WHO's antibiotic-resistant pathogen list designed to encourage R&D

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 also allows other bacteria to become drug-resistant.

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"This list is a new tool to ensure R&D responds to urgent public health needs," says Dr 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."

Classification

The WHO list is divided into three categories according to the urgency of 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 enterobacteriaceae (including 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 multi-drug resistant bacteria.

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.

Excluded pathogens

Tuberculosis – where 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.

Criteria

The criteria for selecting pathogens on the list were: how deadly the infections they cause are; whether their treatment requires long hospital stays; how frequently they are resistant to existing antibiotics when people in communities catch them; how easily they spread between animals, from animals to humans, and from person to person; whether they can be prevented (through good hygiene and vaccination); how many treatment options remain; and whether new antibiotics to treat them are already in the R&D pipeline.

While more R&D is vital, alone, it cannot solve the problem. To address resistance, there must also be better prevention of infections and appropriate use of existing antibiotics in humans and animals, as well as rational use of any new antibiotics that are developed in future.

WHO priority pathogens list

Priority 1: Critical

• Acinetobacter baumannii, carbapenem-resistant
• Pseudomonas aeruginosa, carbapenem-resistant
• Enterobacteriaceae, carbapenem-resistant, ESBL-producing

Priority 2: High

• Enterococcus faecium, vancomycin-resistant
• Staphylococcus aureus, methicillin-resistant, vancomycin-intermediate and resistant
• Helicobacter pylori, clarithromycin-resistant
• Campylobacter spp., fluoroquinolone-resistant
• Salmonellae, fluoroquinolone-resistant
• Neisseria gonorrhoeae, cephalosporin-resistant, fluoroquinolone-resistant

Priority 3: Medium

• Streptococcus pneumoniae, penicillin-non-susceptible
• Haemophilus influenzae, ampicillin-resistant
• Shigella spp., fluoroquinolone-resistant