Biofilm formation is a severe health concern in NICUs and a persistent threat, as it increases both morbidity and mortality. Bacterial biofilms are immobile microbial communities with diverse bacterial cell colonies in groups, which colonize and grow on the surfaces of almost all medical devices or prostheses [82]. The development of biofilm has many stages, including attachment of macro and micro molecules to surfaces, colonization and proliferation of bacterial pathogens, the release of extracellular polymeric substances and biofilm maturation and detachment [83,84,85].

It has been estimated that most bacterial infections in humans are correlated with biofilms and about 50% of the nosocomial infections are indwelling-device associated [86]. Neonates hospitalized in NICUs are at a high risk of biofilm infections, since they often need central lines, endotracheal tubes, umbilical arterial and vein catheters and peripheral central lines for a prolonged duration. Bacterial biofilms are highly resistant to antibiotic treatments and immune responses [87]. Biofilms provide protection to bacteria from the pH, nutrient deficiency and mechanical forces, and also prevent antibiotic and host immune cells from gaining access to their bacteria [83,84,88]. Therefore, biofilms contribute to persistent and resistant chronic infections.

Bacteria that have been associated with biofilm infections in central venous catheters are Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis, while numerous other bacteria have been associated with biofilm infections in other adherent surfaces [83].

Although it is well known that antibiotic treatment is currently the most important and effective measure of control for microbial infections, antibiotic treatments are almost impossible to eradicate biofilm infections [86]. The development of intact biofilms is critical for the spreading and persistence of bacterial infections in the host [84]. Therefore, biofilms give the power to bacteria to become resistant to antibiotics.

As already described, biofilm infections are chronic and can have exacerbations. Antimicrobial therapy can be helpful in mitigating an exacerbation, but cannot fully eradicate the bacteria in a biofilm [86]. Since biofilms are multimicrobial, antibiotic therapy should cover against Gram-positive, Gram-negative and fungal microorganisms, as well as resistant bacteria. The above facts render treatment of a biofilm infection really challenging. Antibiotics are more effective when used in the early stages of biofilm formation, probably because the cells are not completely embedded into biofilm communities [83,89,90]. The antibiotic regimens should have a wide spectrum and employ different modes of action. Removal of the foreign body or replacement of the central venous catheter is almost always mandatory to successfully control a biofilm infection [86]. A short course of intravenous antibiotic treatment is also important to eradicate the bacteria that were released into the bloodstream.

There are many novel approaches under development for the prevention and treatment of biofilm infections. Specific agents may inhibit the initial biofilm attachment, result in the removal of biofilms or inhibit biofilm formation by quorum quenching (the communication process among cells) [91]. Initial biofilm attachment can be inhibited by altering either the chemical or physical properties of the biomaterials. For example, antibiotics, biocides and ion coatings modify the surface of devices and inhibit biofilm formation [92]. Moreover, hydrophilic polymers, such as hyaluronic acid and poly N-vinylpyrrolidone, alter the hydrophobicity of polymeric materials and reduce the adhesion of microbes [93,94]. This occurs in the same way by altering the physical properties of devices, various superhydrophobic surfaces, hydrogel coatings and heparin coatings [95,96]. Another studied field is the novel ways to remove biofilms. Matrix-degrading enzymes have the purpose of dissociating a biofilm matrix and allowing antimicrobials to act more drastically [97]. Furthermore, free fatty acids, specific amino acids and nitric oxide generators have been shown to induce biofilm dispersal against several bacteria [98,99]. Quorum sensing is crucial in biofilm formation, therefore several strategies have been studied to inhibit this system of cellular communication in biofilm [91]. Molecules that degrade, inhibit or antagonize quorum sensing signals have been studied, as well as molecules that inhibit signal transduction or transportation [91]. These novel approaches could lead to anti-biofilm therapies in the future, that are much more effective than current antibiotic treatments [83,84,86,100].