Narrowing the field of antibiotic selection

Health professionals can detect, analyse and recommend treatment for bacterial infections within five hours under a new method devised by a research team based in Western Australia.

It could be a viable answer to the growing risk of antibiotic-resistant bacteria emerging in human populations.

About 1.27 million people die from antibiotic-resistant infections annually.

For those with a serious bacterial infection, every hour that passes without effective treatment increases the risk of death by 6.7%.

But current diagnostics take two to five days to isolate infection-causing bacteria and identify the best antibiotic to treat the problem.

To offset this, broad-spectrum antibiotics can be prescribed as a treatment, but this carries a different set of challenges.

Bacteria build resistance to our antibiotics

And it’s a global problem right now.

In fact, antimicrobial resistance is considered by the World Health Organization to be among the top 10 public health threats facing humanity.

The O’Neill Report commissioned by the UK Government in 2014 found 10 million people could die from antimicrobial-resistant infections each year from 2050.

And although bacteria can adapt to antibiotics naturally, the overuse – or misuse – of antibiotics accelerates adaptations.

Take Staphylococcus aureus, often referred to as golden staph.

This bacterium is usually harmless when it lives on our skin and inside our noses. But it can become problematic if it multiplies and causes a skin infection.

The situation is worse if it strays inside the body and causes staph infection internally.

Fortunately, antibiotics should be able to treat bacterial infections, but use over time has caused their effectiveness to wane.

In the case of S. aureus, some strains successfully withstand some treatments like Methicillin.

This means Methicillin-Resistant Staphylococcus Aureus (MRSA) infections are often untreatable with antibiotics.

It’s one example of why medical professionals are increasingly cautious about prescribing antibiotic treatments.

Broad-spectrum antibiotics provide treatment across a range of bacterial infections. They target both gram-positive and gram-negative bacterial types but growing resistance to these treatments blunts an important line of defence.

“The overuse of broad-spectrum antibiotics is one of the key drivers in the spread of resistance to antibiotics,” explains first author Dr Kieran Mulroney, from the Harry Perkins Institute of Medical Research in WA.

“The biggest problem with prescribing broad-spectrum antibiotics is that it encourages some bacteria to become resistant to the antibiotics.

“This is a growing and serious problem world-wide because antibiotic-resistant bacteria can spread from person to person and reduce treatment options. New tests are urgently needed that give doctors evidence they can rely on to select the right antibiotic.”

Narrowing the hit

Using a specific antibiotic to treat bacterial infections is one way of slowing the growth of bacterial resistance but using narrow-spectrum antibiotics – ones that are optimised for a particular type of bacterium – requires testing.

Once the type of bacteria is known, a specific treatment can be provided.

This process takes two to five days to confirm results, which is of little help when time is critical for patients presenting with severe illness.

Using Peritonitis – an infection that can arise from the administration of peritoneal dialysis – as their test infection, Mulroney and his colleagues developed a new method that cuts diagnosis to hours, rather than days.

It’s a test that removes a bacterial sample from a patient and subjects it to a range of different antibiotics in the lab.

Using instrumentation that measures thousands of individual bacteria in seconds, researchers can quickly determine the damage antibiotics cause to the specimen.

In doing so, the optimum treatment can be provided to a patient, reducing the likelihood of resistance developing in bacteria.

The method, says, Mulroney, is more than 97% accurate and more efficient than the status quo.

“There is a clear and present need for more rapid tests that will return results that will allow doctors to select the right antibiotic, for the right patient, in the right amount of time,” says Mulroney.

“First, we developed a test to confirm if the cause of the patient’s serious illness is a bacterial infection. This test takes 30 minutes, rather than one to two days.

“Once a patient has a confirmed bacterial infection, we then expose the bacteria to different types of antibiotics in the laboratory.

“Using a device that measures hundreds of thousands of individual bacteria in just a few seconds, the research team can detect the damage antibiotics cause to bacteria, and then use this information to confirm which antibiotic will be an effective treatment.”

Although the researchers acknowledge bacterial species are not identified in this process, they state that knowing the type of organism is “useful, but not strictly necessary” to select an optimal treatment for infection.