Molecular analysis of the Enterobacter sakazakii O-antigen gene locus

Structure and gene cluster annotation of the O-antigen of Aeromonas sobria strain K928 isolated from common carp and classified into the new Aeromonas PGO1 serogroup

Aeromonas sobria strain K928 was isolated from a common carp during a Motile Aeromonas Infection/Motile Aeromonas Septicaemia disease outbreak on a Polish fish farm and classified into the new provisional PGO1 serogroup. The lipopolysaccharide of A. sobria K928 was subjected to mild acid hydrolysis, and the O-specific polysaccharide, which was isolated by gel-permeation chromatography, was studied using sugar and methylation analyses and ¹H and ¹³C NMR spectroscopy. The following structure of the branched O-specific polysaccharide repeating unit of A. sobria K928 was established. →2)[α-D-Fucp3NRHb-(1→3)]-α-L-Rhap-(1→3)-β-L-Rhap-(1→4)-α-L-Rhap-(1→3)-β-D-FucpNAc-(1→ The O-antigen gene cluster was identified and characterized in the genome of the A. sobria K928 strain after comparison with sequences in the available databases. The composition of the O-antigen genetic region was found to be consistent with the O-polysaccharide structure, and its organization was proposed.

In silico species identification and serotyping for Cronobacter isolates by use of whole-genome sequencing data

Cronobacter spp. are foodborne pathogens that can cause severe infections in neonates through contaminated powdered infant formula. Accurate and rapid pathogen identification and serotyping are crucial to limit the detrimental effects of bacterial infections, and to prevent outbreaks and sporadic infections. Conventional serotyping is tedious, laborious, and time-consuming; however, with whole-genome sequencing (WGS) becoming faster and cheaper, WGS has vast potential in routine typing and surveillance. Hence, in this study, we developed a publicly available tool, CroTrait (CronobacterTraits), for in silico species identification and O serotyping of Cronobacter isolates based on WGS data. CroTrait showed excellent performance in species identification and O serotyping when 810 genomes with known species identities and 276 genomes with known O serotype were tested. Moreover, CroTrait allows rapid prediction of new potential O serotypes. We identified 11 novel potential O serotypes of Cronobacter using CroTrait. Therefore, CroTrait is a convenient and promising tool for species identification and O serotyping of Cronobacter isolates.

Characterization of a gene cluster containing four genes relevant to biosynthesis of inner core of lipopolysaccharide in Cronobacter sakazakii

Many genes in the biosynthetic pathway of lipopolysaccharide in Cronobacter sakazakii have not been identified. In this study, we demonstrate that an operon containing four genes ESA_RS18945, ESA_RS18950, ESA_RS18955, and ESA_RS18960 is responsible for L-glycero-D-mannoheptose addition on the inner core of lipopolysaccharide in C. sakazakii. The proteins encoded by these four genes are homologous to E. coli WaaQ, WaaC, WaaF, and WaaD. Lipopolysaccharide from the deletion mutants of ESA_RS18945, ESA_RS18950, ESA_RS18955, and ESA_RS18960 (named as △RS18945, △RS18950, △RS18955 and △RS18960, respectively) were analyzed by SDS-PAGE. △RS18945 synthesized lipopolysaccharide with similar length to the wildtype BAA-894, whereas △RS18950, △RS18955, and △RS18960 synthesized much shorter lipopolysaccharide. This suggests that the enzyme encoded by ESA_RS18945 might function as E. coli WaaQ on the sidechain of lipopolysaccharide. When E. coli WaaC, WaaF, and WaaD were overexpressed in △RS18950, △RS18955, and △RS18960, respectively, the full length of lipopolysaccharide was recovered. Mass spectrometry analysis indicates that △RS18950 and △RS18960 only synthesized Kdo₂ -lipid A, confirming that enzymes encoded by ESA_RS18950 and ESA_RS18960 have similar functions to E. coli WaaC and WaaD, respectively. Hep-Kdo₂ -lipid A with a phosphoethanolamine was produced in △RS18955, suggesting that the enzyme encoded by ESA_RS18955 has similar function to E. coli WaaF.

Screening of specific nucleic acid targets for Cronobacter sakazakii and visual detection by loop-mediated isothermal amplification and lateral flow dipstick method in powdered infant formula

Due to the lack of specific genes for rapid detection methods of Cronobacter sakazakii in food samples, whole genome sequence analysis was performed in this investigation using the basic local alignment search tool. Forty-two DNA fragments unique to C. sakazakii were mined, then primers were designed and screened by PCR and loop-mediated isothermal amplification (LAMP). Two primer sets, CS1 and CS31, were found as specific and stable primers, with their corresponding nucleic acid targets the CSK29544_00235 gene and CSK29544_03484 gene, respectively. Furthermore, compared with 3 genes reported previously, these 2 genes were verified as more specific to C. sakazakii among Cronobacter species, by sequence similarity alignment using Cronobacter MLST databases (http://pubmlst.org/cronobacter). The specificity of the LAMP reaction approached 100% by using 48 bacterial strains, which included 22 C. sakazakii strains. Subsequently, LAMP was combined with visual lateral flow dipstick (LFD) based on the above 2 nucleic acid targets, and was demonstrated as a rapid, efficient method with high specificity. Finally, the detection sensitivity of this assay system for pure cultures and artificially contaminated milk was measured as 4.5 × 10⁰ cfu/mL and 5.7 × 10¹ cfu/g, respectively. Total time to detection for this assay was within 2 h. Thus, the establishment of this LAMP-LFD method shows great significance and potential for rapid detection of C. sakazakii in powdered infant formula.

Analysis of the Molecular Diversity Among Cronobacter Species Isolated From Filth Flies Using Targeted PCR, Pan Genomic DNA Microarray, and Whole Genome Sequencing Analyses

Cronobacter species are opportunistic pathogens capable of causing life-threatening infections in humans, with serious complications arising in neonates, infants, immuno-compromised individuals, and elderly adults. The genus is comprised of seven species: Cronobacter sakazakii, Cronobacter malonaticus, Cronobacter turicensis, Cronobacter muytjensii, Cronobacter dublinensis, Cronobacter universalis, and Cronobacter condimenti. Despite a multiplicity of genomic data for the genus, little is known about likely transmission vectors. Using DNA microarray analysis, in parallel with whole genome sequencing, and targeted PCR analyses, the total gene content of two C. malonaticus, three C. turicensis, and 14 C. sakazaki isolated from various filth flies was assessed. Phylogenetic relatedness among these and other strains obtained during surveillance and outbreak investigations were comparatively assessed. Specifically, microarray analysis (MA) demonstrated its utility to cluster strains according to species-specific and sequence type (ST) phylogenetic relatedness, and that the fly strains clustered among strains obtained from clinical, food and environmental sources from United States, Europe, and Southeast Asia. This combinatorial approach was useful in data mining for virulence factor genes, and phage genes and gene clusters. In addition, results of plasmidotyping were in agreement with the species identity for each strain as determined by species-specific PCR assays, MA, and whole genome sequencing. Microarray and BLAST analyses of Cronobacter fly sequence datasets were corroborative and showed that the presence and absence of virulence factors followed species and ST evolutionary lines even though such genes were orthologous. Additionally, zebrafish infectivity studies showed that these pathotypes were as virulent to zebrafish embryos as other clinical strains. In summary, these findings support a striking phylogeny amongst fly, clinical, and surveillance strains isolated during 2010–2015, suggesting that flies are capable vectors for transmission of virulent Cronobacter spp.; they continue to circulate among United States and European populations, environments, and that this “pattern of circulation” has continued over decades.

Whole Genome Sequencing-Based Comparison of Food Isolates of Cronobacter sakazakii

Cronobacter sakazakii is an emerging foodborne pathogen, which is linked to life-threatening infections causing septicemia, meningitis, and necrotizing enterocolitis. These infections have been epidemiologically connected to ingestion of contaminated reconstituted powder infant formula. Even at low water activity C. sakazakii can survive for a long time; it is capable of protective biofilm formation and occasionally shows high virulence and pathogenicity even following stressful environmental conditions. Hence it is a challenging task for the food industry to control contamination of food ingredients and products through the entire production chain, since an increasing number of severe food-related outbreaks of C. sakazakii infections has been observed. The seemingly great capability of C. sakazakii to survive even strict countermeasures combined with its prevalence in many food ingredients requires a greater in depth understanding of its virulence factors to master the food safety issues related to this organism. In this context, we present the whole genome sequence (WGS) of two different C. sakazakii isolated from skimmed milk powder (C7) and ready-to-eat salad mix (C8), respectively. These are compared to other, already sequenced, C. sakazakii genomes. Sequencing of the fusA allele revealed that both isolates were C. sakazakii. We investigated the molecular characteristics of both isolates relevant for genes associated with pathogenesis and virulence factors, resistance to stressful environmental conditions (e.g., osmotic and heat), survival in desiccation as well as conducted a comparative genomic analysis. By using multi-locus sequence typing (MLST), the genetic type of both isolates is assessed and the number of unique genes is determined. DNA of C. sakazakii C8 is shown to hold a novel and unique sequence type; the number of unique genes identified in the genomic sequence of C. sakazakii C7 and C8 were 109 and 188, respectively. Some of the determined unique genes such as the rhs and VgrG genes are linked to the Type VI Secretion System cluster, which is associated with pathogenicity and virulence factors. Moreover, seven genes encoding for multi-drug resistance were found in both isolates. The finding of a number of genes linked to producing capsules and biofilm are likely related to the observed resistance to desiccation.

Species identification and molecular characterization of Cronobacter spp. isolated from food imported over nine years into Beijing, China

Cronobacter spp. are associated with serious infections in neonates with the clinical presentations of necrotizing enterocolitis, bacteraemia and meningitis. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to identify 203 Cronobacter isolates from imported food during 2006-2015 with an optimized in-house database. The isolates were predominantly C. sakazakii (88.18%), followed by C. malonaticus (8.37%), C. muytjensii (1.48%), C. turicensis (0.99%) and C. dublinensis (0.99%). The result was totally consistent with that of fusA allele sequencing. 12.32% (25/203) of isolates gave inconsistent spectra following separate protein extractions. Sixty C. sakazakii isolates and 24 isolates from the other four species were chosen for multi-locus sequence type analyses (MLST) and PCR-serotyping. Thirty-one sequence types were identified. The common sequence types were ST1 (19/60) and ST4 (13/60) for C. sakazakii and ST7 (12/17) for C. malonaticus. The primary serotypes were Csak O:1 (30/60), Csak O:2 (25/60) and Cmal O:2 (16/17) for C. sakazakii and C. malonaticus isolates, respectively. In conclusion, appropriate in-house database could make MALDI-TOF MS method identifying Cronobacter spp. isolates to the species level. But the spectra data were not sufficiently consistent for subtyping, unlike MLST. The Cronobacter spp. isolates have a high diversity including recognized pathovars.

Prevalence and Molecular and Antimicrobial Characteristics of Cronobacter spp. Isolated From Raw Vegetables in China

Cronobacter spp. is a foodborne pathogen that causes life-threatening and invasive diseases, such as necrotizing enterocolitis, meningitis, and sepsis. In this study, we aimed to investigate the prevalence, molecular characteristics and antimicrobial resistance of Cronobacter spp. in raw vegetables marketed in China. Based on dietary habits in China, 403 raw vegetables that could be eaten without additional cooking were collected. Of the 403 samples tested, 122 (30.27%) were positive for Cronobacter spp., and the contamination levels exceeded 110 most probable number (MPN)/g for 16.39% (20/122) of the samples. Coriander samples had the highest contamination rate of 52.81%, and the MPN values of 19.15% of positive coriander samples exceeded 100 MPN/g. Eleven serotypes were identified among 171 isolates, with Cronobacter sakazakii serogroup O1 (41 isolates) being the dominant serotype. Molecular characterization indicated that there was quite high genetic diversity in Cronobacter spp., and multilocus sequence typing analyses yielded 106 sequence types (STs), 55 of which were newly identified. Notably, the most prevalent ST (eight isolates) was C. malonaticus ST60, which appeared in a recent clinical infectious disease study in China. Five C. sakazakii ST4, seven C. malonaticus ST7, and three C. sakazakii ST8 confirmed as pathogenic STs in other countries were also detected in this study. Furthermore, all isolates were susceptible to amikacin, amoxicillin-clavulanic, cefepime, ciprofloxacin, and imipenem, but some isolates exhibited a high ratio of resistance to cephalothin (59.65%). In this study, the high contamination rate and the detection of pathogenic and new STs in raw vegetables indicated potential hazards to customers. To the best of our knowledge, this is the first report to provide valuable information on the contamination status of Cronobacter spp. in vegetables that can be eaten raw in China.

Microbial Source Tracking of Cronobacter spp

Being able to track bacterial pathogens is essential for epidemiological purposes as well as monitoring in-house production facilities. Common bacterial pathogens, such as Salmonella serovars, are already been well defined, and their detection methods are very advanced. However, this will not be the case for emergent bacterial pathogens, as was the case for Cronobacter. The clinical significance of the organism is due to its association with rare sporadic infections in adults, and severe life-threatening outbreaks of necrotizing enterocolitis and meningitis in newborn babies. The main recognized route of infection being through the consumption of contaminated reconstituted powdered infant formula. Key to the advances in being able to track this organism during formula production and outbreaks in neonatal intensive care units has been the use of DNA sequence-based methods, and most recently those which profile whole-genome sequences. This chapter considers how the latest DNA sequence-based methods in genotyping Cronobacter serve as a model for analyzing emergent bacterial pathogens in the future. The methods considered will initially highlight the limitations of phenotyping, then advance from the DNA probe-based methods for serotyping through to DNA sequence-based methods, especially multilocus sequence typing which is supported by an open access database. Finally the development of typing methods based on whole-genomes sequences, CRISPR-cas array profiling and SNP analysis, will be covered. The overall perspective is that emergent pathogens need to be investigated with the most advanced methods in order for robust and reliable control measures to be adopted.

DNA-Sequence Based Typing of the Cronobacter Genus Using MLST, CRISPR-cas Array and Capsular Profiling

The Cronobacter genus is composed of seven species, within which a number of pathovars have been described. The most notable infections by Cronobacter spp. are of infants through the consumption of contaminated infant formula. The description of the genus has greatly improved in recent years through DNA sequencing techniques, and this has led to a robust means of identification. However some species are highly clonal and this limits the ability to discriminate between unrelated strains by some methods of genotyping. This article updates the application of three genotyping methods across the Cronobacter genus. The three genotyping methods were multilocus sequence typing (MLST), capsular profiling of the K-antigen and colanic acid (CA) biosynthesis regions, and CRISPR-cas array profiling. A total of 1654 MLST profiled and 286 whole genome sequenced strains, available by open access at the PubMLST Cronobacter database, were used this analysis. The predominance of C. sakazakii and C. malonaticus in clinical infections was confirmed. The majority of clinical strains being in the C. sakazakii clonal complexes (CC) 1 and 4, sequence types (ST) 8 and 12 and C. malonaticus ST7. The capsular profile K2:CA2, previously proposed as being strongly associated with C. sakazakii and C. malonaticus isolates from severe neonatal infections, was also found in C. turicensis, C. dublinensis and C. universalis. The majority of CRISPR-cas types across the genus was the I-E (Ecoli) type. Some strains of C. dublinensis and C. muytjensii encoded the I-F (Ypseudo) type, and others lacked the cas gene loci. The significance of the expanding profiling will be of benefit to researchers as well as governmental and industrial risk assessors.

Defining the Genetic Features of O-Antigen Biosynthesis Gene Cluster and Performance of an O-Antigen Serotyping Scheme for Escherichia albertii

Escherichia albertii is a newly described and emerging diarrheagenic pathogen responsible for outbreaks of gastroenteritis. Serotyping plays an important role in diagnosis and epidemiological studies for pathogens of public health importance. The diversity of O-antigen biosynthesis gene clusters (O-AGCs) provides the primary basis for serotyping. However, little is known about the distribution and diversity of O-AGCs of E. albertii strains. Here, we presented a complete sequence set for the O-AGCs from 52 E. albertii strains and identified seven distinct O-AGCs. Six of these were also found in 15 genomes of E. albertii strains deposited in the public database. Possession of wzy/wzx genes in each O-AGC strongly suggest that O-antigens of E. albertii were synthesized by the Wzx/Wzy-dependent pathway. Furthermore, we performed an O-antigen serotyping scheme for E. albertii based on specific antisera against seven O-antigens and a high throughput xTAG Luminex assay to simultaneously detect seven O-AGCs. Both methods accurately identified serotypes of 64 tested E. albertii strains. Our data revealed the high-level diversity of O-AGCs in E. albertii. We also provide valuable methods to reliably identify and serotype this bacterium.

Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by Cronobacter spp

Little is known about secretion of outer membrane vesicles (OMVs) by Cronobacter. In this study, OMVs isolated from Cronobacter sakazakii, Cronobacter turicensis, and Cronobacter malonaticus were examined by electron microscopy (EM) and their associated outer membrane proteins (OMP) and genes were analyzed by SDS-PAGE, protein sequencing, BLAST, PCR, and DNA microarray. EM of stained cells revealed that the OMVs are secreted as pleomorphic micro-vesicles which cascade from the cell's surface. SDS-PAGE analysis identified protein bands with molecular weights of 18 kDa to >100 kDa which had homologies to OMPs such as GroEL; OmpA, C, E, F, and X; MipA proteins; conjugative plasmid transfer protein; and an outer membrane auto-transporter protein (OMATP). PCR analyses showed that most of the OMP genes were present in all seven Cronobacter species while a few genes (OMATP gene, groEL, ompC, mipA, ctp, and ompX) were absent in some phylogenetically-related species. Microarray analysis demonstrated sequence divergence among the OMP genes that was not captured by PCR. These results support previous findings that OmpA and OmpX may be involved in virulence of Cronobacter, and are packaged within secreted OMVs. These results also suggest that other OMV-packaged OMPs may be involved in roles such as stress response, cell wall and plasmid maintenance, and extracellular transport.

Simultaneous Rapid Detection and Serotyping of Cronobacter sakazakii Serotypes O1, O2, and O3 by Using Specific Monoclonal Antibodies

Cronobacter sakazakii is a foodborne pathogen associated with rare but often lethal infections in neonates. Powdered infant formula (PIF) represents the most frequent source of infection. Out of the identified serotypes (O1 to O7), O1, O2, and O3 are often isolated from clinical and PIF samples. Serotype-specific monoclonal antibodies (MAbs) suitable for application in enzyme immunoassays (EIAs) for the rapid detection of C. sakazakii have not yet been developed. In this study, we created specific MAbs with the ability to bind toC. sakazakii of serotypes O1, O2, and O3. Characterization by indirect EIAs, immunofluorescence, motility assays, and immunoblotting identified lipopolysaccharide (LPS) and exopolysaccharide (EPS) as the antigenic determinants of the MAbs. The established sandwich EIAs were highly sensitive and were able to detect between 2 × 10(3)and 9 × 10(6)CFU/ml. Inclusivity tests confirmed that 93% of serotype O1 strains, 100% of O2 strains, and 87% of O3 strains were detected at low cell counts. No cross-reactivity with >100 strains of Cronobacter spp. and other Enterobacter iaceae was observed, except for that with C. sakazakii serotype O3 and Cronobacter muytjensii serotype O1. Moreover, the sandwich EIAs detected C. sakazakii in PIF samples artificially contaminated with 1 to 10 bacterial cells per 10 g of sample after 15 h of preenrichment. The use of these serotype-specific MAbs not only allows the reliable detection of C. sakazakii strains but also enables simultaneous serotyping in a simple sandwich EIA method.

Mining for sensitive and reliable species-specific primers for PCR for detection of Cronobacter sakazakii by a bioinformatics approach

Although several studies have reported PCR assays for distinguishing Cronobacter sakazakii from other species in the genus, reports regarding assay sensitivity and specificity, as well as applications for food testing, are lacking. Hence, the objective of this study was to develop a sensitive and reliable PCR-based method for detection of C. sakazakii by screening for specific target genes. The genome sequence of C. sakazakii in the GenBank database was compared with that of other organisms using BLAST. Thirty-eight DNA fragments unique to C. sakazakii were identified, and primers targeting these sequences were designed. Finally, 3 primer sets (CS14, CS21, and CS38) were found to be specific for C. sakazakii by PCR verification. The detection limit of PCR assays using the 3 pairs of primers was 1.35 pg/μL, 135 fg/μL, and 135 fg/μL, respectively, for genomic DNA, and 5.5×10(5), 5.5×10(3), 5.5×10(3) cfu/mL, respectively, using pure cultures of the bacteria, compared with 13.5 pg/μLand 5.5×10(5) cfu/mLfor primer set SpeCronsaka, which has been previously described. Cronobacter sakazakii were detected in artificially contaminated powdered infant formula (PIF) by PCR using primer sets CS21 and CS38 after 8h of enrichment. The detection limit was 5.5×10(-1) cfu/10g of PIF. Thus, the PCR assay can be used for rapid and sensitive detection of C. sakazakii in PIF.

Capsular profiling of the Cronobacter genus and the association of specific Cronobacter sakazakii and C. malonaticus capsule types with neonatal meningitis and necrotizing enterocolitis

Background

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.

Methods

This 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.

Results

Phylogeny 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.

Conclusion

This 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 material

The online version of this article (doi:10.1186/s12864-015-1960-z) contains supplementary material, which is available to authorized users.

Comparative Genotypic and Phenotypic Analysis of Cronobacter Species Cultured from Four Powdered Infant Formula Production Facilities: Indication of Pathoadaptation along the Food Chain

Cronobacter species are opportunistic pathogens commonly found in the environment. Among the seven Cronobacter species, Cronobacter sakazakii sequence type 4 (ST-4) is predominantly associated with recorded cases of infantile meningitis. This study reports on a 26-month powdered infant formula (PIF) surveillance program in four production facilities located in distinct geographic regions. The objective was to identify the ST(s) in PIF production environments and to investigate the phenotypic features that support their survival. Of all 168 Cronobacter isolates, 133 were recovered from a PIF production environment, 31 were of clinical origin, and 4 were laboratory type strains. Sequence type 1 (n = 84 isolates; 63.9%) was the dominant type in PIF production environments. The majority of these isolates clustered with an indistinguishable pulsotype and persisted for at least an 18-month period. Moreover, DNA microarray results identified two phylogenetic lineages among ST-4 strains tested. Thereafter, the ST-1 and -4 isolates were phenotypically compared. Differences were noted based on the phenotypes expressed by these isolates. The ST-1 PIF isolates produced stronger biofilms at both 28°C and 37°C, while the ST-4 clinical isolates exhibited greater swimming activity and increased binding to Congo red dye. Given the fact that PIF is a low-moisture environment and that the clinical environment provides for an interaction between the pathogen and its host, these differences may be consistent with a form of pathoadaptation. These findings help to extend our current understanding of the epidemiology and ecology of Cronobacter species in PIF production environments.

Diversity of O Antigens within the Genus Cronobacter: from Disorder to Order

Cronobacter species are Gram-negative opportunistic pathogens that can cause serious infections in neonates. The lipopolysaccharides (LPSs) that form part of the outer membrane of such bacteria are possibly related to the virulence of particular bacterial strains. However, currently there is no clear overview of O-antigen diversity within the various Cronobacter strains and links with virulence. In this study, we tested a total of 82 strains, covering each of the Cronobacter species. The nucleotide variability of the O-antigen gene cluster was determined by restriction fragment length polymorphism (RFLP) analysis. As a result, the 82 strains were distributed into 11 previously published serotypes and 6 new serotypes, each defined by its characteristic restriction profile. These new serotypes were confirmed using genomic analysis of strains available in public databases: GenBank and PubMLST Cronobacter. Laboratory strains were then tested using the current serotype-specific PCR probes. The results show that the current PCR probes did not always correspond to genomic O-antigen gene cluster variation. In addition, we analyzed the LPS phenotype of the reference strains of all distinguishable serotypes. The identified serotypes were compared with data from the literature and the MLST database (www.pubmlst.org/cronobacter/). Based on the findings, we systematically classified a total of 24 serotypes for the Cronobacter genus. Moreover, we evaluated the clinical history of these strains and show that Cronobacter sakazakii O2, O1, and O4, C. turicensis O1, and C. malonaticus O2 serotypes are particularly predominant in clinical cases.

Genome Sequence of Cronobacter sakazakii Serogroup O:4, Sequence Type 4 Strain CDC 2009-03746, Isolated from a Fatal Case of Infantile Meningitis

We report the draft genome sequence of a Cronobacter sakazakii serogroup O:4, sequence type 4 strain, CDC 2009-03746 (=NM1240=2009-06-01), isolated from a fatal case of infantile meningitis. The draft genome has a size of 4,492,904 bp and a G+C% content of 56.7.

A proposed harmonized LPS molecular-subtyping scheme for Cronobacter species

Cronobacter are opportunistic pathogens, which cause infections in all age groups. To aid the characterization of Cronobacter in foods and environments a harmonized LPS identification scheme for molecular serotyping is needed. To this end, we studied 409 Cronobacter isolates representing the seven Cronobacter species using two previously reported molecular serotyping schemes, described here as Mullane-Jarvis (M-J) and Sun schemes. PCR analysis revealed many overlapping results that were obtained when independently applying the two serotyping schemes. There were complete agreements between the two PCR schemes for Cronobacter sakazakii (Csak) O:1, Csak O:3, and Csak O:7 serotypes. However, only thirty-five of 41 Csak O:4 strains, identified using the M-J scheme, were PCR-positive with the Sun scheme primers. Also the Sun scheme Csak O:5 primers failed to identify this serotype in any of the C. sakazakii strains tested, but did recognize seven Cronobacter turicensis strains, which were identified as Ctur O:3 using the M-J scheme. Similarly, the Sun scheme Csak O:6 primers recognized 30 Cronobacter malonaticus O:2 strains identified with the M-J scheme, but failed to identify this serotype in any C. sakazakii strain investigated. In this report, these findings are summarized and a harmonized molecular-serotyping scheme is proposed which is predicated on the correct identification of Cronobacter species, prior to serotype determination. In summary, fourteen serotypes were identified using the combined protocol, which consists of Csak O:1-O:4, and Csak O:7; Cmal O:1-O:2; Cdub O:1-O:2, Cmuy O:1-O:2, Cuni O:1, as well as Ctur O:1 and Ctur O:3.

Development of a Custom-Designed, Pan Genomic DNA Microarray to Characterize Strain-Level Diversity among Cronobacter spp

Cronobacter species cause infections in all age groups; however neonates are at highest risk and remain the most susceptible age group for life-threatening invasive disease. The genus contains seven species:Cronobacter sakazakii, Cronobacter malonaticus, Cronobacter turicensis, Cronobacter muytjensii, Cronobacter dublinensis, Cronobacter universalis, and Cronobacter condimenti. Despite an abundance of published genomes of these species, genomics-based epidemiology of the genus is not well established. The gene content of a diverse group of 126 unique Cronobacter and taxonomically related isolates was determined using a pan genomic-based DNA microarray as a genotyping tool and as a means to identify outbreak isolates for food safety, environmental, and clinical surveillance purposes. The microarray constitutes 19,287 independent genes representing 15 Cronobacter genomes and 18 plasmids and 2,371 virulence factor genes of phylogenetically related Gram-negative bacteria. The Cronobacter microarray was able to distinguish the seven Cronobacter species from one another and from non-Cronobacter species; and within each species, strains grouped into distinct clusters based on their genomic diversity. These results also support the phylogenic divergence of the genus and clearly highlight the genomic diversity among each member of the genus. The current study establishes a powerful platform for further genomics research of this diverse genus, an important prerequisite toward the development of future countermeasures against this foodborne pathogen in the food safety and clinical arenas.

Strategies for the identification and tracking of cronobacter species: an opportunistic pathogen of concern to neonatal health

Cronobacter species are emerging opportunistic food-borne pathogens, which consists of seven species, including C. sakazakii, C. malonaticus, C. muytjensii, C. turicensis, C. dublinensis, C. universalis, and C. condimenti. The organism can cause severe clinical infections, including necrotizing enterocolitis, septicemia, and meningitis, predominately among neonates <4 weeks of age. Cronobacter species can be isolated from various foods and their surrounding environments; however, powdered infant formula (PIF) is the most frequently implicated food source linked with Cronobacter infection. This review aims to provide a summary of laboratory-based strategies that can be used to identify and trace Cronobacter species. The identification of Cronobacter species using conventional culture method and immuno-based detection protocols were first presented. The molecular detection and identification at genus-, and species-level along with molecular-based serogroup approaches are also described, followed by the molecular sub-typing methods, in particular pulsed-field gel electrophoresis and multi-locus sequence typing. Next generation sequence approaches, including whole genome sequencing, DNA microarray, and high-throughput whole-transcriptome sequencing, are also highlighted. Appropriate application of these strategies would contribute to reduce the risk of Cronobacter contamination in PIF and production environments, thereby improving food safety and protecting public health.

A Cronobacter turicensis O1 antigen-specific monoclonal antibody inhibits bacterial motility and entry into epithelial cells

Cronobacter turicensis is an opportunistic foodborne pathogen that can cause a rare but sometimes lethal infection in neonates. Little is known about the virulence mechanisms and intracellular lifestyle of this pathogen. In this study, we developed an IgG monoclonal antibody (MAb; MAb 2G4) that specifically recognizes the O1 antigen of C. turicensis cells. The antilipopolysaccharide antibody bound predominantly monovalently to the O antigen and reduced bacterial growth without causing cell agglutination. Furthermore, binding of the antibody to the O1 antigen of C. turicensis cells caused a significant reduction of the membrane potential which is required to energize flagellar rotation, accompanied by a decreased flagellum-based motility. These results indicate that binding of IgG to the O antigen of C. turicensis causes a direct antimicrobial effect. In addition, this feature of the antibody enabled new insight into the pathogenicity of C. turicensis. In a tissue culture infection model, pretreatment of C. turicensis with MAb 2G4 showed no difference in adhesion to human epithelial cells, whereas invasion of bacteria into Caco-2 cells was significantly inhibited.

Alterations in Caenorhabditis elegans and Cronobacter sakazakii lipopolysaccharide during interaction

Lipopolysaccharide is one of the pathogen-associated molecular patterns of Gram-negative bacteria which are essential for its pathogenicity. Cronobacter sakazakii is an opportunistic, emergent pathogen, which infects and cause mortality in Caenorhabditis elegans. In this study, modifications in host and C. sakazakii LPS during infections were evaluated. The physiological assays revealed that LPS alone is sufficient to affect the host pharyngeal pumping rate, brood size and cause lethality. FTIR spectra of LPS revealed that C. sakazakii modifies its LPS to escape from the recognition of host immune system. These results indicate that LPS plays a key role in C. sakazakii pathogenicity. qPCR studies revealed that LPS modulated the expression of selected host immune (clec-60, clec-87, lys-7, ilys-3, F08G5.6, atf-7, scl-2, cpr-2) and aging-related genes (skn-1, clk-2, bra-2, age-1, bec-1, daf-16, daf-2). Moreover, it was confirmed that p38 MAPK pathway has a major role in host immune response against LPS-mediated challenges.

Bacteriophage ϕMAM1, a viunalikevirus, is a broad-host-range, high-efficiency generalized transducer that infects environmental and clinical isolates of the enterobacterial genera Serratia and Kluyvera

Members of the enterobacterial genus Serratia are ecologically widespread, and some strains are opportunistic human pathogens. Bacteriophage ϕMAM1 was isolated on Serratia plymuthica A153, a biocontrol rhizosphere strain that produces the potently bioactive antifungal and anticancer haterumalide oocydin A. The ϕMAM1 phage is a generalized transducing phage that infects multiple environmental and clinical isolates of Serratia spp. and a rhizosphere strain of Kluyvera cryocrescens. Electron microscopy allowed classification of ϕMAM1 in the family Myoviridae. Bacteriophage ϕMAM1 is virulent, uses capsular polysaccharides as a receptor, and can transduce chromosomal markers at frequencies of up to 7 × 10(-6) transductants per PFU. We also demonstrated transduction of the complete 77-kb oocydin A gene cluster and heterogeneric transduction of a plasmid carrying a type III toxin-antitoxin system. These results support the notion of the potential ecological importance of transducing phages in the acquisition of genes by horizontal gene transfer. Phylogenetic analyses grouped ϕMAM1 within the ViI-like bacteriophages, and genomic analyses revealed that the major differences between ϕMAM1 and other ViI-like phages arise in a region encoding the host recognition determinants. Our results predict that the wider genus of ViI-like phages could be efficient transducing phages, and this possibility has obvious implications for the ecology of horizontal gene transfer, bacterial functional genomics, and synthetic biology.

The structure of O-polysaccharide isolated from Cronobacter universalis NCTC 9529T

The O-polysaccharide (OPS) was isolated from Cronobacter universalis NCTC 9529(T), a new species in the genus Cronobacter, which was created by the reclassification of the species Enterobacter sakazakii. Purified polysaccharide was analyzed by NMR spectroscopy ((1)H, COSY, TOCSY, ROESY, HSQC, and HSQC-TOCSY) and chemical methods. The monosaccharide derivatives were analyzed by gas chromatography and gas chromatography-mass spectrometry. These experiments enabled the type and number of monosaccharides in the repeating unit of OPS, their positions of linkages, and absolute configuration to be determined. Together the chemical analysis established a structure of the OPS of C. universalis NCTC 9529(T). [structure: see text]. OPS isolated from C. universalis was structurally characterized for the first time.

Genotypic and phenotypic characteristics of Cronobacter species, with particular attention to the newly reclassified species Cronobacter helveticus, Cronobacter pulveris, and Cronobacter zurichensis

In 2013, Enterobacter helveticus, Enterobacter pulveris and Enterobacter turicensis, were reclassified as Cronobacter helveticus, Cronobacter pulveris and Cronobacter zurichensis, respectively. Previously these species had been used as negative controls for some Cronobacter detection assays. This study examined cultural, biochemical and molecular Cronobacter detection and identification assays, with emphasis on the new species. Additionally, 32 Cronobacter genomes were examined for the presence of PCR target genes using the BLAST function of the online Cronobacter PubMLST facility. The results of the cultural methods varied and no single medium was able to correctly detect all Cronobacter spp. Since the supporting databases have not been updated to include the Cronobacter genus, Enterobacter sakazakii was returned for four strains of the newly reclassified species with ID32E and none with API 20E. PCR probes targeting rpoB and ompA could not correctly identify the new Cronobacter spp., due to primer specificity or absent target genes. As neonates have been identified as a high-risk group for infection, international standards require the absence of all Cronobacter species in powdered infant formula. However, many conventional detection methods cannot correctly identify the newly recognized species. Conversely, DNA sequence-based methods can adapt to taxonomic revisions and will likely become more common.

Cronobacter spp.--opportunistic food-borne pathogens. A review of their virulence and environmental-adaptive traits

The genus Cronobacter consists of a diverse group of Gram-negative bacilli and comprises seven species: Cronobacter sakazakii, Cronobacter malonaticus, Cronobacter muytjensii, Cronobacter turicensis, Cronobacter dublinensis, Cronobacter universalis and Cronobacter condimenti. Cronobacter are regarded as opportunistic pathogens, and have been implicated in newborn and infant infections, causing meningitis, necrotizing enterocolitis and bacteraemia or sepsis. Cronobacter virulence is believed to be due to multiple factors. Some strains were found to produce diarrhoea or cause significant fluid accumulation in suckling mice. Two iron acquisition systems (eitCBAD and iucABCD/iutA), Cronobacter plasminogen activator gene (cpa), a 17 kb type VI secretion system (T6SS), and a 27 kb filamentous haemagglutinin gene (fhaBC) and associated putative adhesins locus are harboured on a family of RepFIB-related plasmids (pESA3 and pCTU1), suggesting that these are common virulence plasmids; 98% of 229 tested Cronobacter strains possessed these plasmids. Even though pESA3 and pCTU1 share a common backbone composed of the repA gene and eitCBAD and iucABCD/iutA gene clusters, the presence of cpa, T6SS and FHA loci depended on species, demonstrating a strong correlation with the presence of virulence traits, plasmid type and species. Other factors were observed, in that Cronobacter form biofilms, and show unusual resistance to heat, dry and acid stress growth conditions. The outer-membrane protein A is probably one of the best-characterized virulence markers of Cronobacter. Furthermore, it was reported that Cronobacter employ phosphatidylinositide 3-kinase/Akt signalling, which activates protein kinase C-α and impairs the host cell's mitogen-activated protein kinase pathway, in order to invade cells. Cronobacter can also use immature dendritic cells and macrophages to escape the immune response. This review addresses the various virulence and environmental-adaptive characteristics possessed by members of the genus Cronobacter.

Occurrence and characterization of Cronobacter spp. in powdered formula from Chinese retail markets

Cronobacter spp. (formerly known as Enterobacter sakazakii) are foodborne pathogens that cause rare but life-threatening diseases in neonates and infants through consumption of contaminated powdered infant formula. This study was conducted to investigate the occurrence of Cronobacter spp. in powdered formula in China and to further characterize Cronobacter isolates. Isolates were identified to the species level based on the fusA gene sequence, and strains of C. sakazakii were further subtyped by applying the polymerase chain reaction (PCR)-based serotyping method. A total of 23 strains of Cronobacter spp. isolated from 530 powdered formula samples were identified using conventional biochemical methods and duplex PCR. Cronobacter spp. were detected in 6.25%, 1.82%, 3.64%, 5.45%, and 2.50% of the general formula, infant formula (age <6 months), follow-up formula (6-12 months of age), growing-up formula (1-3 years of age), and children's formula (3-6 years of age), respectively. The individual species were identified as C. sakazakii (22 isolates) and C. malonaticus (1 isolate). Among 22 C. sakazakii isolates, representatives of all but two O-antigen serotypes (serotypes O5 and O6) were recognized.

Cronobacter: an emergent pathogen causing meningitis to neonates through their feeds

The recognition of Cronobacter as a public health concern was raised when powdered infant formula (PIF) was linked to several neonatal meningitis outbreaks. It is an opportunistic pathogen that causes necrotising enterocolitis, infantile septicaemia, and meningitis which carries a high mortality rate among neonates. It has been also linked with cases of infection in adults and elderly. Over the past decade, much focus has been made on developing sensitive and specific characterisation, detection, and isolation methods to ascertain the quality of foods, notably contamination of PIF with Cronobacter and to understand its ability to cause disease. Whole genome sequencing has unveiled several putative virulence factors, yet the full capacity of the pathogenesis of Cronobacter has not yet been elucidated.

Complete genome sequence and phenotype microarray analysis of Cronobacter sakazakii SP291: a persistent isolate cultured from a powdered infant formula production facility

Outbreaks of human infection linked to the powdered infant formula (PIF) food chain and associated with the bacterium Cronobacter, are of concern to public health. These bacteria are regarded as opportunistic pathogens linked to life-threatening infections predominantly in neonates, with an under developed immune system. Monitoring the microbiological ecology of PIF production sites is an important step in attempting to limit the risk of contamination in the finished food product. Cronobacter species, like other microorganisms can adapt to the production environment. These organisms are known for their desiccation tolerance, a phenotype that can aid their survival in the production site and PIF itself. In evaluating the genome data currently available for Cronobacter species, no sequence information has been published describing a Cronobacter sakazakii isolate found to persist in a PIF production facility. Here we report on the complete genome sequence of one such isolate, Cronobacter sakazakii SP291 along with its phenotypic characteristics. The genome of C. sakazakii SP291 consists of a 4.3-Mb chromosome (56.9% GC) and three plasmids, denoted as pSP291-1, [118.1-kb (57.2% GC)], pSP291-2, [52.1-kb (49.2% GC)], and pSP291-3, [4.4-kb (54.0% GC)]. When C. sakazakii SP291 was compared to the reference C. sakazakii ATCC BAA-894, which is also of PIF origin, the annotated genome data identified two interesting functional categories, comprising of genes related to the bacterial stress response and resistance to antimicrobial and toxic compounds. Using a phenotypic microarray (PM), we provided a full metabolic profile comparing C. sakazakii SP291 and the previously sequenced C. sakazakii ATCC BAA-894. These data extend our understanding of the genome of this important neonatal pathogen and provides further insights into the genotypes associated with features that can contribute to its persistence in the PIF environment.

Chemical structure of the O-polysaccharides isolated from Cronobacter turicensis sequence type 5 strains 57, 564, and 566

The Cronobacter spp. are Gram-negative bacterial pathogens that can cause infections in all age groups, and have a high mortality rate in neonates due to necrotizing enterocolitis and meningitis. Recent genotyping studies have revealed a strong clonal lineage in the genus, but this has not been compared with physiological traits. The O-polysaccharides (OPS) were isolated from three C. turicensis sequence type 5 strains (57, 564, and 566) and structurally characterized using (1)H and (13)C NMR spectroscopy, including two-dimensional DQF-COSY, TOCSY, ROESY, and HSQC analysis. Further compositional determination was undertaken using classical chemical methods followed by GLC, and GLC-MS analysis. The repeating unit of the isolated O-polysaccharides consists of GlcNAc, Rha, Glc, and had the structure shown below and therefore complemented the sequence type. [structure: see text].

Comparative analysis of genome sequences covering the seven cronobacter species

BACKGROUND

Species of Cronobacter are widespread in the environment and are occasional food-borne pathogens associated with serious neonatal diseases, including bacteraemia, meningitis, and necrotising enterocolitis. The genus is composed of seven species: C. sakazakii, C. malonaticus, C. turicensis, C. dublinensis, C. muytjensii, C. universalis, and C. condimenti. Clinical cases are associated with three species, C. malonaticus, C. turicensis and, in particular, with C. sakazakii multilocus sequence type 4. Thus, it is plausible that virulence determinants have evolved in certain lineages.

METHODOLOGY/PRINCIPAL FINDINGS

We generated high quality sequence drafts for eleven Cronobacter genomes representing the seven Cronobacter species, including an ST4 strain of C. sakazakii. Comparative analysis of these genomes together with the two publicly available genomes revealed Cronobacter has over 6,000 genes in one or more strains and over 2,000 genes shared by all Cronobacter. Considerable variation in the presence of traits such as type six secretion systems, metal resistance (tellurite, copper and silver), and adhesins were found. C. sakazakii is unique in the Cronobacter genus in encoding genes enabling the utilization of exogenous sialic acid which may have clinical significance. The C. sakazakii ST4 strain 701 contained additional genes as compared to other C. sakazakii but none of them were known specific virulence-related genes.

CONCLUSIONS/SIGNIFICANCE

Genome comparison revealed that pair-wise DNA sequence identity varies between 89 and 97% in the seven Cronobacter species, and also suggested various degrees of divergence. Sets of universal core genes and accessory genes unique to each strain were identified. These gene sequences can be used for designing genus/species specific detection assays. Genes encoding adhesins, T6SS, and metal resistance genes as well as prophages are found in only subsets of genomes and have contributed considerably to the variation of genomic content. Differences in gene content likely contribute to differences in the clinical and environmental distribution of species and sequence types.

Multiplex PCR assay targeting a diguanylate cyclase-encoding gene, cgcA, to differentiate species within the genus Cronobacter

In a comparison to the widely used Cronobacter rpoB PCR assay, a highly specific multiplexed PCR assay based on cgcA, a diguanylate cyclase gene, that identified all of the targeted six species among 305 Cronobacter isolates was designed. This assay will be a valuable tool for identifying suspected Cronobacter isolates from food-borne investigations.

Cronobacter species (formerly known as Enterobacter sakazakii) in powdered infant formula: a review of our current understanding of the biology of this bacterium

Cronobacter species (formerly known as Enterobacter sakazakii) are opportunistic pathogens that can cause necrotizing enterocolitis, bacteraemia and meningitis, predominantly in neonates. Infection in these vulnerable infants has been linked to the consumption of contaminated powdered infant formula (PIF). Considerable research has been undertaken on this organism in the past number of years which has enhanced our understanding of this neonatal pathogen leading to improvements in its control within the PIF production environment. The taxonomy of the organism resulted in the recognition of a new genus, Cronobacter, which consists of seven species. This paper presents an up-to-date review of our current knowledge of Cronobacter species. Taxonomy, genome sequencing, current detection protocols and epidemiology are all discussed. In addition, consideration is given to the control of this organism in the manufacturing environment, as a first step towards reducing the occurrence of this pathogen in PIF.

Structure of the O-antigen polysaccharide present in the lipopolysaccharide ofCronobacter dublinensis(subspecieslactaridiorlausannensis) HPB 3169

Cronobacter dublinensis (formerly Enterobacter sakazakii) HPB 3169 is a pathogenic Gram-negative bacterium that produces a smooth-type lipopolysaccharide in which the antigenic O-polysaccharide component was determined to be a repeating pentasaccharide unit composed of l-rhamnose; 2-acetamido-2-deoxy-d-glucose; 3,6-dideoxy-3-(R)-3-hydroxybutyramido-d-glucose; and 3-deoxy-manno-oct-2-ulosonic acid in the respective molar ratio 2:1:1:1. Chemical and 2D NMR analyses of the O-polysaccharide and a pentasaccharide derived by the mild acid hydrolysis of the ketosyl linkage of the Kdo (3-deoxy-d-manno-2-octulosonic acid) residue in the O-polysaccharide established that the O-antigen is a high molecular mass unbranched polymer of a repeating pentasaccharide unit and has the structure where Bu is a (R)-3-hydroxybutanoyl substituent. The O-antigen is structurally similar to that of the recently reported Cronobacter sakazakii strain G706 (designated as serotype O5), except that in strain G706 the d-Qui3N is in its N-acetyl form, in contrast to its presence as a 3-deoxy-3-(R)-3-hydroxybutyramido derivative in the C. sakazakii HPB 3169 strain O-antigen.

Genetic analysis of the Cronobacter sakazakii O4 to O7 O-antigen gene clusters and development of a PCR assay for identification of all C. sakazakii O serotypes

The Gram-negative bacterium Cronobacter sakazakii is an emerging food-borne pathogen that causes severe invasive infections in neonates. Variation in the O-antigen lipopolysaccharide in the outer membrane provides the basis for Gram-negative bacteria serotyping. The O-antigen serotyping scheme for C. sakazakii, which includes seven serotypes (O1 to O7), has been recently established, and the O-antigen gene clusters and specific primers for three C. sakazakii serotypes (O1, O2, and O3) have been characterized. In this study, the C. sakazakii O4, O5, O6, and O7 O-antigen gene clusters were sequenced, and gene functions were predicted on the basis of homology. C. sakazakii O4 shared a similar O-antigen gene cluster with Escherichia coli O103. The general features and anomalies of all seven C. sakazakii O-antigen gene clusters were evaluated and the relationship between O-antigen structures and their gene clusters were investigated. Serotype-specific genes for O4 to O7 were identified, and a molecular serotyping method for all C. sakazakii O serotypes, a multiplex PCR assay, was developed by screening against 136 strains of C. sakazakii and closely related species. The sensitivity of PCR-based serotyping method was determined to be 0.01 ng of genomic DNA and 10(3) CFU of each strain/ml. This study completes the elucidation of C. sakazakii O-antigen genetics and provides a molecular method suitable for the identification of C. sakazakii O1 to O7 strains.

Localization and molecular characterization of putative O antigen gene clusters of Providencia species

Enterobacteria of the genus Providencia are opportunistic human pathogens associated with urinary tract and wound infections, as well as enteric diseases. The lipopolysaccharide (LPS) O antigen confers major antigenic variability upon the cell surface and is used for serotyping of Gram-negative bacteria. Recently, Providencia O antigen structures have been extensively studied, but no data on the location and organization of the O antigen gene cluster have been reported. In this study, the four Providencia genome sequences available were analysed, and the putative O antigen gene cluster was identified in the polymorphic locus between the cpxA and yibK genes. This finding provided the necessary information for designing primers, and cloning and sequencing the O antigen gene clusters from five more Providencia alcalifaciens strains. The gene functions predicted in silico were in agreement with the known O antigen structures; furthermore, annotation of the genes involved in the three-step synthesis of GDP-colitose (gmd, colD and colC) was supported by cloning and biochemical characterization of the corresponding enzymes. In one strain (P. alcalifaciens O39), no polysaccharide product of the gene cluster in the cpxA-yibK locus was found, and hence genes for synthesis of the existing O antigen are located elsewhere in the genome. In addition to the putative O antigen synthesis genes, homologues of wza, wzb, wzc and (in three strains) wzi, required for the surface expression of capsular polysaccharides, were found upstream of yibK in all species except Providencia rustigianii, suggesting that the LPS of these species may be attributed to the so-called K LPS (K(LPS)). The data obtained open a way for development of a PCR-based typing method for identification of Providencia isolates.

Human isolates of Cronobacter sakazakii bind efficiently to intestinal epithelial cells in vitro to induce monolayer permeability and apoptosis

BACKGROUND

Cronobacter sakazakii (CS) is an emerging opportunistic pathogen that causes life-threatening infections in infants. This pathogen has been implicated in the outbreaks of necrotizing enterocolitis (NEC) with associated rates of high mortality and morbidity. In this study, we compared the abilities of CS strains isolated from human and environmental sources to bind to intestinal epithelial cells and trigger apoptosis.

MATERIALS AND METHODS

CS strains were isolated from human and environmental sources and their abilities to bind to intestinal epithelial cells were determined. Monolayer permeability was determined by transepithelial electrical resistance (TEER) and horseradish peroxidase (HRP) leakage. Apoptosis was examined by ApoTag and AnnexinV-7AAD staining. PKC activation was evaluated by non-radioactive PepTag assay.

RESULTS

Human isolates of CS bind to rat and human enterocytes more efficiently than environmental strains. Additionally, these strains induced increased enterocyte monolayer permeability as indicated by a decrease in TEER and an increase in transcellular leakage of exogenously added HRP. Human isolates also caused tight junction disruption and significant apoptosis of enterocytes compared with environmental strains due to increased production of inducible nitric oxide. We also observed that human CS isolates caused 2-fold increase in the activation of phosphokinase C (PKC) than environmental strains. Blocking the PKC activity in enterocytes by an inhibitor, Gö 6983, suppressed CS-mediated tight junction disruption, monolayer permeability, and apoptosis of the cells.

CONCLUSION

These results suggest that human isolates of CS more efficiently bind to and cause damage to intestinal epithelial cells compared with environmental strains.