Comparison of O-Antigen gene clusters of all O-Serogroups of Escherichia coli and proposal for adopting a new nomenclature for O-Typing

Authors: DEBROY, CHITRITA - Pennsylvania State University; Fratamico, Pina; Yan, Xianghe; BARANZONI, GIAN MARCO - University Of Bologna, Italy; Liu, Yanhong; Needleman, David; TEBBS, ROBERT - Thermo Fisher Scientific; O'CONNELL, CATHERINE - Thermo Fisher Scientific; ALLRED, ADAM - Thermo Fisher Scientific; SWIMLEY, MICHELLE - Thermo Fisher Scientific; MWANGI, MICHAEL - Pennsylvania State University; KAPUR, VIVEK - Pennsylvania State University; RAYGOZA GARAY, JUAN - Pennsylvania State University; KATANI, ROBAB - Pennsylvania State University; ROBERTS, ELISABETH - Pennsylvania State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2016
Publication Date: 1/29/2016
Citation: Debroy, C., Fratamico, P.M., Yan, X., Baranzoni, G., Liu, Y., Needleman, D.S., Tebbs, R., O'Connell, C.D., Allred, A., Swimley, M., Mwangi, M., Kapur, V., Raygoza Garay, J., Katani, R., Roberts, E.L. 2016. Comparison of O-Antigen gene clusters of all O-Serogroups of Escherichia coli and proposal for adopting a new nomenclature for O-Typing. PLoS One. DOI:10.1371/journal.pone.0147434.

Interpretive Summary: The bacterium, Escherichia coli, causes a variety of diseases in humans and animals, and many non-harmful E. coli types (serogroups) also exist. Traditionally, a procedure called serotyping has been used to distinguish among the approximately 196 different E. coli serogroups. This procedure, which relies on the use of antibodies raised in rabbits against different surface polysaccharides of E. coli, can only be performed in specialized laboratories, is labor intensive and may require several days to complete, and one antiserum can react with multiple E. coli serogroups, rendering identification of the specific strain of E. coli difficult. Thus, due to the lack of simple, rapid, and reliable methods for detection and identification of harmful and non-harmful E. coli types, the incidence of disease caused by harmful strains of E. coli may be underestimated, and epidemiological studies are difficult to perform. To develop more rapid and simple genetic-based methods for detection and typing of E. coli, knowledge of the DNA sequence of the genes that encode for the surface polysaccharide chains is needed. Thus, the DNA sequences of these genes in 72 E. coli serogroups were determined, and a comparison of all 196 serogroups was performed, providing useful and interesting information. Many of the designated E. coli serogroups, applied for classification over several decades, exhibited similar nucleotide sequences and also cross-reacted using traditional serotyping. Based on information obtained from this work, many of the serogroups may potentially be eliminated or merged. In addition, this sequence information allows the development of detection and identification platforms for E. coli that are rapid, accurate, and reliable and that can replace conventional serotyping.

Technical Abstract: Escherichia coli strains are classified based on O-antigens that are components of the lipopolysaccharide (LPS) in the cell envelope. O-antigens are important virulence factors, targets of both the innate and adaptive immune system, and play a role in host-pathogen interaction. Because they are highly immunogenic and display antigenic specificity unique for each strain, O-antigens are utilized as biomarkers for designating O-types. Immunologically, 184 O-serogroups and 11 OX- groups have been assigned for classification. Conventional serotyping is based on agglutination reactions between the O-antigen and antisera generated against each O-group. The procedure is labor intensive, not always accurate, and exhibits equivocal results. In this report, we present the sequences of 72 O-antigen gene clusters (O-AGC) and a comparison of all 196 O- and OX- groups. Many of the designated O types, applied for classification over several decades, exhibited similar nucleotide sequences of the O-AGCs and also cross-reacted serologically. Some other O-AGCs carried insertion sequences or had only a few nucleotide differences between them. Therefore, based on this information, many of the O-groups may potentially be eliminated or merged. Molecular diagnostic platforms that are rapid, accurate, and reliable can be developed replacing conventional serotyping. Additionally, with the scientific knowledge presented, new frontiers in the discovery of biomarkers, understanding the roles of O-antigens in the innate and adaptive immune system and pathogenesis, the development of glycoconjugate vaccines, and other investigations, can be explored.