A 2 day old neonate developed respiratory distress due to pneumonia. Most common causative agent is:

Early-onset bacterial infections appear most commonly on day 1 of life, the majority by 12 hours of age. Respiratory distress due to pneumonia is the most common presenting sign. Early-onset infection is most often caused by group B -hemolytic streptococci (GBS) and gram-negative enteric pathogens (most commonly E coli). Other organisms to consider are non-typeable Haemophilus influenzae, Enterococcus, Staphylococcus aureus, other streptococci and Listeria monocytogenes. Late-onset bacterial infection (> 3 days of age) presents with poor feeding, lethargy, hypotonia, temperature instability, altered perfusion, new or increased oxygen requirement, and apnea. It is caused by coagulase-negative staphylococci (most common in infants with indwelling central venous lines), S aureus, GBS, Enterococcus, and gram-negative organisms, in addition to Candida species Ref: Thilo E.H., Rosenberg A.A. (2012). Chapter 2. The Newborn Infant. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds), CURRENT Diagnosis & Treatment: Pediatrics, 21e.