Escherichia coli O157:H7 and Other E. coli Strains Share Physiological Properties Associated with Intestinal Colonization

Escherichia coli isolates (72 commensal and 10 O157:H7 isolates) were compared with regard to physiological and growth parameters related to their ability to survive and persist in the gastrointestinal tract and found to be similar. We propose that nonhuman hosts in E. coli O157:H7 strains function similarly to other E. coli strains in regard to attributes relevant to gastrointestinal colonization.Escherichia coli is well known for its ecological versatility (15). A life cycle which includes both gastrointestinal and environmental stages has been stressed by both Savageau (15) and Adamowicz et al. (1). The gastrointestinal stage would be subjected to acid and detergent stress. The environmental stage is implicit in E. coli having transport systems for fungal siderophores (4) as well as pyrroloquinoline quinone-dependent periplasmic glucose utilization (1) because their presence indicates evolution in a location containing fungal siderophores and pyrroloquinoline quinone (1).Since its recognition as a food-borne pathogen, there have been numerous outbreaks of food-borne infection due to E. coli O157:H7, in both ground beef and vegetable crops (6, 13). Cattle are widely considered to be the primary reservoir of E. coli O157:H7 (14), but E. coli O157:H7 does not appear to cause disease in cattle. To what extent is E. coli O157:H7 physiologically unique compared to the other naturally occurring E. coli strains? We feel that the uniqueness of E. coli O157:H7 should be evaluated against a backdrop of other wild-type E. coli strains, and in this regard, we chose the 72-strain ECOR reference collection originally described by Ochman and Selander (10). These strains were chosen from a collection of 2,600 E. coli isolates to provide diversity with regard to host species, geographical distribution, and electromorph profiles at 11 enzyme loci (10).In our study we compared the 72 strains of the ECOR collection against 10 strains of E. coli O157:H7 and six strains of E. coli which had been in laboratory use for many years (Table ​(Table1).1). The in vitro comparisons were made with regard to factors potentially relevant to the bacteria''s ability to colonize animal guts, i.e., acid tolerance, detergent tolerance, and the presence of the Entner-Doudoroff (ED) pathway (Table ​(Table2).2). Our longstanding interest in the ED pathway (11) derives in part from work by Paul Cohen''s group (16, 17) showing that the ED pathway is important for E. coli colonization of the mouse large intestine. Growth was assessed by replica plating 88 strains of E. coli under 40 conditions (Table ​(Table2).2). These included two LB controls (aerobic and anaerobic), 14 for detergent stress (sodium dodecyl sulfate [SDS], hexadecyltrimethylammonium bromide [CTAB], and benzalkonium chloride, both aerobic and anaerobic), 16 for acid stress (pH 6.5, 6.0, 5.0, 4.6, 4.3, 4.2, 4.1, and 4.0), four for the ability to grow in a defined minimal medium (M63 glucose salts with and without thiamine), and four for the presence or absence of a functional ED pathway (M63 with gluconate or glucuronate). All tests were done with duplicate plates in two or three separate trials. The data are available in Tables S1 to S14 in the supplemental material, and they are summarized in Table ​Table22.

TABLE 1.

E. coli strains used in this study

E. coli strain (n)	Source
ECOR strains (72)	Thomas Whittman
Laboratory adapted (6)
K-12 Davis	Paul Blum
CG5C 4401	Paul Blum
K-12 Stanford	Paul Blum
W3110	Paul Blum
B	Tyler Kokjohn
AB 1157	Tyler Kokjohn
O157:H7 (10)
FRIK 528	Andrew Benson
ATCC 43895	Andrew Benson
MC 1061	Andrew Benson
C536	Tim Cebula
C503	Tim Cebula
C535	Tim Cebula
ATCC 43889	William Cray, Jr.
ATCC 43890	William Cray, Jr.
ATCC 43888	Willaim Cray, Jr.
ATCC 43894	William Cray, Jr.

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TABLE 2.

Physiological comparison of 88 strains of Escherichia coli

Growth medium or condition	Oxygenc	No. of strains with type of growthb
		ECOR strains (n = 72)				Laboratory strains (n = 6)				O157:H7 strains (n = 10)
		Good	Poor	None	Variable	Good	Poor	None	Variable	Good	Poor	None	Variable
LB controla	Both	72	0	0	0	6	0	0	0	10	0	0	0
1% SDS	Aerobic	69	3	0	0	6	0	0	0	8	0	0	2
5% SDS	Aerobic	68	4	0	0	6	0	0	0	8	2	0	0
1% SDS	Anaerobic	53	15	4	0	2	3	1	0	1	7	0	2
5% SDS	Anaerobic	0	68	4	0	0	4	2	0	0	7	0	4
CTABd (all)	Both	0	0	72	0	0	0	6	0	0	0	10	0
0.05% BAC	Aerobic	3	11	58	2	0	2	2	2	0	0	9	1
0.2% BAC	Aerobic	0	1	71	0	1	0	5	0	0	0	10	0
0.05% BAC	Anaerobic	2	3	67	0	0	1	5	0	0	0	9	1
0.2% BAC	Anaerobic	0	0	72	0	0	0	6	0	0	0	10	0
pH 6.5	Both	72	0	0	0	6	0	0	0	10	0	0	0
pH 6	Both	72	0	0	0	6	0	0	0	10	0	0	0
pH 5	Both	70	2	0	0	6	0	0	0	9	0	0	1
pH 4.6	Both	70	2	0	0	6	0	0	0	10	0	0	0
pH 4.3	Aerobic	14	0	1	57	3	1	2	0	3	2	0	5
pH 4.3	Anaerobic	69	3	0	0	3	1	2	0	1	1	0	0
pH 4.1 or 4.2	Aerobic	0	0	72	0		NDg					ND
pH 4.0	Both	0	0	72	0	0	0	6	0	0	0	9	1
M63 with supplemente
Glucose	Aerobicf	69	1	2	0	5	0	1	0	9	0	1	0
Glucose	Anaerobicf	70	0	2	0	5	0	1	0	9	0	1	0
Gluconate	Both	69	1	2	0	5	0	1	0	9	0	1	0
Glucuronate	Aerobic	68	2	2	0	5	0	1	0	9	0	1	0
Glucuronate	Anaerobic	69	1	2	0	5	0	1	0	9	0	1	0

Open in a separate window^aEight LB controls were run, two for each set of LB experiments: SDS, CTAB, benzalkonium chloride (BAC), and pH stress.^bGrowth was measured as either +++, +, or 0 (good, poor, and none, respectively), with +++ being the growth achieved on the LB control plates. “Variable” means that two or three replicates did not agree. All experiments were done at 37°C.^c“Anaerobic” refers to use of an Oxoid anaerobic chamber. Aerobic and anaerobic growth data are presented together when the results were identical and separately when the results were not the same or the anaerobic set had not been done. LB plates were measured after 1 (aerobic) or 2 (anaerobic) days, and the M63 plates were measured after 2 or 3 days.^dCTAB used at 0.05, 0.2%, and 0.4%.^eM63 defined medium (3) was supplemented with glucose, gluconate, or glucuronate, all at 0.2%.^fIdentical results were obtained with and without 0.0001% thiamine.^gND, not determined.