The World Health Organization has identified 12 “priority pathogens” that it says pose the greatest risk to human health in an era where bacteria are increasingly resistant to antibiotic medicines.

The list includes bacteria that cause food poisoning, common sexually-transmitted diseases and subsets of bacteria that are normally considered an essential part of a healthy human digestive tract.

Most people who come into contact with these bacteria won’t get sick and won’t get a drug resistant form, but in some cases these bugs can prove deadly.

Here’s a closer look at the 12 pathogens, based on information from the U.S. Centers for Disease Control and Prevention.

Acinetobacter baumannii

  • Commonly found in soil and water
  • Very little risk to healthy people but risky to those in hospital intensive care units
  • Causes pneumonia (lung infection), blood infections and wound infections

Pseudomonas aeruginosa

  • Usually occurs in people with weakened immune systems or those in hospitals
  • May present as pneumonia, blood infection or wound infection after surgery
  • Healthy people may develop a milder illness after swimming in inadequately chlorinated hot tubs and pools


  • Part of the healthy gut but some versions are drug-resistant, including KPC (Klebsiella pneumoniae carbapenemase) and NDM (New Delhi Metallo-beta-lactamase)
  • Resistant infections usually occur in hospitals and nursing homes

Enterococcus faecium

  • Normally present in the human bowel, as well as the female genital tract and surface water contaminated by animal excrement and untreated sewage
  • Drug-resistant infections most likely to occur in hospitals

Staphylococcus aureus

  • About 30 per cent of people carry it in their noses but it can cause infections of the bloodstream, heart, lungs or bones
  • Injection drug users, people with diabetes, cancer, vascular disease, eczema, and lung disease are most at risk

Helicobacter pylori

  • As many as two-thirds of people are infected with H. pylori, which can cause stomach ulcers and increase the risk of gastric cancers
  • One study found that black people are at a higher risk of drug-resistant inflections

Campylobacter spp.

  • A food-borne illness that’s one of the most common causes of diarrhea in North America
  • Often acquired by eating raw chicken meat


  • A food-borne illness often acquired through raw or undercooked eggs, poultry and other meats
  • A Danish study found drug-resistant salmonellae in that country was highest in patients who had returned from developing countries

Neisseria gonorrhoeae

  • A sexually-transmitted disease that often presents as urethritis (infected urethra) in men or urethritis or cervicitis (infected cervix) in women
  • Most common in youth between the ages 15 to 19

Streptococcus pneumoniae

  • Commonly found in respiratory tract
  • Those who work in childcare centers, nursing homes or HIV-related institutions are at increased risk of resistant infection

Haemophilus influenza

  • Leading cause of bacterial meningitis in children under five
  • In adults, it may cause pneumonia, sinus infection or bronchitis

Shigella spp.

  • A leading cause of diarrhea in North America
  • Infection happens by exposure to tiny amounts of fecal matter in bathrooms, in food or elsewhere