The World Health Organisation (WHO) has published its first ever list of antibiotic-resistant "priority pathogens" - a catalogue of 12 families of bacteria that pose the greatest threat to human health. The list was drawn up in a bid to guide and promote research and development (R&D) of new antibiotics, as part of WHO's efforts to address growing global resistance to antimicrobial medicines. 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. "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," said Marie-Paule Kieny, WHO's Assistant Director-General for Health Systems and Innovation. You may also like to watch: 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 multi-drug 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, WHO said. 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 spur governments to put in place policies that incentivise basic science and advanced R&D by both publicly funded agencies and the private sector investing in new antibiotic discovery, WHO said. 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. "New antibiotics targeting this priority list of pathogens will help to reduce deaths due to resistant infections around the world," said Prof Evelina Tacconelli, Head of the Division of Infectious Diseases at the University of Tubingen in Germany.