A neonate develops encephalitis without any skin lesions. Most probable causative organisms is –
HSV I
HSV II
Meningococci
Streptococci
Herpes simplex viruses


Herpes simplex is an important cause of encephalitis in the neonate, the infection acquired during delivery from the vaginal tract.
But it cause vesicular, ulcerative skin lesions
Even though it causes skin lesions, its our best option, as Nelson writes -
" The hallmark of neonatal HSV infection- the vescicular ulcerative skin lesions are presnt in only 30 to 43% of children at presentation; one third will never manifest skin lesions."
Out of the.two types of Herpes; Neonatal herpes is mainly caused by type II IISV (75 to 80%).

About other options
Meningpcocci

Its a rare cause of infection in neonates as neonates have antibodies (from mother) against meningiococcus which protects them for the initial 3 to 6 months of life.

Streptococci

Though streptococcus B is a common infection of neonates, it does not cause encephalitis.

RAIN TUMORS 
You will frequently read the terms --> Infratentorial, supratentorial, Posterior cronial fossa in relation of Brain tumours, so I am giving very brief introduction

Supratentorial region of the brain is located above the tentorium cerebelli; and contains the cerebrum.
The infratentorial region of the brain is located below the tentorium cerebelli and contains the cerebellum and brainstem.
Brain stem and cerebellum are contained in the posterior cranial fossil.
As brain stem and cerebellum are infratentorial in location and contained in posterior cranial fossa -› Their tumors are infratentorial posterior fossa tumors, e.g., cerebellar astrocytoma, brainstem glioma, medulloblastoma (cerebeller).