Answer: Contamination
Explanation: This is a known contrainst when performing transformation in the lab. Normally the Pglo plasmid asides glowing under UV, possess a Amp gene that codes for resistance to the antibiotics Ampicillin. Transform cells will survive while untransformed cells will normally die. If untransformed (non glowing, non Ampicillin resistant) cells thrive in the medium, it is definitely a case of contamination. Start again but this time, disinfect appropriately bad be cautious of any potential contamination.