A 1 year-old boy presents fever for 2 days with frequently vomiting and convul-sion. Physical examination reveals a lassitude boy with bulging anterior fontanel， rigidity neck and positive brudzinski sign. His CSF examination shows a turbid appearance， in-creased protein， WBC of 1×109/L with 80 % neutrophil， glucose of 2. Ommol/L and chloride of 98mmol/L. The most possible diagnosis is