--- - |2 Abstract Evidence‐based treatment guidelines for managing infections in health care are promoted as tools to prevent unnecessary use of antibiotics. Antibiotic misuse has been examined as regards the doctor‐patient relation and the social context of medical practice. Less attention has been paid to how the very conceptualisation of human‐microbial relations may influence understandings of antibiotic misuse. The article examines a medical controversy concerning guidelines for managing throat infection and antibiotic treatment in Sweden. It demonstrates how this controversy unfolds around two different ways of relating to a specific bacterium – Group A Streptococcus. The analysis shows how two ‘microbiopolitics’, involving different understandings of human‐microbial relations, are created in the controversy and how different antibiotic prescribing practices are justified. By focusing on Group A Streptococcus, which is commonly observed, but also unpredictable and potentially dangerous, the article provides new insights into the relations between bacteria, humans and policy in an age of antimicrobial resistance. It argues, in particular, that the definition of antibiotic misuse is unstable and consequently that policy measures aimed at reducing misuse must be related to how specific infections and bacteria are conceptualised in the actual context the policy addresses. - Sociology of Health & Illness, Volume 40, Issue 7, Page 1127-1141, September 2018.