biofilm细菌矩阵

• 1 Oral bacteria
  • 1.1 Fusospirochetes
  • 1.2 Veillonella
  • 1.3 Aggregatibacter actinomycetemcomitans
  • 1.4 Lactobacillus
• 2 Dental plaque
• 3 Cell-cell communication
• 4 Vaccination(接种疫苗) against oral infections(感染)
• 5 See also
• 6 References
• 7 External links

• 1 重要性
• 2 特點
• 3 結構
• 4 形成
• 5 防止

A biofilm is any group of microorganisms in which cells stick to each other on a surface. Theseadherent(信徒) cells are frequently embedded(栽种) within a self-produced matrix(矩阵) ofextracellular polymeric substance(物质) (EPS). Biofilm(生物膜) EPS, which is also referred to asslime (although not everything described as slime is a biofilm), is a polymeric conglomeration(聚集) generally composed(构成) of extracellular(细胞外的) DNA, proteins, and polysaccharides.Biofilms(生物膜) may form on living or non-living surfaces and can be prevalent(流行的) in natural, industrial(工业股票) and hospital settings.^[2][3] The microbial(微生物的) cells growing in a biofilm are physiologically distinct from planktonic cells of the same organism(有机体), which, by contrast(对比), are single-cells that may float or swim in a liquid medium(方法).

Microbes(细菌) form a biofilm in response to many factors(因素), which may include cellular(细胞的) recognition(识别) of specific(特殊的) or non-specific(不明确的) attachment(附件) sites on a surface, nutritional(营养的) cues(提示), or in some cases, by exposure(暴露) of planktonic(浮游生物的) cells to sub-inhibitory concentrations(浓度) of antibiotics(抗生素).^[4][5] When a cellswitches(开关) to the biofilm(生物膜) mode of growth, it undergoes(经历) a phenotypic shift(移动)in behavior(行为) in which large suites of genes are differentially(微分的) regulated.^[6]

Formation

Formation(形成) of a biofilm(生物膜) begins with the attachment(附件) of free-floatingmicroorganisms(微生物) to a surface. These first colonists(殖民者) adhere(坚持) to the surface initially through weak, reversible(可逆的) adhesion(粘附) via van der Waals forces. If the colonists are not immediately separated from the surface, they can anchor(抛锚) themselves morepermanently(永久地) using cell adhesion structures such as pili.^[7] Hydrophobicity also plays an important role in determining the ability of bacteria to form biofilms, as those with increasedhydrophobicity(疏水性) have reduced repulsion(排斥) between the extracellular matrix and the bacterium.^[8] Some species(物种) are not able to attach(依附) to a surface on their own but are sometimes able to anchor(抛锚) themselves to the matrix(矩阵) or directly to earlier colonists(殖民者). It is during this colonization(殖民) that the cells are able to communicate via quorum sensing using products such as AHL. Some bacteria are unable to form biofilms(生物膜) as successfully due to their limited motility(运动性). Nonmotile(无运动的) bacteria cannot recognize the surface or aggregate(集合) together as easily as motile(能动的) bacteria.^[9] Once colonization has begun, the biofilm grows through a combination(结合) of cell division and recruitment(补充).Polysaccharide matrices(矩阵) typically(典型的) enclose(围绕) bacterial(细菌的) biofilms. In addition to the polysaccharides(多糖), these matrices may also contain material from the surrounding environment, including but not limited to minerals, soil particles(颗粒), and bloodcomponents(成分), such as erythrocytes(红细胞) and fibrin(纤维蛋白).^[10] The final stage of biofilm formation(形成) is known as dispersion(散布), and is the stage in which the biofilm isestablished(确定的) and may only change in shape and size. The development of a biofilm may allow for an aggregate cell colony(殖民地) (or colonies) to be increasingly antibiotic(抗生的)resistant(抵抗者).

Development

Five stages of biofilm(生物膜) development: (1) Initial attachment(附件), (2) Irreversible attachment, (3) Maturation I, (4) Maturation II, and (5) Dispersion. Each stage of development in the diagram is paired with a photomicrograph(显微照片) of a developing P. aeruginosa biofilm. All photomicrographs are shown to same scale(规模).

There are five stages of biofilm development (see illustration(说明) at right):

1. Initial attachment:
2. Irreversible attachment:
3. Maturation I:
4. Maturation II:
5. Dispersion:

Dispersal

Dispersal(分散) of cells from the biofilm colony(殖民地) is an essential stage of the biofilm life cycle. Dispersal enables biofilms to spread and colonize(移于殖民地) new surfaces. Enzymes(酶)that degrade(贬低) the biofilm(生物膜) extracellular(细胞外的) matrix(矩阵), such as dispersin Band deoxyribonuclease, may play a role in biofilm dispersal(分散).^[11][12] Biofilm matrixdegrading(贬低) enzymes(酶) may be useful as anti-biofilm agents.^[13][14] Recent evidence(证据)has shown that a fatty(胖子) acid(酸) messenger(报信者), cis-2-decenoic acid, is capable(能干的)of inducing(产生诱导作用的) dispersion(散布) and inhibiting(抑制作用的) growth of biofilm(生物膜)colonies(殖民地). Secreted(分泌) by Pseudomonas aeruginosa, this compound(复合的) induces cyclo(三轮车) heteromorphic(异形的) cells in several species(物种) of bacteria and the yeast(酵母) Candida albicans.^[15] Nitric(氮的) oxide(氧化物) has also been shown to trigger(引发) the dispersal(分散)of biofilms of several bacteria species ^[16][17] at sub-toxic concentrations(浓度). Nitric oxidehas the potential(潜能) for the treatment of patients that suffer from chronic(慢性的)infections(感染) caused by biofilms.^[18]

Properties

Biofilms(生物膜) are usually found on solid substrates submerged(水下的) in or exposed to anaqueous solution, although they can form as floating mats on liquid surfaces and also on the surface of leaves, particularly in high humidity(湿度) climates. Given sufficient(足够的)resources for growth, a biofilm will quickly grow to be macroscopic(宏观的) (visible(可见物) to the naked(裸体的) eye). Biofilms can contain many different types of microorganism(微生物), e.g.bacteria, archaea, protozoa, fungi and algae; each group performs specialized(专门从事) metabolicfunctions. However, some organisms(有机体) will form single-species films under certain conditions. The social structure(结构) (cooperation(合作), competition) within a biofilm(生物膜)highly depends on the different species(物种) present.^[19]

Extracellular matrix

The biofilm is held together and protected by a matrix(矩阵) of secreted(分泌) polymericcompounds(化合物) called EPS. EPS is an abbreviation(缩写) for either extracellular(细胞外的)polymeric(聚合的) substance(物质) or exopolysaccharide. This matrix protects the cells within it and facilitates(促进) communication among them through biochemical(生物化学的) signals. Some biofilms have been found to contain water channels that help distribute(分配) nutrients and signalling molecules.^[20] This matrix(矩阵) is strong enough that under certain conditions,biofilms(生物膜) can become fossilized (Stromatolites).

Bacteria living in a biofilm usually have significantly(意味深长地) different properties from free-floating bacteria of the same species(物种), as the dense(稠密的) and protected environment of the film allows them to cooperate(合作) and interact(互相影响) in various ways. One benefit(利益) of this environment is increased resistance(阻力) to detergents and antibiotics, as the denseextracellular(细胞外的) matrix and the outer layer of cells protect the interior(内部) of the community. In some cases antibiotic(抗生的) resistance can be increased a thousandfold(千倍地).^[21] Lateral gene transfer is greatly facilitated(促进) in biofilms and leads to a more stable(马厩) biofilm structure(结构).^[22]

However, biofilms(生物膜) are not always less susceptible(易受影响的) to antibiotics(抗生素). Forinstance(举…为例), the biofilm form of Pseudomonas aeruginosa has no greater resistance(阻力) toantimicrobials(抗菌剂) than do stationary-phase planktonic(浮游生物的) cells, although when the biofilm is compared to logarithmic(对数的) phase(相) planktonic cells, the biofilm does have greater resistance to antimicrobials. This resistance to antibiotics in both stationary(固定的)phase cells and biofilms may be due to the presence(存在) of persister cells.^[23]

Examples

Biofilm in Yellowstone National Park. Longest raised mat area is about half a meter long.

Thermophilic(适温的) bacteria in the outflow(流出) of Mickey Hot Springs, Oregon,approximately(大约) 20 mm thick.

Biofilms(生物膜) are ubiquitous(普遍存在的). Nearly every species(物种) of microorganism(微生物), not only bacteria and archaea(古生菌), have mechanisms(机制) by which they can adhere(坚持) to surfaces and to each other. Biofilms will form on virtually(事实上) every non-shedding surface in a non-sterile aqueous(水的) (or very humid(潮湿的)) environment.

• Biofilms can be found on rocks and pebbles(卵石) at the bottom of most streams or rivers and often form on the surface of stagnant pools of water. In fact, biofilms are importantcomponents(成分) of food chains in rivers and streams and are grazed(擦破的) by the aquatic(水生的) invertebrates upon which many fish feed.
• Biofilms can grow in the most extreme(极端的) environments: from, for example, the extremely hot, briny(海水的) waters of hot springs ranging from very acidic(酸的) to very alkaline(碱性的), to frozen glaciers.
• In the human environment, biofilms can grow in showers very easily since they provide amoist(潮湿) and warm environment for the biofilm to thrive(繁荣). Biofilms can form inside water and sewage(污水) pipes and cause clogging(堵塞) and corrosion. Biofilms(生物膜) on floors and counters can make sanitation(环境卫生) difficult in food preparation areas.
• Biofilms in cooling- or heating-water systems are known to reduce heat transfer(转让).^[24]
• Biofilms in marine(船舶的) engineering systems, such as pipelines(管道) of the offshore oil and gas industry,^[25] can lead to substantial(大量的) corrosion(腐蚀) problems. Corrosion is mainly due to abiotic(非生物的) factors(因素); however, at least 20% of corrosion is caused bymicroorganisms(微生物) that are attached(依附) to the metal subsurface(地表下岩石) (i.e.,microbially(微生物的) influenced corrosion).
• Bacterial(细菌的) adhesion(粘附) to boat hulls(船体) serves as the foundation(基础) forbiofouling of seagoing(适于远航的) vessels(船). Once a film of bacteria forms, it is easier for other marine organisms(有机体) such as barnacles(藤壶) to attach. Such fouling(污染) can reduce maximum vessel speed by up to 20%, prolonging(延长) voyages and consuming(消费的) fuel. Time in dry dock(码头) for refitting(改装) and repainting(重新绘制) reduces theproductivity(生产力) of shipping assets(资产), and the useful life of ships is also reduced due to corrosion and mechanical(机械的) removal(免职) (scraping(刮)) of marine organisms from ships‘ hulls.
• Biofilms can also be harnessed(治理) for constructive(建设性的) purposes. For example, manysewage treatment plants include a treatment stage in which waste water passes over biofilms grown on filters, which extract(汁) and digest organic(有机的) compounds(化合物). In such biofilms, bacteria are mainly responsible(负责的) for removal of organic matter (BOD), whileprotozoa and rotifers are mainly responsible(负责的) for removal(免职) of suspended(悬浮的)solids (SS), including pathogens(病原体) and other microorganisms(微生物). Slow sand filtersrely(依靠) on biofilm(生物膜) development in the same way to filter surface water from lake, spring or river sources for drinking purposes. What we regard as clean water is effectively(有效地) a waste material to these microcellular organisms(有机体).
• Biofilms can help eliminate(消除) petroleum oil from contaminated(受污染的) oceans ormarine(船舶的) systems. The oil is eliminated by the hydrocarbon-degrading activities ofmicrobial(微生物的) communities, in particular by a remarkable(卓越的) recently discovered group of specialists, the so-called hydrocarbonoclastic bacteria (HCB).^[26]
• Stromatolites are layered accretionary structures(结构) formed in shallow water by the trapping, binding(结合) and cementation(黏结) of sedimentary(沉淀的) grains by microbial biofilms, especially of cyanobacteria. Stromatolites(叠层) include some of the most ancient records of life on Earth, and are still forming today.
• Biofilms(生物膜) are present on the teeth of most animals as dental plaque, where they may cause tooth decay and gum disease.
• Biofilms are found on the surface of and inside plants. They can either contribute(贡献) to crop disease or, as in the case of nitrogen-fixing Rhizobium on roots, exist symbiotically with the plant.^[27] Examples of crop diseases related to biofilms include Citrus Canker,Pierce‘s Disease of grapes, and Bacterial Spot of plants such as peppers and tomatoes.^[28]
• Biofilms(生物膜) are used in microbial fuel cells (MFCs) to generate(形成) electricity from a variety of starting materials, including complex(复杂的) organic(有机的) waste andrenewable(可再生的) biomass(生物量).^[3]

Biofilms and infectious(传染的) diseases

Biofilms have been found to be involved(包含) in a wide variety of microbial(微生物的)infections(感染) in the body, by one estimate(估计) 80% of all infections.^[29] Infectious processes in which biofilms have been implicated(暗示) include common problems such as urinary tract infections, catheter infections, middle-ear infections, formation of dental plaque,^[30]gingivitis,^[30] coating contact lenses,^[31] and less common but more lethal(致命的) processes such as endocarditis, infections in cystic fibrosis, and infections(感染) of permanent(永久的)indwelling(存在于…之中) devices(装置) such as joint(关节) prostheses and heart valves.^[32][33]More recently it has been noted that bacterial(细菌的) biofilms(生物膜) may impair(损害)cutaneous(皮肤的) wound healing and reduce topical(局部的) antibacterial(抗菌剂) efficiency(效率)in healing or treating infected(被感染的) skin wounds.^[34]

It has recently been shown that biofilms are present on the removed tissue(纸巾) of 80% of patients undergoing(经历) surgery(外科) for chronic(慢性的) sinusitis. The patients with biofilms were shown to have been denuded(剥夺) of cilia and goblet cells, unlike the controls withoutbiofilms(生物膜) who had normal cilia(纤毛) and goblet(酒杯) cell morphology(形态学).^[35] Biofilms were also found on samples(样品) from two of 10 healthy controls mentioned. The species(物种) of bacteria from interoperative cultures did not correspond to the bacteria species in the biofilm on the respective(分别的) patient‘s tissue(纸巾). In other words, the cultures were negative(负的)though the bacteria were present.^[36]

Biofilms can also be formed on the inert(惰性的) surfaces of implanted(种植) devices(装置) such ascatheters(导管), prosthetic(假体的) cardiac(心脏的) valves(阀) and intrauterine(子宫内的) devices.^[37]

New staining(着色) techniques are being developed to differentiate(区分) bacterial(细菌的) cells growing in living animals, e.g. from tissues with allergy-inflammations .^[38]

Research has shown that sub-therapeutic levels of β-lactam antibiotics(抗生素) induce(诱导)biofilm formation(形成) in Staphylococcus aureus. This sub-therapeutic level of antibiotic(抗生素)may result from the use of antibiotics as growth promoters(促进) in agriculture, or during the normal course of antibiotic therapy(治疗). The biofilm(生物膜) formation(形成) induced(诱导) by low-level methicillin(甲氧西林) was inhibited(抑制) by DNase, suggesting that the sub-therapeutic levels of antibiotic also induce extracellular(细胞外的) DNA release.^[39]

Dental plaque

Dental plaque is an oral biofilm that adheres(坚持) to the teeth and consists of many species(物种) of both fungal(真菌的) and bacterial(细菌的) cells (such as Streptococcus mutans and Candida albicans), salivary polymers and microbial(微生物的) extracellular products. The accumulation(积聚) of microorganisms(微生物) subjects the teeth and gingival(齿龈的) tissues(纸巾) to highconcentrations(浓度) of bacterial metabolites which results in dental(牙科的) disease.^[30][40]

Legionellosis

Legionella bacteria are known to grow under certain conditions in biofilms(生物膜), in which they are protected against disinfectants. Workers in cooling towers, persons working in air conditioned rooms and people taking a shower are exposed to Legionella by inhalation(吸入) when the systems are not well designed, constructed, or maintained(维持).^[41]