Prevalence, Concordance, and Risk Factors of Antibiotic Resistance Genes in Breast Milk and Neonatal Oral Cavity of Preterm Mother–Infant Pairs

<b><i>Background:</i></b> Mothers delivering preterm are very often exposed to antibiotics in the peripartum period. We hypothesize this may select bacteria bearing antibiotic resistance genes (ARGs) in the breast milk and be transmitted to the neonate's mouth while feeding. This study aimed to determine the prevalence of ARGs coding for extended-spectrum beta-lactamases (ESBLs) (including AmpC beta-lactamases [ACBLs]) and carbapenemases in breast milk and neonatal oral swab samples of preterm mother-infant pairs, the concordance of ARGs between paired samples, and risk factors of ARGs coding for ESBLs and carbapenemases. <b><i>Methods:</i></b> Breast milk and oral swab samples were obtained aseptically from 100 preterm mother-infant pairs (gestation 28-34 weeks) by postpartum day 10. Multiplex PCR was used to detect 15 common ARGs in these samples. Potential risk factors of the presence of any ARG coding for ESBLs or carbapenemases in breast milk and oral swab samples were studied. <b><i>Results:</i></b> The commonest ARGs for ESBLs, ACBLs, and carbapenemases in breast milk were <i>bla_SHV</i> (28%), <i>bla_CIT</i> (33%), and <i>bla_IMP</i> (49%), respectively; and oral swabs <i>bla_CTX-M1</i> (30%), <i>bla_CIT</i> (58%), and <i>bla_IMP</i> (24%), respectively. ARGs common to breast milk and oral swabs included <i>bla_CIT</i> (13%), <i>bla_IMP</i> (10%), <i>bla_CTX-M-1</i> (9%), and <i>bla_SHV</i> (6%). Formula milk intake was associated with less oral carbapenemase ARGs. <b><i>Conclusion:</i></b> ARGs for ESBLs and carbapenemases are highly prevalent in preterm breast milk and oral swabs.