This joint ID and pulmonary/critical care conference follows a single patient through a prolonged hospitalization after a biliary leak that was never fully source controlled. Over roughly four months he had recurrent VRE and Burkholderia cepacia complex bacteremias, candidemia, repeated pneumonias and intra-abdominal flares, and serial airway cultures that grew multidrug-resistant Pseudomonas aeruginosa with shifting susceptibility patterns, despite more than nine weeks of cefiderocol.
The discussion uses his isolates to challenge the model implied by the lab report: that a culture is one clonal population, that S means the drug kills all of it, and that the S drug cures the patient. It covers why large populations carry resistant subpopulations and what resistance costs the bacterium, how heteroresistance, mixed strains and evolution within the patient look identical on a routine panel, and how an antibiogram is built from the colonies the lab happens to pick. A cefiderocol section reviews heteroresistance, the difficulty of susceptibility testing, cross-resistance with ceftolozane-tazobactam and ceftazidime-avibactam, and CREDIBLE-CR, with MERINO and inducible AmpC as familiar examples of an S that can fail.
The talk closes with the 90-60 rule: about 90% of infections with susceptible isolates respond, and about 60% with resistant isolates still do. Source control, host, site and dose often matter more than the panel, and after long exposure a susceptible result is best treated as a soft S.