recA mediated spontaneous deletions of the icaADBC operon of clinical Staphylococcus epidermidis isolates: A new mechanism of phenotypic variations

  • Titik Nuryastuti, Department of Microbiology, Faculty of Medicine, Gadjah Mada University, Yogyakarta, Indonesia, Indonesia
  • Henk Busscher, Department of BioMedical Engineering, University Medical Center Groningen and University of Groningen, Groningen, The Netherla, The Netherlands
  • Henny Mei, Department of BioMedical Engineering, University Medical Center Groningen and University of Groningen, Groningen, The Netherla, The Netherlands
  • Tholib Aman, Department of Microbiology, Faculty of Medicine, Gadjah Mada University, Yogyakarta, Indonesia, Indonesia
  • Roel Kuijer, Department of BioMedical Engineering, University Medical Center Groningen and University of Groningen, Groningen, The Netherla, The Netherlands
  • Bastiaan Krom, Department of BioMedical Engineering, University Medical Center Groningen and University of Groningen, Groningen, The Netherla, The Netherlands

    • Background
    Phenotypic variation of Staphylococcus epidermidis involving the slime related ica operon results in heterogeneity in surface characteristics of individual bacteria in axenic cultures.

    Objective
    To investigate the role of recA in phenotypic variations of clinical S. epidermidis isolates.

    Material and methods
    Phenotypic variations of clinical S. epidermidis were confirmed by streaking on Congo Red Agar (CRA) and microtiter plate assay. The presence of ica genes and IS256 were investigated using PCR, while the expression of recA was analysed using real time PCR.

    Results
    Five clinical S. epidermidis isolates demonstrated phenotypic variation, i.e. both black and red colonies on Congo Red agar. All red colonies had lost ica and the ability to form biofilms, in contrast to black colonies of the same strain. Real time PCR targeting icaA indicated a reduction in gene copy number within cultures exhibiting phenotypic variation. Loss of ica was irreversible and independent of the mobile element IS256. Instead, in high frequency switching strains, spontaneous mutations in lexA were found which resulted in deregulation of recA expression, as shown by real time PCR.

    Conclusion
    RecA is involved in genetic deletions and rearrangements and we postulate a model representing a new mechanism of phenotypic variation in clinical isolates of S. epidermidis. This is the first report of S. epidermidis strains irreversibly switching from biofilm-positive to biofilm-negative phenotype by spontaneous deletion of icaADBC.