ORIGINAL PAPER Arginine-dependent acid-resistance pathway in Shigella boydii Kelvin Goh • Darren Chua • Brian Beck • Marian L. McKee • Arvind A. Bhagwat Received: 1 September 2010 / Revised: 12 October 2010 / Accepted: 29 October 2010 / Published online: 7 December 2010 Ó Springer-Verlag (outside the USA) 2010 Abstract Ability to survive the low pH of the human stom- ach is considered be an important virulent determinant. It was suggested that the unique acid tolerance of Shigella boydii 18 CDPH, the strain implicated in a 1998 outbreak, may have played an important role in surviving the acidic food (bean salad). The strain was capable of inducing arginine-dependent acid-resistance (ADAR) pathway. This pathway was assumed to be absent in Shigella sp. Here, we have examined occurrence and efficacy of ADAR pathway in 21 S. boydii strains obtained from the American Type Culture Collection (ATCC) along with strains of S. flexneri (n = 7), S. sonnei (n = 4), and S. dysenteriae (n = 2). The eight S. boydii strains were able to induce ADAR to survive the acid challenge at pH 2.0; addi- tional 8 strains could tolerate acid challenge at pH 2.5 but not at pH 2.0. The remaining five S. boydii strains were not able to induce ADAR pathway and could not survive acid challenge even at pH 2.5. ADAR pathway also appears to be present in all four Shigella sp. Shigella ADAR pathway was induced when cells were grown under partial oxygen pressure while its expression in E. coli required mere fermentative growth on glucose. Keywords Microbial food safety Á Acid resistance Á Traveler’s diarrhea Introduction Shigella boydii is one of four Shigella species namely Shigella dysenteriae, Shigella sonnei, and Shigella flexneri (Bopp et al. 1999; Lampel and Maurelli 2001). Shigella has no human reservoir and is normally transmitted from person to person via the fecal–oral route. All four species and especially S. dysenteriae continue to be the significant cause of human gastroenteritis. The incidences of shigellosis are more common among European travelers to tropical and developing countries (Vargas et al. 1999; Chart et al. 2009). The risk of contracting shigellosis is much high due to the fact that as few as 10–500 ingested Shigella cells can cause illness (Kotloff et al. 1995; Lampel and Maurelli 2001). The low infection dose (ID) associated with Shigella species is attributed to the organism’s acid-resistant nature. The importance of acid survival in pathogenesis is underscored by the fact that Vibrio cholera, non-typhi Salmonella sp., and Shigella flexneri have oral infection doses of 10 9 , 10 5 , and 10 2 respectively (Abe et al. 2004). These infection doses correlate with the level of acid resistance demonstrated by each organism, with V. cholera being the most acid sensitive and S. flexneri being most acid resistant (Abe et al. 2004; Allos et al. 2004). Communicated by Erko Stackebrandt. K. Goh Á D. Chua Á A. A. Bhagwat (&) Environmental Microbial & Food Safety Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, USDA, 10300 Baltimore Avenue, Bldg. 002, Room 117, BARC-W, Beltsville, MD 20705-2350, USA e-mail: arvind.bhagwat@ars.usda.gov B. Beck Á M. L. McKee ATCC, 1080 University Boulevard, Manassas, Virginia 20110-2209, USA Present Address: K. Goh Á D. Chua School of Life Sciences & Chemical Technology, Ngee Ann Polytechnic, 535 Clementi Road, Singapore 599489, Singapore Present Address: M. L. McKee BioReliance Corporation, 14920 Broschart Road, Rockville, MD 20850, USA 123 Arch Microbiol (2011) 193:179–185 DOI 10.1007/s00203-010-0656-7