Table 2. Resistance to serum killing among E. coli bloodstream infection isolates, stratified by multilocus sequence type (ST).

A serum bactericidal assay was performed on each E. coli isolate, and survival was determined by number of colonies in the serum-treated sample (either 25% or 50% serum) divided by the number of colonies in the negative serum control. The mean survival and range of survival values for each E. coli ST with ≥5 isolates in our study population are shown here. P-values were calculated with t-tests (e.g., proportion of surviving bacteria in ST12 relative to non-ST12 isolates). P-values ≤0.05 are in bold.

		25% serum			50% serum
ST	# isolates	Mean proportion surviving	Range of proportion surviving	P-value	Mean proportion surviving	Range of proportion surviving	P-value
12	7	0.72	0.65–0.90	0.21	0.71	0.66–0.89	0.20
69	12	0.70	0.65–0.93	0.41	0.69	0.61–0.94	0.41
73	12	0.68	0.61–0.77	0.97	0.67	0.58–0.72	0.88
95	18	0.68	0.62–0.92	0.84	0.68	0.59–0.93	0.60
127	5	0.68	0.66–0.70	1.00	0.67	0.64–0.71	1.00
131	67	0.67	0.61–0.74	0.05	0.66	0.60–0.73	0.05
393	10	0.66	0.57–0.76	0.17	0.66	0.60–0.74	0.41
405	6	0.67	0.64–0.70	0.29	0.66	0.62–0.68	0.50