This is the first report on the complete core operon sequence of an O25 ST131 isolate. Recently, two groups reported on the total genome sequences of O25 ST131 (Avasthi et al., 2011; Totsika KU-60019 concentration et al., 2011) and deposited it in GenBank; however, none of them contained the complete waa cluster. In strain EC958 (Totsika et al., 2011), the locus annotated as ‘O-antigen 2’ and available as parts of two nonoverlapping contigs (GenBank CAFL01000107.1 and CAFL01000108.1) contained the waa genes, which, with the exception of a 293-bp-long fragment missing from the waaR gene, exhibited 100% identity with the waa operon of strain #81009. Similarly, the sequences of the waaA,

waaQ, waaG, waaP, waaC, waaF, and waaD genes of another O25 ST131 strain (NA114) (Avasthi et al., 2011) were 100% identical to the respective genes of our isolate. However, a large fragment corresponding to the sequence between 4715–12806 bp of our ST131 isolate (GenBank JQ241150) was missing from the sequence available in the database. As this represents a considerable part of the waa operon, including the complete waaB,

waaI, waaR, waaY, waaZ, waaU genes and parts of waaS and waaL genes, an extensive comparison between the waa operons of stains #81009 and NA114 was not possible. The high level of similarity in the genetic background of core synthesis of the ST131 strains to that of strain MG1655 suggests that it is also likely to be similar to the known structure of the K-12 core, but definitely different from those of the other E. coli LPS Caspase inhibitor core types (Muller-Loennies et al., 2007). However, it remains to be elucidated whether the 4–10% nonidentity of the LPS synthesis enzymes of the tested ST131 strain and the prototype K-12 MG1655 strain is reflected in any differences in the chemical composition of the outer core. It is interesting to note that an Evodiamine unusual glycoform composition of the K-12 core was recently described in a strain isolated from bovine mastitis, although no sequence of the encoding locus has been made available for comparison (Duda et al., 2011). In light of the previously found low

frequency of the K-12 core type among E. coli strains, it is intriguing to contemplate why the highly successful ESBL-producing ST131 clone carries this type seldom harbored by pathogenic E. coli (Amor et al., 2000). Unlike the strain MG1655, that is, a phylogenetic group A strains characterized with limited virulence, members of the ST131 clone, and in general, those of the B2 phylogenetic group are characterized with considerable extraintestinal pathogenic potential (Totsika et al., 2011; Van der Bij et al., 2012). Although the role of anticore antibodies in interfering with bacterial colonization is still speculative, a hypothesis was recently proposed regarding their contribution to prevent mucosal infections, such as the one caused by E. coli O157 (Currie et al., 2001).