Ith E. coli NC101 or ibpAB-deficient NC101 (NC101ibpAB) for the indicated times and then quantified viable gentamicin-resistant (i.e. intracellular) bacteria by plating macrophage lysates on agar. At each time point examined after addition of bacteria, we detected significantly fewer intra-macrophage NC101ibpAB vs. NC101 in wt BMDMs (Fig. 5A). However, no significant differences in intra-macrophage NC101 vs. NC101ibpAB numbers were VercirnonMedChemExpress GSK-1605786 observed at any time point in gp91phox-/- BMDMs suggesting that ibpAB expression in E. coli NC101 protects intracellular E. coli from killing by macrophage-derived ROS. Interestingly, when wePLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,7 /IbpAB Protect Commensal E. coli against ROSFig 5. IbpAB protect commensal E. coli NC101, but not pathogenic E. coli O157:H7 from reactive oxygen species-mediated killing SP600125 biological activity within macrophages. Viable, gentamicin-resistant (i.e. intracellular) E. coli were measured at the indicated timepoints after infection of wt or gp91phox-/- BMDMs with E. coli NC101 / E. coli NC101ibpAB (A) or E. coli O157:H7 / E. coli O157:H7ibpAB (B). Data are presented as means ?sem (n = 3? wells/timepoint, *p<0.05 vs. all other conditions in panel A and vs. both E. coli strains in gp91phox-/- BMDMs in panel B). doi:10.1371/journal.pone.0120249.gperformed the same experiments with pathogenic E. coli O157:H7, we found that wt BMDMs kill E. coli O157:H7 more efficiently than E. coli NC101 and that ibpAB has no effect on intramacrophage survival (Fig. 5B). However, unlike results observed with E. coli NC101, gp91phox-/- BMDMs kill E. coli O157:H7 less efficiently than wt BMDMs at 1 and 4 hrs post infection. Therefore, ibpAB protect E. coli NC101, but not E. coli O157:H7, from ROS-mediated killing in macrophages. Since E. coli O157:H7 are killed more efficiently by wt BMDMs than E. coli NC101 and since the ibpAB-mediated protection from intra-macrophage killing presumably requires adequate expression of ibpAB, we asked whether E. coli O157:H7 upregulate ibpAB after phagocytosis to a similar degree as E. coli NC101. To answer this question, we compared ibpAB expression in phagocytosed E. coli NC101 with E. coli O157:H7 in wt BMDMs. Although E. coli O157:H7 slightly increase ibpAB expression after infection of BMDMs, they do so to a much lesser extent compared with E. coli NC101 (Fig. 6). Therefore, it is conceivable that the increased killing of E. coli O157:H7 compared with E. coli NC101 by wt BMDMs may be due toPLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,8 /IbpAB Protect Commensal E. coli against ROSFig 6. Commensal E. coli NC101, but not pathogenic E. coli O157:H7 upregulate ibpAB after phagocytosis by macrophages. A and B) IbpA and ibpB mRNA in intracellular E. coli was measured using real-time PCR at the indicated times following infection of wt BMDMs with E. coli NC101 or E. coli O157:H7. Data are presented as means ?sd (n = at least 3 wells/timepoint, *p<0.05 vs. E. coli O157:H7). doi:10.1371/journal.pone.0120249.ginsufficient ibpAB expression in E. coli O157:H7. These results support the concept that the E. coli ibpAB operon is a virulence factor that is upregulated in certain strains of E. coli, including NC101, during macrophage infection, and protects E. coli from killing by macrophagederived ROS.DiscussionSeveral functions of E. coli ibpAB have previously been identified, including protection of bacteria from elevated temperatures, carbon monoxide, tellurite and copper toxicity, an.Ith E. coli NC101 or ibpAB-deficient NC101 (NC101ibpAB) for the indicated times and then quantified viable gentamicin-resistant (i.e. intracellular) bacteria by plating macrophage lysates on agar. At each time point examined after addition of bacteria, we detected significantly fewer intra-macrophage NC101ibpAB vs. NC101 in wt BMDMs (Fig. 5A). However, no significant differences in intra-macrophage NC101 vs. NC101ibpAB numbers were observed at any time point in gp91phox-/- BMDMs suggesting that ibpAB expression in E. coli NC101 protects intracellular E. coli from killing by macrophage-derived ROS. Interestingly, when wePLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,7 /IbpAB Protect Commensal E. coli against ROSFig 5. IbpAB protect commensal E. coli NC101, but not pathogenic E. coli O157:H7 from reactive oxygen species-mediated killing within macrophages. Viable, gentamicin-resistant (i.e. intracellular) E. coli were measured at the indicated timepoints after infection of wt or gp91phox-/- BMDMs with E. coli NC101 / E. coli NC101ibpAB (A) or E. coli O157:H7 / E. coli O157:H7ibpAB (B). Data are presented as means ?sem (n = 3? wells/timepoint, *p<0.05 vs. all other conditions in panel A and vs. both E. coli strains in gp91phox-/- BMDMs in panel B). doi:10.1371/journal.pone.0120249.gperformed the same experiments with pathogenic E. coli O157:H7, we found that wt BMDMs kill E. coli O157:H7 more efficiently than E. coli NC101 and that ibpAB has no effect on intramacrophage survival (Fig. 5B). However, unlike results observed with E. coli NC101, gp91phox-/- BMDMs kill E. coli O157:H7 less efficiently than wt BMDMs at 1 and 4 hrs post infection. Therefore, ibpAB protect E. coli NC101, but not E. coli O157:H7, from ROS-mediated killing in macrophages. Since E. coli O157:H7 are killed more efficiently by wt BMDMs than E. coli NC101 and since the ibpAB-mediated protection from intra-macrophage killing presumably requires adequate expression of ibpAB, we asked whether E. coli O157:H7 upregulate ibpAB after phagocytosis to a similar degree as E. coli NC101. To answer this question, we compared ibpAB expression in phagocytosed E. coli NC101 with E. coli O157:H7 in wt BMDMs. Although E. coli O157:H7 slightly increase ibpAB expression after infection of BMDMs, they do so to a much lesser extent compared with E. coli NC101 (Fig. 6). Therefore, it is conceivable that the increased killing of E. coli O157:H7 compared with E. coli NC101 by wt BMDMs may be due toPLOS ONE | DOI:10.1371/journal.pone.0120249 March 23,8 /IbpAB Protect Commensal E. coli against ROSFig 6. Commensal E. coli NC101, but not pathogenic E. coli O157:H7 upregulate ibpAB after phagocytosis by macrophages. A and B) IbpA and ibpB mRNA in intracellular E. coli was measured using real-time PCR at the indicated times following infection of wt BMDMs with E. coli NC101 or E. coli O157:H7. Data are presented as means ?sd (n = at least 3 wells/timepoint, *p<0.05 vs. E. coli O157:H7). doi:10.1371/journal.pone.0120249.ginsufficient ibpAB expression in E. coli O157:H7. These results support the concept that the E. coli ibpAB operon is a virulence factor that is upregulated in certain strains of E. coli, including NC101, during macrophage infection, and protects E. coli from killing by macrophagederived ROS.DiscussionSeveral functions of E. coli ibpAB have previously been identified, including protection of bacteria from elevated temperatures, carbon monoxide, tellurite and copper toxicity, an.
