**5.3 Hydrodynamics**

*Bacterial Biofilms*

three assumptions have been made:

antibacterial effects [2].

chemical reactions [7].

difficult to eradicate [12].

**5.1 Substratum effects**

having hydrophilic properties.

tially better than antibiotic monotherapy [12].

**5. Factors affecting biofilm formation**

antibacterial drugs) for killing biofilm cells of *Staphylococcus aureus* as compared with its planktonic form [9]. Moreover, as compared to planktonic form, bacteria in biofilms shows a discrete physiology like reduced metabolic rate and enhanced cell to cell communication which helps in developing resistance to antibiotics or reduce their effects [10]. In the attempt to describe the resistance of biofilms to antibiotics,

1. Slow or partial diffusion of antibiotics into inner layers of biofilm. This is due to EPS matrix which has biofilm entrenched bacteria, act as a diffusive barrier [2].

2.In the biofilm microenvironment, some microbial cells fall into a state of slow growth or starvation due to nutrient limitation or accumulation of harmful metabolites. These are not vulnerable to many antimicrobial agents [2, 11].

3.The differentiation of a bacterial subpopulation resembles the process of spore formation. It has a distinctive and highly resistance phenotype (a biologically programmed response to bacterial sessile life form) that protects them from

Presence of neutralizing enzymes also contributes to the antibiotic resistance in the biofilm. These proteinaceous enzymes degrade or inactivate antibiotics by mechanisms like hydrolysis and modification of antimicrobials by different bio-

Although, intensive and insistent treatment of antibiotic is effective in reducing the biofilm and controlling the exacerbations of chronic biofilm infections but are not able to eliminate biofilm infections it is possibly because the minimal concentration of antibiotic (required to eliminate a mature biofilm) is challenging to reach *in vivo*. Hence, if a bacterial biofilm infection is established, it becomes much

Experimental studies suggested that in most of the cases antibiotic treatment alone is not sufficient to eliminate infections of biofilm [12]. In a study, a nanoparticle called ciprofloxacin-loaded poly (lactic-co-glycolic acid), that were functionalized with DNase I, were prepared to observe their antibiofilm activity against *P. aeruginosa* biofilms. It has been found that they release ciprofloxacin in a controlled manner, as well as they effectively target and disassemble the biofilm by degrading the extracellular DNA that stabilizes the EPS [10]. Biofilm combination therapy is usually recommended for treating biofilm infections as this is found to be substan-

A number of factors such as substratum effects, hydrodynamics and various properties of cell surface play an important role in microbial attachment [1].

As the surface roughness increases microbial colonization increases because as the roughness increases, surface area increases and shear forces get diminished. And considering extent and rate of attachment, it has been seen that microorganisms get attached to more rapidly to hydrophobic and nonpolar surfaces as Teflon and other plastics rather than to glass and other materials

**152**

The hydrodynamic flow layer is the zone of negligible flow which is found at the immediately adjacent to the substratum/liquid interface. The flow velocity of this zone is negligible and its thickness is inversely proportional to the linear velocity. Substantial mixing or turbulence is the main characteristics shown by the region outside the boundary layer. The hydrodynamic boundary layer can considerably affect the interaction between cells and substratum. The velocity characteristic of the liquid governs the association of cells with the submerged surfaces. At, very low linear velocities, the cells must navigate through the hydrodynamic boundary layer, and cell size and cell motility govern its association with the surface. The boundary layer decreases, as the velocity increases and cells will be exposed to progressively larger turbulence and mixing. Therefore, higher linear velocities would be supposed to form a more rapid association with the surface, at least until velocities become high enough to apply abundant shear forces on the attaching cells, that results in detachment of these cells [1].

## **5.4 Characteristics of the aqueous medium**

Characteristics of the aqueous medium such as temperature, pH, nutrient level and ionic strength possibly play an important role in attachment of microbes with the substratum. As an example, it has been found that the attachment of *Pseudomonas fluorescens* to glass surface is affected by an increase in the concentration of several cations (sodium, calcium, lanthanum, ferric iron), perhaps by reducing the repulsive forces between the negatively charged bacterial cells and the glass surfaces.
