Table 2.

Available Shigella Challenge Strains

Shigella Product	Lot No.	Release Date	Volume (mL) per Tube and CFU/mL	Strain Source
				WRAIR	PATH	CVD
S. flexneri 2a strain 2457T (PCB) [21]	1617	25 Jan 2011	1.0 1.8 × 108	Yes	Yes	Yes
S. flexneri 3a strain J17B (PCB)	1654	7 Apr 2011	1.0 1.5 × 108	Yes	Yes	No
S. sonnei strain 53G [46] lyophilized	1794	14 Mar 2014	2.0 2.0 × 109	Yes	No	No

It is anticipated that good manufacturing practice master cell bank and PCB for S. flexneri serotypes 6 (strain CCH060) and 1a (strain to be determined) will be produced by WRAIR in 2019–2020. Lyophilized preparations of S. flexneri serotypes 2a (2457T) and 3a (J17B) are projected for 2019 at WRAIR. Strain J17B has yet to be evaluated in a controlled human infection model. With eventual production of the S. flexneri 6 and 1a cell banks, challenge strains would be available for the Shigella serotypes most commonly associated with moderate to severe diarrhea in the recent Global Enteric Multicenter Study [47].

Abbreviations: CFU, colony-forming units; CVD, Center for Vaccine Development, University of Maryland School of Medicine; PCB, production cell bank; WRAIR, Walter Reed Army Institute of Research.