The first ever list of antibiotic-resistant “priority pathogens” — a catalogue of 12 families of bacteria that pose the greatest threat to human health — has been published by the World Health Organisation.

The list highlights in particular the threat of gram-negative bacteria that are resistant to multiple antibiotics.

These bacteria have built-in abilities to find new ways to resist treatment and can pass along genetic material that allows other bacteria to become drug-resistant as well.

The list was drawn to guide and promote research and development of new antibiotics, as part of WHO’s efforts to address the growing global resistance to antimicrobial medicines.

“This list is a new tool to ensure R&D responds to urgent public health needs,” said Marie-Paule Kieny, WHO’s assistant director-general for health systems and innovation.

“Antibiotic resistance is growing, and we are fast running out of treatment options. If we leave it to market forces alone, the new antibiotics we most urgently need are not going to be developed in time,” Ms Kieny added.

The WHO list is divided into three categories according to the urgency of the need for new antibiotics: Critical, high and medium priority.

The most critical group of all includes multidrug resistant bacteria that pose a particular threat in hospitals, nursing homes, and among patients whose care requires devices such as ventilators and blood catheters.

They include Acinetobacter, Pseudomonas and various Eterobacteriaceae (Klebsiella, E. coli, Serratia, and Proteus). They can cause severe and often deadly infections such as bloodstream infections and pneumonia.

“These bacteria have become resistant to a large number of antibiotics, including carbapenems and third generation cephalosporins — the best available antibiotics for treating multidrug resistant bacteria,” said the WHO.

The second and third tiers in the list — the high and medium priority categories —contain other increasingly drug-resistant bacteria that cause more common diseases such as gonorrhoea and food poisoning caused by salmonella.

The list is intended to motivate governments to give incentives for basic science and advanced R&D by both publicly funded agencies and the private sector investing in new antibiotic discovery.

It will provide guidance to new R&D initiatives such as the WHO/DNDi Global Antibiotic R&D Partnership that is engaging in not-for-profit development of new antibiotics.

Tuberculosis — whose resistance to traditional treatment has been growing in recent years — was not included in the list because it is targeted by other dedicated programmes. Other bacteria that were not included, such as streptococcus A and B and chlamydia, have low levels of resistance to existing treatments and do not currently pose a significant public health threat.

The criteria for selecting pathogens on the list were: How deadly the infections they cause are; whether their treatment requires long hospital stays; and how frequently they are resistant to existing antibiotics when people in communities catch them.