This study investigated the cecal microbiome of broilers raised under specific antimicrobial feeding programs (AFPs). A total of 2304 day-old Ross-708 male (M, n = 1152) and female (F, n = 1152) chicks were distributed into 48 floor pens which were allocated to one of three AFPs: Conventional, raised without medically important antibiotics (RWMIA), and raised without antibiotics (RWA). At 28 (D28) and 41 (D41) days of age, cecal contents were collected for culture dependent and independent analyses. At both 28 and 41 days, Enterococcus was more abundant in RWA-raised broilers than other groups with the most abundance of this bacterium being found in female birds ( P < 0.05). At D41, the most abundant Eimeria tenella counts was observed in RWA-raised broiler ceca ( P < 0.05). Sex effects were observed on the abundances of four of the 248 identified antimicrobial resistance genes while abundances of 10 were modulated by AFPs ( P < 0.05). Ceca of females birds showed more tssB than males, and ceca of RWMIA-raised birds contained the highest abundance of chuY genes regardless of sex. This study showed that in a specific feeding program, cecal resistome can be affected by chicken’s sex contributing to understand the AMR related to the AMU.

Alternative feed additives are being investigated due to the restriction of antibiotics use to decrease antimicrobial resistance (AMR) in food-producing animals. This study investigated the effects of dietary American cranberry (Vaccinium macrocarpon) and wild blueberry (V. angustifolium) pomaces on the cecal microbiota and resistome profiles as well as the short-chain fatty acid levels. Male broiler chickens Cobb500 were fed a basal diet with either 55 ppm bacitracin methylene disalicylate (BMD); 0.5% (CRP0.5) and 1% (CRP1) cranberry pomace; and 0.5% (LBP0.5) and 1% (LBP1) lowbush blueberry pomace with or without a multienzyme mixture (ENZ). The results showed that at 21 days of age, the total coliform counts decreased in the CRP0.5-fed birds compared to BMD (p < 0.05). The use of pomace significantly increased the abundance of Lactobacillus and Bacteroides regardless of ENZ, while CRP decreased the Proteobacteria phylum abundance. In-feed ENZ tended to increase the relative abundance of genes conferring aminoglycoside resistance. Treatment with CRP0.5 decreased the abundance of cepA genes encoding for macrolide (MACROLIDE) and lincomycin (InuD) resistance while increasing those for tetracycline (tetO and tetX) resistance. These results showed, for the first time, the potential of the studied enzymes in influencing berry pomace’s effects on antimicrobial resistance gene profiles in broilers.

Staphylococcus shinii is a recently proposed staphylococcal species identified in animal-associated microbiomes and fermented foods, with promising probiotic and biotechnological applications. However, its genomic diversity, functional traits and safety profile need to be well established. Here, we report the first recovery and genome sequencing of 41 S . shinii isolates from blueberry fruit washes and surrounding air. Phylogenomic analysis, including reference genomes, revealed at least 15 well-supported intra-species lineages (genomovars) defined by phylogenetic relationship and average nucleotide identity (>99.5% within genomovars; <99.5% between them). Pangenome analysis showed a highly conserved core genome comprising 83.3% of genes, alongside diverse accessory genes across genomovars. Core functions in S. shinii included carbohydrate metabolism, vitamin biosynthesis and short-chain fatty acid production, traits potentially linked to probiotic properties. Biosynthetic gene clusters for bioactive compounds were broadly conserved, although genes encoding ribosomally synthesized and post-translationally modified peptides varied among genomovars. About 10–18 antimicrobial resistance genes (ARGs) were identified per S. shinii genome, several of which were located on the chromosome. Phenotypic testing confirmed susceptibility to ciprofloxacin, gentamicin and ampicillin, while resistance to other antimicrobials varied and was often plasmid-associated. Resistance patterns differed across genomovars, emphasizing the need for intra-species resolution in risk assessment. Although major virulence factors listed in the Virulence Factor Database were absent, putative pathogenicity-related genes were found in the core genome using the Pathogen–Host Interaction Database. Their presence, along with ARGs, underscores the need for caution in clinical contexts. Nonetheless, the absence of major virulence determinants and the presence of beneficial traits in some S. shinii isolates support their potential use in the agri-food system or environmental biotechnology, pending strain-specific safety evaluation.