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

The Identification, Antibiotic Resistance, Virulence Characteristics, and Genome Analysis of Cronobacter spp. Isolated from Infant Rice Cereal in Nanchang, China

Cronobacter spp. are well known to be resistant to osmotic and dry stresses and can persist in a variety of foods. C. sakazakii and C. malonaticus are currently considered to be the primary pathogenic species that cause severe diseases. There are few studies on the prevalence of Cronobacter spp. in infant rice cereal. Information on the diversity, pathogenicity, and virulence of Cronobacter species obtained from foods is still relatively scarce and fragmentary. In this article, a total of 67 Cronobacter spp. strains were isolated from infant rice cereal in Nanchang, China. Forty-seven strains of C. sakazakii and 11 strains of C. malonaticus were identified by polymerase chain reaction (PCR). The resistance to 10 antibiotics was analyzed, showing that all isolates were sensitive except two strains. PCR detection for the five virulence genes (cpa, aut, hly, inv, and sip) and whole genome sequencing were performed. Co-existence of CSA or CMA with ampH was found in C. sakazakii and C. malonaticus strains. Compared with C. sakazakii, C. malonaticus lacked various virulence genes including yeeJ, stjC, and nanAKT genes. Another important observation was the presence of csg in the C. malonaticus genomes, while it was not found in the C. sakazakii. Notably, STs 1, 7, and 4, which are frequently associated with clinical infections, were observed. C. sakazakii and C. malonaticus strains induced higher apoptosis rate in Caco-2 cell in comparison with other Cronobacter species.

Structural and Functional Characterization of a Putative Type VI Secretion System Protein in Cronobacter sakazakii as a Potential Therapeutic Target: A Computational Study

Background

Cronobacter sakazakii, a foodborne pathogen with a fatality rate of 33%, is a rod-shaped, Gram-negative, non-spore-forming bacterium responsible for causing meningitis, bacteremia, and necrotizing enterocolitis. Despite many unknown functions of hypothetical proteins in bacterial genomes, bioinformatic techniques have successfully annotated their roles in various pathogens.

Objectives

The aim of this investigation is to identify and annotate the structural and functional properties of a hypothetical protein (HP) from Cronobacter sakazakii 7G strain (accession no. WP_004386962.1, 277 residues) using computational tools.

Methods

Multiple bioinformatic tools were used to identify the homologous protein and to construct and validate its 3D structure. A 3D model was generated using SWISS-MODEL and validated using tools, developing a reliable 3D structure. The STRING and CASTp servers provided information on protein-protein interactions and active sites, identifying functional partners.

Results

The putative protein was soluble, stable, and localized in the cytoplasmic membranes, indicating its biological activity. Functional annotation identified TagJ (HsiE1) within the protein, a member of the ImpE superfamily involved in the transport of toxins and a part of the bacterial type VI secretion system (T6SS). The 3-dimensional structure of this protein was validated through molecular docking involving 6 different compounds. Among these, ceforanide demonstrated the strongest binding scores, -7.5 kcal/mol for the hypothetical protein and -7.2 kcal/mol for its main template protein (PDB ID: 4UQX.1).

Conclusion

Comparative genomics study suggests that the protein found in C. sakazakii may be a viable therapeutic target because it seems distinctive and different from human proteins. The results of multiple sequence alignment (MSA) and molecular docking supported HP's potential involvement as a T6SS. These in silico results represent that the examined HP could be valuable for studying C. sakazakii infections and creating medicines to treat C. sakazakii-mediated disorders.

Cronobacter Surveillance in Minnesota, United States, 2002-2024

Cronobacter sakazakii is an opportunistic pathogen associated with bloodstream infections and meningitis in neonates and infants. C. sakazakii isolated from infants under 1 year of age has been reportable in Minnesota since 2003. Invasive Cronobacter infections in infants was recently made notifiable nationally in 2024. Therefore, this summary of over 20 years of reportable surveillance for C. sakazakii from Minnesota infants will inform other jurisdictions. During 2002-2024, 23 C. sakazakii cases in infants, including 8 invasive and 15 non-invasive cases, were identified and confirmed using MALDI-TOF or conventional biochemical methods. Invasive cases were younger (median, 18 days; range, 8 days to 10 months) than non-invasive cases (median, 98 days; range, 7 days to 8 months). Cronobacter isolates from infant (21), child (4), and adult (15) cases were submitted for whole genome sequencing (WGS) to obtain a contextual understanding of potential relatedness. In addition, C. sakazakii isolated from powdered infant formula (PIF) in 2003 was sequenced for comparison. Sequence type (ST) 4 was responsible for the majority of C. sakazakii cases overall (65%) and invasive infant cases (88%). Opened and unopened PIF was cultured from 10 investigations representing both invasive and non-invasive cases. Two (25%) opened PIF samples tested positive for C. sakazakii ST 4 while one (11%) unopened PIF sample tested positive for C. sakazakii ST 4. WGS demonstrated that no clinical cases were associated with a recognized outbreak. Several cases were likely due to contamination of PIF in the home during preparation, highlighting the importance of infant caregiver education to prevent infections.

Cronobacter sakazakii induced sepsis-associated arrhythmias through its outer membrane vesicles

Sepsis-induced arrhythmia, linked to sudden cardiac death, is associated with gut microbiota, though the exact relationship is unclear. This study aimed to elucidate the relationship between Cronobacter sakazakii (C. sakazakii) and arrhythmia. The relative abundance of C. sakazakii was increased in cecal ligation and puncture (CLP)-induced septic mice. Live C. sakazakii, supernatant, and outer membrane vesicles (OMVs) resulted in premature ventricular beat (PVB), sinus arrhythmia (SA), and increased arrhythmia and mortality in sepsis model through dysregulated ion channel proteins. Moreover, short-chain fatty acids (SCFAs) showed antibacterial effects in vitro. We confirmed sodium acetate (C2) and sodium butyrate (C4) protect from C. sakazakii-induced arrhythmia, and C2 and C4 protected from septic arrhythmia by activating free fatty acid receptor 2 and 3 (FFAR2 and FFAR3) in mice. These findings point to how C. sakazakii's OMVs trigger arrhythmia, and SCFAs may be a treatment for septic arrhythmia.

Genome Mining of Novel Targets and Construction of Ladder-shaped melting temperature isothermal amplification Assays for the Identification of Cronobacter sakazakii and Cronobacter malonaticus

Cronobacter species are potential pathogens that can contaminate powdered infant formula. C. sakazakii and C. malonaticus are the most common species of Cronobacter associated with infections. This study mined new molecular targets for the detection of C. sakazakii and C. malonaticus by using comparative genome approaches. Specific target genes mngB and ompR were obtained and used to detect C. sakazakii and C. malonaticus, respectively. A novel detection method, termed ladder-shape melting temperature isothermal amplification (LMTIA), was developed and evaluated. The detection limit for pure C. sakazakii DNA was 1 pg per reaction and 1 fg per reaction for C. malonaticus. The C. sakazakii, C. malonaticus, and the reference stains were all correctly identified. The amplicons can be successfully visualized and identified by naked eyes when hydroxy naphthol blue dye (HNB dye) was used in the reaction. Therefore, the LMTIA assays developed in this study showed potential application for microorganism identification and detection.

Mechanisms of bacterial immunity, protection, and survival during interbacterial warfare

Most bacteria live in communities, often with closely related strains and species with whom they must compete for space and resources. Consequently, bacteria have acquired or evolved mechanisms to antagonize competitors through the production of antibacterial toxins. Similar to bacterial systems that combat phage infection and mechanisms to thwart antibiotics, bacteria have also acquired and evolved features to protect themselves from antibacterial toxins. Just as there is a large body of research identifying and characterizing antibacterial proteins and toxin delivery systems, studies of bacterial mechanisms to resist and survive assault from competitors' weapons have also expanded tremendously. Emerging data are beginning to reveal protective processes and mechanisms that are as diverse as the toxins themselves. Protection against antibacterial toxins can be acquired by horizontal gene transfer, receptor or target alteration, induction of protective functions, physical barriers, and other diverse processes. Here, we review recent studies in this rapidly expanding field.

Subtractive genomics study for the identification of therapeutic targets against Cronobacter sakazakii: A threat to infants

Cronobacter sakazakii is an opportunistic pathogen that has been associated with severe infection in neonates such as necrotizing enterocolitis (NEC), neonatal meningitis, and bacteremia. This pathogen can survive in a relatively dry environment, especially in powdered infant formula (PIF). Unfortunately, conventional drugs that were once effective against C. sakazakii are gradually losing their efficacy due to rising antibiotic resistance. In this study, a subtractive genomic approach was followed in order to identify potential therapeutic targets in the pathogen. The whole proteome of the pathogen was filtered through a step-by-step process, which involved removing paralogous proteins, human homologs, sequences that are less essential for survival, proteins with shared metabolic pathways, and proteins that are located in cells other than the cytoplasmic membrane. As a result, nine novel drug targets were identified. Further, the analysis also unveiled that the FDA-approved drug Terbinafine can be repurposed against the Glutathione/l-cysteine transport system ATP-binding/permease protein CydC of C. sakazakii. Moreover, molecular docking and dynamics studies of Terbinafine and CydC suggested that this drug can be used to treat C. sakazakii infection in neonates. However, for clinical purposes further in vitro and in vivo studies are necessary.

Group selective aptamers: Broad-spectrum recognition of target groups in Cronobacter species and implementation of electrochemical biosensors as receptors

Aptamers are a versatile class of receptors with a high affinity and selectivity for specific targets. Although their ability to recognize individual targets has been extensively studied, some scenarios require the development of receptors capable of identifying all target groups. This study investigated the use of aptamers to achieve the broad-spectrum recognition of groups instead of individual targets. Aptamers were screened for selectively distinct groups of Cronobacter species associated with foodborne diseases. Seven Cronobacter spp. were divided into Group A (C. sakazakii, C. malonaticus, C. turicensis, and C. muytjensii) and Group B (C. dublinensis, C. condimenti, and C. universalis). Aptamers with exclusive selectivity for each group were identified, allowing binding to the species within their designated group while excluding those from the other group. The screened aptamers demonstrated reliable affinity and specificity with dissociation constants ranging from 1.3 to 399.7 nM for Group A and 4.0-24.5 nM for Group B. These aptamers have also been successfully employed as receptors in an electrochemical biosensor platform, enabling the selective detection of each group based on the corresponding aptamer (limit of detection was 7.8 and 3.2 CFU for Group A and Group B, respectively). The electrochemical sensor effectively detected the extent of infection in each group in powdered infant formula samples. This study highlights the successful screening and application of group-selective aptamers as sensing receptors, emphasizing their potential for diverse applications in different fields such as food safety, environmental monitoring, and clinical diagnostics, where the selective biosensing of target groups is crucial.

Maltodextrin-binding protein as a key factor in Cronobacter sakazakii survival under desiccation stress

Cronobacter sakazakii (C. sakazakii) is a notorious pathogen responsible for infections in infants and newborns, often transmitted through contaminated infant formula. Despite the use of traditional pasteurization methods, which can reduce microbial contamination, there remains a significant risk of pathogenic C. sakazakii surviving due to its exceptional stress tolerance. In our study, we employed a comparative proteomic approach by comparing wild-type strains with gene knockout strains to identify the essential genes crucial for the successful survival of C. sakazakii during desiccation. Our investigation revealed the significance of envZ-ompR, recA, and flhD gene cassettes in contributing to desiccation tolerance in C. sakazakii. Furthermore, through our comparative proteomic profiling, we identified the maltodextrin-binding protein encoded by ESA_03421 as a potential factor influencing dry tolerance. This protein is regulated by EnvZ-OmpR, RecA, and FlhD. Notably, the knockout of ESA_03421 resulted in a 150% greater reduction in Log CFU compared to the wild-type C. sakazakii. Overall, our findings offer valuable insights into the mechanisms underlying C. sakazakii desiccation tolerance and provide potential targets for the development of new antimicrobial strategies aimed at reducing the risk of infections in infants and newborns.

Effect of ferric ions on Cronobacter sakazakii growth, biofilm formation, and swarming motility

Cronobacter sakazakii (C. sakazakii) is a common food-borne pathogen that induces meningitis, sepsis, and necrotizing enterocolitis, primarily in newborns and infants. Iron plays a pivotal role in the growth of cells and biofilm formation. However, the effects of hemin (ferric ion donor) on C. sakazakii cells are scarcely known. Here, we explored the effect of ferric ions on the growth of planktonic C. sakazakii, biofilm formation, and swarming motility by crystal violet staining (CVS), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and swarming assay. Our study demonstrated that ferric ions facilitated the growth of planktonic C. sakazakii, while hemin at concentrations ranging from 50 to 800 μmol/L promoted biofilm formation and at concentrations between 50 and 200 μmol/L enhanced the swarming motility of C. sakazakii. Furthermore, high hemin concentrations (400-800 μmol/L) were found to reduce flagellar length, as confirmed by transmission electron microscopy (TEM). These findings indicated that ferric ions mediated the swarming motility of C. sakazakii by regulating flagellar assembly. Finally, transcriptomic analysis of C. sakazakii was performed at hemin concentrations of 0, 50, and 200 μmol/L, which revealed that several genes associated with iron transport and metabolism, and flagellar assembly were essential for the survival of C. sakazakii under hemin treatment. Our findings revealed the molecular basis of ferric ions on C. sakazakii growth and biofilm formation, thus providing a novel perspective for its prevention and control.

Characterization of Cronobacter sakazakii and Cronobacter malonaticus Strains Isolated from Powdered Dairy Products Intended for Consumption by Adults and Older Adults

The objective of this study was to characterize Cronobacter spp. and related organisms isolated from powder dairy products intended for consumption by adults and older adults using whole-genome sequencing (WGS), and to identify genes and traits that encode antibiotic resistance and virulence. Virulence (VGs) and antibiotic resistance genes (ARGs) were detected with the Comprehensive Antibiotic Resistance Database (CARD) platform, ResFinder, and MOB-suite tools. Susceptibility testing was performed using disk diffusion. Five presumptive strains of Cronobacter spp. were identified by MALDI-TOF MS and ribosomal MLST. Three C. sakazakii strains were of the clinical pathovar ST1, one was ST31, and the remaining isolate was C. malonaticus ST60. In addition, Franconibacter helveticus ST345 was identified. The C. sakazakii ST1 strains were further distinguished using core genome MLST based on 2831 loci. Moreover, 100% of the strains were resistant to cefalotin, 75% to ampicillin, and 50% to amikacin. The C. sakazakii ST1 strains were multiresistant (MDR) to four antibiotics. Additionally, all the strains adhered to the N1E-115 cell line, and two invaded it. Eighteen ARGs mainly involved in antibiotic target alteration and antibiotic efflux were detected. Thirty VGs were detected and clustered as flagellar proteins, outer membrane proteins, chemotaxis, hemolysins, and genes involved in metabolism and stress. The pESA3, pSP291-1, and pCMA1 plasmids were detected, and the prevalent mobile genetic elements (MGEs) were ISEsa1, ISEc52, and IS26. The isolates of C. sakazakii and C. malonaticus exhibited multiresistance to antibiotics, harbored genes encoding various antibiotic resistance proteins, and various virulence factors. Consequently, these contaminated powdered dairy products pose a risk to the health of hypersensitive adults.

Environmental risk factors associated with the survival, persistence, and thermal tolerance of Cronobacter sakazakii during the manufacture of powdered infant formula

Cronobacter sakazakii is an opportunistic foodborne pathogen of concern for foods having low water activity such as powdered infant formula (PIF). Its survival under desiccated stress can be attributed to its ability to adapt effectively to many different environmental stresses. Due to the high risk to neonates and its sporadic outbreaks in PIF, C. sakazakii received great attention among the scientific community, food industry and health care providers. There are many extrinsic and intrinsic factors that affect C. sakazakii survival in low-moisture foods. Moreover, short- or long-term pre-exposure to sub-lethal physiological stresses which are commonly encountered in food processing environments are reported to affect the thermal resistance of C. sakazakii. Additionally, acclimation to these stresses may render C. sakazakii resistance to antibiotics and other antimicrobial agents. This article reviews the factors and the strategies responsible for the survival and persistence of C. sakazakii in PIF. Particularly, studies focused on the influence of various factors on thermal resistance, antibiotic or antimicrobial resistance, virulence potential and stress-associated gene expression are reviewed.

Cronobacter spp. in foods of plant origin: occurrence, contamination routes, and pathogenic potential

Cronobacter is an emerging bacterial pathogen associated with infections such as necrotizing enterocolitis, sepsis, and meningitis in neonates and infants, related to the consumption of powdered infant formula. In addition, this bacterium can also cause infections in adults by the ingestion of other foods. Thus, this review article aims to report the occurrence and prevalence of Cronobacter spp. in foods of plant origin, as well as the possible sources and routes of contamination in these products, and the presence of pathogenic strains in these foods. Cronobacter was present in a wide variety of cereal-based foods, vegetables, herbs, spices, ready-to-eat foods, and foods from other categories. This pathogen was also found in cultivation environments, such as soils, compost, animal feces, rice and vegetable crops, as well as food processing industries, and domestic environments, thus demonstrating possible contamination routes. Furthermore, sequence types (ST) involved in clinical cases and isolates resistant to antibiotics were found in Cronobacter strains isolated from food of plant origin. The identification of Cronobacter spp. in plant-based foods is of great importance to better elucidate the vehicles and routes of contamination in the primary production chain and processing facility, until the final consumption of the food, to prevent infections.

Effects of ESA_00986 Gene on Adhesion/Invasion and Virulence of Cronobacter sakazakii and Its Molecular Mechanism

Cronobacter sakazakii is an opportunistic Gram-negative pathogen that has been identified as a causative agent of severe foodborne infections with a higher risk of mortality in neonates, premature infants, the elderly, and immunocompromised populations. The specific pathogenesis mechanisms of C. sakazakii, such as adhesion and colonization, remain unclear. Previously, we conducted comparative proteomic studies on the two strains with the stronger and weaker infection ability, respectively, and found an interesting protein, ESA_00986, which was more highly expressed in the strain with the stronger ability. This unknown protein, predicted to be a type of invasitin related to invasion, may be a critical factor contributing to its virulence. This study aimed to elucidate the precise roles of the ESA_00986 gene in C. sakazakii by generating gene knockout mutants and complementary strains. The mutant and complementary strains were assessed for their biofilm formation, mobility, cell adhesion and invasion, and virulence in a rat model. Compared with the wild-type strain, the mutant strain exhibited a decrease in motility, whereas the complementary strain showed comparable motility to the wild-type. The biofilm-forming ability of the mutant was weakened, and the mutant also exhibited attenuated adhesion to/invasion of intestinal epithelial cells (HCT-8, HICE-6) and virulence in a rat model. This indicated that ESA_00986 plays a positive role in adhesion/invasion and virulence. This study proves that the ESA_00986 gene encodes a novel virulence factor and advances our understanding of the pathogenic mechanism of C. sakazakii.

Cronobacter Species in the Built Food Production Environment: A Review on Persistence, Pathogenicity, Regulation and Detection Methods

The powdered formula market is large and growing, with sales and manufacturing increasing by 120% between 2012 and 2021. With this growing market, there must come an increasing emphasis on maintaining a high standard of hygiene to ensure a safe product. In particular, Cronobacter species pose a risk to public health through their potential to cause severe illness in susceptible infants who consume contaminated powdered infant formula (PIF). Assessment of this risk is dependent on determining prevalence in PIF-producing factories, which can be challenging to measure with the heterogeneity observed in the design of built process facilities. There is also a potential risk of bacterial growth occurring during rehydration, given the observed persistence of Cronobacter in desiccated conditions. In addition, novel detection methods are emerging to effectively track and monitor Cronobacter species across the food chain. This review will explore the different vehicles that lead to Cronobacter species' environmental persistence in the food production environment, as well as their pathogenicity, detection methods and the regulatory framework surrounding PIF manufacturing that ensures a safe product for the global consumer.

[The pathogenicity of Cronobacter in the light of bacterial genomics]

Cronobacter spp. is a genus of Gram-negative bacteria belonging to the family Enterobacteriaceae. Species of the genus Cronobacter, particularly C. sakazakii, are implicated in the development of severe disease in newborns, which occurs with necrotizing enterocolitis, sepsis and meningitis. The disease has been frequently associated with powdered infant formula (PIF) and can therefore occur in the form of outbreaks. The genus Cronobacter has undergone extensive diversification in the course of its evolution, with some species being clearly pathogenic to humans while the impact of other species on human health is uncertain or unknown. Whole genome sequencing is used both in population genetic studies to identify the limited number of genotypes associated with the disease and to detect genes associated with antibiotic resistance or virulence, ultimately allowing more precise epidemiological links to be established between pediatric disease and infant foods.

Emerging of Multidrug-Resistant Cronobacter sakazakii Isolated from Infant Supplementary Food in China

Cronobacter is a foodborne pathogen associated with severe infections in restricted populations and particularly with high mortality in neonates and infants. The prevalence and antimicrobial resistance (AMR) phenotype of Cronobacter cultured from powdered infant formula and supplementary food were studied. The virulence factors, AMR genes, and genomic environments of the multidrug-resistant isolates were further studied. A total of 1,055 Cronobacter isolates were recovered from 12,105 samples of powdered infant formula and supplementary food collected from 29 provinces between 2018 and 2019 in China. Among these, 1,048 isolates were from infant supplementary food and 7 were from powdered infant formula. Regarding antimicrobial resistance susceptibility, 11 (1.0%) isolates were resistant and two showed resistance to four antimicrobials (ampicillin [AMP], tetracycline [TET], sulfamethoxazole-trimethoprim [SXT], and chloramphenicol [CHL]), defined as MDR. These two MDR isolates were subsequently identified as Cronobacter sakazakii sequence type 4 (ST4) (C. sakazakii Crono-589) and ST40 (C. sakazakii Crono-684). Both MDR isolates contain 11 types of virulence genes and 7 AMR genes on their genomes. Meanwhile, the IncFIB plasmids of both MDR C. sakazakii isolates also harbored 2 types of virulence genes. Results of the genomic comparative analysis indicated that food-associated C. sakazakii could acquire antimicrobial resistance determinants through horizontal gene transfer (HGT). IMPORTANCE As a foodborne pathogen, Cronobacter can cause serious infections in restricted populations and lead to death or chronic sequelae. Although a number of investigations showed that Cronobacter isolates are susceptible to most antimicrobial agents, MDR Cronobacter isolates, isolated mainly from clinical cases but occasionally from foods, have been reported in recent years. In this study, we successfully identified two MDR Cronobacter sakazakii isolates from infant foods based on nationwide surveillance and genome sequencing in China. Genomic analysis revealed that these two MDR C. sakazakii strains acquired resistance genes from other species via different evolution and transmission routes. It is important to monitor MDR C. sakazakii isolates in infant foods, and appropriate control measures should be taken to reduce the contamination with and transmission of this MDR bacterium.

The role of the gut microbiota in health and cardiovascular diseases

The gut microbiota is critical to human health, such as digesting nutrients, forming the intestinal epithelial barrier, regulating immune function, producing vitamins and hormones, and producing metabolites to interact with the host. Meanwhile, increasing evidence indicates that the gut microbiota has a strong correlation with the occurrence, progression and treatment of cardiovascular diseases (CVDs). In patients with CVDs and corresponding risk factors, the composition and ratio of gut microbiota have significant differences compared with their healthy counterparts. Therefore, gut microbiota dysbiosis, gut microbiota-generated metabolites, and the related signaling pathway may serve as explanations for some of the mechanisms about the occurrence and development of CVDs. Several studies have also demonstrated that many traditional and latest therapeutic treatments of CVDs are associated with the gut microbiota and its generated metabolites and related signaling pathways. Given that information, we summarized the latest advances in the current research regarding the effect of gut microbiota on health, the main cardiovascular risk factors, and CVDs, highlighted the roles and mechanisms of several metabolites, and introduced corresponding promising treatments for CVDs regarding the gut microbiota. Therefore, this review mainly focuses on exploring the role of gut microbiota related metabolites and their therapeutic potential in CVDs, which may eventually provide better solutions in the development of therapeutic treatment as well as the prevention of CVDs.

Clustered regularly interspaced short palindromic repeats-Cas system: diversity and regulation in Enterobacteriaceae

Insights into the arms race between bacteria and invading mobile genetic elements have revealed the intricacies of the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system and the counter-defenses of bacteriophages. Incredible spacer diversity but significant spacer conservation among species/subspecies dictates the specificity of the CRISPR-Cas system. Researchers have exploited this feature to type/subtype the bacterial strains, devise targeted antimicrobials and regulate gene expression. This review focuses on the nuances of the CRISPR-Cas systems in Enterobacteriaceae that predominantly harbor type I-E and I-F CRISPR systems. We discuss the systems' regulation by the global regulators, H-NS, LeuO, LRP, cAMP receptor protein and other regulators in response to environmental stress. We further discuss the regulation of noncanonical functions like DNA repair pathways, biofilm formation, quorum sensing and virulence by the CRISPR-Cas system. The review comprehends multiple facets of the CRISPR-Cas system in Enterobacteriaceae including its diverse attributes, association with genetic features, regulation and gene regulatory mechanisms.

Virulence, antimicrobial susceptibility, and phylogenetic analysis of Cronobacter sakazakii isolates of food origins from Jordan

AIMS

to characterize a collection of Cronobacter sakazakii isolates collected from various origins in Jordan.

METHODS AND RESULTS

the isolates were characterized using 16S rRNA sequencing, DNA microarray, multi-locus sequence typing (MLST), O-serotyping, virulence gene identification, and antibiotic susceptibility testing. The identities and phylogenetic relatedness revealed that C. sakazakii sequence type 4 (ST4) and Csak O:1 serotype was the most prevalent STs and serovars among these C. sakazakii strains. PCR screening of putative virulence genes showed that the siderophore-interacting protein gene (sip) and iron acquisition gene clusters (eitCBAD and iucABCD/iutA) were the most detected genes with noticeable variability in the type 6 secretion system (T6SS) and filamentous hemagglutinin/adhesion (FHA) gene loci. The antibiotic resistance profiles revealed that the majority of the isolates were susceptible to all antibiotics used despite harboring a class C β-lactamase resistance gene.

CONCLUSIONS

the results described in this report provide additional insights about the considerable genotypic and phenotypic heterogeneity within C. sakazakii.

SIGNIFICANCE AND IMPACT OF THE STUDY

the information reported in this study might be of great value in understanding the origins of C. sakazakii isolates, in addition to their diversity and variability, which might be helpful in preventing future outbreaks of this pathogen.

Insights into the mechanisms of Cronobacter sakazakii virulence

Cronobacter species have adapted to survive harsh conditions, particularly in the food manufacture environment, and can cause life-threatening infections in susceptible hosts. These opportunistic pathogens employ a multitude of mechanisms to aid their virulence throughout three key stages: environmental persistence, infection strategy, and systemic persistence in the human host. Environmental persistence is aided by the formation of biofilms, development of subpopulations, and high tolerance to environmental stressors. Successful infection in the human host involves several mechanisms such as protein secretion, motility, quorum sensing, colonisation, and translocation. Survival inside the host is achieved via competitive acquisition and utilization of minerals and metabolites respectively, coupled with host immune system evasion and antimicrobial resistance (AMR) mechanisms. Across the globe, Cronobacter sakazakii is associated with often fatal systemic infections in populations including neonates, infants, the elderly and the immunocompromised. By providing insight into the mechanisms of virulence utilised by this pathogen across these three stages, this review identifies current gaps in the literature. Further research into these virulence mechanisms is required to inform novel mitigation measures to improve global food safety with regards to this food-borne pathogen.

Prevalence, characterization, and antibiotic susceptibility of Cronobacter spp. in a milk powder processing environment: The first reported case in Serbia

Cronobacter spp. are opportunistic foodborne pathogens that most often infect neonates and infants through contaminated powdered infant formula. No reports have been published in Serbia on the prevalence of Cronobacter spp. in powdered milk production environments. Consequently, this study aimed to determine the prevalence, molecular characterization, antimicrobial susceptibility, and biofilm-forming ability of Cronobacter spp. isolated from a milk powder plant. Hundred samples were collected from the production facility. Fifteen Cronobacter sakazakii strains were isolated and identified, giving a contamination rate of 15%. Using multi-locus sequence typing, the isolates were divided into five sequence types (STs). Cronobacter sakazakii ST4 (50%), ST1 (16.67%), and ST83 (16.67%) were the dominant STs isolated. A novel sequence type (ST759) was identified and registered in the Cronobacter MLST database. The results of the antibiotic susceptibility testing indicated that C. sakazakii strains were susceptible to piperacillin/tazobactam, ampicillin/sulbactam, and amoxicillin/clavulanate, especially to meropenem and cefotaxime. Most of the ST4 showed moderate-to-strong biofilm-forming ability. The presence of clinically relevant isolates (ST4, ST1, ST83, and ST8) revealed that the production plant is likely a potential concern for public health. Finally, finding new sequence types like the one detected in this study (ST759) underlines evolving genetic changes in C. sakazakii.

Processing environment monitoring in low moisture food production facilities: Are we looking for the right microorganisms?

Processing environment monitoring is gaining increasing importance in the context of food safety management plans/HACCP programs, since past outbreaks have shown the relevance of the environment as contamination pathway, therefore requiring to ensure the safety of products. However, there are still many open questions and a lack of clarity on how to set up a meaningful program, which would provide early warnings of potential product contamination. Therefore, the current paper aims to summarize and evaluate existing scientific information on outbreaks, relevant pathogens in low moisture foods, and knowledge on indicators, including their contribution to a "clean" environment capable of limiting the spread of pathogens in dry production environments. This paper also outlines the essential elements of a processing environment monitoring program thereby supporting the design and implementation of better programs focusing on the relevant microorganisms. This guidance document is intended to help industry and regulators focus and set up targeted processing environment monitoring programs depending on their purpose, and therefore provide the essential elements needed to improve food safety.

The role of PhoP/PhoQ two component system in regulating stress adaptation in Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic foodborne bacterial pathogen that shows resistance to multiple stress conditions. The PhoP/PhoQ two component system is a key regulatory mechanism of stress response and virulence in various bacteria, but its role in C. sakazakii has not been thoroughly studied. In this study, we found the PhoP/PhoQ system in C. sakazakii ATCC BAA-894 enhanced bacterial growth in conditions with low Mg²⁺, acid pH, and the presence of polymyxin B. Moreover, the ΔphoPQ strain significantly reduced survival following exposure to heat, high osmotic pressure, oxidative or bile salts compared with WT strain. Furthermore, the RNA-seq analysis indicated that 1029 genes were upregulated and 979 genes were downregulated in ΔphoPQ strain. The bacterial secretion system, flagella assembly, beta-Lactam resistance and two-component system pathways were significantly downregulated, while the ABC transporters and microbial metabolism in diverse environments pathways were upregulated. qRT-PCR analysis further confirmed that twelve genes associated with stress tolerance were positively regulated by the PhoP/PhoQ system. Therefore, these findings suggest that the PhoP/PhoQ system is an important regulatory mechanism for C. sakazakii to resist various environmental stress.

Antibiotic administration exacerbates acute graft vs. host disease-induced bone marrow and spleen damage in lymphopenic mice

Background

Hematopoietic stem cell transplantation is a potential cure for certain life-threatening malignant and nonmalignant diseases. However, experimental and clinical studies have demonstrated that pre-transplant myeloablative conditioning damages the gut leading to translocation of intestinal bacteria and the development of acute graft vs. host disease (aGVHD). The overall objective of this study was to determine whether administration of broad spectrum antibiotics (Abx) affects the onset and/or severity of aGVHD in lymphopenic mice that were not subjected to toxic, pre-transplant conditioning.

Results

We found that treatment of NK cell-depleted recombination activating gene-1-deficient (-NK/RAG) recipients with an Abx cocktail containing vancomycin and neomycin for 7 days prior to and 4 weeks following adoptive transfer of allogeneic CD4⁺ T cells, exacerbated the development of aGVHD-induced BM failure and spleen damage when compared to untreated–NK/RAG recipients engrafted with syngeneic or allogeneic T cells. Abx-treated mice exhibited severe anemia and monocytopenia as well as marked reductions in BM- and spleen-residing immune cells. Blinded histopathological analysis confirmed that Abx-treated mice engrafted with allogeneic T cells suffered significantly more damage to the BM and spleen than did untreated mice engrafted with allogeneic T cells. Abx-induced exacerbation of BM and spleen damage correlated with a dramatic reduction in fecal bacterial diversity, marked loss of anaerobic bacteria and remarkable expansion of potentially pathogenic bacteria.

Conclusions

We conclude that continuous Abx treatment may aggravate aGVHD-induced tissue damage by reducing short chain fatty acid-producing anaerobes (e.g. Clostridium, Blautia) and/or by promoting the expansion of pathobionts (e.g. Akkermansia) and opportunistic pathogens (Cronobacter).

Genomic Landscape and Phenotypic Assessment of Cronobacter sakazakii Isolated From Raw Material, Environment, and Production Facilities in Powdered Infant Formula Factories in China

Cronobacter is a foodborne pathogen associated with severe infections and high mortality in neonates. The bacterium may also cause gastroenteritis, septicemia, and urinary tract and wound infectious in adults. A total of 15 Cronobacter isolates collected from 617 raw materials and environment samples from Powdered Infant Formula manufacturing factories during 2016 in Shaanxi, China, were analyzed for antimicrobial susceptibilities, species identification, biofilm formation, and whole-genome sequencing. The results showed that all 15 isolates were Cronobacter sakazakii, while the antimicrobial susceptibility test showed that all 15 C. sakazakii were pan susceptible. Most isolates were able to produce a weak biofilm, and two isolates from soil samples produced a strong biofilm formation. All isolates were classified into seven STs including ST4, ST40, ST64, ST93, ST148, ST256, and ST494, with ST64 (4/15, 26.7%) being dominant, and most were clinically related. The isolates harbored at least 11 virulence genes and two plasmids, with one isolate being positive for all virulence genes. Phylogenetic and ANI analysis showed strong clustering by sequence types and isolates from different sources or regions with a similar genomic background. The fact that isolates were obtained from raw materials and environment samples of PIF facilities shared a close phylogeny with one another suggests that cross-contamination events may have occurred between the processing room and external environments, which may give rise to a recurring risk of a continuous contamination during production.

Occurrence, Virulence and Antimicrobial Susceptibility Profiles of Cronobacter spp. from Ready-to-Eat Foods

Cronobacter spp. can cause foodborne diseases in infants, but Cronobacter infections in healthy adults and vulnerable people have also been reported. These bacteria have ubiquitous nature and can contaminate various foods. Therefore, we assessed the presence of Cronobacter spp. in popularly consumed ready-to-eat (RTE) food products. In the present study, 51 (15%) of the 340 RTE food samples were contaminated with Cronobacter spp The highest contamination rates were found in spices (46.7%), meat-free cig koftes (44.4%), desserts (23.3%), cereals (23.1%), doners (12.2%), and ice cream (11.1%). Phenotypic and molecular methods, including 16S rRNA, gluA, rpoB, cgcA genes, and fusA allele sequencing were tested to identify Cronobacter species. Of the 51 contaminated samples, 54 isolates were identified as C. sakazakii (n = 43), C. malonaticus (n = 7), C. muytjensii (n = 3) and C. turicensis (n = 1) using fusA analysis. These isolates were assigned to 15 different fusA alleles, two of which (191 and 192) were new alleles. Putative virulence factors such as the ompA and zpx gene, biofilms, and siderophores were detected in most of the Cronobacter isolates (> 85%). Cronobacter isolates were resistant to cephalothin (85.2%), cefoxitin (33.3%), cefotaxime (14.8%), ampicillin (11.1%), cefepime (5.6%), aztreonam (5.6%), and piperacillin (1.9%). The multidrug resistance (against three or more classes of antimicrobial agents) was 7.4%. The results indicated presence of Cronobacter spp. in RTE foods, which may be a risk to human health. It is important to adopt rigorous hygiene and sanitization practices to ensure the microbiological safety of these foods consuming without any processing.

Food Safety and Invasive Cronobacter Infections during Early Infancy, 1961-2018

Contaminated powdered infant formula from opened containers is the most commonly identified transmission vehicle.

Invasive Cronobacter infections among infants are associated with severe neurologic disabilities and death. Early Cronobacter reports typically featured hospitalized and preterm infants and recognized contaminated powdered infant formula (PIF) as a transmission vehicle. To clarify recent epidemiology, we reviewed all cases of bloodstream infection or meningitis among infants that were reported to the Centers for Disease Control and Prevention and in the literature (1961–2018; n = 183). Most infants were neonates (100/150 [67%]); 38% (42/112) died, and 79% (81/102) had reported recent PIF consumption. In the final quarter of the study period (2004–2018), case counts were significantly higher (global average 8.7 cases/year); among US cases, significantly higher proportions occurred among full-term (56% [27/48]) and nonhospitalized (78% [42/54]) infants. PIF contamination, most commonly from opened containers, was identified in 30% (21/71) of investigations. Our findings reaffirm the need to promote safer alternatives for infant feeding, particularly among neonates.

Multivariate analysis of adaptive response to ferulic acid and p-coumaric acid after physiological stresses in Cronobacter sakazakii

AIM

The present study demonstrated the antimicrobial activity of ferulic acid and p-coumaric acid against unstressed and stressed (cold stressed, starved and desiccated) Cronobacter sakazakii in laboratory media (37°C) and reconstituted powdered infant formulation (PIF) with mild heat treatment (50°C).

METHODS AND RESULTS

Five phenolics, namely, quercetin, rutin, caffeic acid, ferulic acid and p-coumaric acid, were tested for antimicrobial activities against five strains of C. sakazakii either unstressed or stressed. Strain specific higher resistance to ferulic acid and p-coumaric acid was observed after stress adaptation in laboratory media. The effect of cross protection was validated using reconstituted PIF as delivery vehicle of selected compounds. Both p-coumaric acid and ferulic acid showed inhibition of C. sakazakii in a dose and time dependent manner as revealed by their viable cell counts. Principal component analysis revealed that the desiccated cells were more sensitive to phenolics in reconstituted PIF.

CONCLUSIONS

Only ferulic acid and p-coumaric acid showed marked antibacterial activity with minimum inhibitory concentration in the range of 2·5-5 mg ml^-1 for unstressed C. sakazakii cells in tryptone soy broth. The maximum inhibition was achieved with 20 mg ml^-1 of both the tested polyphenols in reconstituted PIF. Cold stress and starvation stress did not impart any protection nor increased the susceptibility of C. sakazakii, whereas desiccation resulted in increased susceptibility to phenolic compounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained in this study helps in understanding the effect of environmental stresses during processing on susceptibility of C. sakazakii to natural antimicrobial agents. Future transcriptomic studies and functional genetic studies are warranted to understand the strain specific stress responses for the development of better control methods possibly by using these natural antagonists.

The Changing Face of the Family Enterobacteriaceae (Order: "Enterobacterales"): New Members, Taxonomic Issues, Geographic Expansion, and New Diseases and Disease Syndromes

The family Enterobacteriaceae has undergone significant morphogenetic changes in its more than 85-year history, particularly during the past 2 decades (2000 to 2020). The development and introduction of new and novel molecular methods coupled with innovative laboratory techniques have led to many advances. We now know that the global range of enterobacteria is much more expansive than previously recognized, as they play important roles in the environment in vegetative processes and through widespread environmental distribution through insect vectors. In humans, many new species have been described, some associated with specific disease processes. Some established species are now observed in new infectious disease settings and syndromes. The results of molecular taxonomic and phylogenetics studies suggest that the current family Enterobacteriaceae should possibly be divided into seven or more separate families. The logarithmic explosion in the number of enterobacterial species described brings into question the relevancy, need, and mechanisms to potentially identify these taxa. This review covers the progression, transformation, and morphogenesis of the family from the seminal Centers for Disease Control and Prevention publication (J. J. Farmer III, B. R. Davis, F. W. Hickman-Brenner, A. McWhorter, et al., J Clin Microbiol 21:46-76, 1985, https://doi.org/10.1128/JCM.21.1.46-76.1985) to the present.

Current and Future Perspectives on the Role of Probiotics, Prebiotics, and Synbiotics in Controlling Pathogenic Cronobacter Spp. in Infants

Cronobacter species, in particular C. sakazakii, is an opportunistic bacterial pathogen implicated in the development of potentially debilitating illnesses in infants (<12months old). The combination of a poorly developed immune system and gut microbiota put infants at a higher risk of infection compared to other age groups. Probiotics and prebiotics are incorporated in powdered infant formula and, in addition to strengthening gut physiology and stimulating the growth of commensal gut microbiota, have proven antimicrobial capabilities. Postbiotics in the cell-free supernatant of a microbial culture are derived from probiotics and can also exert health benefits. Synbiotics, a mixture of probiotics and prebiotics, may provide further advantages as probiotics and gut commensals degrade prebiotics into short-chain fatty acids that can provide benefits to the host. Cell-culture and animal models have been widely used to study foodborne pathogens, but sophisticated gut models have been recently developed to better mimic the gut conditions, thus giving a more accurate representation of how various treatments can affect the survival and pathogenicity of foodborne pathogens. This review aims to summarize the current understanding on the connection between Cronobacter infections and infants, as well as highlight the potential efficacy of probiotics, prebiotics, and synbiotics in reducing invasive Cronobacter infections during early infancy.

Prevalence of Cronobacter spp. and Salmonella in Milk Powder Manufacturing Facilities in the United States

ABSTRACT

The U.S. Food and Drug Administration (FDA) conducted a sampling assignment in 2014 to ascertain the prevalence of Cronobacter spp. and Salmonella in the processing environment of facilities manufacturing milk powder. Cronobacter was detected in the environment of 38 (69%) of 55 facilities. The average prevalence of Cronobacter in 5,671 subsamples (i.e., swabs and sponges from different facility locations) was 4.4%. In the 38 facilities where Cronobacter was detected, the average prevalence of positive environmental subsamples was 6.25%. In 20 facilities where zone information of the sampling location was complete, Cronobacter was most frequently detected in zone 4, followed by zone 3, then zone 2, with zone 1 yielding the lowest percentage of positive samples. The prevalence of Cronobacter across the zones was statistically different (P < 0.05). There was no significant association between product type (i.e., lactose, whey products, buttermilk powder, and nonfat dried milk) and prevalence of Cronobacter in the facility. Salmonella was detected in the environment of three (5.5%) of the 55 facilities; all three facilities produced dried whey product. The overall prevalence of Salmonella in 5,714 subsamples was 0.16%. In facilities in which Salmonella was detected, the average prevalence was 2.5%. Salmonella was most frequently detected in zone 4, followed by zone 3. Salmonella was not detected in zone 1 or zone 2. The disparity between Salmonella and Cronobacter prevalence indicates that additional measures may be required to reduce or eliminate Cronobacter from the processing environment.

HIGHLIGHTS

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.

Isolation, comparison of identification methods and antibiotic resistance of Cronobacter spp. in infant foods

Cronobacter spp. are opportunistic pathogens that cause serious infections, especially in infants, elderly, and immunocompromised people. Dehydrated infant foods are the main vehicle associated with infections caused by these bacteria. Thus, this study aims to investigate the occurrence of Cronobacter spp. in 152 commercial samples of dehydrated infant formulas (77 samples) and dehydrated infant cereals (75 samples), as well as characterize the isolates. Polymerase Chain Reaction (PCR) and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF/MS) methods for isolate identification were used, and their results compared. Furthermore, the susceptibility to 11 antibiotics was tested, and DNA sequencing of one isolate with multi-drug resistance was analyzed. No contamination in the infant formula samples was found, whereas 17.33% (13/75) of the infant cereal samples presented contamination with Cronobacter sakazakii. The identification results by PCR and MALDI-TOF/MS were divergent for some isolates. The antimicrobial resistance results showed a high incidence of resistance to cefazolin (94.4%) besides resistance to amoxicillin (9.45%), cefpodoxime (5.55%), streptomycin (1.35%), and trimethoprim/sulfamethoxazole (1.35%). Whole genome sequencing of one multi-drug resistant isolate showed six genes associated with antimicrobial resistance and an 82% possibility of being a human pathogen based on the presence of virulence factors. The presence of Cronobacter spp. in infant foods represents a risk for the infant's health. Moreover, the presence of a pathogenic multi-drug resistant isolate in infant's food reinforces the necessity of improving food safety policies to protect young children.

Labchip-based diagnosis system for on-site application: Sensitive and easy-to-implement detection of single recoverable Cronobacter in infant formula without post-enrichment treatment

Microfluidic labchips have achieved much advancement in the molecular diagnosis of foodborne pathogens. Whereas difficulties in the flow control during the transportation of liquid fluids can occur and should be overcome. Manipulations of reaction temperature and the complex procedures from sample pre-treatment to analysis in a single chip device are major obstacles for the on-site application. Thus, the efficient temperature control of samples without any flow of reaction fluids in microfluidic channels of plastic chip and the simplest protocol omitting post-enrichment processing steps may overcome these limitations represented by the stability and the complexity, respectively. This study aims to develop a novel type of labchip and thermocycler specialized for the gene amplification in microfluidic channels and to evaluate the detectability by sensing the minimum recoverable level of Cronobacter in powdered infant formula (PIF). We developed a thermocycling device accelerating reactions through dual heating-blocks optimized to control temperatures of samples in microfluidic-channels by direct contact with labchip sequentially and repetitively. The structural design of microfluidic channels was to eliminate interference factors associated with the optical detection of fluorescent signals (without distortion due to air bubbles in the reaction chamber). To improve the applicability, a portable device and simplified operation to allow direct loading of samples in the chip without post-enrichment procedures were also adopted. Detection performance was evaluated by a sensitivity/specificity tests using 50 isolates of Cronobacter. Cross-reactivity tests for non-Cronobacter organisms and gDNA [human, raw materials of PIF (cow, soybean)] showed that there was no interference-factor causing false-positive results. In terms of the applied research conducted by using PIF, the enrichment of samples without broth medium (distilled water) displayed outstanding performance and 12 h of incubation facilitated detecting target at concentration as low as 1 CFU/300 g PIF (as initial contamination level) without post-enrichment treatment. Validation of the operation conditions using 30 commercial PIF products was also consistent. The present study presents a novel approach of microfluidic technology with perspective to not only the performance and the practicability [easy-to-implement protocol, portable materials, cost-effectiveness (the use of a miniaturized plastic chip requires a minimum level of materials)] for on-site diagnosis.

The Characterization of Two-Component System PmrA/PmrB in Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic Gram-negative pathogen that could cause meningitis and necrotizing enterocolitis. Several Gram-negative bacteria use the PmrA/PmrB system to sense and adapt to environmental change by resistance to cationic antimicrobial peptides of host immune systems. The PmrA/PmrB two-component system regulates several genes to modify LPS structure in the bacterial outer membrane. The role of PmrA/PmrB of C. sakazakii has been studied within the current study. The results suggest that PmrA/PmrB plays a crucial role in modifying LPS structure, cationic antimicrobial peptide susceptibility, cell membrane permeability and hydrophobicity, and invading macrophage.

The Secretion of Toxins and Other Exoproteins of Cronobacter: Role in Virulence, Adaption, and Persistence

: Cronobacter species are considered an opportunistic group of foodborne pathogenic bacteria capable of causing both intestinal and systemic human disease. This review describes common virulence themes shared among the seven Cronobacter species and describes multiple exoproteins secreted by Cronobacter, many of which are bacterial toxins that may play a role in human disease. The review will particularly concentrate on the virulence factors secreted by C. sakazakii, C. malonaticus, and C. turicensis, which are the primary human pathogens of interest. It has been discovered that various species-specific virulence factors adversely affect a wide range of eukaryotic cell processes including protein synthesis, cell division, and ion secretion. Many of these factors are toxins which have been shown to also modulate the host immune response. These factors are encoded on a variety of mobile genetic elements such as plasmids and transposons; this genomic plasticity implies ongoing re-assortment of virulence factor genes which has complicated our efforts to categorize Cronobacter into sharply defined genomic pathotypes.

Global transcriptomic analysis of Cronobacter sakazakii CICC 21544 by RNA-seq under inorganic acid and organic acid stresses

Cronobacter sakazakii is a common foodborne pathogen that can tolerate various stress conditions. Acidic environment is a common stress condition encountered by bacteria in food processing and gastrointestinal digestion, including both inorganic and organic acids. In order to elucidate the Acid Tolerance Response (ATR) of C. sakazakii, we performed high-throughput RNA-seq to compare gene expression under hydrochloric acid and citric acid stresses. In this study, 107 differentially expressed genes (DEGs) were identified in both acids, of which 85 DEGs were functionally related to the regulation of acid tolerance. Multiple layers of mechanisms may be applied by C. sakazakii in response to acid stress: Firstly, in order to reduce excessive intracellular protons, C. sakazakii pumps them out through trans-membrane proteins or consumes them through metabolic reactions. Secondly, under acidic conditions, a large amount of reactive oxygen species and hydroxyl radicals accumulate in the cells, resulting in oxidative damage. C. sakazakii protects cells by up-regulating the antioxidant stress genes such as soxS and madB. Thirdly, C. sakazakii chooses energy efficient metabolic pathways to reduce energy consumption and maintain necessary processes. Finally, genes involved in chemotaxis and motility were differentially expressed to respond to different acidic conditions. This study systematically analyzed the acid-resistant mechanism of C. sakazakii under the stress of organic and inorganic acids, and provided a theoretical basis for better control of its contamination in food.

Antibiotic resistance, putative virulence factors and curli fimbrination among Cronobacter species

This study aimed to investigate antibiotic resistance and putative virulence factors among Cronobacter sakazakii isolated from powdered infant formula and other sources. The following 9 cultures (CR1-9) were collected from our culture collection: C. sakazakii and 3 Cronobacter species: C. sakazakii ATCC® 29544™, C. muytjensii ATCC® 51329™, C. turicensis E866 were used in this study. Isolates were subjected to antibiotic susceptibility and the following virulence factors (protease, DNase, haemolysin, gelatinase, motility and biofilm formation) using phenotypic methods. All the bacteria were able to form biofilm on agar at 37 °C and were resistant to ampicillin, erythromycin, fosfomycin and sulphamethoxazole. It was observed from this study that tested strains formed weak and strong biofilm with violet dry and rough (rdar), brown dry and rough (bdar), red mucoid and smooth (rmas) colony morphotypes on Congo red agar. Rdar expresses curli and fimbriae, while bdar expresses curli. Both biofilm colony morphotypes are commonly found in Enterobacteriaceae including Salmonella species. This study also reveals a new colony morphotypes in Cronobacter species. Conclusively, there was correlation between putative virulence factors and antibiotic resistance among the tested bacteria. Further study on virulence and antibiotic resistance genes is hereby encouraged.

Cronobacter spp. in Common Breast Milk Substitutes, Bogotá, Colombia

In Bogotá, Colombia, a large number of babies are fed with breast milk substitutes made from corn and plantain starch. We found 34.3% of tested samples to be contaminated with Cronobacter spp.; C. sakazakii was the most recovered species. Our findings underscore the risk for contamination of breast milk substitutes.

Occurrence of virulence factors in Cronobacter sakazakii and Cronobacter malonaticus originated from clinical samples

BACKGROUND

Cronobacter spp. are Gram-negative, facultative-anaerobic, non-spore forming, enteric coliform bacteria, which belongs to the Enterobacteriaceae family. Cronobacter spp. are opportunistic pathogens that have brought rare but life-threatening infections such as meningitis, necrotizing enterocolitis and bloodstream infections in neonates and infants. Information on the diversity, pathogenicity and virulence of Cronobacter species obtained from various sources is still relatively scarce and fragmentary. The aim of this study was to examine and analyse different pathogenicity and virulence factors among C. sakazakii and C. malonaticus strains isolated from clinical samples.

METHODS

The thirty-six clinical Cronobacter strains have been used in this study. This bacterial collection consists of 25 strains of C. sakazakii and 11 strains of C. malonaticus, isolated from different clinical materials. Seven genes (ompA, inv, sip, aut, hly, fliC, cpa) were amplified by PCR. Moreover, the motility and the ability of these strains to adhere and invade human colorectal adenocarcinoma (HT-29) and mouse neuroblastoma (N1E-115) cell lines were investigated.

RESULTS

Our results showed that all tested strains were able to adhere to both used cell lines, HT-29 and N1E-115 cells. The invasion assay showed that 66.7% (24/36) of isolates were able to invade N1-E115 cells while 83% (30/36) of isolates were able to invade HT-29 cells. On the average, 68% of the C. sakazakii strains exhibited seven virulence factors and only 18% in C. malonaticus. All strains amplified ompA and fliC genes. The other genes were detected as follow: sip 97% (35/36), hlyA 92% (33/36), aut 94% (34/36), cpa 67% (24/36), and inv 69% (25/36).

CONCLUSIONS

C. sakazakii and C malonaticus strains demonstrate the diversity of the virulence factors present among these pathogens. It is necessary to permanently monitor the hospital environment to appropriately treat and resolve cases associated with disease. Furthermore, in-depth knowledge is needed about the source and transmission vehicles of pathogens in hospitals to adopt pertinent prevention measures.

Occurrence of Cronobacter Spp. in Ready-to-Eat Vegetable Products, Frozen Vegetables, and Sprouts Examined Using Cultivation and Real-Time PCR Methods

Environmental matrices and food products are hypothesized to be sources of Cronobacter spp. The severity of neonatal infections, increasing number of cases in elderly and immunocompromised individuals, as well as isolation of Cronobacter spp. from clinical materials demands that more attention should be paid to Cronobacter spp. detection and occurrence of the bacteria in food products. Here, a total of 175 samples of ready-to-eat vegetables, frozen vegetables, and sprouted seeds were collected during a period of 1 year and examined for the presence of Cronobacter spp. using a cultivation method with two different sample preparations and real-time polymerase chain reaction (qPCR). In total, Cronobacter spp. were detected in 22.3% of tested samples using cultivation. In comparison, direct qPCR detected Cronobacter spp. in 37.7% of these samples (p < 0.01; Fisher's exact test) and the numbers of genome equivalents per gram reached 10⁸ in some samples of sprouts. Cronobacter spp. were isolated from 51.4%, 37.2%, and 5.2% samples of sprouts, frozen vegetables, and cut green leaves/salads, respectively. Using qPCR, the most frequently contaminated sample types were sprouts (91.4%) and frozen vegetables (60.5%), whereas the rate of positivity for cut green leaves/salads was, in comparison, only 8.2% (p < 0.01; χ² -test for independence). PRACTICAL APPLICATION: This study provided valuable information on the occurrence of Cronobacter spp. in ready-to-eat vegetables using cultivation and qPCR. Cronobacter spp. are emerging opportunistic pathogens that can be present in food of plant origin. Cronobacter spp. were isolated from sprouts, frozen vegetables, and cut green leaves/salads, and the numbers of genome equivalents per gram reached 10⁸ in some samples of sprouts.

Evaluation of Bacterial Contamination in Goat Milk Powder Using PacBio Single Molecule Real-Time Sequencing and Droplet Digital PCR

Goat milk powder is a nutritious and easy-to-store product that is highly favored by consumers. However, the presence of contaminating bacteria and their metabolites may significantly affect the flavor, solubility, shelf life, and safety of the product. To comprehensively and accurately understand the sanitary conditions in the goat milk powder production process and potential threats from bacterial contamination, a combination of Pacific Biosciences single molecule real-time sequencing and droplet digital PCR was used to evaluate bacterial contamination in seven goat milk powder samples from three dairies. Ten phyla, 119 genera, and 249 bacterial species were identified. Bacillus, Paenibacillus, Lactococcus, and Cronobacter were the primary genera. Bacillus cereus, Lactococcus lactis, Alkaliphilus oremlandii, and Cronobacter sakazakii were the dominant species. With droplet digital PCR, 6.3 × 10⁴ copies per g of Bacillus cereus and 1.0 × 10⁴ copies per g of Cronobacter spp. were quantified, which may increase the risk of food spoilage and the probability of foodborne illness and should be monitored and controlled. This study offers a new approach for evaluating bacterial contamination in goat milk powder and supplies a reference for the assessment of food safety and control of potential risk, which will be of interest to the dairy industry.