Table 1.

Toxin Genotypes and In Vitro Enterotoxin Production Levels for ETEC Strains Used in Volunteer Challenge Experiments

Strain	Strain information			Serotypea	CF typeb	LT		ST
	Year of isolation	Country of origin	Case profile			Genotypec	Production (ng/mL)d, e	Genotypec	Production (ng/mL)d, e
LSN03-016011/A	2003	Turkey	U.S. expatriate	O8:H-	CS17	+	59	−	ndf
WS0115A	1993	Egypt	Infant	O114:H-	CS19	+	60	+ (STp)	129
DS26-1	1990	Saudi Arabia	U.S. soldier	O8:H9	CS19	+	8	−	Nd

NB, All strains were susceptible to ciprofloxacin and trimethoprim-sulfamethoxazole.

^aSerotype was determined by classic serological methods at the Universidad Nacional Autónoma de México (UNAM). H- indicates non-motility.

^bCF identity was initially determined by colony immunoblot analysis with CF-specific monoclonal antibodies, and confirmed by DNA sequence analysis of the fimbrial major subunit and Western blot analysis of bacterial heat extracts with monospecific rabbit antisera against each CF.

^cToxin genotypes were confirmed by Southern blot hybridization with plasmid preparations from each strain, using probes specific for LT STp, and STh [10].

^dQuantitation of ST and LT was performed using GM1-ELISA methods [11]. Bacteria were grown in LB liquid culture at 37°C overnight for the assay. The reported concentrations of ST and LT were measured in culture supernatants and sonicates, respectively. Toxin values were interpolated from a standard curve using known quantities of each purified toxin. Strain DS26-1 produced 20 ng/ml of LT in the culture supernatant, the only one for which this value was higher than that in the corresponding sonicate preparation.

^eETEC strain H10407 (LTSThSTp; CFA/I; O78:H11), a well-characterized and highly pathogenic strain, was used as a reference control in the enterotoxin assays, producing 66 and 99 ng/ml of LT and STa, respectively.

^fNot determined.