Presence of mycobacterial L-forms in human blood: Challenge of BCG vaccination

Hum Vaccin Immunother. 2015;11(5):1192-200. doi: 10.1080/21645515.2015.1016682.


Possible persistence of bacteria in human blood as cell wall deficient forms (L-forms) represents a top research priority for microbiologists. Application of live BCG vaccine and L-form transformation of vaccine strain may display a new intriguing aspect concerning the opportunity for occurrence of unpredictable colonization inside the human body by unusual microbial life forms. L-form cultures were isolated from 141 blood samples of people previously vaccinated with BCG, none with a history of exposure to tuberculosis. Innovative methodology to access the unusual L-form elements derived from human blood was developed. The methodology outlines the path of transformation of non- cultivable L-form element to cultivable bacteria and their adaptation for growth in vitro. All isolates showed typical L-forms growth features ("fried eggs" colonies and biofilm). Electron microscopy revealed morphology evidencing peculiar characteristics of bacterial L-form population (cell wall deficient polymorphic elements of variable shape and size). Regular detection of acid fast bacteria in smears of isolated blood L-form cultures, led us to start their identification by using specific Mycobactrium spp. genetic tests. Forty five of 97 genetically tested blood cultures provided specific positive signals for mycobacteria, confirmed by at least one of the 3 specific assays (16S rRNA PCR; IS6110 Real Time PCR and spoligotyping). In conclusion, the obtained genetic evidence suggests that these L-forms are of mycobacterial origin. As the investigated people had been vaccinated with BCG, we can assume that the identified mycobacterial L-forms may be produced by persisting live BCG vaccine.

Keywords: BCG vaccinated people; L-forms; human blood; mycobacteria; persistence.

MeSH terms

  • Adolescent
  • Adult
  • BCG Vaccine / administration & dosage*
  • Biofilms / growth & development
  • Blood / microbiology*
  • Child
  • Child, Preschool
  • DNA Transposable Elements
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • DNA, Ribosomal / chemistry
  • DNA, Ribosomal / genetics
  • Female
  • Humans
  • Infant
  • L Forms / genetics
  • L Forms / isolation & purification*
  • L Forms / physiology
  • L Forms / ultrastructure
  • Male
  • Microscopy, Electron
  • Middle Aged
  • Molecular Typing
  • Mycobacterium / genetics
  • Mycobacterium / isolation & purification*
  • Mycobacterium / physiology
  • Mycobacterium / ultrastructure
  • RNA, Ribosomal, 16S / genetics
  • Real-Time Polymerase Chain Reaction
  • Young Adult


  • BCG Vaccine
  • DNA Transposable Elements
  • DNA, Bacterial
  • DNA, Ribosomal
  • RNA, Ribosomal, 16S