Virulence Mechanisms of Cutibacterium acnes In Association with Lumbar Disc Herniations

  • Gurpreet Gill

Student thesis: Doctoral ThesisDoctor of Philosophy


Cutibacterium acnes (C. acnes) (formerly known as Propionibacterium acnes) forms part of the normal resident host microflora of the skin, large intestine and oral cavity. Despite
increasing evidence for the opportunistic pathogenic role of this species within intervertebral disc (IVD) herniation and associated Modic changes, C. acnes is considered a low virulence
microorganism. This thesis aimed to investigate the virulence characteristics of 67 clinical C. acnes isolates belonging to phylotypes IA1, IB, II and III obtained from human herniated
IVD tissue material and eight acne lesion isolates. Phenotypic isolate characterisation was undertaken using crystal violet biofilm formation assays, Galleria mellonella (G. mellonella) waxworm infection assays, exocellular enzyme production agar assays and Western blot protein analysis. Associations between phylotype grouping and site of isolation of the isolates were then investigated. Biofilm formation crystal violet assays showed that
phylotype III disc tissue isolates failed to form significant biofilms. Semi-quantitative biofilm formation classification criteria identified the majority of disc tissue and acne lesion isolates as weak biofilm formers over 7-days, indicative of the slow growth rate of this species. Phylotype-specific exocellular enzyme production demonstrated that phylotype IA1and IB isolates commonly produced β-haemolysins (84% and 67%, respectively). Gelatinaseproduction was phylotype and site of isolation-specific. The highest rates of non-specific protease enzyme production were recorded for C. acnes phylotypes IA1 and III, with 100%
of these isolates showing protease activity. Ubiquitous lipase production was recorded amongst all C. acnes disc tissue and acne lesion isolates tested. Comparison of waxworm larvae mortality rates between differing C. acnes phylotypes and culture preparation techniques (cell-free, heat-killed and cell-containing inoculum preparations) showed no significant effects on G. mellonella survival rates, suggesting that C. acnes does not induce significant mortality within this infection model. However, all phylotypes of C. acnespromoted G. mellonella melanisation, indicative of insect humoral immune response activation, with cell-containing cultures of C. acnes isolates 82 (IB) and 80 (III) leading to the greatest degrees of melanisation. Therefore, the G. mellonella infection model issensitive and can discriminate between the pathogenicity of C. acnes belonging to a range of
phylotypes. Additionally, following Western blotting, disc tissue C. acnes samples produced CAMP factor 1 protein. Overall, site of C. acnes isolation (IVD or acne lesion) and phylotype appeared to influence phenotypic characteristics. This suggests that the role of C. acnes within lumbar disc herniation etiology should not be readily dismissed and highlights the need for further research into the applicability of anti-CAMP factor vaccines within C. acnes disc disease management.
Date of Award2021
Original languageEnglish
Awarding Institution
  • Coventry University
SupervisorJess Rollason (Supervisor) & Lauren Acton (Supervisor)


  • Cutibacterium acnes
  • biofilm
  • haemolysis
  • DNase
  • protease
  • gelatinase
  • lipase
  • CAMP factor 1
  • growth curve
  • Galleria mellonella

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