Concordance of Beta-Lactam Resistance Profiles in Mother-Placenta-Newborn Triads: Evidence for Vertical Transmission in Brazzaville, Congo

Mother-to-child transmission of beta-lactam-resistant Enterobacteriaceae is a growing public health concern in sub-Saharan Africa, yet few studies sample the mother, the placenta and the newborn simultaneously, and none in the region measures how often two unrelated isolates share a resistance profile by chance. This analytical cross-sectional study was conducted from October 2022 to July 2025 at the Marien Ngouabi Integrated Health Centre in Brazzaville. Ninety-one mother-newborn-placenta triads were included. Three specimens were collected per triad: a maternal rectal swab on the day of delivery, a neonatal rectal swab between the 1st hour of life and the 4th day, and a swab of the inner surface of the placenta after disinfection of the fetal side with 90% alcohol. Isolates were identified with API 20E strips and 16S rRNA gene sequencing; susceptibility to seven beta-lactams was determined by agar diffusion and ESBL production was sought by the double-disc synergy test. Observed concordance was compared with a null distribution generated by 20,000 species-stratified permutations. Enterobacteriaceae were isolated from 91 of 91 mothers, 66 of 91 newborns (73%) and 57 of 91 placentas (63%). Thirty-three triads were positive in all three compartments and formed the analysis population, yielding 267 identified isolates, of which 241 (90.3%) belonged to the genera Escherichia, Enterobacter and Klebsiella. Among these 241 isolates, 48.5% were resistant to at least one third-generation cephalosporin and 28.2% to at least one carbapenem. Seventy-nine triads contained an isolate of the same species in all three compartments, and 37 of them (47%) showed a strictly identical resistance profile in the mother, in the placenta and in the newborn. Fewer than one such triad would be expected under the hypothesis of independence, and across 20,000 random reallocations this number never exceeded seven. Among unrelated isolates, profile identity was only 1.9%. An extended-spectrum beta-lactamase was produced by 67 of the 111 isolates from concordant triads (60.4%). Concordance within triads therefore far exceeds chance and supports peripartum mother-to-child transmission of resistant Enterobacteriaceae; molecular typing remains necessary to establish clonal identity.