*3.5. Aurein 1.2*

This is an amphipathic, alpha-helical peptide composed of only 13 amino acids. It has demonstrated antimicrobial activity in vitro against Gram-positive cocci at concentrations ranging from 1 to 16 mg/litre and synergistic activity when administered in combination with clarithromycin and minocycline. In particular, aurein 1.2 exerts its action by making the membrane more permeable and less organised, allowing the entry of hydrophobic substrates [43].

Other peptides that demonstrated antimicrobial activity in vitro against Gram positive cocci include palmitol (pal)-lys-lys-NH2 and pal-lys-lys, uperine 3.6, and citropin 1.1.

The lipopeptides showed in vitro efficacy mainly against enterococci and streptococci compared with Staphylococci and *Rhodococcus equi*. Their efficacy was higher when combined with beta-lactams and vancomycin; they also proved effective against both susceptible and multidrug-resistant germs.

Uperine 3.6 is a broad-spectrum antibiotic peptide isolated from the Australian amphibian *Uperoleia mjobergii*. It consists of only 17 amino acids, and for this reason, represents the smallest of the antibiotic peptides isolated from amphibians. Although most of the antibiotics tested were more effective than uperine 3.6, it was effective against both susceptible and multiresistant germs [44].

Citropin 1.1 is an antimicrobial peptide derived from the Australian frog *Litoria citropa*. It is a small peptide consisting of 16 amino acids produced by both the dorsal and submental glands of *Litoria citropa*. It has been shown to be effective in vitro against 12 nosocomial isolates of *Rhodococcus equi* at concentrations ranging from 2 to 8 mg/L. The peptide presented synergistic activity against this germ when combined with clarithromycin, doxycycline, and rifampicin. In addition, other in vitro studies have demonstrated its efficacy against staphylococci and streptococci at concentrations ranging from 1 to 16 mg/L. Synergy was demonstrated when citropin 1.1 was combined with hydrophobic antibiotics such as clarithromycin and doxyxline [45,46].
