Temporal dynamics & determinants of antibiotic resistance gene profiles in the infant gut during the first year of life.

Background & objectives To evaluate the progressive changes in the antibiotic resistance gene (ARG) profile by investigating their presence at different time points in the gut of infants during early life. Methods Stool samples of 54 full-term healthy infants at birth at 6, 14, and 36 wk were processed to examine the presence of 20 antibiotic-resistance genes. McNemar's test was used to check the statistical significance of the change in prevalence of genes across various time points. Chi-square test and logical regression were performed to evaluate the influence of clinical and demographic factors on the carriage of ARGs during early life. Results Infants predominantly carried genes that conferred resistance to beta-lactams (80.6%), macrolides (MSLB) (70%), and the sulphonamide (61%) class of antibiotics. ARG carriage peaked at 6 wk and 14 wk with a significant increase in the proportion of genes like blaTEM, catB, oqxA, sul1, ermB, tet, blaSHV (P: <0.05) from birth to 6 wk. Caesarean-section [P = 0.001; odds ratio (OR): 6.93; confidence interval (CI): 2.06-23.26] and maternal exposure to cephalosporins postpartum (P value = 0.013; OR: 4.16; CI: 1.31-13.17) had a significant influence on the increased carriage of the blaCTX-M gene at 6 wk of life. Interpretation & conclusions Our findings demonstrate that infants carry a diverse range of ARGs, with peak prevalence observed at 6 and 14 wk. Delivery mode and maternal antibiotic exposure significantly impact ARG carriage, emphasising the need for targeted interventions to reduce antibiotic resistance in early life.