LYNN – A 2-month-old girl is alive but in serious condition in Massachusetts General Hospital after a Baker Street teenager admitted to police he shook the infant.Police and prosecutors Monday said Alonso Guzman’s actions seriously injured the baby and an MGH doctor told police the child’s head trauma “was consistent with a non-accidental injury.”Guzman, 18, of 30 Baker St., #2, pleaded innocent to assault and battery with serious injury on a child and Judge Albert Conlon ordered him held without bail until a dangerousness hearing on May 5. Essex District Attorney spokesman Steve O’Connell said the baby belongs to Guzman’s girlfriend, whom he resides with on Baker Street.Police and firefighters responded to a report of a baby not breathing at that address on Saturday at 8 p.m. Medical personnel transported the infant girl to North Shore Children’s Hospital where she was taken by helicopter to Boston.Police reports quote Guzman as initially telling officers he was changing the girl’s diaper and turned away from her to prepare a bottle for her feeding. When he turned back to her “she appeared to have trouble breathing.”He told officers he tried rubbing her torso to stimulate breathing and sought help after about five minutes.MGH Dr. Danielle Dwyer told police Sunday the child had sustained a head injury and investigators subsequently questioned Guzman who told them sometime during the previous week he was “holding the baby and she fell on her face.””He admitted to shaking (Lizbeth). He said he moved her and he lost control,” Officer Joseph Chadbourne stated in his report, quoting Guzman.Essex Assistant District Attorney Jennifer Kirshenbaum told the court that the baby’s prognosis is grim.The case is being investigated by Lynn Police and State Police detectives assigned to the Office of Essex District Attorney Jonathan W. Blodgett.