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Sialic acid utilization by Cronobacter sakazakii.

Joseph S, Hariri S, Masood N, Forsythe S - Microb Inform Exp (2013)

Bottom Line: Whole genome sequencing has revealed that the nanAKT gene cluster required for the utilisation of exogenous sialic acid is unique to the C. sakazakii species (ESA_03609-13).Sialic acid is found in breast milk, infant formula, intestinal mucin, and gangliosides in the brain, hence its metabolism by C. sakazakii is of particular interest.Although the ganglioside GM1 was also used as carbon source, no candidate sialidase genes were found in the genome, instead the substrate degradation is probably due to β-galactosidase activity.This has possibly resulted in additional virulence factors contributing to severe life-threatening infections in neonates due to the utilization of sialic acid from breast milk, infant formula, milk (oligosaccharides), mucins lining the intestinal wall, and even gangliosides in the brain after passing through the blood-brain barrier.

View Article: PubMed Central - HTML - PubMed

Affiliation: Pathogen Research Centre, School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK. stephen.forsythe@ntu.ac.uk.

ABSTRACT

Background: The Cronobacter genus is composed of seven species, and can cause infections in all age groups. Of particular concern is C. sakazakii, as this species is strongly associated with severe and often fatal cases of necrotizing enterocolitis and meningitis in neonates and infants. Whole genome sequencing has revealed that the nanAKT gene cluster required for the utilisation of exogenous sialic acid is unique to the C. sakazakii species (ESA_03609-13).Sialic acid is found in breast milk, infant formula, intestinal mucin, and gangliosides in the brain, hence its metabolism by C. sakazakii is of particular interest. Therefore its metabolism could be an important virulence factor. To date, no laboratory studies demonstrating the growth of C. sakazakii on sialic acid have been published nor have there been reports of sialidase activity. The phylogenetic analysis of the nan genes is of interest to determine whether the genes have been acquired by horizontal gene transfer.

Results: Phylogenetic analysis of 19 Cronobacter strains from 7 recognised species revealed the nanAKTR genes formed a unique cluster, separate from other Enterobacteriaceae such as E. coli K1 and Citrobacter koseri, which are also associated with neonatal meningitis. The gene organisation was similar to Edwardsiella tarda in that nanE gene (N-acetylmannosamine-6-phosphate-2epimerase) was not located within the nanATK cluster. Laboratory studies confirmed that only C. sakazakii, and not the other six Cronobacter species, was able to use sialic acid as a carbon source for growth. Although the ganglioside GM1 was also used as carbon source, no candidate sialidase genes were found in the genome, instead the substrate degradation is probably due to β-galactosidase activity.

Conclusions: Given the relatively recent evolution of both C. sakazakii (15-23 million years ago) and sialic acid synthesis in vertebrates, sialic acid utilization may be an example of co-evolution by one species of the Cronobacter genus with the mammalian host. This has possibly resulted in additional virulence factors contributing to severe life-threatening infections in neonates due to the utilization of sialic acid from breast milk, infant formula, milk (oligosaccharides), mucins lining the intestinal wall, and even gangliosides in the brain after passing through the blood-brain barrier.

No MeSH data available.


Related in: MedlinePlus

Maximum-likelihood tree of (a) the NagA protein sequences (382 aa) and (b) NagB protein sequences (266 aa) of Cronobacter spp. and related Enterobacteriaceae members, constructed using PhyML, with 1000 bootstrap replicates.
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Figure 4: Maximum-likelihood tree of (a) the NagA protein sequences (382 aa) and (b) NagB protein sequences (266 aa) of Cronobacter spp. and related Enterobacteriaceae members, constructed using PhyML, with 1000 bootstrap replicates.

Mentions: The predicted amino acid sequences of the proteins encoded by these nan cluster genes were analysed and their phylogenetic relationships with closely related Gram-negative bacteria is shown in Figures 1, 2, 3 and 4. Each predicted protein sequence from C. sakazakii formed an independent cluster, with the other Enterobacteriaceae members clustering on the neighbouring branches. In the NanA and NanR (Figure 1) phylogenetic trees, the C. sakazakii cluster appeared to evolve on the same branch as E. cloacae and Enterobacter spp., with the others forming a separate clade. In comparison, the NanK and NanT (Figure 2) C. sakazakii clusters appear to have greater phylogenetic distance from the other enteric members, with a clear split of the population into two clades, one of them being that of the C. sakazakii cluster. The nanE gene is found across the Cronobacter genus, and the phylogenetic analysis of the NanE protein sequences (Figure 3) revealed the Cronobacter cluster to have a common and closely related evolutionary clade with E. cloacae, E. hormaechei, Enterobacter spp., Cit. freundii and Pantoea agglomerans. The NanC protein in the C. sakazakii genomes could be located with >50% homology only in the genomes of E. cloacae, E. hormaechei, Cit. koseri and E. coli K1. Of these, the E. coli K1 NanC appeared to be very distantly related to the rest of the population studied (Figure 3). Both the nagA and nagB genes were found in the genomes of all the Cronobacter species (Figure 4). Phylogenetic analysis of these proteins showed the Cronobacter spp. sequences formed a distinct clade, with other Enterobacteriaceae members forming a neighbouring clade, both with a common evolutionary lineage. The newly identified species C. condimenti always branched within the Cronobacter genus cluster (Figures 3 and 4). Phylogenetic analysis of Cit. koseri and Cit. freundii nan gene sequences revealed different patterns in their branching, which indicates possible independent evolutionary paths for the nan genes within the Citrobacter genus.


Sialic acid utilization by Cronobacter sakazakii.

Joseph S, Hariri S, Masood N, Forsythe S - Microb Inform Exp (2013)

Maximum-likelihood tree of (a) the NagA protein sequences (382 aa) and (b) NagB protein sequences (266 aa) of Cronobacter spp. and related Enterobacteriaceae members, constructed using PhyML, with 1000 bootstrap replicates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3716653&req=5

Figure 4: Maximum-likelihood tree of (a) the NagA protein sequences (382 aa) and (b) NagB protein sequences (266 aa) of Cronobacter spp. and related Enterobacteriaceae members, constructed using PhyML, with 1000 bootstrap replicates.
Mentions: The predicted amino acid sequences of the proteins encoded by these nan cluster genes were analysed and their phylogenetic relationships with closely related Gram-negative bacteria is shown in Figures 1, 2, 3 and 4. Each predicted protein sequence from C. sakazakii formed an independent cluster, with the other Enterobacteriaceae members clustering on the neighbouring branches. In the NanA and NanR (Figure 1) phylogenetic trees, the C. sakazakii cluster appeared to evolve on the same branch as E. cloacae and Enterobacter spp., with the others forming a separate clade. In comparison, the NanK and NanT (Figure 2) C. sakazakii clusters appear to have greater phylogenetic distance from the other enteric members, with a clear split of the population into two clades, one of them being that of the C. sakazakii cluster. The nanE gene is found across the Cronobacter genus, and the phylogenetic analysis of the NanE protein sequences (Figure 3) revealed the Cronobacter cluster to have a common and closely related evolutionary clade with E. cloacae, E. hormaechei, Enterobacter spp., Cit. freundii and Pantoea agglomerans. The NanC protein in the C. sakazakii genomes could be located with >50% homology only in the genomes of E. cloacae, E. hormaechei, Cit. koseri and E. coli K1. Of these, the E. coli K1 NanC appeared to be very distantly related to the rest of the population studied (Figure 3). Both the nagA and nagB genes were found in the genomes of all the Cronobacter species (Figure 4). Phylogenetic analysis of these proteins showed the Cronobacter spp. sequences formed a distinct clade, with other Enterobacteriaceae members forming a neighbouring clade, both with a common evolutionary lineage. The newly identified species C. condimenti always branched within the Cronobacter genus cluster (Figures 3 and 4). Phylogenetic analysis of Cit. koseri and Cit. freundii nan gene sequences revealed different patterns in their branching, which indicates possible independent evolutionary paths for the nan genes within the Citrobacter genus.

Bottom Line: Whole genome sequencing has revealed that the nanAKT gene cluster required for the utilisation of exogenous sialic acid is unique to the C. sakazakii species (ESA_03609-13).Sialic acid is found in breast milk, infant formula, intestinal mucin, and gangliosides in the brain, hence its metabolism by C. sakazakii is of particular interest.Although the ganglioside GM1 was also used as carbon source, no candidate sialidase genes were found in the genome, instead the substrate degradation is probably due to β-galactosidase activity.This has possibly resulted in additional virulence factors contributing to severe life-threatening infections in neonates due to the utilization of sialic acid from breast milk, infant formula, milk (oligosaccharides), mucins lining the intestinal wall, and even gangliosides in the brain after passing through the blood-brain barrier.

View Article: PubMed Central - HTML - PubMed

Affiliation: Pathogen Research Centre, School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, UK. stephen.forsythe@ntu.ac.uk.

ABSTRACT

Background: The Cronobacter genus is composed of seven species, and can cause infections in all age groups. Of particular concern is C. sakazakii, as this species is strongly associated with severe and often fatal cases of necrotizing enterocolitis and meningitis in neonates and infants. Whole genome sequencing has revealed that the nanAKT gene cluster required for the utilisation of exogenous sialic acid is unique to the C. sakazakii species (ESA_03609-13).Sialic acid is found in breast milk, infant formula, intestinal mucin, and gangliosides in the brain, hence its metabolism by C. sakazakii is of particular interest. Therefore its metabolism could be an important virulence factor. To date, no laboratory studies demonstrating the growth of C. sakazakii on sialic acid have been published nor have there been reports of sialidase activity. The phylogenetic analysis of the nan genes is of interest to determine whether the genes have been acquired by horizontal gene transfer.

Results: Phylogenetic analysis of 19 Cronobacter strains from 7 recognised species revealed the nanAKTR genes formed a unique cluster, separate from other Enterobacteriaceae such as E. coli K1 and Citrobacter koseri, which are also associated with neonatal meningitis. The gene organisation was similar to Edwardsiella tarda in that nanE gene (N-acetylmannosamine-6-phosphate-2epimerase) was not located within the nanATK cluster. Laboratory studies confirmed that only C. sakazakii, and not the other six Cronobacter species, was able to use sialic acid as a carbon source for growth. Although the ganglioside GM1 was also used as carbon source, no candidate sialidase genes were found in the genome, instead the substrate degradation is probably due to β-galactosidase activity.

Conclusions: Given the relatively recent evolution of both C. sakazakii (15-23 million years ago) and sialic acid synthesis in vertebrates, sialic acid utilization may be an example of co-evolution by one species of the Cronobacter genus with the mammalian host. This has possibly resulted in additional virulence factors contributing to severe life-threatening infections in neonates due to the utilization of sialic acid from breast milk, infant formula, milk (oligosaccharides), mucins lining the intestinal wall, and even gangliosides in the brain after passing through the blood-brain barrier.

No MeSH data available.


Related in: MedlinePlus