Invasive Enterobacter sakazakii disease in infants

Multiplex Determination of K-Antigen and Colanic Acid Capsule Variants of Cronobacter sakazakii

Cronobacter sakazakii is associated with the ingestion of contaminated reconstituted powdered infant formula (PIF), resulting in necrotizing enterocolitis, sepsis and meningitis in neonatal infants. Potential virulence determinants include the variable capsular polysaccharides; K-antigen and colanic acid (CA). Strains encoding for the capsule variant K2:CA2 have been strongly associated with neonatal meningitis cases. This study aimed to develop and apply a multiplex PCR assay to determine C. sakazakii K-antigen and colanic acid types. Twenty-six strains of C. sakazakii which had previously been isolated from food and environmental sources were used. These cover 18 multilocus sequence types and four serotypes. Based on our research findings, we have identified two K-antigen types present. Specifically, the K1-antigen was observed in sequence types ST1, ST8, ST20, ST23, ST64, ST198, ST263, ST264 and ST406, while the K2-antigen was present in ST4, ST9, ST12, ST13, ST136, ST233, ST245 and ST405. Additionally, we detected colanic acid (CA) type 1 in sequence types ST1, ST8, ST9, ST20, ST245 and ST405, and colanic acid (CA) type 2 in ST4, ST12, ST13, ST23, and ST64. We compared the predicted K-antigen and colanic acid types with the entire genome sequences of the strains. The comparison showed complete agreement between the PCR amplification results and the genomic analysis of the K-antigen and colanic acid-encoding regions. This assay is a useful tool for rapid identification of C. sakazakii, K-antigen and colanic acid types, in routine diagnoses and foodborne investigations. In addition, it will contribute to our knowledge of virulence factors associated with life-threatening neonatal meningitis.

Effect of Bacterial Endophytes Isolated from Tropical Fruits against Listeria monocytogenes and Cronobacter sakazakii in Model Food Products

Listeria monocytogenes and Cronobacter sakazakii are two important foodborne bacterial pathogens. Bacterial endophytes, which reside in plant cells, can produce antimicrobial compounds to protect the host organism or inhibit pathogens. This study investigated the bacterial community of tropical fruits for their potential to inactivate L. monocytogenes or C. sakazakii in cantaloupe and liquid infant formula, respectively. Tropical fruits including papayas, dragon fruits, and sugar apples, were sourced from several countries. Candidate bacterial endophytes were recovered from these tropical fruits using blood agar and Reasoner's 2A (R2A) agar and tested for potential inhibition against L. monocytogenes and C. sakazakii. A total of 196 bacterial endophytes were recovered from papayas, dragon fruits, and sugar apples. Among these bacterial endophytes, 33 (16.8%) and 13 (6.6%) of them demonstrated an inhibition zone against L. monocytogenes and C. sakazakii, respectively. The inhibitory strains were identified using 16S rRNA sequencing as Bacillus spp., Enterobacter spp., Klebsiella spp., Microbacterium spp., Pantoea spp., and Pseudomonas spp. A cocktail of Pantoea spp. and Enterobacter spp. was used in challenge studies with cantaloupe and significantly reduced the number of L. monocytogenes by approximately 2.5 log10 CFU/g. In addition, P. stewartii demonstrated antagonistic activity against C. sakazakii in liquid infant formula, i.e., it significantly decreased the number of C. sakazakii by at least 1 log10 CFU/mL. Thus, the use of bacterial endophytes recovered from fruits and vegetables could be a promising area of research. Their use as potential biocontrol agents to control bacterial pathogens in ready-to-eat foods warrants further investigation.

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.

Integrating Recombinase Polymerase Amplification and Photosensitization Colorimetric Detection in One Tube for Fast Screening of C. sakazakii in Formula Milk Powder

Cronobacter sakazakii (C. sakazakii) is a widely existing opportunistic pathogen and thus threatens people with low immunity, especially infants. To prevent the outbreak, a rapid and accurate on-site testing method is required. The current standard culture-based method is time-consuming (3-4 days), while the nucleic acid amplification (PCR)-based detection is mostly carried out in central laboratories. Herein, isothermal recombinase polymerase amplification (RPA) coupled with a photosensitization colorimetric assay (PCA) was adopted for the on-site detection of C. sakazakii in powdered infant formulas (PIFs). The lowest visual detection concentration of C. sakazakii is 800 cfu/mL and 2 cfu/g after 8 h bacteria pre-enrichment. Furthermore, to avoid typical cap opening-resulted aerosol pollution, the PCA reagents were lyophilized onto the cap of the RPA tube (containing lyophilized RPA reagents). After amplification, the tube was subjected to simple shaking to mix the PCA reagents with the amplification products for light-driven color development. Such a one-tube assay offered a lowest concentration of 1000 copies of genomic DNA of C. sakazakii within 1 h. After 8 h of bacterial enrichment, the lowest detecting concentration could be pushed down to 5 cfu/g bacteria in PIF. To facilitate on-site monitoring, a portable, battery-powered PCA device was designed to mount the typical RPA 8-tube strip, and a color analysis cellphone APP was further employed for facile readout.

Biofilm formation and associated gene expression changes in Cronobacter from cereal related samples in China

Cronobacter is an important foodborne pathogen that can cause severe neonatal meningitis, necrotizing enterocolitis, and bacteremia. Currently, there is limited knowledge of biofilm formation in Cronobacter. In the present study, biofilm formation ability and associated gene expression changes in Cronobacter from cereal related samples was carried out systematically. Our results from 307 Cronobacter isolates analyzed for 48 h showed strong biofilm-forming ability in 14 strains (4.6%), moderate in 47 strains (15.3%), weak in 142 strains (46.2%), and no such ability in the remaining 104 strains (33.9%). Further studies on five strains with strong biofilm-forming ability showed that maximum biofilm formation in Cronobacter occurred after 24 h of cultivation, reaching a peak around 48 h-72 h, reducing gradually thereafter. Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that differentially expressed genes (DEGs) involved in flagellar assembly, oxidative phosphorylation, ribosome, photosynthesis, O-Antigen nucleotide sugar biosynthesis, citrate cycle (tricarboxylic acid cycle, TCA) and bacterial chemotaxis were enriched in biofilm forming cells. The genes involved these enrichment pathways were mostly downregulated when compared to planktonic cells. Several transcriptional regulator genes such as csrA and bolA, and the cell surface composition regulator gene glgS were significantly upregulated. 12 of 13 (92.3%) selected genes was found to be in agreement with the RNA-Seq of planktonic and biofilm cells by Quantitative real-time PCR analysis, thus increasing confidence in our data. Our research lays a sound theoretical basis for further studies on mechanisms regulating biofilm formation and provides a foundation for development of new food safety measures, clinical disease prevention and control.

Sensitive detection of viable Cronobacter sakazakii by bioluminescent reporter phage emitting stable signals with truncated holin

As outbreaks of foodborne illness caused by the opportunistic pathogen Cronobacter sakazakii (Cs) continue to occur, particularly in infants consuming powdered infant formula (PIF), the need for sensitive, rapid, and easy-to-use detection of Cs from food and food processing environments is increasing. Here, we developed bioluminescent reporter bacteriophages for viable Cs-specific, substrate-free, rapid detection by introducing luciferase and its corresponding substrate-providing enzyme complex into the virulent phage ΦC01. Although the reporter phage ΦC01_lux, constructed by replacing non-essential genes for phage infectivity with a luxCDABE reporter operon, produced bioluminescence upon Cs infection, the emitted signal was quickly decayed due to the superior bacteriolytic activity of ΦC01. By truncating the membrane pore-forming protein holin and thus limiting its function, the bacterial lysis was delayed and the resultant engineered reporter phage ΦC01_lux_Δhol could produce a more stable and reliable bioluminescent signal. Accordingly, ΦC01_lux_Δhol was able to detect at least an average of 2 CFU/ml of Cs artificially contaminated PIF and Sunsik and food contact surface models within a total of 7 h of assays, including 5 h of pre-enrichment for Cs amplification. The sensitive, easy-to-use, and specific detection of live Cs with the developed reporter phage could be applied as a novel complementary tool for monitoring Cs in food and food-related environments for food safety and public health.

Neonatal Meningitis Due to Cronobacter sakazakii

Cronobacter sakazakii is a new emerging foodborne bacterial pathogen associated with fatal infections such as meningitis, necrotizing enterocolitis, and septicemia in neonates. Powdered infant formula milk has been recognized as one of the main transmission vehicles and contaminated sources of this pathogen. Educating parents about the importance of hygienic reconstitution of powdered infant formula, storage practices, and hand hygiene is crucial to reducing the risk of this life-threatening infection. The clinician should be aware of the special considerations for antimicrobial treatment selection as well as further necessary evaluation. Here, we report a case of a twin neonate who presented with C. sakazakii meningitis and septicemia. [Pediatr Ann. 2023;52(11):e430-e433.].

Cronobacter brain abscess and refractory epilepsy in a newborn: role of epilepsy surgery. Illustrative case

BACKGROUND

Neonatal meningitis due to Cronobacter is associated with powdered infant formula. Prompt recognition of this rare but aggressive infection is critical.

OBSERVATIONS

The authors report a unique case of neonatal Cronobacter meningoencephalitis complicated by brain abscess and status epilepticus, requiring surgical intervention in a preterm 4-week-old male and related to contaminated powdered infant formula. They discuss the medical and surgical management in this patient, as well as the role of epilepsy surgery in acute drug-resistant epilepsy. This is paired with a literature review examining Cronobacter infections in infants to provide a summative review of the existing literature.

LESSONS

Cronobacter contamination in powdered infant formula and breast pumps is rare but can cause life-threatening infections. When evaluating patients with Cronobacter central nervous system infections, serial neuroimaging, infection control, and prompt surgical management are essential. Future studies are needed regarding the role of epilepsy surgery in the acute infectious period.

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.

Protective Effects and Mechanism of a Novel Probiotic Strain Ligilactobacillus salivarius YL20 against Cronobacter sakazakii-Induced Necrotizing Enterocolitis In Vitro and In Vivo

Exposure to probiotics in early life contributes to host intestinal development and prevention of necrotizing enterocolitis (NEC). Cronobacter sakazakii (C. sakazakii), an opportunistic pathogen, can cause NEC, bacteremia, and meningitis in neonates, but the research of probiotics against C. sakazakii is limited relative to other enteropathogens. Here, the protective effect and mechanism of a novel probiotic Ligilactobacillus salivarius (L. salivarius) YL20 isolated from breast milk on C. sakazakii-induced intestinal injury were explored by using two in vitro models, including an C. sakazakii-infected intestinal organoid model and intestinal barrier model, as well as an in vivo experimental animal model. Our results revealed that L. salivarius YL20 could promote epithelial cell proliferation in intestinal organoids, rescue budding-impaired organoids, prevent the decrease of mRNA levels of leucine-rich repeat containing G protein-coupled receptor 5 (Lgr5), zonula occludens-1 (Zo-1) and Occludin, and reverse C. sakazakii-induced low level of Mucin 2 (MUC2) in intestinal organoids. Additionally, YL20 could inhibit C. sakazakii invasion, increase the expression of ZO-1 and occludin in C. sakazakii-infected HT-29 cells, and reverse TEER decrease and corresponding permeability increase across C. sakazakii-infected Caco-2 monolayers. Furthermore, YL20 administration could alleviate NEC in C. sakazakii-infected neonatal mice by increasing the mice survival ratio, decreasing pathology scores, and downregulating pro-inflammatory cytokines. Meanwhile, YL20 could also enhance intestinal barrier function in vivo by increasing the number of goblet cells, the level of MUC-2 and the expression of ZO-1. Our overall findings demonstrated for the first time the beneficial effects of L. salivarius YL20 against C. sakazakii-induced NEC by improving intestinal stem cell function and enhancing intestinal barrier integrity.

Crystal structures of YeiE from Cronobacter sakazakii and the role of sulfite tolerance in gram-negative bacteria

YeiE has been identified as a master virulence factor of Cronobacter sakazakii. In this study, we determined the crystal structures of the regulatory domain of YeiE in complex with its physiological ligand sulfite ion (SO₃²⁻). The structure provides the basis for the molecular mechanisms for sulfite sensing and the ligand-dependent conformational changes of the regulatory domain. The genes under the control of YeiE in response to sulfite were investigated to reveal the functional roles of YeiE in the sulfite tolerance of the bacteria. We propose the molecular mechanism underlying the ability of gram-negative pathogens to defend against the innate immune response involving sulfite, thus providing a strategy to control the pathogenesis of bacteria.

Cronobacter sakazakii is an emerging gram-negative pathogenic bacterium that causes meningitis, bacteremia, and necrotizing enterocolitis in infants and has a high mortality rate. The YeiE homolog (gpESA_01081) was identified as a global virulence regulator of bacterial pathogenesis in C. sakazakii. YeiE is a LysR-type transcriptional regulator (LTTR) composed of a DNA binding domain and a regulatory domain to recognize the unknown ligand. To reveal the molecular mechanism and function of YeiE, we determined the crystal structure of the regulatory domain of YeiE. A sulfite ion was bound at the putative ligand-binding site, and subsequent studies revealed that the sulfite is the physiological ligand for YeiE. Structural comparisons to its sulfite-free structure further showed the sulfite-dependent conformational change of YeiE. The essential role of YeiE in defending against toxicity from sulfite during the growth of C. sakazakii and Escherichia coli was examined. Furthermore, the target genes and functional roles of YeiE in H₂S production and survival capability from neutrophils were investigated. Our findings provide insights into the sophisticated behaviors of pathogenic gram-negative bacteria in response to sulfite from the environment and host.

Role of sigma factor RpoS in Cronobacter sakazakii environmental stress tolerance

Cronobacter sakazakii is a food-borne, conditionally pathogenic bacterium that mainly infects neonates, especially premature infants. Previous studies have indicated that an important route of infection for C. sakazakii is through infant formula, suggesting a high stress resistance of the bacterium. RpoS is a σ-factor that is closely related to the bacterial resistance mechanisms. In this study, a C. sakazakii BAA894 model strain was used. An rpoS-deficient mutant strain Δrpos was constructed using Red homologous recombination, and the differences between the mutant and the wild-type strains were compared. To investigate the functions of the rpoS gene, the membrane formation and cell wall properties of the strains were studied, and the tolerance of each strain to acid, osmotic pressure, desiccation, and drug resistance were compared. The results showed that the membrane formation ability in the mutant strain was increased, auto-aggregation was enhanced, motility, acid resistance and hyperosmotic resistance were alternated to different degrees, and desiccation resistance was stronger than observed in the wild type grown in LB medium but weaker than the wild type cultured in M9 medium. These results showed that rpoS is involved in environmental stress resistance in C. sakazakii BAA894. Finally, transcriptome analysis verified that the deletion of the rpoS gene caused differential expression of resistance-related genes and instigated changes in related metabolic pathways. These messenger RNA results were consistent with the functional experimental results and help explain the phenotypic changes observed in the mutant strain.

Bioprospecting Antimicrobials from Lactiplantibacillus plantarum: Key Factors Underlying Its Probiotic Action

Lactiplantibacillus plantarum (L. plantarum) is a well-studied and versatile species of lactobacilli. It is found in several niches, including human mucosal surfaces, and it is largely employed in the food industry and boasts a millenary tradition of safe use, sharing a long-lasting relationship with humans. L. plantarum is generally recognised as safe and exhibits a strong probiotic character, so that several strains are commercialised as health-promoting supplements and functional food products. For these reasons, L. plantarum represents a valuable model to gain insight into the nature and mechanisms of antimicrobials as key factors underlying the probiotic action of health-promoting microbes. Probiotic antimicrobials can inhibit the growth of pathogens in the gut ensuring the intestinal homeostasis and contributing to the host health. Furthermore, they may be attractive alternatives to conventional antibiotics, holding potential in several biomedical applications. The aim of this review is to investigate the most relevant papers published in the last ten years, bioprospecting the antimicrobial activity of characterised probiotic L. plantarum strains. Specifically, it focuses on the different chemical nature, the action spectra and the mechanisms underlying the bioactivity of their antibacterial and antiviral agents. Emerging trends in postbiotics, some in vivo applications of L. plantarum antimicrobials, including strengths and limitations of their therapeutic potential, are addressed and discussed.

A simple and sensitive aptasensor with rolling circle amplification for viable Cronobacter sakazakii detection in powdered infant formula

Cronobacter sakazakii is a foodborne, emerging opportunistic pathogen that causes severe bacteremia, necrotizing enterocolitis, and sepsis with a mortality rate of up to 80%. In this study, we developed a simple and sensitive fluorescent turn-off aptasensor with rolling circle amplification assay for viable C. sakazakii detection in powdered infant formula. The results showed that the proposed aptasensor has good performance and specificity for detecting viable C. sakazakii in pure culture and powdered infant formula samples within 3 h. Under the optimal reaction conditions, there is a linear relationship between fluorescent intensity at 490 nm and logarithmic concentration of C. sakazakii in the range of 2.7 × 10⁵ to 2.7 × 10² cfu/mL, with a limit of detection of 2.7 × 10² cfu/mL in pure culture. The proposed aptasensor achieved a recovery of 104 to 111% in pure culture, and 96 to 107% in spiked powdered infant formula samples. The proposed aptasensor does not require complicated DNA extraction steps or antibodies, and can be performed at 37°C, making it a convenient and sensitive strategy for C. sakazakii detection.

Two Cases of Cronobacter Sakazakii Meningitis in Infants: The Importance Of Early Advanced Brain Imaging and Public Health Reporting

We report 2 infants hospitalized with Cronobacter sakazakii meningitis. Each infant had exposure to powdered infant formula at home. Both infants survived, but 1 infant had a subdural empyema drained and developed left sensorineural hearing loss. Early advanced brain imaging is recommended in infants with C. sakazakii meningitis. Reporting to state and federal public health officials may help identify outbreaks.

Null mutation in sspA of Cronobacter sakazakii influences its tolerance to environmental stress

Cronobacter sakazakii is a known foodborne opportunistic pathogen that can affect the intestinal health of infants. Despite undergoing complex manufacturing processes and low water concentration in the finished product, infant formula has been associated with Cronobacter infections, suggesting that C. sakazakii's pathogenicity may be related to its tolerance to stress. In this study, the effect of the stringent starvation protein A (SspA), which plays an important role in E. coli cellular survival under environmental stresses, on the stress tolerance of C. sakazakii BAA894 was investigated by creating an sspA-knockout mutant. The effects of this mutation on the acid, desiccation and drug tolerance were assessed, and results showed that acid tolerance decreased, while desiccation tolerance increased in LB and decreased in M9. Moreover, the MICs of 10 antibiotics in LB medium and 8 antibiotics in M9 medium were determined and compared of the wild-type and ΔsspA. Transcriptome analysis showed that 27.21% or 37.78% of the genes in ΔsspA were significantly differentially expressed in LB or M9 media, the genes relevant to microbial metabolism in diverse environments and bacterial chemotaxis were detailed analyzed. The current study contributes towards an improved understanding of the role of SspA in C. sakazakii BAA894 stress tolerance.

Invited review: Stress resistance of Cronobacter spp. affecting control of its growth during food production

Members of the Cronobacter genus include food-borne pathogens that can cause infections in infants, with a mortality rate as high as 40 to 80%. The high fatality rate of Cronobacter and its isolation from numerous types of food, especially from powdered infant formula, demonstrate the serious nature of this organism. The source tracking of Cronobacter spp. and the analysis of high-frequency species from different sources are helpful for a more targeted control. Furthermore, the persistence during food processing and storage may be attributed to strong resistance of Cronobacter spp. to environment stresses such as heat, pH, and desiccation. There are many factors that support the survival of Cronobacter spp. in harsh environments, such as some genes, regulatory systems, and biofilms. Advanced detection technology is helpful for the strict monitoring of Cronobacter spp. In addition to the traditional heat treatment, many new control techniques have been developed, and the ability to control Cronobacter spp. has been demonstrated. The control of this bacteria is required not only during manufacture, but also through the selection of packaging methods to reduce postprocessing contamination. At the same time, the effect of inactivation methods on product quality and safety must be considered. This review considers the advances in our understanding of environmental stress response in Cronobacter spp. with special emphasis on its implications in food processing.

Application of MALDI-TOF mass spectrometry, and DNA sequencing-based SLST and MLST analysis for the identification of Cronobacter spp. isolated from environmental surveillance samples

Cronobacter spp. are emerging infectious foodborne bacteria that can cause acute meningitis and necrotizing enterocolitis in neonates and immunocompromised individuals. Although, little is known about its reservoirs or transmission routes, it has been linked to powdered infant formula worldwide. Three Cronobacter spp. (C. sakazakii, C. malonaticus, and C. turicensis) have been described as more virulent, and isolated frequently from infant meningitis cases. The estimated mortality rates are as high as 80% in infants. Thus, surveillance and typing of Cronobacter spp. isolated from food and environmental samples is essential to prevent contamination and spread of this pathogen. In this study, we have characterized 83 Cronobacter isolates recovered from various environmental samples by conventional microbiologic protocols. Species identification was accomplished by VITEK 2 system and real-time PCR analysis. Subsequently, these isolates were analyzed using VITEK MS system. Single locus sequence typing (SLST) was achieved by characterizing the regions of 16S rRNA and rpoB genes. Multilocus sequence typing (MLST) was performed by sequence characterization of seven housekeeping genes (atpD, fusA, glnS, gltB, gyrB, infB, and pps) using ABI 3500XL Genetic Analyzer. VITEK MS system identified, the majority of isolates as Cronobacter sakazakii with a high confidence value (99.9%). MLST analysis ascertained 12 distinct clonal complexes (CC1, CC4, CC8, CC13, CC17, CC21, CC31, CC40, CC52, CC64, CC73, and CC83) for the recovered C. sakazakii isolates. The results suggest that the MALDI-TOF MS is a reliable diagnostic tool for rapid species identification whereas 7-loci MLST is a powerful technique to discriminate and differentiate Cronobacter spp. isolates.

Meningitis and brain abscess formation caused by Cronobacter malonaticus sequence type 440 in a full-term neonate

Cronobacter spp. cause serious diseases, such as necrotizing enterocolitis, bacteremia, and meningitis in neonates and infants. Most Cronobacter-associated meningitis is reportedly due to C. sakazakii and the majority of infections caused by C. malonaticus occur in adults and are less severe. We report the case of meningitis and brain abscess caused by C. malonaticus Sequence Type (ST) 440 in a healthy full-term neonate. We should consider the possibility that full-term neonates may develop meningitis due to C. malonaticus and treat appropriately because its mortality rate is very high, and survivors are usually left with severe neurologic impairment. In addition, C. malonaticus ST440 may have virulence factors that cause neonatal meningitis akin to the previous report of meningitic ST307 strain.

Bacterial Distribution, Biogenic Amine Contents, and Functionalities of Traditionally Made Doenjang, a Long-Term Fermented Soybean Food, from Different Areas of Korea

Since doenjang quality depends on the bacterial composition, which ambient bacteria in the environment and production conditions influence, a complete understanding of the bacteria community in traditionally madetraditionally made doenjang (TMD) from different regions is needed. We aimed to investigate the bacteria composition and quality of TMD in the following areas: Chonbuk (CB), Chonnam (CN), Kyungsang (KS), Kangwon (KW), Chungchung (CC) provinces, and Jeju island (JJ) of Korea. Twenty-nine TMD samples from different regions were used to assess biogenic amine contents, bacteria composition using next-generation methods, and metabolic functions of the bacteria using Picrust2. Bacillus spp. were isolated, and their antioxidant and fibrinolytic activities were determined. Most TMD contained high amounts of beneficial bacteria (Bacillus, Lactobacillus, Pediococcus and Weissella). However, some KS samples contained harmful bacteria (Cronobacter, Proteus and Acinetobacter) and less beneficial B. velezensis bacteria. There was no similarity among the regional groups, and each TMD showed a different bacteria composition. Shannon index, α-diversity index, was lower in TMD from JJ and CB than the other areas, but there was no β-diversity among TMD from the six area groups. Picrust2 analysis revealed that the functional potential for arachidonic acid metabolism was lowest in JJ and CN, that for supporting insulin action was highest in KS and JJ, and that for carbohydrate digestion and absorption was lowest in CB and JJ among all groups (p < 0.05) according to the Kyoto Encyclopedia of Genes and Genomes Orthology. Histamine contents were lower in CN and CC, and tyramine contents did not differ significantly. B. velezensis, B. subtilis, B. licheniformis, B. siamensis, and B. amyloliquefaciens were isolated from TMD. None of the isolated Bacillus spp. contained the B. cereus gene. B. subtilis from CN had the highest fibrinolytic activity, and B. velezensis from CB had the highest antioxidant activity. In conclusion, TMD mainly contained various Bacillus spp., and the predominant one was B. velezensis, which had antioxidant and fibrinolytic activity regardless of the regional origin.

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.

Comparative genomics reveals environmental adaptation differences between Cronobacter species

The genus Cronobacter is an opportunistic food-borne pathogen which is able to adapt to diverse environments and shows considerable genetic diversity. Genomic analysis can be used to reveal the variation across the genus with respect to virulence, drug resistance and factors involved in horizontal gene transfer mechanisms, such as integrons, conjugative plasmids, and recombinases. In this study, whole-genome comparative analysis of 27 Cronobacter genomes (12 existing and 15 newly assembled genomes) was performed. A total of 110,010 protein-coding genes were grouped into 11,262 clusters, including 2637 core genes, 4814 strain-specific genes and 3811 dispensable genes. Clusters of Orthologous Groups (COG) analysis indicated that 97.35% of the core genes were for substrate transport and metabolism, and the antibiotic resistance genetic determinants were classified into 136 antibiotic resistance ontologies (AROs). A total of 80 genomic islands (GIs) were identified which contained several type VI secretion system gene clusters, and these were likely to have been acquired by horizontal gene transfer. This study has generated a comprehensive characterization of the genus Cronobacter, leading to a better understanding of the mechanisms and ecological functions among the genome features, speciation, and environmental adaptation strategies.

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.

Role of the multiple efflux pump protein TolC on growth, morphology, and biofilm formation under nitric oxide stress in Cronobacter malonaticus

Nitric oxide (NO) is a biological signal molecule that can control and prevent the growth of most pathogens. Cronobacter species are a group of gram-negative foodborne pathogens that cause severe diseases, including neonatal meningitis, septicemia, and necrotizing enterocolitis, especially among newborns and infants consuming contaminated powdered infant formula. Cronobacter species might be tolerant to NO, resulting in severe infections. However, the specific mechanism of tolerance to NO in Cronobacter species is unclear. Here, we explore the effects of a key component, the protein TolC, of a multiple efflux pump on the growth, morphological changes, and biofilm formation of Cronobacter malonaticus under NO stress. We found that deletion of tolC resulted in a decreased growth rate under 100 mM sodium nitroprusside (NO donor) and led to more disruptive morphological injury to the bacterial cells. Furthermore, C. malonaticus lacking the TolC protein (ΔtolC mutant) showed weaker biofilm formation than the wild-type strain under normal or NO stress conditions. We have proved that TolC plays an important role in cell growth and biofilm formation of C. malonaticus. Therefore, our results may provide valuable theoretical basis for formulating clinical guidelines for treatment of disease caused by C. malonaticus and ensuring food safety.

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.

Molecular Characterization of Cronobacter sakazakii Strains Isolated from Powdered Milk

Cronobacter spp. are opportunistic pathogens of the Enterobacteriaceae family. The organism causes infections in all age groups, but the most serious cases occur in outbreaks related to neonates with meningitis and necrotizing enterocolitis. The objective was to determine the in silico and in vitro putative virulence factors of six Cronobacter sakazakii strains isolated from powdered milk (PM) in the Czech Republic. Strains were identified by MALDI-TOF MS and whole-genome sequencing (WGS). Virulence and resistance genes were detected with the Ridom SeqSphere+ software task template and the Comprehensive Antibiotic Resistance Database (CARD) platform. Adherence and invasion ability were performed using the mouse neuroblastoma (N1E-115 ATCCCRL-2263) cell line. The CRISPR-Cas system was searched with CRISPRCasFinder. Core genome MLST identified four different sequence types (ST1, ST145, ST245, and ST297) in six isolates. Strains 13755-1B and 1847 were able to adhere in 2.2 and 3.2 × 106 CFU/mL, while 0.00073% invasion frequency was detected only in strain 1847. Both strains 13755-1B and 1847 were positive for three (50.0%) and four virulence genes, respectively. The cpa gene was not detected. Twenty-eight genes were detected by WGS and grouped as flagellar or outer membrane proteins, chemotaxis, hemolysins, and invasion, plasminogen activator, colonization, transcriptional regulator, and survival in macrophages. The colistin-resistance-encoding mcr-9.1 and cephalothin-resis-encoding blaCSA genes and IncFII(pECLA) and IncFIB(pCTU3) plasmids were detected. All strains exhibited CRISPR matrices and four of them two type I-E and I-F matrices. Combined molecular methodologies improve Cronobacter spp. decision-making for health authorities to protect the population.

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.

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.

Genomics and Experimental Analysis Reveal a Novel Factor Contributing to the Virulence of Cronobacter sakazakii Strains Associated With Neonate Infection

BACKGROUND

Cronobacter sakazakii causes meningitis and necrotizing enterocolitis in premature infants. However, its virulence determinants, especially those specific for strains associated with neonate infections, remain largely unknown.

METHODS

In this study, we performed a comparative genomic analysis of 209 C. sakazakii genomes, and 8 clonal groups (CGs) were revealed.

RESULTS

CG1 and CG2 were found to be significantly associated with neonate infections, and significantly prevalent genes in these 2 CGs were identified. Of these, a gene encoding the LysR-type regulator, CklR, was shown to contribute to bacterial pathogenicity based on animal experiments. We found that CklR directly binds and activates the suf Fe-S cluster biosynthesis operon, and high expression of the suf operon increases bacterial resistance to oxidative stress, which increases survival within the host. This leads to a high degree of bacteremia, which contributes to the development of meningitis.

CONCLUSIONS

Our work revealed a novel virulence factor specific to predominant pathogenic C. sakazakii strains.

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.

Effect of hydrolysis and microwave treatment on the antibacterial activity of native bovine milk lactoferrin against Cronobacter sakazakii

Bovine lactoferrin (bLF) is an iron-binding glycoprotein used in functional and therapeutic products due to its biological properties, the most important being its antimicrobial activity. In this study, hydrolysates of bovine lactoferrin (bLFH) obtained with pepsin, chymosin and microbial rennet were assayed against Cronobacter sakazakii (10⁴ CFU/mL) in different media: phosphate buffered saline (PBS), bovine skim milk and whey, and reconstituted powdered infant formula (PIFM). The results obtained have shown that hydrolysis of bLF enhances its antibacterial activity against C. sakazakii. The three types of bLFH dissolved in PBS reduced C. sakazakii growth from a concentration of 0.1 mg/mL and inhibited it completely above 0.5 mg/mL, after 4 and 8 h of incubation at 37 °C. The three bLFH (1 and 2 mg/mL) did not show any antibacterial activity in skim milk, whey and reconstituted PIFM after 8 h of incubation at 37 °C. However, C. sakazakii growth was completely inhibited in whey when pepsin and chymosin bLFH (2 mg/mL) were combined with undigested bLF (2 mg/mL), after 8 h of incubation at 37 °C. On the other hand, the combination of any of the three hydrolysates with bLF showed very low activity in skim milk and practically no activity in reconstituted PIFM. Furthermore, the effect of temperature after reconstitution (4, 23 and 37 °C), on the antibacterial activity of bLF (2.5 and 5 mg/mL) in reconstituted PIFM contaminated with C. sakazakii (10-10² CFU/mL) was also investigated. bLF at 5 mg/mL significantly reduced (p < .05) the proliferation of C. sakazakii in reconstituted PIFM at 37 °C until 2 h. C. sakazakii did not grow at 4 °C for 6 days in reconstituted PIFM with or without bLF. The effect of microwave heating (450, 550 and 650 W for 5, 10 and 15 s) on the antibacterial activity and stability of bLF (2.5 mg/mL) in reconstituted PIFM contaminated with C. sakazakii (10-10² CFU/mL) was also studied. The antibacterial activity of bLF was maintained after treatments at 450 and 550 W for 5 s, which kept 94 and 89% of bLF immunoreactivity, respectively. Moreover, microwave treatments of reconstituted PIFM with or without bLF, at 650 W for 5 s, and at 450, 550 and 650 W for 10 and 15 s, completely inactivated C. sakazakii.

Prevalence, Distribution, and Phylogeny of Type Two Toxin-Antitoxin Genes Possessed by Cronobacter Species where C. sakazakii Homologs Follow Sequence Type Lineages

Cronobacter species are a group of foodborne pathogenic bacteria that cause both intestinal and systemic human disease in individuals of all age groups. Little is known about the mechanisms that Cronobacter employ to survive and persist in foods and other environments. Toxin-antitoxin (TA) genes are thought to play a role in bacterial stress physiology, as well as in the stabilization of horizontally-acquired re-combinatorial elements such as plasmids, phage, and transposons. TA systems have been implicated in the formation of a persistence phenotype in some bacterial species including Escherichia coli and Salmonella. This project's goal was to understand the phylogenetic relatedness among TA genes present in Cronobacter. Preliminary studies showed that two typical toxin genes, fic and hipA followed species evolutionary lines. A local database of 22 TA homologs was created for Cronobacter sakazakii and a Python version 3 shell script was generated to extract TA FASTA sequences present in 234 C. sakazakii genomes previously sequenced as part of Center for Food Safety and Applied Nutrition's (CFSAN) GenomeTrakr project. BLAST analysis showed that not every C. sakazakii strain possessed all twenty-two TA loci. Interestingly, some strains contained either a toxin or an antitoxin component, but not both. Five common toxin genes: ESA_00258 (parDE toxin-antitoxin family), ESA_00804 (relBE family), ESA_01887 (relBE family), ESA_03838 (relBE family), and ESA_04273 (YhfG-Fic family) were selected for PCR analysis and the primers were designed to detect these genes. PCR analysis showed that 55 of 63 strains possessed three of these genes Sequence analysis identified homologs of the target genes and some of the strains were PCR-negative for one or more of the genes, pointing to potential nucleotide polymorphisms in those loci or that these toxin genes were absent. Phylogenetic studies using a Cronobacter pan genomic microarray showed that for the most part TAs follow species evolutionary lines except for a few toxin genes possessed by some C. malonaticus and C. universalis strains; this demonstrates that some TA orthologues share a common phylogeny. Within the C. sakazakii strains, the prevalence and distribution of these TA homologs by C. sakazakii strain BAA-894 (a powdered infant formula isolate) followed sequence-type evolutionary lineages. Understanding the phylogeny of TAs among the Cronobacter species is essential to design future studies to realize the physiological mechanisms and roles for TAs in stress adaptation and persistence of Cronobacter within food matrices and food processing environments.

Evaluation of Methods for Inoculating Dry Powder Foods with Salmonella enterica, Enterococcus faecium, or Cronobacter sakazakii

Salmonella and Cronobacter are two bacteria of concern in powdered food ingredients with low water activity, due to their ability to remain viable for long periods of time. There is great interest in studying the survival of these bacteria in powdered foods, but discrepancies have been reported between broth-grown and lawn-grown bacterial cells and their thermal resistance and desiccation tolerance once inoculated onto powdered foods. The purpose of this study was to evaluate three different powdered food inoculation methods, two broth-grown and one lawn-grown. To evaluate these methods on three types of powdered food matrices, Salmonella enterica serovar Typhimurium LT2 (ATCC 700720), Salmonella surrogate Enterococcus faecium (NRRL B-2354), and Cronobacter sakazakii (ATCC 29544) were inoculated onto nonfat dry milk powder, organic soy flour, and all-purpose flour using one of the three previously developed inoculation methods. In the first broth-grown method, labeled broth-grown pelletized inoculation, a bacterial cell pellet was added to powdered foods directly and mixed with a sterile wooden stick. The second broth-grown method, labeled broth-grown spray inoculation, used a chromatography reagent sprayer to spray the bacterial cell suspension onto the powdered foods. The third inoculation method, lawn-grown liquid inoculation, made use of a spot inoculation and a stomacher to incorporate each bacterium into the powdered foods. Results indicated that the method of inoculation of each powder impacted repeatability and bacteria survivability postequilibration (4 to 6 days). Broth-grown spray inoculation, regardless of the powder and bacterium, resulted in the highest log reduction, with an average ∼1-log CFU/g reduction following equilibration. Broth-grown pelletized inoculation resulted in the second-highest log reduction (∼0.79 log CFU/g), and finally, lawn-grown liquid inoculation was the most stable inoculation method of the three, with ∼0.52-log CFU/g reduction. Overall, the results from this inoculation study demonstrate that inoculation methodologies impact the desiccation tolerance and homogeneity of C. sakazakii, E. faecium, and Salmonella Typhimurium LT2.

Novel Multidrug-Resistant Cronobacter sakazakii Causing Meningitis in Neonate, China, 2015

We report a case of meningitis in a neonate in China, which was caused by a novel multidrug-resistant Cronobacter sakazakii strain, sequence type 256, capsular profile K1:CA1. We identified genetic factors associated with bacterial pathogenicity and antimicrobial drug resistance in the genome and plasmids. Enhanced surveillance of this organism is warranted.

Evaluation of commercial probiotic lactic cultures against biofilm formation by Cronobacter sakazakii

BACKGROUND/AIMS

Cronobacter sakazakii, an emergent pathogen is considered as a major concern to infants and neonates fed on reconstituted powdered infant milk formula. In conjunction with many other factors, biofilm forming capacity adds to its pathogenic potential. In view of the facts that infants are at highest risk to C. sakazakii infections, and emerging antibiotic resistance among pathogens, it is imperative to evaluate probiotic cultures for their efficacy against C. sakazakii. Therefore, pure probiotic strains were isolated from commercial probiotic products and tested for their antimicrobial and anti-biofilm activities against C. sakazakii.

METHODS

A total of 6 probiotic strains were tested for their antibiotic susceptibility followed by antimicrobial activity using cell-free supernatant (CFS) against C. sakazakii. The inhibitory activity of CFS against biofilm formation by C. sakazakii was determined using standard crystal violet assay and microscopic observations.

RESULTS

All the probiotic strains were sensitive to ampicillin, tetracycline, vancomycin and carbenicillin whereas most of the strains were resistant to erythromycin and novobiocin. Four of the 6 probiotic derived CFS possessed antimicrobial activity against C. sakazakii at a level of 40 μL. A higher biofilm inhibitory activity (>80%) was observed at initial stages of biofilm formation with weaker activity during longer incubation upto 48 hours (50%-60%).

CONCLUSIONS

The study indicated the efficacy of isolated commercial probiotics strains as potential inhibitor of biofilm formation by C. sakazakii and could be further explored for novel bioactive molecules to limit the emerging infections of C. sakazakii.

Outbreak History, Biofilm Formation, and Preventive Measures for Control of Cronobacter sakazakii in Infant Formula and Infant Care Settings

Previously known as Enterobacter sakazakii from 1980 to 2007, Cronobacter sakazakii is an opportunistic bacterium that survives and persists in dry and low-moisture environments, such as powdered infant formula. Although C. sakazakii causes disease in all age groups, infections caused by this pathogen are particularly fatal in infants born premature and those younger than two months. The pathogen has been isolated from various environments such as powdered infant formula manufacturing facilities, healthcare settings, and domestic environments, increasing the chance of infection through cross-contamination. The current study discusses the outbreak history of C. sakazakii and the ability of the microorganism to produce biofilms on biotic and abiotic surfaces. The study further discusses the fate of the pathogen in low-moisture environments, articulates preventive measures for healthcare providers and nursing parents, and delineates interventions that could be utilized in infant formula manufacturing to minimize the risk of contamination with Cronobacter sakazakii.

RNA Sequencing-Based Transcriptional Overview of Xerotolerance in Cronobacter sakazakii SP291

Cronobacter sakazakii is a xerotolerant neonatal pathogen epidemiologically linked to powdered infant food formula, often resulting in high mortality rates. Here, we used transcriptome sequencing (RNA-seq) to provide transcriptional insights into the survival of C. sakazakii in desiccated conditions. Our RNA-seq data show that about 22% of the total C. sakazakii genes were significantly upregulated and 9% were downregulated during desiccation survival. When reverse transcription-quantitative PCR (qRT-PCR) was used to validate the RNA-seq data, we found that the primary desiccation response was gradually downregulated during the tested 4 hours of desiccation, while the secondary response remained constitutively upregulated. The 4-hour desiccation tolerance of C. sakazakii was dependent on the immediate microenvironment surrounding the bacterial cell. The removal of Trypticase soy broth (TSB) salts and the introduction of sterile infant formula residues in the microenvironment enhanced the desiccation survival of C. sakazakii SP291. The trehalose biosynthetic pathway encoded by otsA and otsB, a prominent secondary bacterial desiccation response, was highly upregulated in desiccated C. sakazakii C. sakazakii SP291 ΔotsAB was significantly inhibited compared with the isogenic wild type in an 8-hour desiccation survival assay, confirming the physiological importance of trehalose in desiccation survival. Overall, we provide a comprehensive RNA-seq-based transcriptional overview along with confirmation of the phenotypic importance of trehalose metabolism in Cronobacter sakazakii during desiccation.IMPORTANCE Cronobacter sakazakii is a pathogen of importance to neonatal health and is known to persist in dry food matrices, such as powdered infant formula (PIF) and its associated production environment. When infections are reported in neonates, mortality rates can be high. The success of this bacterium in surviving these low-moisture environments suggests that Cronobacter species can respond to a variety of environmental signals. Therefore, understanding those signals that aid the persistence of this pathogen in these ecological niches is an important step toward the development of strategies to reduce the risk of contamination of PIF. This research led to the identification of candidate genes that play a role in the persistence of this pathogen in desiccated conditions and, thereby, serve as a model target to design future strategies to mitigate PIF-associated survival of C. sakazakii.

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.

Virulence and Antibiotic Resistance Profiles of Cronobacter sakazakii and Enterobacter spp. Involved in the Diarrheic Hemorrhagic Outbreak in Mexico

Cronobacter spp. are bacterial pathogens that cause neonatal meningitis, septicemia, and necrotizing enterocolitis in infants with a lethality rate of 40–80%. Powdered infant formulas (PIF) have been implicated as the main vehicles of transmission. This pathogen can also cause infection through contaminated expressed breast milk, and it has been recovered from neonatal feeding tubes of neonates not fed reconstituted PIF and milk kitchen areas. This study analyzed antibiotic resistance profiles and the tissue virulence tests of Cronobacter sakazakii and Enterobacter spp. recovered from PIF, infant fecal matter‘s, and milk kitchen environment involved in a diarrheic hemorrhagic outbreak in 2011 in Mexico. The strains isolated from the outbreak had similar antibiotic resistance profiles and pathogenicity irrespective of isolation site, however, C. sakazakii strains isolated from PIF showed significantly higher invasive profiles than Enterobacter spp. (p = 0.001) and 83% were resistant to more than one antibiotic. The findings of this study can be used to complement existing information to better control Cronobacter and Enterobacter spp. contamination in PIF production, prevent its transmission, and improve infant food safety.