Porphyrin dye sterilises bone for surgery
An antimicrobial dye (porphyrin) activated by light could help reduce the rate of infection after bone surgery according to a new study published in Clinical Orthopaedics and Related Research.
Researchers at Thomas Jefferson University in Philadelphia, USA, used a porphyrin dye that adheres to bone to prevent bacteria from growing on bone fragments used in reconstructive surgery, and remove any bacteria that has already attached, effectively sterilising the bone for surgery.
“Porphyrins are tolerated very well by the body in the dark and appear to have excellent antimicrobial properties in the presence of light,” said author Noreen Hickok, associate professor of orthopaedic surgery at Thomas Jefferson. “These properties allow sterilisation during surgical procedures, which occur in bright light.”
The rate of infection after joint replacement or reconstructive surgery remains around 5 per cent, with much higher figures seen following reconstruction after tumour removal, despite efforts to sterilise the bone materials used with various detergents and high-pressure steam.
“Bacteria really love to hide and grow in the nooks and crannies of porous bone and bone fragments – it’s one of the most perfect surfaces for bacterial growth,” said Hickok.
Into the light
The researchers treated bone chips with 5,10,15,20-tetrakis-(4-aminophenyl)-porphyrin (TAPP), a green dye that is stable in the dark; when the lights go on, TAPP becomes active, producing reactive oxygen species that rapidly kill the bacteria present. They first treated the bone putty with TAPP and then exposed those fragments to bacteria. As long as the lights were on, bacteria were unable to attach and grow on the surface of the bone.
Hickok and colleagues showed that, as well as preventing bacterial growth, TAPP can also break up bacterial slime, or biofilms, already growing on bone fragments. They demonstrated this by first allowing bacteria to colonise the bone and then treating with TAPP. Finally, they demonstrated that the dye binds tightly to the bone, without any trace of leaching out into surrounding fluid, suggesting that it could be safe and non-toxic to normal tissue once implanted.
In theory, said Hickok, TAPP could be added to the currently used protocols for sterilising bone prior to surgery: “Sterilisation could then occur in two steps – one which was achieved with a targeted illumination, and the other would be the continuation of the activation in the bright lights of the surgical suite so that the sterilising effects of the reactive oxygen species release could continue well into surgery and implantation.
“We need to continue testing in conditions that more closely resemble the surgical suite,” she added, “but we think that this method could offer a more effective method to help improve patient outcomes by reducing infection rates.”
Dastgheyb, S.S., Toorkey, C.B., Shapiro, I.M. & Hickok, N.J. (2015) Porphyrin-adsorbed allograft bone: a photoactive, antibiofilm surface. Clin. Orthopaed. Rel. Res. doi: 10.1007/s11999-015-4299-5