Contact: Lucy Goodchild
Society for General Microbiology
Milk may help bacteria survive against low levels of antibiotics
Milk may help prevent potentially
dangerous bacteria like Staphylococcus from being killed by antibiotics
used to treat animals, scientists heard today (Monday 8 September 2008)
at the Society for General Microbiology's Autumn meeting being held
this week at Trinity College, Dublin.
Bacteria sometimes form
structures called biofilms that protect them against antibiotics and
the body's natural defences. Now scientists have discovered that one of
the most important micro-organisms that causes mastitis in cows and
sheep, called Staphylococcus, can evade the animal's defences and
veterinary medicines by forming these protective biofilms. Mastitis is
an infection of the udder in cattle and sheep. It is often a painful
condition for the cows and can even cause death.
a difficult disease to control. It causes risks for public health if
people drink infected milk and is expensive for farmers as it usually
causes severe milk production losses, increased treatment costs and
means the animals may have to be culled," said Dr Manuela Oliveira from
the Faculty of Veterinary Medicine at the Technical University of
Lisbon, Portugal. "When the staphylococci produce a biofilm, the
structure protects them against host defences and antibiotic treatment,
allowing the bacteria to persist in the udder."
In the past,
scientists studying mastitis have conducted most of their experiments
under laboratory conditions rather than mimicking the conditions found
in living animals. This may mean that they have missed important
contributory factors. However, Dr Oliveira and her colleagues have used
realistic conditions to overcome this problem.
discovered that milk may also protect bacteria against low
concentrations of antibiotics – in the presence of milk, three of the
five antibiotics tested, penicillin, gentamicin and sulphamethoxazole
combined with trimethoprim, were less effective against Staphylococcus
when compared with the same experiment performed in the absence of
milk," said Dr Oliveira.
The Lisbon team is currently trying
to identify the correct antibiotic concentrations needed to stop
biofilms forming in the first place and also the concentrations needed
to destroy a biofilm that has already formed. The scientists are also
looking at the influence of the forces acting inside an udder during
milking to see whether these help or hinder the bacteria in producing
"This will allow for a better control of
staphylococcal mastitis, cut disease costs and give an important
improvement in the protection of consumers' health," said Dr Manuela
Oliveira. "If we can get the doses right, and the animals are cured
quicker, we will have less antibiotic residue in the environment and
the risk of bacteria such as
Staphylococcus aureus developing and spreading antibiotic resistance is lower."