Pandemic fears: Antibiotics prove ineffective as new superbugs are now biggest global threat

Superbugs thought to have spread from animals have smashed through the last line in antibiotic defences and pose a global threat, scientists say.

Researchers identified a gene that makes infectious bacteria such as Escherichia coli (E.coli) highly resistant to polymyxins, the last group of antibiotics left after all others have failed.

The discovery in China, described as “extremely worrying” by one scientist, suggests the gene can easily be transferred to bacteria with the potential to cause epidemics.

Besides E. coli they include the pneumonia bug Klebsiella pneumoniae and Pseudomonas aeruginosa, which can trigger serious lung, blood and surgical infections.

An E.coli strain showing resistance to the polymyxin drug colistin was isolated from an intensively-farmed pig in Shanghai during routine testing.

Scientists found the bug was able to transfer its immunity to the drug to other strains via the mobile gene mcr-1.

This led to further tests of bacterial samples collected from pigs at slaughter in four Chinese provinces, and pork and chicken sold in 30 open markets and 27 supermarkets across Guangzhou province between 2011 and 2014.

Bacteria from infected patients at two hospitals in Guangdong and Zhejiang provinces were also tested.

A high prevalence of the resistance gene was found in E. coli bugs isolated from animals and raw meat samples.

The gene was also identified in 16 E.coli and K. pneumoniae samples taken from 1,322 hospitalised patients.

Alarmingly, the proportion of samples testing positive for the super-resistance gene increased from year to year, said the scientists.

Lead researcher Professor Jian-Hua Liu, from the South China Agricultural University in Guangzhou, said: “These are extremely worrying results. The polymyxins (colistin and polymyxin B) were the last class of antibiotics in which resistance was incapable of spreading from cell to cell.

"Until now, colistin resistance resulted from chromosomal mutations, making the resistance mechanism unstable and incapable of spreading to other bacteria.

"Our results reveal the emergence of the first polymyxin resistance gene that is readily passed between common bacteria such as Escherichia coli and Klesbsiella pneumoniae, suggesting that the progression from extensive drug resistance to pan-drug resistance is inevitable.”

Increasingly heavy use of colistin by Chinese farmers may have helped E.coli to acquire the gene, they added. Worldwide, the demand for colistin in agriculture was expected to reach almost 12,000 tonnes per year by the end of this year, rising to 16,500 tonnes by 2021.

The Chinese Ministry of Agriculture has launched a risk assessment of colistin use in animal feed additives.

British experts called the discovery “alarming”.

Dr David Burch, veterinary surgeon and an independent member of the Ruma (Responsible Use of Medicines in Agriculture) Alliance, pointed out that China’s pig farming industry is the largest in the world, more than twice the size of Europe’s.

The use of generic antimicrobial drugs in animals is not normally under veterinary control in China.

The risk of the resistance gene spreading has grown with increased trade and tourism bridging China and the West, said Dr Burch.

Professor Nigel Brown, president of the Microbiology Society, said: “This discovery that resistance to colistin can be transferred between bacteria is alarming.”

He added: “Now that it has been demonstrated that resistance can be transferred between bacteria and across bacterial species, another line of defence against infection is in danger of being breached.

"We need careful surveillance to track the potential global spread of this resistance, and investment in research to discover new drugs with different modes of action.”

1. What is a superbug?

Superbugs are strains of bacteria that are resistant to several types of antibiotics. One of the reasons for this resistance is the overuse of antibiotics. The Irish are heavier users of antibiotics than many other Europeans. C Diff and MRSA are the most well-known superbugs seen in Ireland.

2. What is this latest discovery?

Researchers in China have discovered a gene that makes bacteria highly resistant to a last-resort class of antibiotics. The gene makes infectious bacteria such as Escherichia coli (E.coli) highly resistant to polymyxins, the last group of antibiotics left after all others have failed.

3. Why is this so alarming?

The news has been described as “extremely worrying” by scientists for a number of reasons. Firstly, the gene makes bacteria resistant to antiobiotics such as Colistin - the last antiobiotic a doctor will use in terms of treating a completely resistant bacteria.

Secondly, the gene — MCR-1 — can be easily transferred to a range of bacteria with the potential to cause epidemics. Although confined to China, the researchers said the gene “is likely to emulate other resistance genes and spread worldwide”.

4. What types of bacteria can use the gene to develop resistance?

As well as E.coli, other bacteria to which the gene can be transferred include the pneumonia bug Klebsiella pneumoniae and Pseudomonas aeruginosa, which can trigger serious lung, blood and surgical infections.

5. Are there super antibiotics in the pipeline to be last line of defence?

At the moment no.

The major global pharmaceutical companies that normally develop and test our drugs have moved away from developing antibiotics because they do not result in major profits.

Developing a new antiobiotic and bringing it to a stage where it could be used on humans is a process that takes years.

6. Alternatives to antiobiotics?

Cork Institute of Technology is examining the possibilities offered by phage therapy which uses viruses to attack and kill bacteria. Phage treatments were discovered in 1917 but abandoned with the rise of penicillin in the 1940s.

Last year, the World Health Organisation (WHO) warned that the world is entering a post-antibiotic era in which common infections and minor injuries can kill.

It said the spread of deadly superbugs that evade even the most powerful antibiotics is no longer a prediction but is happening across the world.