The E. coli MHT18 and MHX43 isolates and P. mirabilis MH438 and MH42F isolates were isolated by the Clinical Microbiology Service at Memorial Hospital, Memorial Sloan Kettering Cancer Center. Antimicrobial susceptibility testing of these isolates was performed using a Neg MIC 43 panel on a Microscan System (Beckman Coulter) by the Clinical Microbiology Service at Memorial Hospital. The K. pneumoniae MH258 and MH189 isolates were previously described (Xiong et al., 2015 (link)). These isolates of K. pneumoniae, E. coli, and P. mirabilis were routinely grown overnight in LB broth (BD) with 100 µg/ml ampicillin (Fisher Scientific) at 37°C under aerobic conditions. E. coli Nissle 1917 and the isogenic E. coli Nissle 1917 cydAB/napA/narG/narZ strain were routinely grown in LB broth as previously described (Byndloss et al., 2017 (link)).