FIG. 7.

The length of the LPS core determines OmpX-conferred serum resistance. E. coli K-12 D21 (rough LPS) and its three isogenic derivatives D21e7 (rough LPS), D21f1 (deep rough LPS), and D21f2 (deep rough LPS) with or without pOmpX were grown to mid-exponential phase at 37°C, incubated in 50% normal human serum (NHS) or heat-inactivated serum (HIS) for 1 h at 37°C, and plated on LB agar. Results are means ± SEM from data derived from two assays performed on separate days (n = 4). The asterisk (*) indicates the difference (Kruskal-Wallis test, P < 0.001) between E. coli carrying pOmpX and its respective cell control strain after incubation with NHS.