formation include many steps (Crouzet, Le Senechal et al. 2014)
Bacterial attachment to a surface –
specific proteins like Bap in Staphylococcus aureus helped in the initial attachment to any abiotic surface
during the time of biofilm formation (Cucarella,
Solano et al. 2001). Operons including icABCD gene
clusters in S epidermis and S aureus are important as they lead to attachment
and further biofilm production, might be the reason of increased antibiotic
resistances among these strains (Nourbakhsh
and Namvar 2016). Ability of biofilms to grow on
surfaces of inanimate objects is mainly responsible for most of the hospital
acquired infections as these surfaces host biofilm production. A serine
aspartate repeat protein Sdr C is involved in homophillic bond formation that
commence the adhesion process in Staphylococcus aureus (Feuillie,
Formosa-Dague et al. 2017).
Microcolony formation- there is a change
in colony morphology, aggregation of the bacterial cells forms a distinct
microcolony. In a study on Pseudomonas
aeruginosa it was experimentally proved that when a suitable media is
provided this bacteria experience tighter colony morphology (Sriramulu, Lunsdorf et al. 2005). biofilm developed comprises
mushroom-shaped microcoloniesof bacteria that are surrounded by an
extracellular polysaccharide matrix and separated by fluid-filled channels.
Maturation- during this step they show
the synthesis of EPS matrix, antibiotic resistance, increased genetic changes
altered biodegradative properties and also exhilarated genetic exchange (O’Toole and Kolter 1998). EPS is not
just polysaccharide matrix but also contain a wide variety of proteins, glycoproteins,
and glycolipids and some extracellular DNA (e-DNA) (Flemming, Neu et al. 2007).
3.1 Components of EPS matrix- study has
declared that in Pseudomonas aeruginosa
the matrix comprises of alginate (O’Toole
and Kolter 1998). The bacterial isolates from the
lung tend to produce more alginate matrix which might be a factor in causing
resistance for antibiotics tobramycin which was used as
antibiotic for cystic fibrosis patients. (Hoyle and Costerton 1991). Colanic acid
is the most important EPS in E coli but
plays no role in initial colonization. CPSs may be important in mature biofilms, aiding in the
maintenance of biofilm size and dispersal in V vulinficans (Limoli, Jones et al. 2015).
A. baumannii Bap protein is required for stabilility
of mature biofilms on glass surface (Loehfelm, Luke et al. 2008).
resistance due to the EPS matrix- several researches in past have established
that multiple antibiotic resistance (mar) operon genes were not induced while
the formation of biofilms, E coli mar mutant strains tend to show
antibiotic resistance during the formation of biofilms within it (Maira-Litrán, Allison et al. 2000) proving that
biofilm does induce antibiotic resistance. Strains of Pseudomonas aeruginosa that were
devoid of MexAB-OprM efflux pumps also remained resistance to ciprofloxacin (Brooun, Liu et al. 2000). There have
been proposed different mechanisms for the antibiotic resistance property
showed by the bacteria.
Slow or incomplete penetration of the
antibiotics due to the presence of thick polysaccharide matrix.
Alteration of the chemical
microenvironment which forces the cells to enter in a non growing state hence
can’t be easily targeted by the antibiotics.
present in biofilms might also form subpopulation that is very distinct, unique
and highly protective spore like state.
Dispersal of biofilms- Cells within the
biofilms are capable of motility which builds a shape of the biofilm this
allows them to escape the stress conditions and also allows its dispersal.
Microorganisms capable of biofilm formation usually exhibit one or more of the
three main types of motility – swimming, twitching and swarming – which depend
on flagella and type IV pili (or frimbriae) (Guttenplan and Kearns 2013). Pseudomonas aeruginosa, is one of the rare bacterial species that
possess the capability of all three types of motility (O’Toole and Kolter 1998). In times of
nutrient deprivation bacteria detach from the surface enters the planktonic
mode of growth which allow the easy search of fresh new source of nutrition (Kolter, Siegele et al. 1993).