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Title: Arginine-dependent acid-resistance pathway in Shigella boydii

item GOH, KELVIN - Ngee Ann Polytechnic
item CHUA, DARREN - Ngee Ann Polytechnic
item BECK, BRIAN - American Type Culture Collections
item MCKEE, MARIAN - American Type Culture Collections
item Bhagwat, Arvind

Submitted to: Archives of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2010
Publication Date: 12/7/2010
Citation: Goh, K., Chua, D., Beck, B., Mckee, M., Bhagwat, A.A. 2010. Arginine-dependent acid-resistance pathway in Shigella boydii. Archives Of Microbiology. 193(3):179-185.

Interpretive Summary: The ability of human pathogens to survive in an acidic environment plays a crucial role in food and water borne diseases. Acidic produce, such as apple cider and apple juice, as well as fresh-cut melons and tomatoes have been implicated in recent outbreaks of infections caused by enteric human pathogens. In this study we show that the outbreak-associated strain of Shigella boydii, isolated by the CDC in the year 2000, as well as other Shigella species possess a new acid resistance pathway which was presumed to be absent in all Shigella species. This pathway is operative in the presence of externally supplied arginine. The availability of oxygen during bacterial growth played an important role in activating acid-tolerance pathway of Shigella strains. Understanding the acid tolerance pathways will advance our knowledge of how enteric human pathogens survive on fresh-cut produce. The research will benefit the fresh produce industry, as well as increase the microbial food safety of Americans food supply.

Technical Abstract: Ability to survive the low pH of the human stomach is considered be an important virulent determinant. Acid tolerance of Shigella boydii 18 CDPH, the strain implicated in an 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 16 other strains of S. flexneri, S. sonnei and S. dysenteriae. The eight S. boydii strains were able to induce ADAR to survive the acid challenge at pH 2.0; additional 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 effectively and could not survive acid challenge even at pH 2.5. ADAR pathway appears to be present in several Shigella sp. since the genome comparison among strains of E. coli O157:H7 EDL933 and S. boydii, S. flexneri, S. sonnei, and S. dysenteriae showed conserved arrangement of three key genes encoding biodegradative arginine decarboxylse (adiA), putative transcriptional activator (adiY) and arginine-agmatin membrane transporter (yjdE/adiC). However the ADAR pathway was induced in Shigella spp. only when cells were grown under partial oxygen pressure while its expression in E. coli required mere semi-aerobic growth on glucose. This may explain why ADAR pathway was presumed to be lacking in Shigella sp. using conditions similar to those used for E. coli.