title: In vitro analysis of bacterial morphology by atomic force microscopy of low level laser therapy 660, 830 and 904 nm.
abstract: OBJECTIVE
  The objective of this study was to analyze the bacterial morphology by atomic force microscopy (AFM) after the application of low-level laser therapy (LLLT) in in vitro culture of Staphylococcus aureus ATCC 29213.
  
  
  BACKGROUND
  Infections caused by S. aureus are among the highest occurring in hospitals and can often colonize pressure ulcers. LLLT is among the methods used to accelerate the healing of ulcers. However, there is no consensus on its effect on bacteria.
  
  
  METHODS
  After being cultivated and seeded, the cultures were irradiated using wavelengths of 660, 830, and 904 nm at fluences of 0, 1, 2, 3, 4, 5, and 16 J/cm(2). Viable cells of S. aureus strain were counted after 24 h incubation. To analyze the occurrence of morphological changes, the topographical measurement of bacterial cells was analyzed using the AFM.
  
  
  RESULTS
  The overall assessment revealed that the laser irradiation reduced the S. aureus growth using 830 and 904 nm wavelengths; the latter with the greatest inhibition of the colony-forming units (CFU/mL) (331.1±38.19 and 137.38±21.72). Specifically with 660 nm, the statistical difference occurred only at a fluence of 3 J/cm(2). Topographical analysis showed small changes in morphological conformity of the samples tested.
  
  
  CONCLUSIONS
  LLLT reduced the growth of S. aureus with 830 and 904 nm wavelengths, particularly with 904 nm at a fluence of 3 J/cm(2), where the greatest topographical changes of the cell structure occurred.
authors.affiliation: Department of Physical Therapy, FAMINAS-School of Minas, Minas Gerais, Brazil.
authors.forename: Natanael Teixeira Alves
authors.initials: NT
authors.lastname: de Sousa
authors.forename: Rinaldo Roberto de Jesus
authors.initials: RR
authors.lastname: Guirro
authors.forename: Henrique Freitas
authors.initials: HF
authors.lastname: Santana
authors.forename: Carla Cilene Matos
authors.initials: CC
authors.lastname: Silva
mesh_terms: D015169:Colony Count, Microbial; D028022:Low-Level Light Therapy; D018625:Microscopy, Atomic Force; D011829:Radiation Dosage; D013211:Staphylococcus aureus / Q000254:growth & development* / Q000528:radiation effects*