Recurrent joint infection caused by a multidrug-resistant capnophilic Escherichia coli ST131 O25H4 strain

We report a case of a native knee septic arthritis and subsequent osteomyelitis due to a CO2-dependent (capnophilic) multidrug-resistant E. coli ST131 O25:H4 strain. Capnophilic phenotype made microbiology investigation challenging; susceptibility testing could not be performed and the organism did not grow in the urine culture using standard method. The combination of unique virotype and capnophilia may have contributed to the aggressiveness of this organism and the initial unsuccessful carbapenem course, leading to recurrent infection.