# Anti-Biofilm Agents to Overcome _Pseudomonas aeruginosa Antibiotic Resistance_
## 3 Anti-Biofilm Agents to Tackle _P. aeruginosa_
### Analogs of Native Autoinducers
#### 3.1.5 Conventional Antibiotic Repurposing and Anti-Biofilm Nanocarriers  
Like antimicrobial peptides, some conventional antibiotics also show anti-biofilm efficacy at sub-MIC concentrations. Although their anti-virulence targets mostly remain uncertain, their action against the biofilm formation or in favor of its dispersion seems  
Figure 14: Anti-biofilm activities of AMPs developed de novo by rational design and/or by computer-assisted conception [93; 94; 95; 96; 97; 98; 101].  
promising. For instance, 5-nitro-8-hydroxyquinoline (nitroroline, **ABA-51**) inhibits 60% of biofilm formation at 42 uM (8 ug/mL, % MIC) by complex essential ions for the bacterial metabolism such as iron or zinc (Figure 15) [102]. Moreover, nitroroline stimulates the dispersal of 65% of a preformed biofilm, according to the stimulation of twitching motility. In 2014, a study conducted by [PERSON] and [PERSON] also highlighted the anti-biofilm potential of six other conventional ATBs against _P. aeruginosa_[103]. Ceftazidime (**ABA-52**), doripenem (**ABA-53**), piperacillin (**ABA-54**), ciprofloxacin (**ABA-55**), tobramycin (**ABA-56**) and colistin (**ABA-57**) inhibited the formation of biofilm by 40 to 68% at 1/10 MIC, i.e., in the range of a tenth of a micromolar. Those ATBs decrease between 22 and 62% bacterial attachment during the four first hours of biofilm establishment, at 1/10 MIC. However, they have no effect on mature biofilms. Colistin appears the most interesting conventional ATB for use as an ABA by reducing 45% of biofilm formation at 2 nM, i.e., 1/100 MIC. It is yet a last-resort ATB because of its high nephrotoxicity.  
Figure 15: Anti-biofilm activities of conventional antibiotics [102; 103].  
Nanocarriers are another novel promising anti-virulence approach for biofilm inhibition. In fact, the last few years have seen a growing interest in the development of liposomal formulations able to restore ATBs' efficacy by improving their penetration inside the extracellular matrix. The encapsulation of molecules or their attachment to the nanovector surface protects them from metabolization, improves their bioavailability, reduces their toxicity and increases their efficacy by ensuring a targeted delivery (Figure 16) [104]. Moreover, it has been shown that small spherical nanocarriers can diffuse through the extracellular matrix and could therefore deliver ATBs. Liposomes, biomimetics of cell membranes, offer a transport for both hydrophilic (inside the core) and hydrophobic (in the lipidic bilayer) molecules. The liposomal formulas are easily modifiable, enabling the refinement of their physicochemical properties such as their size, shape, charge, hydrophilicity or lipophilicity to optimize the drug's transport towards the action site. Their surface can be functionalized with polyethylene glycols (PEGs), which improve their biodistribution by protecting them from macrophages. The surface charge and the pegylation of liposomes also influence their interactions with biofilms. Hence, [PERSON] et al. have described that cationic pegylated liposomes are more efficient against biofilms than their anionic counterparts as they possess stronger electrostatic affinity with the negatively charged biofilm surface and a better matrix permeability [105]. Interestingly, a treatment with empty liposomes can also destabilize the biofilm and trigger its dispersal.