3.1 Gram-negative pathogens

Gram-negative pathogens are a significant cause of morbidity both in community-acquired infection such as enteric fever and urinary tract infection (UTI) and in healthcare-associated infections (HCAI). It is notable that all the organisms in the WHO priority R&D ‘critical’ category are all Gram-negative: P. aeruginosa,A. baumannii and Enterobacterales.

In animal health, Gram-negatives are found as gut commensals and as pathogens. They are an important source of resistance genes getting into the human food chain, especially as it is hard to totally prevent contamination of meat with faecal material at slaughter.

Figure 3 Salmonella and E. coli are a common cause of health problems in piglets, leading to antibiotic use.

Production of β-lactamases and carbapenemases are the biggest problem with infections caused by Gram-negative organisms owing to the relative lack of antimicrobials available outside these classes to treat them. Quinolone resistance is also a problem.