BIOFILMS

BIOFILM

Biofilms:

Microorganisms’ populations which multiply when adhered to a surface and embedded usually in an extracellular matrix (mainly exopolysaccharides)

Bacteria in the planktonic phase (free “swimming”)

Fixed bacteria (sessile) Surface able to be colonized

(rough)

(The presence of nutrients conditions the change from reversible adhesion to not-reversible adhesion phases)

BIOFILM’s FUNCTIONS To protect microorganisms from external attacks

• There is a barrier effect created by the polysaccharides, limiting the diffusion of foreign molecules. Directly, is only effective against big molecules (e.g. antibiotics) but increases the enzymatic effect even with small molecules like hydrogen

• Ionic effect of the usually negatively charged polysaccharides, which fix the positively charged molecules reaching the biofilm, like aminoglycosylated antibiotics or quaternary ammonia

• Enzymatic effect. Immobilization of several enzymes, like b-lactamase or peroxidase in the extracellular matrix

• Chemical effect. Reaction of the extracellular polysaccharides with several disinfectant molecules, like hypochlorite

• Physiological effect. In the biofilm suboptimal conditions are created, representing a stress condition, where bacteria use to be more resistant than in optimal conditions

• Genetic effect. Due to existing proximity conditions and relationships, gene transfer causing increased resistance to several agents (e.g. antibiotics) can be described usually

Nutrients are fixed by the biofilm

BIOFILM FORMATION

• Pseudomonas fragi over inox steel, after 24h at 23ºC

The presence of exopolysaccharides branches can be observed This initiates the microorganisms anchorage

• Ps fragi (PS) over inox steel, after 10 days at 7ºC

It is to note the accumulation of extracellular material (exopolysaccharides) entrapping dirt

• Joint development of Ps fragi and Listeria monocitogenes over inox steel, after 7 days at 7ºC

One of the microorganisms (Ps fragi) is mainly forming the biofilm, where the other organism is embedded with the dirt not decomposed

BIOFILM

Biofilm formed by Ps aeruginosa, over a nitrilic rubber, after 64 hours incubation

Biofilm formed by Ps aeruginosa, over a inox steel surface, after 93 hours incubation

THEORETICAL PROCESS OF BIOFILM FORMATION

BIOFILM ELIMINATION

If surfaces are not being cleaned before disinfection:

• The real focuses of pollution are not being eliminated

• A basis of substrate remains which is a culture media for new development of microorganisms

• Layers of material remain which impede the access of disinfectants to the target microorganisms

If surfaces are not disinfected after cleaning, an excessive number of organisms remain on the surfaces; they will easily multiply again

BIOFILM IMPORTANCE

Nevertheless, Biofilms are important in nature and water treatment, since (e.g.)

• Are the basis for a number of water treatments • Constitute the major system of self-treatment in water bodies