**4. AMPs and Wound Infection**

We report on four studies whose purpose was to evaluate the efficacy of new experimental AMPs in the management of infected surgical wounds in mouse models. The infection was established using MRSA, the most frequent aetiological agent in cSSTIs. In these studies, the role of antimicrobial peptides in infected wounds was evaluated mostly by considering bacterial growth (quantitative cultures of excised tissues) and healing parameters such as collagen organisation, degree of re-epithelialisation, granulation tissue formation, angiogenesis, and VEGF expression. The results were compared with data from control groups, such as animals with no infected wounds (treated and untreated), animals with infected but untreated wounds, and animals treated with other conventional antibiotics.

In 2013, Cirioni et al. studied the activity of the AMP IB-367 (a synthetic protegrin) as an immunomodulator and immune enhancer, evaluating whether pretreatment with this peptide resulted in an enhancement of antibiotic efficacy (daptomycin and teicoplanin) against MRSA wound infection in a mouse model. The main outcome measures were quantitative bacterial culture and analysis of natural killer (NK) cytotoxicity and leukocyte phenotype. Antibiotics alone showed a comparable antimicrobial efficacy, but their association with IB-367 significantly enhanced the antimicrobial activities. When compared to antibiotics alone (2 log reduction), IB-367 plus daptomycin showed a 4 log reduction in bacterial growth, with IB-367 plus daptomycin showing the highest efficacy (reduction in bacterial load of 2.7 × <sup>10</sup><sup>3</sup> ± 0.3 × <sup>10</sup><sup>3</sup> c.f.u. mL-1). IB-367 action is also related to a modulation of the innate immune response, mainly represented by an increase in NK cell activity (but not NK cell number) and increasing the number of both CD11b and Gr-1 cells 3 days after MRSA challenge, over the levels observed in the respective controls [47].

LL-37 is the only human antimicrobial peptide that belongs to the cathelicidins. LL-37 showed a broad-spectrum against several different pathogens, such as Gram-positive and Gram-negative bacteria, viruses, and fungi [48]. Moreover, LL-37 revealed other biological activities, such as regulation of responses to inflammation and demonstration of an important activity in wound closure and angiogenesis [49].

Simonetti et al. (2021) evaluated the efficacy of synthetic cathelicidin LL-37 in MRSAinfected surgical wounds in mice, in comparison with teicoplanin treatment. The results of the study showed that LL-37 had a stronger effect than teicoplanin on the wound healing process in MRSA-infected mice, although with a lower effect on bacterial culture growth. LL-37 reduced bacterial numbers to 7.1 × 105 ± 0.6 × 105 CFU/g, and 6.9 × <sup>10</sup><sup>2</sup> ± 0.4 × 102 CFU/g when combined with topical LL-37, while i.p. teicoplanin produced a bacterial count of 7.4 × 104 ± 1.0 × 104 CFU/g and 3.0 × <sup>10</sup><sup>2</sup> ± 1.2 × <sup>10</sup><sup>2</sup> CFU/g when associated with topical teicoplanin. LL-37, after topical and parenteral administration, enhanced wound closure via stimulation of granulation tissue formation associated with a better angiogenesis process and better organised collagen deposition and reconstitution of the epithelium in comparison with the teicoplanin treatment group [50].

Another study evaluated the efficacy of distinctin, a heterodimeric peptide from the Amazonian frog *Phyllomedusa distincta*, in the management of cutaneous MRSA wound infections in an experimental mouse model. It was found that topical distinctin combined with parenteral teicoplanin inhibited bacterial growth to 3.4 × 101 ± 1.0 × <sup>10</sup><sup>1</sup> (levels comparable with those observed in uninfected animals), but the combination of topical and parenteral teicoplanin proved to be the most effective in reducing bacterial counts (4.7 × <sup>10</sup><sup>1</sup> ± 1.6 × <sup>10</sup>1). Furthermore, when compared to mice treated only with teicoplanin, wounded areas of animals treated with distinctin were characterised by a more mature granulation tissue, a more organised and denser type of connective tissue, and a significant reduction in fibrinous exudation [51].

In 2007, Simonetti et al. conducted a study on temporin A, investigating the effect of its topical use in mouse models of MRSA-infected wounds. Temporin-A treatment combined with teicoplanin injection significantly reduced the bacterial load to 0.85 × <sup>10</sup><sup>1</sup> ± 0.1 × <sup>10</sup><sup>1</sup> CFU/mL. Histological examination showed that infected mice receiving temporin A-soaked Allevyn (with or without teicoplanin) had a higher degree of granulation tissue formation and collagen deposition compared to the other treated groups. A significant increase in serum VEGF expression was observed in mice receiving temporin A topically with or without intraperitoneal teicoplanin [52].
