Erythromycin (ERY) is a wide-spectrum macrolide antibiotic that acts by interfering with protein synthesis. ERY is active against gram-positive and gram-negative pathogens, and it is among the antibiotics used by the major aquaculture producers to treat infectious diseases . It is commonly used for controlling lactococcosis ( Lactococcus garviae), bacterial kidney disease (Renibacterium salmoninarum), and streptococcosis (Streptococcus spp.), and it is also prescribed for extra-label use. Nonetheless, the treatment can be challenging due to ERY’s hydrophobic characteristics , poor aqueous solubility, instability in an acidic medium, low bioavailability, and bitter taste . This study aimed to encapsulate ERY in lipid formulations to overcome these disadvantages, enhancing ERY’s antimicrobial efficacy. The nanostructured lipid carrier systems (NLCs) loaded with ERY were prepared by hot emulsification using high-speed homogenization followed by ultrasonication . The lipid matrix, composed of solid and liquid lipids, is biocompatible and biodegradable. The study investigated the use of various surfactants, including Whey protein concentrate, Poloxamer, Quillaja saponins, and Gellucire, on NLC properties and product stability throughout 28 days. The resulting NLCs formulations are presented in Table 1.
The characterization of NLCs was evaluated through pH and conductivity analysis, particle size, polydispersity index (PdI), and zeta potential (n=3), and the results are shown in Table 2.
The pH and conductivity contribute to emulsion stability . The particle size can be related to the surfactant used. Zeta potential values (>|30| mV) demonstrate physical stability . Formulations F 1 and F2 showed lower polydispersity , while F3 and F4 showed medium polydispersity. The bactericidal activity of F1, F2, and F3 was assessed using the microdilution broth method against Aeromonas spp. isolated from fish , revealing that these lipid formulations, especially those with natural surfactants (quillaja saponins and whey protein concentrate), demonstrated enhanced efficacy. Lipid formulations have a significant potential to improve ERY’s solubility, stability, and bioavailability, and they also have the advantage of being biocompatible and biodegradable systems. Considering that disease outbreaks are one of the main challenge s to the sustainab le development of aquaculture, it is important to develop effective alternatives that promote the safe use of antimicrobials, considering animal, human, and environmental health.