Beetroot white skin mould
From a study titled "Production of Penicillin by Fungi Growing on Food Products: Identification of a Complete Penicillin Gene Cluster in Penicillium griseofulvum and a Truncated Cluster in Penicillium verrucosum", moulds on food items were analyzed for fungi that could produce penicillin. The conclusion drawn was 


  Among different fungal species belonging to the genus Penicillium that
  are currently used as starter cultures in the food industry or that
  are frequently isolated from cured meat products, only P. griseofulvum
  (in addition to the previously reported P. chrysogenum and P.
  nalgiovense) was found to produce penicillin and possess the three
  penicillin biosynthetic genes (pcbAB, pcbC, and penDE).


Even penicillin should be avoided as the paper states that 


  The presence of penicillin in food must be avoided, since it can lead
  to allergic reactions and the arising of penicillin resistance in
  human-pathogenic bacteria.


During world war two, a strain of Penicillium chrysogenum was isolated from the mould growing on a cantaloupe (reference) for the development of penicillin. This was after searching through many mould families developing on different food items so penicillin strains do develop but are rare.

The problem faced is that moulds cannot be differentiated from each other through sight nor is all penicillin moulds safe (reference). Whatever be the case, I hope that you didn't venture to try and eat that beetroot.