Effect of one prophylactic dose of azithromycin on Bifidobacterium infantis colonization in infants from the Mumta trial

Objectives: The effects of antibiotics on the microbiome remain incompletely understood. Azithromycin (AZ) has been shown to improve child survival and infant growth outcomes. This study aimed to assess the impact of AZ on Bifidobacterium infantis colonization and bacterial enteropathogen count in the infant gut. Methods: We analyzed clinical, biomarker, B. infantis and enteropathogen data from 150 mother-infant dyads from the MUMTA Lactating Women study. Colonization of B. infantis was assessed using quantitative polymerase chain reaction (PCR) of fecal samples. We utilized a customized PCR-based TaqMan Array Card for enteropathogen detection. Results: AZ administration was associated with a 1.99-fold (95% confidence intervals [CI] 1.33-2.97) increase in colonization by B. infantis. B. infantis colonization was highest when inflammatory biomarker levels were within normal range. Mode of delivery (RR 2.43; 95% CI: 1.58, 3.76) and colostrum (RR2.05; 95% CI: 1.41, 2.98) given to the infant within 24 h of birth were associated with B. infantis colonization. A single dose of AZ on day 42 reduced bacterial enteropathogen count in the AZ group on day 56, as compared to the pre-AZ count. Bacterial enteropathogen count for infants with wasting (weight for length z-score WLZ <−2) was 1.43-fold higher (95% CI: 1.00-2.03) than for infants with WLZ ≥ −2. Over 60% of infants harbored with the macrolide resistance mph(A) gene Conclusion: AZ administration increases B. infantis colonization and reduces bacterial enteropathogen count in infants.