MICROBE OF THE MONTH: The fleece and the phage: a yarn from down under

A bacterium attacking sheep in Australia may have met its match, says Bernard Dixon

Louis Pasteur, the centenary of whose death falls later this year, would not have understood our present-day compulsion to categorise science as "pure" or "applied". Virtually all the great French chemist's work, on subjects ranging from beer- and wine-making to silkworm disease and anthrax in sheep, fully merited both adjectives. It revealed fundamental features of the biological world, while at the same time served the needs of industry and practicality.

So I like to think that Pasteur would have chuckled appreciatively over a paper in the current issue of Letters in Applied Microbiology. It demonstrates a hitherto unrecognised natural relationship between two different microbes, and also suggests a strategy for controlling a condition that causes substantial problems for Australia's wool industry.

The condition investigated by Douglas Kurtboke and his colleagues in Western Australia is known as lumpy wool, an infection caused by the bacterium Dermatophilus congolensis. It affects merino sheep in particular, though it poses a greater problem by impairing the quality of the wool than by seriously threatening the health of the animals.

D. congolensis invades the sheep's skin follicles, where it multiplies and provokes inflammation. The inflamed skin releases pus, containing the bacterium, which mats the wool, creating "lumpy wool scabs". As the scabs dry, the bacteria form spores to protect themselves from desiccation. When the animal next becomes wet, perhaps after a rain shower, the spores again release bacteria. These infect further skin follicles, initiating the whole cycle once more.

Damp conditions not only facilitate this process of reinfection, but also allow D. congolensis to pass from affected sheep to unaffected ones. Although lumpy wool may be an acute and short-lived condition, it often becomes chronic and can last for a year or more. The scabs downgrade the quality of the fleece, sometimes making it unusable.

Present methods of dealing with lumpy wool leave much to be desired. Penicillin is partially effective, though only when given for lengthy periods. This encourages the development of antibiotic-resistant bacteria, and can leave residues - a potential problem if the meat is intended for human consumption. Chemicals applied externally may fail to reach the bacterium in the hair follicles. Vaccination can promote recovery - without, however, preventing the formation of infectious scabs. In practice, farmers often resort simply to cutting out affected areas of wool and culling badly infected sheep.

Kurtboke and his collaborators decided to explore an alternative approach. Just as bacteria attack humans and other animals, so they in turn are preyed upon by much smaller microbes - viruses known as phages. There is a relationship between a particular phage and the specific bacterium or bacteria that it can invade. Phages also differ in their virulence. Some destroy their prey quickly. Others are comparatively benign, co- existing in a permanent partnership with the bacteria they infect.

By no means all bacteria are known to be susceptible to phages. Moreover, phages are not uniformly distributed. In another parallel with populations of humans and of disease-causing bacteria, a phage that is relatively common in one region may be absent from another environment.

All of this encouraged the Australian scientists to search for a phage capable of attacking D. congolensis. If they found one, they might be able to administer it to infected sheep. A further possibility was genetically engineering such a phage, making the naturally occurring one more virulent by altering its genes or introducing new ones.

The normal method of finding phages is simply by examining environments inhabited by the bacteria upon which they prey. For example, bacteriologists searching for phages capable of attacking Escherichia coli, a common inhabitant of the human bowel, usually screen samples of sewage. The Australians turned therefore to four different sheep farms in Western Australia, where they obtained samples of both infected wool and other materials such as soil.

They tested the specimens by spotting them on to glass dishes containing nutrient medium and D. congolensis, the prospective target for phage attack. Wool from three of the farms proved negative, as did all the soil and other materials. After incubation, the dishes showed D. congolensis growing over the entire area, unaffected by the added specimens. But the fourth farm's wool was positive. It produced clear circles in the nutrient medium where a phage from the wool had invaded and destroyed the bacterium.

Kurtboke and his colleagues confirmed their discovery when they examined the specimens under the electron microscope and saw a previously unknown type of phage. Further tests showed that it was highly specific, attacking D. congolensis but not one of 39 other species of bacteria tested.

The investigators added the phage to samples of ground scab from infected sheep, and found that it reduced the population of D. congolensis to less than a third of that without phage.

The phage's specificity would be a big advantage in its use for combating the microbe responsible for lumpy wool. It would be unlikely, for example, to attack beneficent bacteria. Above all, such a natural, biological approach would be preferable to the use of antibiotics or other chemicals, with their attendant risks of residues and resistance. Pasteur would have appreciated that.

Suggested Topics
Start your day with The Independent, sign up for daily news emails
ebookA unique anthology of reporting and analysis of a crucial period of history
peopleMathematician John Nash inspired the film Beautiful Mind
Richard Blair is concerned the trenches are falling into disrepair
newsGeorge Orwell's son wants to save war site that inspired book
Life and Style
Audrey Hepburn with Hubert De Givenchy, whose well-cut black tuxedo is a 'timeless look'
fashionIt may be a paradox, but the industry loves it
Arts and Entertainment
The pair in their heyday in 1967
Life and Style
fashionFrom bathing dresses in the twenties to modern bikinis
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Guru Careers: Software Developer / C# Developer

£40-50K: Guru Careers: We are seeking an experienced Software / C# Developer w...

Guru Careers: Software Developer

£35 - 40k + Benefits: Guru Careers: We are seeking a Software Developer (JavaS...

SThree: Trainee Recruitment Consultant / Resourcer

£18000 - £23000 per annum + Commission: SThree: As a Trainee Recruitment Consu...

Ashdown Group: UI Developer - (UI, HTML, CSS, JavaScript, AngularJS)

£25000 - £40000 per annum: Ashdown Group: UI Developer - (UI, JavaScript, HTML...

Day In a Page

Abuse - and the hell that came afterwards

Abuse - and the hell that follows

James Rhodes on the extraordinary legal battle to publish his memoir
Why we need a 'tranquility map' of England, according to campaigners

It's oh so quiet!

The case for a 'tranquility map' of England
'Timeless fashion': It may be a paradox, but the industry loves it

'Timeless fashion'

It may be a paradox, but the industry loves it
If the West needs a bridge to the 'moderates' inside Isis, maybe we could have done with Osama bin Laden staying alive after all

Could have done with Osama bin Laden staying alive?

Robert Fisk on the Fountainheads of World Evil in 2011 - and 2015
New exhibition celebrates the evolution of swimwear

Evolution of swimwear

From bathing dresses in the twenties to modern bikinis
Sun, sex and an anthropological study: One British academic's summer of hell in Magaluf

Sun, sex and an anthropological study

One academic’s summer of hell in Magaluf
From Shakespeare to Rising Damp... to Vicious

Frances de la Tour's 50-year triumph

'Rising Damp' brought De la Tour such recognition that she could be forgiven if she'd never been able to move on. But at 70, she continues to flourish - and to beguile
'That Whitsun, I was late getting away...'

Ian McMillan on the Whitsun Weddings

This weekend is Whitsun, and while the festival may no longer resonate, Larkin's best-loved poem, lives on - along with the train journey at the heart of it
Kathryn Williams explores the works and influences of Sylvia Plath in a new light

Songs from the bell jar

Kathryn Williams explores the works and influences of Sylvia Plath
How one man's day in high heels showed him that Cannes must change its 'no flats' policy

One man's day in high heels

...showed him that Cannes must change its 'flats' policy
Is a quiet crusade to reform executive pay bearing fruit?

Is a quiet crusade to reform executive pay bearing fruit?

Dominic Rossi of Fidelity says his pressure on business to control rewards is working. But why aren’t other fund managers helping?
The King David Hotel gives precious work to Palestinians - unless peace talks are on

King David Hotel: Palestinians not included

The King David is special to Jerusalem. Nick Kochan checked in and discovered it has some special arrangements, too
More people moving from Australia to New Zealand than in the other direction for first time in 24 years

End of the Aussie brain drain

More people moving from Australia to New Zealand than in the other direction for first time in 24 years
Meditation is touted as a cure for mental instability but can it actually be bad for you?

Can meditation be bad for you?

Researching a mass murder, Dr Miguel Farias discovered that, far from bringing inner peace, meditation can leave devotees in pieces
Eurovision 2015: Australians will be cheering on their first-ever entrant this Saturday

Australia's first-ever Eurovision entrant

Australia, a nation of kitsch-worshippers, has always loved the Eurovision Song Contest. Maggie Alderson says it'll fit in fine