The addition of inulin and/or a probiotic to feed mixtures for pigs can lead to changes in microflora composition and production of short-chain organic acids (SCFA) in the final segment of the digestive tract. The aim of the study was to determine the effect of an inulin and/or a probiotic supplement on Enterobacteriaceae taxa, the susceptibility of the bacteria to six antibiotics, and SCFA content in the cecum and colon, as well as changes in the histological structure of the intestines. The experiment was conducted on 80 fattening pigs with an initial body weight of 30.0 ± 0.5 kg, divided into 4 groups: control (I-C) and three experimental ones, fed the diets either with a probiotic (group II-P), inulin (III-I) or a both additives (group IV-PI). The animals were given ad libitum access to grower (30-70 kg) and finisher (71-115 kg) feed mixtures. During slaughter, from 8 pigs of each group, samples of contents and tissue from the cecum and colon were collected for laboratory analysis. The results of the study indicate differences in the expression of antibiotic resistance in the Enterobacteriaceae isolates depending on the type of dietary supplement. The inulin supplement caused changes in SCFA concentration, mainly an increase in the concentration of propionic and butyric acid, and also increased the thickness of the muscular layer. The synbiotic (mixture of prebiotics and probiotics) was confirmed to have a beneficial effect on the gastrointestinal microbiome, which may be of significance in preventing the spread of Enterobacteriaceae infections in pigs.