Comparison of bacterial profiles in human milk from mothers of term and preterm infants

Abstract Background Bacteria in human milk (HM) can be endogenous or exogenous, and the latter can carry the risk of various infections in very low-birth weight infants because of the possibility of contamination with pathogenic bacteria. The mother's lifestyle and environment have a major influence on such bacterial contamination, and it is thought that there are differences in the number and types of bacteria cultured from HM between term mothers whose infants are at home and mothers of preterm infants in neonatal intensive care units (NICUs). This research aimed to compare the bacterial profiles of HM among mothers of term and preterm infants. Methods The data comprised 214 milk samples (term: 75, preterm: 139) donated by 47 registered donors (term: 31, preterm: 16) from January to November 2021. Bacterial culture results were compared between term and preterm HM samples. Differences in the mean total bacterial count and bacterial species count per batch were analyzed using Welch’s t-test and Student's t-test, respectively. The bacterial contamination rate was analyzed using Chi-square test or Fisher's exact test. Results Coagulase-negative Staphylococci, Staphylococcus aureus, and Pseudomonas fluorescens were frequently found in both term and preterm HM. Serratia liquefaciens (p < 0.001) and two other bacteria contaminated term HM, while five types of bacteria, including Enterococcus faecalis and Enterobacter aerogenes (p < 0.001) contaminated preterm HM. The mean (SD) total bacterial count was 351,141 (1,060,949) CFU/100 µL for term HM and 872,272 (2,324,477) CFU/100 µL for preterm HM (p = 0.026). Similarly, the number of bacterial species in HM was more diverse in preterm donors (p < 0.001). Conclusions This study revealed that HM from preterm donors has a higher total bacterial count and greater diversity and characterization of bacterial types compared with HM from term donors. These results also suggested there was a trend toward greater contamination with nosocomial-infection-causing bacteria in the NICU. Enhanced hygiene instructions for preterm donors may reduce the need to dispose of valuable donated HM as well as the risk of BM pathogen transmission to infants in the NICU.