An 81 year old woman with a long term, indwelling urinary catheter is admitted with fever and hypotension thought to be due to septicaemia secondary to urinary tract infection. She is treated empirically with intravenous cefotaxime and gentamicin, but her condition deteriorates over 24 hours, with increasing hypotension and continuing fever. For broader spectrum coverage, her empirical antibiotic treatment is changed to intravenous meropenem. The next day, urine and blood cultures grow an Escherichia coli producing an extended spectrum β lactamase (ESBL), conferring resistance to cefotaxime and gentamicin but not to meropenem. The meropenem is continued for seven days, with clinical and bacteriological resolution of the patient’s infection.