, 1994). Other species are more frequently associated with enteric disease, particularly travelers’ diarrhea (Yoh et al., 2005), although sporadic cases of meningitis (Sipahi et al., 2010) and ocular infections (Koreishi et al., 2006) also have been reported. The serological scheme of P. stuartii, P. rustigianii, and P. alcalifaciens used RGFP966 molecular weight in

serotyping of clinical isolates is based on O-antigens present on the cell surface and flagella H-antigens; it includes 63 O-serogroups and 30 H-serogroups (Ewing, 1986). Recently, it has been found that strains representing serotypes O58:H9 and O59:H18 must be reclassified from the genus Providencia to Morganella morganii (A. Rozalski, unpublished data). The O-antigen represents the O-polysaccharide chain of the lipopolysaccharide (LPS) built up of oligosaccharide repeats (O-units). Some Providencia O-antigens show a similarity to those of a closely related genus Proteus (Torzewska et al., 2004a, b) as well as taxonomically remote bacteria, such as Pseudoalteromonas flavipulchra (Kocharova et al., 2006) and Shewanella fidelis (Kocharova et al., 2011) from the family Alteromonadaceae. To create a molecular basis for the serological classification of

Providencia and to substantiate their antigenic relationships to other bacteria, the O-antigen structures have been elucidated in the majority of Providencia O-serogroups

(Knirel, 2011). Biosynthesis of the O-antigen by the FK506 solubility dmso next most common O-antigen polymerase (Wzy)-dependent pathway (Valvano, 2011) requires three major groups of enzymes: (i) sugar biosynthetic pathway enzymes that synthesize the nucleotide-activated form of each unique sugar present in the O-unit; (ii) glycosyltransferases that sequentially transfer the precursor sugars to assemble an O-unit on the undecaprenyl diphosphate lipid carrier anchored into the inner membrane facing the cytoplasmic side; and (iii) O-antigen processing proteins that are involved in translocation of the O-unit across the inner membrane to the periplasmic side (flippase Wzx) and polymerization (O-antigen polymerase Wzy and modal chain length regulator Wzz). Most of the genes encoding these enzymes are not scattered around the chromosome but are combined into a gene cluster that maps between two conserved genes. Recently, putative O-antigen gene clusters have been found between the cpxA and yibK genes and characterized in nine Providencia strains (Ovchinnikova et al., 2012). In this paper, we report on the O-antigen structure of P. alcalifaciens O40 and its serological relationships to the O-antigens of some other Providencia serogroups. In addition, the O40-antigen gene cluster was sequenced and analyzed and found to be in agreement with the O-polysaccharide structure established.