Abstract
BackgroundCronobacter sakazakii and C. malonaticus can cause serious diseases especially in infants where they are associated with rare but fatal neonatal infections such as meningitis and necrotising enterocolitis.MethodsThis study used 104 whole genome sequenced strains, covering all seven species in the genus, to analyse capsule associated clusters of genes involved in the biosynthesis of the O-antigen, colanic acid, bacterial cellulose, enterobacterial common antigen (ECA), and a previously uncharacterised K-antigen.ResultsPhylogeny of the gnd and galF genes flanking the O-antigen region enabled the defining of 38 subgroups which are potential serotypes. Two variants of the colanic acid synthesis gene cluster (CA1 and CA2) were found which differed with the absence of galE in CA2. Cellulose (bcs genes) were present in all species, but were absent in C. sakazakii sequence type (ST) 13 and clonal complex (CC) 100 strains. The ECA locus was found in all strains. The K-antigen capsular polysaccharide Region 1 (kpsEDCS) and Region 3 (kpsMT) genes were found in all Cronobacter strains. The highly variable Region 2 genes were assigned to 2 homology groups (K1 and K2). C. sakazakii and C. malonaticus isolates with capsular type [K2:CA2:Cell+] were associated with neonatal meningitis and necrotizing enterocolitis. Other capsular types were less associated with clinical infections.ConclusionThis study proposes a new capsular typing scheme which identifies a possible important virulence trait associated with severe neonatal infections. The various capsular polysaccharide structures warrant further investigation as they could be relevant to macrophage survival, desiccation resistance, environmental survival, and biofilm formation in the hospital environment, including neonatal enteral feeding tubes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1960-z) contains supplementary material, which is available to authorized users.
Highlights
Cronobacter sakazakii and C. malonaticus can cause serious diseases especially in infants where they are associated with rare but fatal neonatal infections such as meningitis and necrotising enterocolitis
Diversity of Cronobacter O-antigen The O-antigen polymerase and O-antigen flippase genes, wzy and wzx respectively, within the rfb locus have been the targets for molecular serotyping of Cronobacter species using Polymerase chain reactions (PCR) primers [23, 24]
The extracted wzx and wzy sequences from Genbank as well as those from 104 genomes were aligned and phylogenetically analysed. The purpose of this analysis was to show the clustering of the predefined serotypes based on those presumed O-antigen specific sequences
Summary
Cronobacter sakazakii and C. malonaticus can cause serious diseases especially in infants where they are associated with rare but fatal neonatal infections such as meningitis and necrotising enterocolitis. Capsular polysaccharides (CPS) are major bacterial virulence factors and environmental fitness traits. In Gramnegative bacteria, the CPS forms a surface layer of water-saturated, high molecular weight polysaccharides which enable the organism to evade host response mechanisms such as phagocytosis as well as facilitate biofilm formation and desiccation survival [1]. CPS vary considerably between organisms, and even between strains of the same species. Capsular diversity has been the basis for a number of bacterial differentiation methods including serotyping of Salmonella serovars and the K-antigen classification scheme of E. coli [2]. The use of whole genome data can serve to expand and clarify these schemes. Such analysis can reveal the extent of horizontal gene transfer leading to the lack of congruence between serotype and phylogeny due to the transference of loci Such analysis can reveal the extent of horizontal gene transfer leading to the lack of congruence between serotype and phylogeny due to the transference of loci (ie. rfb locus) between strains
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