Structural and Molecular Approaches to Observe Biofilms

There are several complementary approaches used such as microscopic imaging, molecular and omics, and quantitative assays.

3.1 Microscopic Techniques

3.1.1 Light Microscopy

Light microscopy is a simple, fast evaluation of the presence of biofilm and morphology. Biofilm aggregates can be seen by staining with Gram or using fluorescent dyes in order to increase contrast. Light microscopy can be used to track the progress of biofilm growth over time on transparent surfaces although it is not particularly versatile in terms of resolution (24).

3.1.2 Confocal Laser Scanning Microscopy (CLSM)

CLSM allows a three dimensional and high-resolution imaging of hydrated biofilms without mechanical disturbance. CLSM can be used to provide spatial data on the architecture, thickness, and distribution of biofilm using fluorescent dyes or genetically encoded fluorescent proteins to give information on live/dead cells. This method is popular in the study of biofilm heterogeneity and dynamics of its structure (4).

3.1.3 Scanning Electron Microscopy (SEM)

SEM also provides a high-resolution surface imaging of biofilms, which provides detailed control of microcolony arrangement, extracellular matrix distribution, and surface adhesion properties. To fix and dehydrate samples, which leads to possible distortions of native biofilm morphology, SEM is still used to visualize the ultrastructure of the surface.

3.1.4 Transmission Electron Microscopy (TEM)

TEM can be used to perform the analysis of internal ultrastructural features of biofilm cells and the EPS matrix. The subcellular structures, EPS composition, and cell-cell interactions are presented through thin sectioning and staining and can help gain knowledge about biofilm physiology on a nanoscale.

3.2 Spectroscopic and Imaging Methodologies.

3.2.1 Fourier-Transform Infrared (FTIR) Spectroscopy.

The chemical composition of biofilms is analyzed by FTIR spectroscopy to identify functional groups of polysaccharides, proteins, lipids and nucleic acids. The approach will give information at a molecular level regarding the composition of EPS and its variation during biofilm maturation.

3.2.2 Raman Spectroscopy

Molecular fingerprinting of biofilms can be achieved non-invasively using the Raman spectroscopy. It also enables the in situ examination of chemical or metabolic states and biofilm heterogeneity without destroying the sample.

3.2.3 Atomic Force Microscopy (AFM)

AFM offers high topographical and mechanical resolution of biofilm surface. AFM can be used to measure biofilm stiffness, adhesion strength, and viscoelasticity at the AFM level by measuring the forces, which is significant in the context of biofilm stability and resistance.

3.3 Molecular and Omics-Based Methodologies

3.3.1 PCR/qPCR

Polymerase Chain Reaction (PCR) and quantitative PCR (qPCR) are used to identify and measure biofilm-associated genes, including adhesins genes, enzymes of EPS synthesis, or antibiotic resistance genes. These are fast, sensitive, and applicable in the monitoring of the populations in biofilms.

3.3.2 Metagenomics

The taxonomic structure and potential functions of microbial communities in biofilms are identified by metagenomic sequencing. It allows the characterisation of unculturable species and predicting metabolic potential of relevance to biofilm formation and persistence.

3.3.3 Proteomics and Transcriptomics

Gene and protein expression in biofilm communities is quantified by transcriptomic and proteomic methods. Such analyses can be used to determine regulatory pathways, stress response pathways, and biofilm-specific virulence factors.

3.3.4 Fluorescence In Situ Hybridization (FISH)

FISH involves the mapping of microbial species in biofilms using fluorescently labeled probes. It enables spatial visualization of the organization of microbes, interspecies interaction, and community dynamics within complex biofilm structures (24, 4).

3.4 Quantification Methods

3.4.1 Crystal Violet Assay

Crystal violet staining has been extensively used in determining the total biofilm biomass. Quantitative estimate of biofilm growth is done speedily through the solubilization of stained biofilms and the absorbance measured spectrophotometrically.

3.4.2 Dry Weight Determination

Quantification of biofilm biomass may be done through harvesting and drying of biofilm. This technique is labor intensive, destructive, and offers direct quantification of biofilm mass.

3.4.3 Colony-Forming Unit (CFU) Enumeration

Biofilm cells are dispersed and then plated to find viable cell counts. The culturable fraction of biofilms is determined by CFU enumeration and is applicable to comparing growth in different conditions.

3.4.4 ATP Bioluminescence Assays

ATP-based assays used to quantify metabolically active biofilm cells through intracellular ATP quantification by luminescence reactions. This method contributes to the quick and delicate estimate of biofilm viability.