*2.3. Temporin A*

Temporin A is a hydrophobic, basic, antimicrobial peptide amide with antibiotic activity against a wide spectrum of microorganisms, including antibiotic-resistant Grampositive cocci [23]. Temporin A is thought to act in conjunction with the formation of the ion channel in the bacterial cytoplasmic membrane [24].

Ghiselli et al. investigated the efficacy of temporin A as a prophylactic agent against methicillin sodium-susceptible (MS) and methicillin sodium-resistant (MR) *Staphylococcus epidermidis* vascular graft infection. In vitro studies revealed that both MR and MS were similarly susceptible to temporin A. In vivo studies support these results, showing that the use of a temporin A-soaked Dacron graft in vascular surgery can result in substantial bacterial growth inhibition (from 1.9 × <sup>10</sup><sup>7</sup> to 3.4 × 103 CFU/mL against *S. epidermidis* MS and from 3.9 × <sup>10</sup><sup>7</sup> to 6.1 × 103 CFU/mL against MR). Most of the antibiotic prophylactic treatments were helpful; nevertheless, only the association of a temporin A-soaked graft and intraperitoneal vancomycin hydrochloride inhibited bacterial growth for both the MR and MS strains [23].

Another study tested the efficacy of topical temporin A and RNAIII-inhibiting peptide (RIP) compared to rifampicin in preventing *S. epidermidis* and *S. aureus* graft infection in a rat pouch model [25].

RIP is a heptapeptide that has strong activity against *S. aureus* and *S. epidermidis*. Considering its mechanism of action, RIP inhibits cell-cell communication, also known as quorum sensing, preventing bacterial adhesion and virulence [26].

The results of this study showed that the use of temporin A-soaked and RIP-soaked Dacron grafts induced a significant bacterial growth inhibition. In fact, the combination of RIP and temporin A showed the lowest bacterial growth (negative quantitative cultures for VISE4 and from 6 × <sup>10</sup><sup>7</sup> to 6.9 × <sup>10</sup><sup>1</sup> CFU/mL for VISA4). More specifically, temporin A had a high antistaphylococcal activity, independent of the level of resistance shown by the isolates. RIP was more effective against staphylococcal strains when used alone than temporin A or rifampicin alone [25].

Giacometti et al. (2004) investigated the efficacy of temporin A soaking in combination with intraperitoneal linezolid in the prevention of vascular graft infection in a rat model of infection with *Staphylococcus epidermidis* with intermediate resistance to glycopeptides (GISE). The in vitro results show that temporin A and linezolid both have high activity against the GISE clinical strain. The in vivo study confirmed the strong activity against *S. epidermidis* of temporin A and linezolid, and it showed that the combination of temporin A with a parenteral antibiotic, such as linezolid (from 6.9 × <sup>10</sup><sup>6</sup> to 3.8 × 102 CFU/mL with linezolid and to 3.4 × 103 with temporin A), may become a valid opportunity for chemoprophylaxis in vascular surgery [27].

Temporin A, citropin 1.1, CA (1-7)M (2-9)NH2, and Pal-KGK-NH2 were also studied in 2019 for their synergistic activity against methicillin-resistant *Staphylococcus aureus* (MRSA) biofilms developed on polystyrene surfaces (PSS) and central venous catheters (CVC). The study highlighted that antimicrobial peptides have strong activity in inhibiting biofilm formation on both PSS (citropin 1.1 inhibited biofilm formation of all MRSA strains tested) and CVC (citropin 1.1 caused a biomass reduction for the reference strain with an OD570 of

0.152 compared with the control). The eradication of preformed biofilms, on the other hand, was more difficult and took 24 hours after contact between the AMP and biofilms. The combination of AMP had synergistic activity, leading to an improvement in the performance of all the peptides in the removal of biofilms [28].
