Which neonatal infections are caused by bacteria that makes up the bulk of human fecal flora soon after birth?

The right answer is Escherichia coli.

After birth, the term newborn and a fortiori the premature are very vulnerable to infection (germs of the mother and the entourage) and a rigorous hygiene is essential to avoid this post-natal infection. Neonatal infection is a major cause of morbidity and mortality. The diagnosis must be early in order to start an effective treatment quickly. The treatment is urgent because an infection can kill a newborn in a few hours.
Among the most commonly involved germs are Streptococcus B followed by Escherichia coli (which already exists in the human intestinal flora) by causing meningitis. Other agents may also be involved: Staphylococcus, listeriosis agent, gonococcus, anaerobes, etc.

Yes they are correct good day