Probiotic consortia for poultry gut health and environmental resistome control: a critical evaluation of the evidence gap

Abstract

Poultry production forms a connected gut-manure environmental system in which resistant bacteria, antimicrobial-resistance genes (ARGs) and mobile genetic elements (MGEs) move from birds into litter, stored manure, soil, water and airborne particles. Host-associated probiotics could reduce dependence on antibiotic-driven production, but most studies assess growth, gut-community composition or pathogen inhibition rather than absolute resistance release and downstream transmission. This structured critical narrative synthesis evaluates evidence linking probiotic characterization, poultry gut and excreta resistomes, resistant hosts, MGEs, manure processes and environmental fate. The direct intervention core comprised five poultry studies: two metagenomic studies of resistome profiles and three culture-based or isolate-characterization studies of resistant bacterial hosts. None followed the same experimental units through the complete gut-excreta-manure-environment pathway, and the heterogeneous interventions, matrices and endpoints did not support quantitative pooling. Across the evidence, probiotic performance varies with strain genome, dose, viability, consortium compatibility, bird age, diet, baseline microbiome, antimicrobial history and co-selective pressures. Declines in relative ARG abundance can reflect susceptible-population expansion, host replacement or altered sequencing denominators rather than lower ARG mass. Probiotic strains carrying transferable determinants may also preserve or redistribute resistance. The review therefore develops a selection-to-containment framework linking genomic safety, consortium function, gut reconfiguration, excreta loading, manure treatment and downstream verification. Current evidence supports effects on selected hosts or ARG profiles, but it does not yet demonstrate reproducible environmental resistome containment.