Objective To investigate the effects of meropenem and amikacin on gut microbiota diversity and composition in a neonatal rat model of necrotizing enterocolitis(NEC).Methods Neonatal SD rats(1～2 d,weighing 5～10 g,both sexes)were subjected to establish a NEC model through artificial formula feeding,hypoxic-cold stress,and lipopolysaccharide(LPS)gavage.The rats were randomly divided into normal control group(Group C,n=12),NEC group(Group N,n=20),meropenem intervention group(Group M,n=20),and amikacin intervention group(Group A,n=20).Following modeling,Group M and Group A received intraperitoneal injections of meropenem(125 mg/kg)or amikacin(468 mg/kg),twice daily for 3 consecutive days.Groups C and N were administered an equal volume of normal saline.At the end of the intervention,colonic contents or fecal samples were collected.The gut microbiota structure was analyzed using 16S rDNA high-throughput sequencing.Bioinformatics analysis was performed using the QIIME2 platform.Alpha diversity was evaluated using Chao1,Shannon,and Simpson indices.Beta diversity was assessed based on Bray-Curtis distance through principal coordinate analysis(PCoA)and non-metric multidimensional scaling(NMDS).Venn and UpSet plots were generated to visualize the composition and overlap of operational taxonomic units(OTUs).Linear discriminant analysis effect size(LEfSe)was applied to identify differentially abundant taxa across groups.Results High-throughput 16S rDNA sequencing showed that the N group had significantly lower 3 indices of α diversity than the C group(P<0.01),that is,a Chao1 index from 230 to 40,a Shannon index from 1.65 to 0.85,and a Simpson index from 0.65 to 0.42.After antibiotic intervention,both the M group and A group obtained obvious increases in the Chao1 index than the N group(P<0.001),with a greater increase observed in the M group than in the A group(P<0.05).However,neither antibiotic group exhibited notable improvements in the Shannon index or Simpson index compared with the N group(P>0.05).Venn and UpSet analyses revealed that the M group had the highest number of unique OTUs(283),while the A group shared the most OTUs(63)with the C group.PCoA and NMDS analyses indicated that the microbial structure of the A group was closer to that of the C group,with better clustering.Taxonomic composition and LEfSe analysis demonstrated that the N group was enriched with potentially pathogenic taxa such as Escherichia coli B2 and Klebsiella under the phylum Proteobacteria,while beneficial bacteria including Lactobacillaceae and Bifidobacteriaceae(phylum Firmicutes)were significantly reduced,indicating severe dysbiosis.In contrast,the A group exhibited a significant increase in beneficial bacteria and a structural tendency toward ecological recovery.The M group,however,was enriched with various conditionally pathogenic and environmentally associated genera,displaying a microbial configuration notably deviating from a healthy state.Conclusion Meropenem and amikacin exhibit differential regulatory effects on the intestinal microbiota in the context of NEC.Amikacin demonstrates superior efficacy in restoring microbial stability and levels of beneficial bacteria,whereas meropenem,although effective for early infection control,warrants caution due to its potential long-term impact on the gut microbiome.