Comparative genomics of Staphylococcus epidermidis isolates from breast milk

Abstract:

Objective Staphylococcus epidermidis is a coagulase-negative, Gram-positive coccobacillus that is widely found in the skin, breast milk, and blood. Bacteria in breast milk play a crucial role in the establishment of the gut microbiota in the intestinal tract and in the enhancement of immunity of infants. We then performed comparative genomic analyses to understand the genetic diversity and functional genes of breast milk-derived S. epidermidis.Methods We used the Illumina NovaSeq platform to sequence the genomes of 110 strains of S. epidermidis preliminarily isolated from healthy breast milk by our research team. We then performed comparative genomic analyses for the 110 strains and 263 skin, blood, and breast milk-derived S. epidermidis strains publicly available from the NCBI.Results The genome size of the 373 strains of S. epidermidis was (2.50±0.33) Mb, with the G+C content was (32.0±0.1)%, and the number of coding sequences (CDs) being 2 331±368. Differences existed in genome size and number of CDs among breast, blood, and skin isolates (P<0.05), with blood isolates having the largest genome size and the highest number of CDs. The phylogenetic tree showed that the S. epidermidis isolates of the same source had obvious aggregation, and the breast milk isolates and blood isolates were more closely related. There were differences in the number of virulence factors and drug resistance genes among the strains of three sources (P<0.05). The blood-derived strains exhibited the highest diversity of virulence and resistance genes, whereas the breast milk-derived strains displayed the lowest diversity of such genes.Conclusion S. epidermidis has undergone adaptive evolution to different habitats. Compared with skin- and blood-derived strains, breast milk-derived strains carry few genes related to biofilm synthesis, drug resistance, and virulence. This study gives new insights into the adaptive evolution of S. epidermidis and provides a theoretical basis for subsequent research on the genetic background of breast milk isolates.