Table 2.

Classification and characteristics of MGEs.

MGEs class	Representative	ARGs types	Main mechanisms	Common hosts	Characteristics in poultry gut and environment
Plasmids	IncF, IncI1, IncX, IncC	blaCTX-M, mcr-1, tetA, sul1	Mediate HGT both within and across bacterial genera through conjugation; serve as key vectors for multidrug resistance islands.	Escherichia, Klebsiella, Salmonella	Widely detected in broiler intestinal tracts and poultry-farm wastewater; frequently harbor multidrug resistance regions facilitating rapid ARGs dissemination (Lemlem et al., 2024; Zalewska et al., 2024).
Integrons	class I integron (intI1, aadA, dfrA)	sul1, aadA, qacEΔ1	Capture, rearrange, and express gene cassettes, enabling stepwise ARGs accumulation and promoting genetic “platform” formation for ARGs polymerization.	Escherichia, Enterobacter, Proteus	Function as core nodes of HGT networks; abundance strongly correlates with ARGs prevalence in poultry production environments (Kalantari et al., 2021).
Transposons	Tn3, Tn21, Tn916	tetM, ermB, sul1	Excise and reinsert between chromosomes and plasmids, promoting inter-replicon mobility of ARGs and facilitating co-selection under antibiotic exposure.	Enterococcus, Clostridium, E. coli	Enriched in broiler fecal samples under high antibiotic pressure; abundance patterns strongly reflect selective intensity in production systems (Zahoor et al., 2024).
Integrative and Conjugative Elements	SXT/R391 family, ICEBs1	blaOXA, tetX, ermB	Combine site-specific integration with conjugation-mediated transfer; integrate stably into host genomes while maintaining mobility potential.	Enterococcus, Streptococcus, E. coli	Co-evolve with antimicrobial resistance genes, enhancing host stress tolerance, and environmental adaptability (Sun et al., 2022; Zheng et al., 2023).
Phage	prophage, λ-like elements	blaCTX-M, mefA, tetW	Transfer ARGs via transduction, enabling dissemination independent of cell-to-cell contact.	Salmonella, E. coli, Streptococcus	Frequently detected in poultry manure and surrounding environmental matrices; may act as environmental ARGs reservoirs (Anastassopoulou et al., 2025).
Insertion sequences	IS26, ISCR1, IS1216	mcr-1, blaNDM, tetA	Drive ARGs recombination, copy-number expansion, and formation of composite transposons; serve as powerful amplifiers of multidrug-resistant regions.	E. coli, Klebsiella, Enterococcus	Promote assembly of multidrug-resistance islands in poultry-associated microbiota; enriched in both gut and environmental samples (Tang et al., 2024; Wang and Dagan, 2024).