Another method to deal with this exceptionally anti-biotic resistant infection is through vibroacoustic therapy or audio resonance EMF fields.     

These are a few of Raymond Rife's EMF frequencies specific to Serratia Marcescens.   You can play them in either tone frequency or sawtooth (which is usually preferable) with zero side effects and continuously for days on end. 
 
Essentially if you've been given a positive diagnosis of this infection these usually begin working within a few hours to a day.

Use this online tone generator and plug the exact frequency in.   You can play all three as they emit distinct frequencies.

Rife Frequencies for Serratia M.   866.2,  970.03, 872.76