THE temperatures routinely used to sterilise surgical instruments in British
hospitals might actually help to spread the deadly brain disease CJD, say
researchers in Scotland. However, the finding could lead to more effective ways
of disinfecting surgical instruments contaminated by prions, the rogue proteins
thought to cause the disease.
Concerns that surgeons鈥� instruments might pass on new variant
Creutzfeldt-Jakob disease (vCJD), the human form of BSE, intensified last month
with news that the infection is present throughout the lymph tissue of victims,
not just in the central nervous system
(This Week, 23 January, p 5).
Because there is no sure way of sterilising instruments contaminated with prions, the
discovery prompted calls for surgeons to use disposable instruments for
operations involving lymph tissue. But so far the British government has not
committed itself because of the high costs.
Now there is evidence that attempts to disinfect instruments by 鈥減ressure
cooking鈥� them at high temperatures in an autoclave might do more harm than good.
David Taylor of the Institute for Animal Health in Edinburgh found that
increasing the temperature of the autoclave actually made it harder to destroy
CJD prions. In one experiment, infected tissue samples were heated at 134 掳C
for 9, 18 and 30 minutes. The treated samples were not infectious. However, when
the experiment was repeated at 138 掳C, the tissue was still infectious. In
Britain, the standard temperature range for autoclaving instruments is 134 to
138 掳C.
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Taylor believes the slightly higher temperature 鈥渇ixed鈥� the prion, allowing
chemical links to form that made the molecules more stable. He is preparing his
results for publication.
Mark Pepys, who specialises in the chemistry of brain disorders at the Royal
Postgraduate Medical School in London, says Taylor鈥檚 explanation 鈥渋nvolves a lot
of speculation because we just don鈥檛 know enough about the agent that causes CJD
yet鈥�. But the suggestion doesn鈥檛 surprise him. Even very small temperature
changes can cause changes in a protein molecule鈥檚 shape, he says. This might
involve bonds that by themselves are quite weak. 鈥淏ut if there were enough of
them, perhaps hundreds, the effect of strengthening the molecule could be
dramatic,鈥� he says.
鈥淭aylor鈥檚 work highlights the difficulty in inactivating prions,鈥� says John
Barbara, a microbiology consultant to Britain鈥檚 National Blood Authority. He
says the findings strengthen the case for developing ways of physically
excluding prions from blood products.
In terms of surgical instruments, Taylor says that a strong solution of
sodium hydroxide for one hour followed by autoclaving at 136 掳C for one hour
is fairly effective. 鈥淚f we combine alkali solutions with the right grade
surgical steel that can stand up to it, it will be possible to improve
sterilisation,鈥� he says.
For now, though, he says that the only completely safe way to deal with
contaminated items is to throw them away.