Broad-Spectrum Antimicrobial Activity of Priestia megaterium Isolated from a Lettuce Grown Nutrient Film Technique Hydroponic System

Controlled-environment agriculture production systems, such as hydroponics, have experienced rapid growth in recent years, providing a nutrient source that supports the presence and growth of diverse microorganisms. This study examined the prevalence of constitutive microbiota and predominance of antimicrobial molecules of Priestia megaterium isolated from a Hydroponic Nutrient Film Technique system. 3M Sponge swabs were used to collect samples from the hydroponic tubing, water pump, drainage area, and reservoir. All samples were plated on Tryptic Soy Agar and incubated at 37°C for 24 h. Isolates identification was performed using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. A competitive exclusion study was conducted on identified species, with 120 combinations. Priestia megaterium emerged as the predominant species in the constitutive microbiota, and its antimicrobial peptide was isolated by centrifugation and subsequently concentrated by freeze-drying. This study provides insight into the constitutive microbiota and informs the development of effective antimicrobial strategies. The broad-spectrum efficacy of P. megaterium AMP, previously isolated from biofilm microbiota, was assessed using an agar well assay. Both gram-positive and gram-negative bacterial strains were susceptible to P. megaterium AMP, with strong inhibition observed. Salmonella enterica exhibited greater inhibition (16 mm) as compared to Salmonella Tennessee (12 mm) and E. coli O157:H7 (11.5 mm). Listeria monocytogenes Scott A showed greater inhibition (17 mm) than the other outbreak strains. These findings highlight the potential of P. megaterium antimicrobial peptides as a natural strategy for disinfection to limit biofilm formation and reduce microbial risks in hydroponic systems.