7/8 We hypothesized porins may not be critical during infection of an immunocompromised host (the common victim of Enterobacter infections). Indeed, porin mutants were able to cause lethal infection in a neutropenic mouse model, and in an ex vivo model of human bacteremia.

6/8 However, porin loss did promote carbapenem resistance in the ST78 isolates, an important phenomenon in multidrug-resistant Gram-negatives.

5/8 Deletion of these porin genes in two otherwise virulent isolates rendered the isolates avirulent.

4/8 These analyses suggested loss-of-function mutations in two porin-encoding genes may be the culprit.

3/8 In a mouse model of infection, only E. hormaechei sequence type 78 (ST78) caused lethal infection. In a cluster of closely related ST78 isolates, we identified an avirulent outlier that we used for comparative genomics.