of gram-positive and gram-negative bacteria on the surface of UV illuminated TiO₂ films (wavelength of 380 nm) is shown. A 29, 45, and 47% decrease in bacterial viability of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli, respectively, was seen after 12-min exposition. It was first discovered that the reuse of TiO₂ films to test a bacterial suspension for viability removes UV-induced bactericidal activity. However, annealing of TiO₂ at a temperature above 400°C restores the photoinduced bactericidal activity to its initial state.     

Inactivation of human pathogens and spoilage bacteria on the surface and internalized within fresh produce by using a combination of ultraviolet light and hydrogen peroxide

Aims: To evaluate the efficacy of ultraviolet (UV) light (254 nm) combined with hydrogen peroxide (H₂O₂) to inactivate bacteria on and within fresh produce. Methods and Results: The produce was steep inoculated in bacterial cell suspension followed by vacuum infiltration. The inoculated samples were sprayed with H₂O₂ under constant UV illumination. The log count reduction (LCR) of Salmonella on and within lettuce was dependent on the H₂O₂ concentration, temperature and treatment time with UV intensity being less significant. By using the optimized parameters (1·5% H₂O₂ at 50°C, UV dose of 37·8 mJ cm^?2), the surface Salmonella were reduced by 4·12 ± 0·45 and internal counts by 2·84 ± 0·34 log CFU, which was significantly higher compared with H₂O₂ or UV alone. Higher LCR of Escherichia coli O157:H7, Pectobacterium carotovora, Pseudomonas fluorescens and Salmonella were achieved on leafy vegetables compared with produce, such as cauliflower. In all cases, the surface LCR were significantly higher compared with the samples treated with 200 ppm hypochlorite. UV–H₂O₂‐treated lettuce did not develop brown discolouration during storage but growth of residual survivors occurred with samples held at 25°C. Conclusions: UV–H₂O₂ reduce the bacterial populations on and within fresh produce without affecting the shelf‐life stability. Significance of the Study: UV–H₂O₂ represent an alternative to hypochlorite washes to decontaminate fresh produce.     

The effects of copper additives on the quantity and cell viability of adherent Staphylococcus epidermidis in silicone implants

This in vitro study evaluated the antibacterial effect of copper additives in silicone implants. Specimens of a standard silicone material used in breast augmentation and modified copper-loaded silicone specimens were prepared and incubated in a Staphylococcus epidermidis suspension (2 h, 37°C). After the quantification of adhering staphylococci using a biofluorescence assay (Resazurin), the viability of the adhering bacterial cells was quantified by live or dead cell labeling in combination with fluorescence microscopy. In the Resazurin fluorometric quantification, a higher amount of adhering S. epidermidis cells was detected on pure silicone (4612 [2319/7540] relative fluorescence units [rfu]) than on silicone with copper additives (2701 [2158/4153] rfu). Additionally, a significantly higher amount of adhering bacterial cells (5.07% [2.03%/8.93%]) was found for pure silicone than for silicone with copper additives (1.72% [1.26%/2.32%]); (p < 0.001). Calculations from live or dead staining showed that the percentage of dead S. epidermidis cells adhered on pure silicone (52.1%) was significantly lower than on silicone with copper additives (79.7%); (p < 0.001). In vitro, silicone material with copper additives showed antibacterial effects against S. epidermidis. Copper-loaded silicone may prevent bacterial colonization, resulting in lower infection rates of silicone implants.     

Production of Metallogenium-like particles by heterotrophic manganese-oxidizing bacteria collected from a lake

As a model of chemically stratified structure of environment typical to the chemocline of lakes, a semisolid gradient medium was prepared to cultivate heterotrophic manganese-oxidizing bacteria originally collected from a lake. The bacteria growing under the conditions described produced extracellularly Metallogenium-like particles similar to those which are often detected in the chemocline of lakes. This suggested that the naturally occurring Metallogenium-like particles originated in activities of such heterotrophic manganese-oxidizing bacteria. The manganese oxidation activity usually appeared only at the stationary phase of bacterial growth. The oxidation of Mn²⁺ and the formation of Metallogenium-like particles by the bacteria were observed at neutral or slightly acidic pH. not under alkaline conditions, which is a conspicuous difference from the inorganic oxidation of Mn²⁺ by O₂. Bacterial manganese oxidation was stimulated by bicarbonate (50 or 500 M). An experiment of addition of H₂O₂ to the incubation tubes isolated from atmosphere failed to confirm the availability of externally added H₂O₂ as the electron acceptor, suggesting that the bacterial manganese oxidation required the presence of O₂.     

Biomolecules in multilayer film for antimicrobial and easy-cleaning stainless steel surface applications

Microorganisms are able to attach to, grow on, and ultimately form biofilms on a large variety of surfaces, such as industrial equipment, food contact surfaces, medical implants, prostheses and operating rooms. Once organized into biofilms, bacteria are difficult to remove and kill, which increases the risk of cross-contamination and infection. One way to address the problem may thus be to develop antibacterial, anti-adhesion, ‘easy cleaning’ surfaces. In this study, stainless steel (SS) surfaces with antibacterial properties were created by embedding several antimicrobial peptides in a multilayer film architecture. The biocidal effect of these surfaces was demonstrated against both Gram-positive and Gram-negative bacteria according to two ISO tests. Also, coating SS surfaces with either mucin or heparin led to a reduction of S. epidermidis adhesion of almost 95% vs the bare substratum. Finally, by combining both antibacterial and anti-adhesion biomolecules in the same multilayer film, SS surfaces with better cleanability were produced. This surface coating property may help to delay the buildup of a dead bacterial layer which is known to progressively reduce exposure of the coating, leading to an undesirable decrease in the antibacterial effect of the surface.     

The efficacy and sterilisation of human decellularised dermal allografts with combinations of cupric ions and hydrogen peroxide

Decellularised tissue allografts have been used in reconstructive surgical applications and transplantation for many years. Some of the current methods of sterilisation have a detrimental effect on the tissue graft structure and function. The anti-microbial activity of cupric ions and hydrogen peroxide (H₂O₂) are well known however their combined application is not currently utilised as a decontamination agent in the tissue banking world sector. The aim of this study was to determine the combined concentrations of copper chloride (CuCl₂) and H₂O₂ that have the optimal bactericidal and sporicidal activity on decellularised (dCELL) human dermis. The first part of this study established the decimal reduction time (D-value) of CuCl₂ (0.1 mg/L and 1 mg/L) together with H₂O₂ (0.01, 0.1, 0.5 and 1%) for Staphylococcus epidermidis, Escherichia coli and Bacillus subtilis spores. The second part of this study identified the most effective CuCl₂ and H₂O₂ concentration that decontaminated dCELL human dermis inoculated with these pathogens. Of all the concentrations tested, 0.1 mg/L CuCl₂ in combination with 1% H₂O₂ had the shortest D-value; S. epidermidis D = 3.15 min, E. coli D = 2.62 min and B. subtilis spores D = 18.05 min. However when adsorbed onto dCELL dermis, S. epidermidis and E. coli were more susceptible to 1 mg/L CuCl₂ together with 0.5% H₂O₂. These studies show promise of CuCl₂–H₂O₂ formulations as potential sterilants for decellularised dermal allografts.     

Photocatalytic Antibacterial Effects Are Maintained on Resin-Based TiO2 Nanocomposites after Cessation of UV Irradiation

Photocatalysis induced by TiO₂ and UV light constitutes a decontamination and antibacterial strategy utilized in many applications including self-cleaning environmental surfaces, water and air treatment. The present work reveals that antibacterial effects induced by photocatalysis can be maintained even after the cessation of UV irradiation. We show that resin-based composites containing 20% TiO₂ nanoparticles continue to provide a pronounced antibacterial effect against the pathogens Escherichia coli, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus mutans and Enterococcus faecalis for up to two hours post UV. For biomaterials or implant coatings, where direct UV illumination is not feasible, a prolonged antibacterial effect after the cessation of the illumination would offer new unexplored treatment possibilities.     

Biofilm control in water by a UV-based advanced oxidation process

An ultraviolet (UV)-based advanced oxidation process (AOP), with hydrogen peroxide and medium-pressure (MP) UV light (H₂O₂/UV), was used as a pretreatment strategy for biofilm control in water. Suspended Pseudomonas aeruginosa cells were exposed to UV-based AOP treatment, and the adherent biofilm formed by the surviving cells was monitored. Control experiments using H₂O₂ or MP UV irradiation alone could inhibit biofilm formation for only short periods of time (<24 h) post-treatment. In a H₂O₂/filtered-UV (>295 nm) system, an additive effect on biofilm control was shown vs filtered-UV irradiation alone, probably due to activity of the added hydroxyl radical (OH?). In a H₂O₂/full-UV (ie full UV spectrum, not filtered) system, this result was not obtained, possibly due to the germicidal UV photons overwhelming the AOP system. Generally, however, H₂O₂/UV prevented biofilm formation for longer periods (days) only when maintained with residual H₂O₂. The ratio of surviving bacterial concentration post-treatment to residual H₂O₂ concentration played an important role in biofilm prevention and bacterial regrowth. H₂O₂ treatments alone resulted in poorer biofilm control compared to UV-based AOP treatments maintained with similar levels of residual H₂O₂, indicating a possible advantage of AOP.     

Investigation of critical inter‐related factors affecting the efficacy of pulsed light for inactivating clinically relevant bacterial pathogens

Aims: To investigate critical electrical and biological factors governing the efficacy of pulsed light (PL) for the in vitro inactivation of bacteria isolated from the clinical environment. Development of this alternative PL decontamination approach is timely, as the incidence of health care–related infections remains unacceptably high. Methods and Results: Predetermined cell numbers of clinically relevant Gram‐positive and Gram‐negative bacteria were inoculated separately on agar plates and were flashed with ≤60 pulses of broad‐spectrum light under varying operating conditions, and their inactivation measured. Significant differences in inactivation largely occurred depending on the level of the applied lamp discharge energy (range 3·2–20 J per pulse), the amount of pulsing applied (range 0–60 pulses) and the distance between light source and treatment surface (range 8–20 cm) used. Greater decontamination levels were achieved using a combination of higher lamp discharge energies, increased number of pulses and shorter distances between treatment surface and the xenon light source. Levels of microbial sensitivity also varied depending on the population type, size and age of cultures treated. Production of pigment pyocynanin and alginate slime in mucoid strains of Pseudomonas aeruginosa afforded some protection against lethal action of PL; however, this was evident only by using a combination of reduced amount of pulsing at the lower lamp discharge energies tested. A clear pattern was observed where Gram‐positive bacterial pathogens were more resistant to cidal effects of PL compared to Gram negatives. While negligible photoreactivation of PL‐treated bacterial strains occurred after full pulsing regimes at the different lamp discharge energies tested, some repair was evident when using a combination of reduced pulsing at the lower lamp discharge energies. Strains harbouring genes for multiple resistances to antibiotics were not significantly more resistant to PL treatments. Slight temperature rises (≤4·2°C) were measured on agar surfaces after extended pulsing at higher lamp discharge energies. Presence of organic matter on treatment surface did not significantly affect PL decontamination efficacy, nor did growth of PL‐treated bacteria on selective agar diminish survival compared to similarly treated bacteria inoculated and enumerated on nonselective agar plates. Conclusions: Critical inter‐related factors affecting the effective and repeatable in vitro decontamination performance of PL were identified during this study that will aid further development of this athermal process technology for applications in health care and in industry. Very rapid reductions (c. 7 log₁₀ CFU cm^?2 within ≤10 pulses) occurred using discharge energy of 20 J for all tested clinically relevant bacteria under study when treated at 8 cm distance from xenon light source. While no resistant flora is expected to develop for treatment of microbial pathogens on two‐dimensional surfaces, careful consideration of scale up factors such as design and operational usage of this PL technique will be required to assure operator safety. Significance and Impact of the Study: Findings and conclusions derived from this study will enable further development and optimization of this decontamination technique in health care and in food preparation settings, and will advance the field of nonthermal processing technologies.     

In Vitro Model of Bacterial Biofilm Formation on Polyvinyl Chloride Biomaterial

The aim of the study was to establish an in vitro model of Staphylococcus epidermidis biofilms on polyvinyl chloride (PVC) material, and to investigate bacterial biofilm formation and its structure using the combined approach of confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM). Staphylococcus epidermidis bacteria (stain RP62A) were incubated with PVC pieces in Tris buffered saline to form biofilms. Biofilm formation was examined at 6, 12, 18, 24, 30, and 48 h. Thicknesses of these biofilms and the number, and percentage of viable cells in biofilms were measured. CT scan images of biofilms were obtained using CLSM and environmental SEM. The results of this study showed that Staphylococcus epidermidis biofilm is a highly organized multi-cellular structure. The biofilm is constituted of large number of viable and dead bacterial cells. Bacterial biofilm formation on the surface of PVC material was found to be a dynamic process with maximal thickness being attained at 12–18 h. These biofilms became mature by 24 h. There was significant difference in the percentage of viable cells along with interior, middle, and outer layers of biofilms (P < 0.05). Staphylococcus epidermidis biofilm is sophisticated in structure and the combination method involving CLSM and SEM was ideal for investigation of biofilms on PVC material.     

兼性厌氧细菌硫化氢的产生机理及其生理功能

硫化氢(H_2S)是继一氧化氮(NO)和一氧化碳(CO)后发现的第3种气态信号分子,但其细菌生理学研究才刚刚起步。本文根据作者对奥内达希瓦氏菌的研究,结合新近文献,就细菌的H_2S产生机理及其生理功能作了较为全面的阐述。细菌的H_2S产生途径主要有2条,一是通过降解半胱氨酸产生,二是通过厌氧呼吸产生。产生的H_2S除可为互生性微生物提供能源、供氢体和无机矿质营养外,还具有抑制竞争性微生物的生长,有效占领生态位的作用。H_2S在氧化应答中也起着重要的作用,一方面可抑制过氧化氢酶活性,增加过氧化氢对细菌的杀灭效果;另一方面可作为信号分子激活细菌的氧化应答,诱导拮抗系统的表达,保护细胞免受氧化损伤。这两种看似"矛盾"的作用与H_2S的处理时间有关:短时间处理以抑制为主,而延长处理时间则以保护为主。细菌H_2S产生机理及生理功能的阐明可为硫元素生物地球化学循环规律的揭示和感染性病原细菌的控制提供有益的参考。     

The involvement of coordinative interactions in the binding of dihydrolipoamide dehydrogenase to titanium dioxide—Localization of a putative binding site

Titanium (Ti) and its alloys are widely used in orthodontic and orthopedic implants by virtue to their high biocompatibility, mechanical strength, and high resistance to corrosion. Biointegration of the implants with the tissue requires strong interactions, which involve biological molecules, proteins in particular, with metal oxide surfaces. An exocellular high‐affinity titanium dioxide (TiO₂)–binding protein (TiBP), purified from Rhodococcus ruber , has been previously studied in our lab. This protein was shown to be homologous with the orthologous cytoplasmic rhodococcal dihydrolipoamide dehydrogenase (rhDLDH). We have found that rhDLDH and its human homolog (hDLDH) share the TiO₂‐binding capabilities with TiBP. Intrigued by the unique TiO₂‐binding properties of hDLDH, we anticipated that it may serve as a molecular bridge between Ti‐based medical structures and human tissues. The objective of the current study was to locate the region and the amino acids of the protein that mediate the protein‐TiO₂ surface interaction. We demonstrated the role of acidic amino acids in the nonelectrostatic enzyme/dioxide interactions at neutral pH. The observation that the interaction of DLDH with various metal oxides is independent of their isoelectric values strengthens this notion. DLDH does not lose its enzymatic activity upon binding to TiO₂, indicating that neither the enzyme undergoes major conformational changes nor the TiO₂ binding site is blocked. Docking predictions suggest that both rhDLDH and hDLDH bind TiO₂ through similar regions located far from the active site and the dimerization sites. The putative TiO₂‐binding regions of both the bacterial and human enzymes were found to contain a CHED (Cys, His, Glu, Asp) motif, which has been shown to participate in metal‐binding sites in proteins.     

Physiological changes induced in four bacterial strains following oxidative stress

In order to study the behavior and resistance of bacteria under extreme conditions, physiological changes associated with oxidative stress were monitored using flow cytometry. The study was conducted to assess the maintenance of membrane integrity and potential as well as the esterase activity, the intracellular pH and the production of superoxide anions in four bacterial strains (Ralstonia metallidurans, Escherichia coli, Shewanella oneidensis and Deinococcus radiodurans). The strains were chosen for their potential use in bioremediation. Suspensions of R. metallidurans, E. coli, S. oneidensis and D. radiodurans were submitted to 1 h of oxidative stress (H₂O₂ at various concentrations from 0 to 880 mM). Cell membrane permeability (propidium iodide) and potential (rhodamine-123,3,3’-dihexyloxacarbocyanine iodide), intracellular esterase activity (fluorescein diacetate), intracellular-reactive oxygen species concentration (hydroethidine) and intracellular pH (carboxy-fluorescein diacetate succinimidyl ester 5-(6)) were monitored to evaluate the physiological state and the overall fitness of individual bacterial cells under oxidative stress. The four bacterial strains exhibited varying sensitivities towards H₂O₂. However, for all the bacterial strains, some physiological damage could already be observed from 13.25 mM H₂O₂ onwards, in particular with regard to their membrane permeability. Depending on the bacterial strains, moderate to high physiological damage could be observed between 13.25 mM and 220 mM H₂O₂. The membrane potential, esterase activity, intracellular pH and production of superoxide anion production were in all four strains considerably modified at high H₂O₂ concentrations. In conclusion, we show that a range of significant physiological alterations occur when bacteria are challenged with H₂O₂ and fluorescent staining methods coupled with flow cytometry are used for monitoring the changes induced not only by oxidative stress, but also by other stresses like temperature, radiation, pressure, pH, etc. The text was submitted by the authors in English.     

Use of carbon monoxide and hydrogen by a bacteria–animal symbiosis from seagrass sediments

The gutless marine worm Olavius algarvensis lives in symbiosis with chemosynthetic bacteria that provide nutrition by fixing carbon dioxide (CO₂) into biomass using reduced sulfur compounds as energy sources. A recent metaproteomic analysis of the O. algarvensis symbiosis indicated that carbon monoxide (CO) and hydrogen (H₂) might also be used as energy sources. We provide direct evidence that the O. algarvensis symbiosis consumes CO and H₂. Single cell imaging using nanoscale secondary ion mass spectrometry revealed that one of the symbionts, the γ3‐symbiont, uses the energy from CO oxidation to fix CO₂. Pore water analysis revealed considerable in‐situ concentrations of CO and H₂ in the O. algarvensis environment, Mediterranean seagrass sediments. Pore water H₂ concentrations (89–2147 nM) were up to two orders of magnitude higher than in seawater, and up to 36‐fold higher than previously known from shallow‐water marine sediments. Pore water CO concentrations (17–51 nM) were twice as high as in the overlying seawater (no literature data from other shallow‐water sediments are available for comparison). Ex‐situ incubation experiments showed that dead seagrass rhizomes produced large amounts of CO. CO production from decaying plant material could thus be a significant energy source for microbial primary production in seagrass sediments.     

Modulation of sensory perception by hydrogen peroxide enables Caenorhabditis elegans to find a niche that provides both food and protection from hydrogen peroxide

Hydrogen peroxide (H₂O₂) is the most common chemical threat that organisms face. Here, we show that H₂O₂ alters the bacterial food preference of Caenorhabditis elegans, enabling the nematodes to find a safe environment with food. H₂O₂ induces the nematodes to leave food patches of laboratory and microbiome bacteria when those bacterial communities have insufficient H₂O₂-degrading capacity. The nematode’s behavior is directed by H₂O₂-sensing neurons that promote escape from H₂O₂ and by bacteria-sensing neurons that promote attraction to bacteria. However, the input for H₂O₂-sensing neurons is removed by bacterial H₂O₂-degrading enzymes and the bacteria-sensing neurons’ perception of bacteria is prevented by H₂O₂. The resulting cross-attenuation provides a general mechanism that ensures the nematode’s behavior is faithful to the lethal threat of hydrogen peroxide, increasing the nematode’s chances of finding a niche that provides both food and protection from hydrogen peroxide.     

Molybdenum doped titanium dioxide photocatalytic coatings for use as hygienic surfaces: the effect of soiling on antimicrobial activity

Titanium dioxide (TiO₂) surfaces doped with molybdenum (Mo) were investigated to determine if their photocatalytic ability could enhance process hygiene in the brewery industry. Doping TiO₂ with Mo showed a 5-log reduction in bacterial counts within 4 to 24?h and a 1-log reduction in yeast numbers within 72?h. The presence of a dilute brewery soil on the surface did not interfere with antimicrobial activity. The TiO₂–Mo surface was also active in the dark, showing a 5-log reduction in bacteria within 4 to 24?h and a 1-log reduction in yeast numbers within 72?h, suggesting it could have a novel dual function, being antimicrobial and photocatalytic. The study suggests the TiO₂–Mo coating could act as a secondary barrier in helping prevent the build-up of microbial contamination on surfaces within the brewery industry, in particular in between cleaning/disinfection regimes during long production runs.     

Effect of Biocides on Biofilm Bacteria from Dental Unit Water Lines

Microbial biofilm formation in dental unit water lines (DUWL) is a phenomenon that has been recognized for nearly four decades. Water delivered by DUWL can harbor high numbers of bacteria, including opportunistic pathogens. Biofilms on tubing within DUWL may serve as a reservoir for these microorganisms and should therefore be controlled. In this study, the effects of eight biocides were monitored on DUWL biofilms individually and in combination by epifluorescence microscopy and total viable counts (TVC). The effects of sodium dodecyl sulphate (SDS), hydrogen peroxide (H₂O₂), sodium hypochlorite (NaOCl), phenol (Phe), Tween 20 (Tw 20), ethylenediaminetetraacetic acid (EDTA), chlorohexidine gluconate (CHX), and povidine iodine (PI) were tested on DUWL biofilms alone and in combination. PI was found to have negligible effects on biofilm removal either applied alone or in combined form with CHX. Applying all biocides simultaneously did not completely eliminate viable bacteria nor did they remove biofilm. Overall, when combined, the biocides performed better than singly applied products. The most effective biocides were NaOCl and Phe (both alone and in combination).     

The Screening of Hydrogen Peroxide-Producing Lactic Acid Bacteria and Their Application to Inactivating Psychrotrophic Food-Borne Pathogens

Lactic acid bacteria were isolated from various food samples and evaluated for hydrogen peroxide (H₂O₂) production. Cells suspended in 0.5% (wt/vol) glucose plus 0.5% (wt/vol) lactate (pH 7.0) were incubated for 5 h at 37°C under aeration. Among 193 strains, 27 strains accumulated 201-300 ppm H₂O₂, and 4 strains accumulated more than 301 ppm H₂O₂ in the cell suspensions. Among the 9 high-level H₂O₂-producing strains, 8 strains were identified as Lactococcus lactis subsp. lactis. The cell-free filtrate from Lc. lactis subsp. lactis AI 62, which contained approximately 350 ppm H₂O₂, was evaluated for antimicrobial activity against Enterococcus faecalis, Ent. faecium, enterotoxigenic Escherichia coli, Listeria ivanovii, Staphylococcus aureus, Yersinia enterocolitica, and Aeromonas hydrophila. After 1 h incubation at 30°C in the cell-free filtrate, the initial viable cell counts of the target bacteria (5.53–6.00 log cfu/mL) were reduced by 0.12-5.00 log units, except in the case of enterococci. The sensitivity varied with the bacterial species and pH. The enterococci were resistant to the treatment. Our results show that H₂O₂ accumulated by lactic acid bacteria in a cell suspension is very effective in reducing the viable cell count of food-borne pathogens.Received: 7 October 2002 / Accepted: 4 November 2002     

Crystal structure of the Haemophilus influenzae Hap adhesin reveals an intercellular oligomerization mechanism for bacterial aggregation

Bacterial biofilms are complex microbial communities that are common in nature and are being recognized increasingly as an important determinant of bacterial virulence. However, the structural determinants of bacterial aggregation and eventual biofilm formation have been poorly defined. In Gram‐negative bacteria, a major subgroup of extracellular proteins called self‐associating autotransporters (SAATs) can mediate cell–cell adhesion and facilitate biofilm formation. In this study, we used the Haemophilus influenzae Hap autotransporter as a prototype SAAT to understand how bacteria associate with each other. The crystal structure of the H. influenzae Hap_S passenger domain (harbouring the SAAT domain) was determined to 2.2 Å by X‐ray crystallography, revealing an unprecedented intercellular oligomerization mechanism for cell–cell interaction. The C‐terminal SAAT domain folds into a triangular‐prism‐like structure that can mediate Hap–Hap dimerization and higher degrees of multimerization through its F1–F2 edge and F2 face. The intercellular multimerization can give rise to massive buried surfaces that are required for overcoming the repulsive force between cells, leading to bacterial cell–cell interaction and formation of complex microcolonies.