In vitro antagonistic activity of Bacillus spp. and Pseudomonas putida M5 isolated from feces of the violet-crowned hummingbird (Ramosomyia violiceps) from an urban environment

The gut microbiome of wild birds contributes to host fitness by supporting nutrient absorption, toxin processing, and immune function. It also fights bacterial pathogens through competitive exclusion and the production of antimicrobial metabolites. This study analyzed the in vitro antagonistic activity of bacteria isolated from the feces of the violet-crowned hummingbird (Ramsomyia violiceps) against strains of Bacillus spp., Escherichia coli, Salmonella enterica, and Acinetobacter baumannii. Mist nets were placed in three parks within the Guadalajara Metropolitan Area. Fecal samples were collected from captured R. violiceps and inoculated into culture media. Bacteria exhibiting antagonist activity were identified using molecular techniques that targeted the V1-V9 region of the 16S rRNA gene. The gut strains Bacillus sp. 1, Bacillus sp. 2, B. altitudinis, B. thuringiensis, and B. subtilis exhibited antagonistic activity against Bacillus cereus, B. tequilensis, and A. baumannii. Pseudomonas putida M5 antagonized Bacillus spp., E. coli, S. enterica, and A. baumannii. This result indicates that some Bacillus spp. and Pseudomonas spp. in the cultivable bacterial assembly of the gut of R. violiceps produce secondary metabolites that can inhibit the growth of both Gram-positive and Gram-negative strains. Since diet plays a determining role in the gut bacterial assemblage of birds, our results suggest that the strains that showed antagonistic activity in vitro could be related to the nectar consumed by the hummingbird. This may help promote the synthesis of antimicrobial compounds as a resistance mechanism.