Genes involved in Cronobacter sakazakii biofilm formation

The role of DsbA and PepP genes in the environmental tolerance and virulence factors of Cronobacter sakazakii

Cronobacter sakazakii, an opportunity foodborne pathogen, could contaminate a broad range of food materials and cause life-threatening symptoms in infants. The bacterial envelope structure contribute to bacterial environment tolerance, biofilm formation and virulence in various in Gram-negative bacteria. DsbA and PepP are two important genes related to the biogenesis and stability of bacterial envelope. In this study, the DsbA and PepP were deleted in C. sakazakii to evaluate their contribution to stress tolerance and virulence of the pathogen. The bacterial environment resistance assays showed DsbA and PepP are essential in controlling C. sakazakii resistance to heat and desiccation in different mediums, as well as acid, osmotic, oxidation and bile salt stresses. DsbA and PepP also played an important role in regulating biofilm formation and motility. Furthermore, DsbA and PepP deletion weaken C. sakazakii adhesion and invasion in Caco-2, intracellular survival and replication in RAW 264.7. qRT-PCR results showed that DsbA and PepP of C. sakazakii played roles in regulating the expression of several genes associated with environment stress tolerance, biofilm formation, bacterial motility and cellular invasion. These findings indicate that DsbA and PepP played an important regulatory role in the environment resisitance, biofilm formation and virulence of C. sakazakii, which enrich understanding of genetic determinants of adaptability and virulence of the pathogen.

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.

Electrotransformation of Foodborne Pathogen Cronobacter sakazakii by a Simple Method

Cronobacter sakazakii is an opportunistic foodborne pathogen that mainly infects infants and immunocompromised people, with a high mortality rate. However, the efficient transformation method of this bacterium has not been systematically reported. In this study, we developed a fast and efficient transformation method for C. sakazakii by cold sucrose treatment. Compared with CaCl2 or glycerol treatment, the transformation efficiency of this method is significantly high when bacteria were cultured overnight at 42°C before cold sucrose treatment. Furthermore, applying this method, we successfully knocked out the pppA gene by direct electroporation. Collectively, our study provides a simple, time-saving, and efficient method for competent cell preparation of C. sakazakii, which is conducive to the further research of C. sakazakii.

Co-culture of Cronobacter sakazakii and Staphylococcus aureus: Explore the influence of mixed biofilm formation and regulation of Cronobacter sakazakii biofilm formation genes

Bacterial biofilm is a protective matrix composed of metabolites secreted by bacteria that envelop bacteria. By forming a biofilm, bacteria can considerably improve their environmental tolerance. In food-related processing environment, different types of microorganisms are often present in biofilms. The main contaminating strain in the powdered infant formula (PIF) processing environment, Cronobacter sakazakii and Staphylococcus aureus continues to pollute the PIF processing environment after biofilm production. This study selected Cronobacter sakazakii with a weak biofilm-forming ability as one of the test organisms. The coexistence of Cronobacter sakazakii and Staphylococcus aureus on the surface of production equipment was simulated to analyze the interaction. Biofilm formation in the co-culture group was significantly higher than the others. In-depth study of the effect of Staphylococcus aureus on the biofilm formation genes of Cronobacter sakazakii. Results show two bacteria can coexist on the surface of a metal device, forming a more compact hybrid biofilm structure. Under co-culture conditions, S. aureus increased bcsA and fliD expression in Cronobacter sakazakii, whereas decreased bcsC expression. Signaling molecules produced by Staphylococcus aureus (Autoinducer 2) significantly promoted the biofilm formation of Cronobacter sakazakii at the concentration of 0-500 ng/mL (0.099-0.177) and up-regulated the expression of bcsA, filD and flhD genes.

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.

High-throughput functional trait testing for bacterial pathogens

Functional traits are characteristics that affect the fitness and metabolic function of a microorganism. There is growing interest in using high-throughput methods to characterize bacterial pathogens based on functional virulence traits. Traditional methods that phenotype a single organism for a single virulence trait can be time consuming and labor intensive. Alternatively, machine learning of whole-genome sequences (WGS) has shown some success in predicting virulence. However, relying solely on WGS can miss functional traits, particularly for organisms lacking classical virulence factors. We propose that high-throughput assays for functional virulence trait identification should become a prominent method of characterizing bacterial pathogens on a population scale. This work is critical as we move from compiling lists of bacterial species associated with disease to pathogen-agnostic approaches capable of detecting novel microbes. We discuss six key areas of functional trait testing and how advancing high-throughput methods could provide a greater understanding of pathogens.

Anti-Biofilm Activity of Laurel Essential Oil against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a primary seafood-associated pathogen that could cause gastroenteritis. It can attach to various surfaces and form a biofilm, which poses serious threats to food safety. Hence, an effective strategy is urgently needed to control the biofilm formation of V. parahaemolyticus. Laurel essential oil (LEO) is used in food, pharmaceutical and other industries, and is commonly used as a flavoring agent and valuable spice in food industries. The potential antibiofilm effects of LEO against V. parahaemolyticus were examined in this study. LEO obviously reduced biofilm biomass at subinhibitory concentrations (SICs). It decreased the metabolic activity and viability of biofilm cells. Microscopic images and Raman spectrum indicted that LEO interfered with the structure and biochemical compositions of biofilms. Moreover, it also impaired swimming motility, decreased hydrophobicity, inhibited auto-aggregation and reduced attachment to different food-contact surfaces. RT-qPCR revealed that LEO significantly downregulated transcription levels of biofilm-associated genes of V. parahaemolyticus. These findings demonstrate that LEO could be potentially developed as an antibiofilm strategy to control V. parahaemolyticus biofilms in food industries.

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.

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.

Outer Membrane Protein F Is Involved in Biofilm Formation, Virulence and Antibiotic Resistance in Cronobacter sakazakii

In some Gram-negative bacteria, ompF encodes outer membrane protein F (OmpF), which is a cation-selective porin and is responsible for the passive transport of small molecules across the outer membrane. However, there are few reports about the functions of this gene in Cronobacter sakazakii. To investigate the role of ompF in detail, an ompF disruption strain (ΔompF) and a complementation strain (cpompF) were successfully obtained. We find that OmpF can affect the ability of biofilm formation in C. sakazakii. In addition, the variations in biofilm composition of C. sakazakii were examined using Raman spectroscopy analyses caused by knocking out ompF, and the result indicated that the levels of certain biofilm components, including lipopolysaccharide (LPS), were significantly decreased in the mutant (ΔompF). Then, SDS-PAGE was used to further analyze the LPS content, and the result showed that the LPS levels were significantly reduced in the absence of ompF. Therefore, we conclude that OmpF affects biofilm formation in C. sakazakii by reducing the amount of LPS. Furthermore, the ΔompF mutant showed decreased (2.7-fold) adhesion to and invasion of HCT-8 cells. In an antibiotic susceptibility analysis, the ΔompF mutant showed significantly smaller inhibition zones than the WT, indicating that OmpF had a positive effect on the influx of antibiotics into the cells. In summary, ompF plays a positive regulatory role in the biofilm formation and adhesion/invasion, which is achieved by regulating the amount of LPS, but is a negative regulator of antibiotic resistance in C. sakazakii.

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.

Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure

The bacterial flagellum is a complex and dynamic nanomachine that propels bacteria through liquids. It consists of a basal body, a hook, and a long filament. The flagellar filament is composed of thousands of copies of the protein flagellin (FliC) arranged helically and ending with a filament cap composed of an oligomer of the protein FliD. The overall structure of the filament core is preserved across bacterial species, while the outer domains exhibit high variability, and in some cases are even completely absent. Flagellar assembly is a complex and energetically costly process triggered by environmental stimuli and, accordingly, highly regulated on transcriptional, translational and post-translational levels. Apart from its role in locomotion, the filament is critically important in several other aspects of bacterial survival, reproduction and pathogenicity, such as adhesion to surfaces, secretion of virulence factors and formation of biofilms. Additionally, due to its ability to provoke potent immune responses, flagellins have a role as adjuvants in vaccine development. In this review, we summarize the latest knowledge on the structure of flagellins, capping proteins and filaments, as well as their regulation and role during the colonization and infection of the host.

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.

Biofilm Formation by Listeria monocytogenes 15G01, a Persistent Isolate from a Seafood-Processing Plant, Is Influenced by Inactivation of Multiple Genes Belonging to Different Functional Groups

Listeria monocytogenes is a ubiquitous foodborne pathogen that results in a high rate of mortality in sensitive and immunocompromised people. Contamination of food with L. monocytogenes is thought to occur during food processing, most often as a result of the pathogen producing a biofilm that persists in the environment and acting as the source for subsequent dispersal of cells onto food. A survey of seafood-processing plants in New Zealand identified the persistent strain 15G01, which has a high capacity to form biofilms. In this study, a transposon library of L. monocytogenes 15G01 was screened for mutants with altered biofilm formation, assessed by a crystal violet assay, to identify genes involved in biofilm formation. This screen identified 36 transposants that showed a significant change in biofilm formation compared to the wild type. The insertion sites were in 27 genes, 20 of which led to decreased biofilm formation and seven to an increase. Two insertions were in intergenic regions. Annotation of the genes suggested that they are involved in diverse cellular processes, including stress response, autolysis, transporter systems, and cell wall/membrane synthesis. Analysis of the biofilms produced by the transposants using scanning electron microscopy and fluorescence microscopy showed notable differences in the structure of the biofilms compared to the wild type. In particular, inactivation of uvrB and mltD produced coccoid-shaped cells and elongated cells in long chains, respectively, and the mgtB mutant produced a unique biofilm with a sandwich structure which was reversed to the wild-type level upon magnesium addition. The mltD transposant was successfully complemented with the wild-type gene, whereas the phenotypes were not or only partially restored for the remaining mutants.IMPORTANCE The major source of contamination of food with Listeria monocytogenes is thought to be due to biofilm formation and/or persistence in food-processing plants. By establishing as a biofilm, L. monocytogenes cells become harder to eradicate due to their increased resistance to environmental threats. Understanding the genes involved in biofilm formation and their influence on biofilm structure will help identify new ways to eliminate harmful biofilms in food processing environments. To date, multiple genes have been identified as being involved in biofilm formation by L. monocytogenes; however, the exact mechanism remains unclear. This study identified four genes associated with biofilm formation by a persistent strain. Extensive microscopic analysis illustrated the effect of the disruption of mgtB, clsA, uvrB, and mltD and the influence of magnesium on the biofilm structure. The results strongly suggest an involvement in biofilm formation for the four genes and provide a basis for further studies to analyze gene regulation to assess the specific role of these biofilm-associated genes.

Impact of pmrA on Cronobacter sakazakii planktonic and biofilm cells: A comprehensive transcriptomic study

Cronobacter sakazakii is an emerging opportunistic foodborne pathogen causing rare but severe infections in neonates. Furthermore, the formation of biofilm allows C. sakazakii to persist in different environments. We have demonstrated that the mutator phenotype ascribed to deficiency of the pmrA gene results in more biomass in the first 24 h but less during the post maturation stage (7-14 d) compared with BAA 894. The present study aimed to investigate the regulatory mechanism modulating biofilm formation due to pmrA mutation. The transcriptomic analyses of BAA 894 and s-3 were performed by RNA-sequencing on planktonic and biofilm cells collected at different time points. According to the results, when comparing biofilm to planktonic cells, expression of genes encoding outer membrane proteins, lysozyme, etc. were up-regulated, with LysR family transcriptional regulators, periplasmic proteins, etc. down-regulated. During biofilm formation, cellulose synthase operon genes, flagella-related genes, etc. played essential roles in different stages. Remarkably, pmrA varies the expression of a number of genes related to motility, biofilm formation, and antimicrobial resistance, including srfB, virK, mviM encoding virulence factor, flgF, fliN, etc. encoding flagellar assembly, and marA, ramA, etc. encoding AraC family transcriptional regulators in C. sakazakii. This study provides valuable insights into transcriptional regulation of C. sakazakii pmrA mutant during biofilm formation.

Role of fliC on biofilm formation, adhesion, and cell motility in Cronobacter malonaticus and regulation of luxS

Cronobacter malonaticus is one of the important foodborne pathogens causing infections mainly in adults. Biofilm formation, adhesion, and motility in Cronobacter have been documented, but the implying molecular mechanism has received little attention. Here, a comparison in biofilm formation, adhesion ability, and cell motility among wild type (WT), △luxS, and △fliC strains were analyzed using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). The thickest biofilm was formed by WT, followed by △luxS and △fliC. Furthermore, the deletion of fliC caused the loss of cell motility and the failure to flagella biosynthesis and mature biofilm formation. Besides, the adhesion abilities of △luxS and △fliC to biotic cells (LoVo and IEC-6) and abiotic surface (glass) were significantly decreased compared to WT, revealing that fliC might have an important role in the organism's invasion properties. We further demonstrated that the expression of negative regulator (flgM) of flagellin in △luxS was higher than that in WT, which indicated that luxS indirectly contributed to fliC expression. Our findings provided a novel perspective for precaution and control of C. malonaticus through intercepting fliC-mediated adhesion to biotic cells and abiotic surface.

Proteomics profiles of Cronobacter sakazakii and a fliF mutant: Adherence and invasion in mouse neuroblastoma cells

Cronobacter sakazakii is an opportunistic foodborne pathogen associated with necrotizing enterocolitis, bacteremia, and meningitis in infants. A comparative proteomic study of C. sakazakii ATCC BAA-894 (CS WT) and a fliF::Tn5 mutant was performed, including the ability of both strains to adhere to and invade N1E-115 cells. To achieve this goal, a nonmotile C. sakazakii‬ ATCC BAA-894 fliF::Tn5 (CS fliF::Tn5) strain was generated using an EZ-Tn5 <KAN-2>Tnp Transposome kit. Analysis of differential protein expression showed that 81.49% (361/443) of the proteins were expressed in both strains, 8.35% (37/443) were exclusively expressed in the CS WT strain, and 10.16% (45/443) were exclusively expressed in the CS fliF::Tn5 strain. The main exclusively expressed proteins in the CS WT strain were classified into the "cell motility" and "signal transduction mechanisms" subcategories. The proteins exclusively expressed in the CS fliF::Tn5 strain were classified into the following subcategories: "intracellular trafficking, secretion, and vesicular transport", "replication, recombination, and repair", "nucleotide transport and metabolism", "carbohydrate transport and metabolism", "coenzyme transport and metabolism", and "lipid transport and metabolism". Expression of the Cpa protein was detected in both strains, but Cpa was more abundant in the CS WT strain than in the CS fliF::Tn5 strain. A significant increase (p = 0.0001) in adherence to N1E-115 cells was observed in the nonmotile CS fliF::Tn5 strain (31.3 × 10⁶ CFU/mL) compared to the CS WT strain (14.5 × 10⁶ CFU/mL). Additionally, the CS WT strain showed a 0.17% invasion frequency in N1E-115 cells, which was significantly higher (p = 0.01) than that of the nonmotile CS fliF::Tn5 strain. In conclusion, the proteins involved in the motility were mainly identified by proteomic analysis in the CS WT strain compared to the CS fliF::Tn5 strain. Our data indicate that flagella are required to promote the invasion of N1E-115 cells and that the absence of flagella significantly increases the adherence to N1E-115 cells.

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.

Random Mutagenesis Applied to Reveal Factors Involved in Oxidative Tolerance and Biofilm Formation in Foodborne Cronobacter malonaticus

Cronobacter species are linked with life-treating diseases in neonates and show strong tolerances to environmental stress. However, the information about factors involved in oxidative tolerance in Cronobacter remains elusive. Here, factors involved in oxidative tolerance in C. malonaticus were identified using a transposon mutagenesis. Eight mutants were successfully screened based on a comparison of the growth of strains from mutant library (n = 215) and wild type (WT) strain under 1.0 mM H₂O₂. Mutating sites including thioredoxin 2, glutaredoxin 3, pantothenate kinase, serine/threonine protein kinase, pyruvate kinase, phospholipase A, ferrous iron transport protein A, and alanine racemase 2 were successfully identified by arbitrary PCR and sequencing alignment. Furthermore, the comparison about quantity and structure of biofilms formation among eight mutants and WT was determined using crystal violet staining (CVS), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Results showed that the biofilms of eight mutants significantly decreased within 48 h compared to that of WT, suggesting that mutating genes play important roles in biofilm formation under oxidative stress. The findings provide valuable information for deeply understanding molecular mechanism about oxidative tolerance of C. malonaticus.

Characterization of Biofilm Formation by Cronobacter spp. Isolates of Different Food Origin under Model Conditions

Cronobacter spp. are opportunistic human pathogens that cause serious diseases in neonates and immunocompromised people. Owing to their biofilm formation on various surfaces, both their detection and their removal from production plants constitute a major challenge. In this study, food samples were randomly collected in Austria and examined for the presence of Cronobacter spp. Presumptive isolates were identified by a polyphasic approach. Five percent of the samples were positive for C. sakazakii and 2.4% for C. dublinensis. Individual growth of the isolates was characterized based on lag time, growth rate, and generation time. During an incubation period of 6 to 72 h, biofilm formation of 11 selected isolates was quantified under model conditions by a crystal violet staining assay with 96-well plates with different carbon sources (lactose, glucose, maltose, sucrose, and sodium acetate) and NaCl levels and under variable temperature and pH conditions. Biofilm formation was more pronounced at lactose concentrations between 0.25 and 3% compared with 5% lactose, which lead to thinner layers. C. sakazakii isolate C7, isolated from infant milk powder, was the strongest biofilm producer at 10 mM Mg²⁺ and 5 mM Mn²⁺, 0.5% sodium acetate, at pH levels between 7 and 9 at 37°C for 24 h. C. sakazakii strain C6 isolated from a plant air filter was identified as a moderate biofilm former and C. sakazakii strain DSM 4485, a clinical isolate, as a weak biofilm former. Based on PCR detection, genes bcsA, bcsB, and bcsG encoding for cellulose could be identified as markers for biofilm formation. Isolates carrying bcsA and bcsB showed significantly stronger biofilm formation than isolates without these genes ( P < 0.05), in strong correlation with the results obtained in the crystal violet assay. Further investigations using confocal laser scanning microscopy revealed that extracellular polymeric substances and glycocalyx secretions were the dominating components of the biofilms and that the viable fraction of bacteria in the biofilm decreased over time.

Silver nanoparticles: A novel antibacterial agent for control of Cronobacter sakazakii

Silver nanoparticles (AgNP) have been widely applied because of their broad spectrum of antimicrobial activities against bacteria, fungi, and viruses. However, little research has been done to evaluate their effects on Cronobacter sakazakii, an opportunistic pathogen usually infecting infants and having a high fatality rate. The aims of this work were to investigate the antibacterial property of novel, synthesized, positively charged silver nanoparticles against C. sakazakii and to discuss the potential antibacterial mechanisms involved. In this study, the spherical and face-centered cubic silver nanoparticles had a mean particle size of 31.2 nm and were synthesized by reducing Ag⁺ using citrate and dispersed by glycerol and polyvinylpyrrolidone (PVP) under alkaline conditions. Minimum inhibitory concentrations (MIC) and inhibition zone tests showed that the AgNP exhibited strong antibacterial activity against 4 tested C. sakazakii strains with mean MIC of 62.5 to 125 mg/L and average inhibition zone diameters of 13.8 to 16.3 mm. Silver nanoparticles caused cell membrane injury accompanied by adsorption of AgNP onto the cell surface, as shown by changes in cell morphology, cell membrane hyperpolarization, and accelerated leakage of intracellular reducing sugars and proteins outward from the cytoplasm. In addition, dysfunction of the respiratory chain was induced after treatment with AgNP, which was supported by a decrease in intracellular ATP and inhibition of related dehydrogenases. This research indicates that AgNP could be a novel and efficient antibacterial agent to control C. sakazakii contamination in environments producing powdered infant formulas from milk.

Survival of Cronobacter in powdered infant formula and their variation in biofilm formation

Cronobacter is a ubiquitous Gram-negative pathogen bacterium capable of surviving in low water activity environments, in particular powdered infant formula (PIF). Seven Cronobacter strains representing four different species (C. sakazakii, n = 4; C. malonaticus, n = 1; C. muytjensii, n = 1; C. turicensis, n = 1) were subjected to dry stress and stored in PIF at room temperature. The resulting survivor curves showed that Cronobacter sp. can survive for extended periods of at least 3 months with a significant, but moderate, variability regarding the level of resistance between species; however, no correlation was evident regarding the origin of strains. These results are evaluated with regard to other key characteristics, including genomic profiles and biofilm formation capacities of the strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cronobacter can survive extended periods of at least 3 months in PIF, with moderately significant interspecific variability in desiccation resistance. Results are evaluated with regard to genomic profiles and biofilm formation capacities of the strains, and contribute to an improved understanding of the environmental persistence of Cronobacter in contaminated PIF, and subsequent risk to infant exposure.

Genes involved in tolerance to osmotic stress by random mutagenesis in Cronobacter malonaticus

Cronobacter malonaticus is one of the opportunistic food-borne pathogens in powdered infant formula and has unusual abilities to survive under environmental stresses such as osmotic conditions. However, the genes involved in osmotic stress have received little attention in C. malonaticus. Here, genes involved in osmotic stress were determined in C. malonaticus using a transposon mutagenesis approach. According to the growth of mutants (n = 215) under 5.0% NaCl concentration, the survival of 5 mutants under osmotic stress was significantly decreased compared with that of the wild type strain. Five mutating sites, including potassium efflux protein KefA, inner membrane protein YqjF, peptidylprolyl isomerase, Cys-tRNA(Pro)/Cys-tRNA(Cys) deacylase, and oligogalacturonate lyase were successfully identified. In addition, the biofilm formation of 5 mutants was determined using crystal violet staining, scanning electron microscopy, and confocal laser scanning microscopy, and the biofilms of 5 mutants significantly decreased within 72 h compared with that of wild type strain. This is the first report to determine the genes involved in osmotic tolerance in C. malonaticus. The findings provided valuable information for deep understanding of the mechanism of survival of C. malonaticus under osmotic stress, and a possible relationship between biofilm formation and tolerance to osmotic stress was also demonstrated in C. malonaticus.

The Glutaredoxin Gene, grxB, Affects Acid Tolerance, Surface Hydrophobicity, Auto-Aggregation, and Biofilm Formation in Cronobacter sakazakii

Cronobacter species are foodborne pathogens that can cause neonatal meningitis, necrotizing enterocolitis, and sepsis; they have unusual abilities to survive in environmental stresses such as acid stress. However, the factors involved in acid stress responses and biofilm formation in Cronobacter species are poorly understood. In this study, we investigated the role of grxB on cellular morphology, acid tolerance, surface hydrophobicity, auto-aggregation (AAg), motility, and biofilm formation in Cronobacter sakazakii. The deletion of grxB decreased resistance to acid stresses, and notably led to weaker surface hydrophobicity, AAg, and biofilm formation under normal and acid stress conditions, compared with those of the wild type strain; however, motility was unaffected. Therefore, grxB appears to contribute to the survival of C. sakazakii in acid stresses and biofilm formation. This is the first report to provide valuable evidence for the role of grxB in acid stress responses and biofilm formation in C. sakazakii.

New virulence factor CSK29544_02616 as LpxA binding partner in Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic pathogen that can cause meningitis and necrotizing enterocolitis in premature infants, but its virulence determinants remain largely unknown. In this study, a transposon-mediated random-mutant library of C. sakazakii was used to identify new virulence factors. Compared to wild-type bacteria, a mutant lacking CSK29544_02616 (referred to as labp) was defective in invasion into intestinal epithelial cells (by at least 1000-fold) and showed less phagocytosis by macrophages (by at least 50-fold). The lack of labp in C. sakazakii changed the profile of outer membrane proteins, decreased the production of lipopolysaccharides, and increased the production of membrane phospholipids. Bacterial physiological characteristics including surface hydrophobicity and motility were also altered in the absence of labp, presumably because of changes in the bacterial-envelope structure. To systematically determine the role of labp, ligand fishing was conducted using Labp as a bait, which revealed LpxA as a binding partner of Labp. LpxA is UDP-N-acetylglucosamine (GlcNAc) acyltransferase, the first enzyme in the pathway of lipid A biosynthesis. Labp increased the enzymatic activity of LpxA without influencing lpxA expression. Considering multifaceted roles of lipopolysaccharides in virulence regulation, Labp is a novel virulence factor that promotes the production of lipid A by LpxA in Cronobacter.

Thymoquinone Inhibits Virulence Related Traits of Cronobacter sakazakii ATCC 29544 and Has Anti-biofilm Formation Potential

The aim of this study was to determine whether thymoquinone, the principal active ingredient in the volatile oil of Nigella sativa seeds, could suppress certain virulence traits of Cronobacter sakazakii ATCC 29544 which contribute to infection. Sub-inhibitory concentrations of thymoquinone significantly decreased motility, quorum sensing, and endotoxin production of C. sakazakii ATCC 29544 and biofilm formation of C. sakazakii 7-17. Thymoquinone substantially reduced the adhesion and invasion of C. sakazakii ATCC 29544 to HT-29 cells and decreased the number of intracellular bacterial cells within the RAW 264.7 macrophage cells. Thymoquinone also repressed the transcription of sixteen genes involved in the virulence. These findings suggest that thymoquinone could attenuated virulence-related traits of C. sakazakii ATCC 29544, and its effects on other C. sakazakii strains and in vivo C. sakazakii infection need further investigation.

Comparative Outer Membrane Protein Analysis of High and Low-Invasive Strains of Cronobacter malonaticus

Cronobacter are an important group of foodborne pathogens that has been linked to life-threatening infections in both infants and adults. The major infections associated with Cronobacter species are neonatal meningitis, necrotizing enterocolitis, and septicaemia. There are seven species in the Cronobacter genus, of which only three are of clinical importance; Cronobacter sakazakii, Cronobacter malonaticus, and Cronobacter turicensis. To date most studies have focussed on C. sakazakii as it is the major species associated with neonatal infections. However, recently C. malonaticus, in particular sequence type 7 (ST7), has been noted as being prevalent in adult infections and therefore warranting further investigation. In this study, eight strains of C. malonaticus ST7, that had been isolated from a wide range of sources and varied in their in vitro virulence, were chosen for proteomic analysis of their outer membrane proteins (OMPs). One-dimensional gel analysis revealed a ~29 kDa size band that was only present in the highly invasive strains. Subsequent mass spectrometric analysis identified several peptides that matched the flagellin protein. The presence of flagellin protein was confirmed in 2D gel spot. Mass spectrometry analysis of total OMPs revealed that the four highly invasive C. malonaticus strains expressed the main flagellum proteins that were absent from the four low invasive strains. These were the flagellar hook protein FlgE, flagellar hook-associated protein 1, flagellar hook-associated protein, flagellin, and flagellar hook-filament junction protein FlgL. This data indicates that C. malonaticus flagellar proteins may have an important role in the organism's invasion properties.

A Negative Regulator of Cellulose Biosynthesis, bcsR, Affects Biofilm Formation, and Adhesion/Invasion Ability of Cronobacter sakazakii

Cronobacter sakazakii is an important foodborne pathogen that causes neonatal meningitis and sepsis, with high mortality in neonates. However, very little information is available regarding the pathogenesis of C. sakazakii at the genetic level. In our previous study, a cellulose biosynthesis-related gene (bcsR) was shown to be involved in C. sakazakii adhesion/invasion into epithelial cells. In this study, the detailed functions of this gene were investigated using a gene knockout technique. A bcsR knockout mutant (ΔbcsR) of C. sakazakii ATCC BAA-894 showed decreased adhesion/invasion (3.9-fold) in human epithelial cell line HCT-8. Biofilm formation by the mutant was reduced to 50% of that exhibited by the wild-type (WT) strain. Raman spectrometry was used to detect variations in biofilm components caused by bcsR knockout, and certain components, including carotenoids, fatty acids, and amides, were significantly reduced. However, another biofilm component, cellulose, was increased in ΔbcsR, suggesting that bcsR negatively affects cellulose biosynthesis. This result was also verified via RT-PCR, which demonstrated up-regulation of five crucial cellulose synthesis genes (bcsA, B, C, E, Q) in ΔbcsR. Furthermore, the expression of other virulence or biofilm-related genes, including flagellar assembly genes (fliA, C, D) and toxicity-related genes (ompA, ompX, hfq), was studied. The expression of fliC and ompA in the ΔbcsR mutant was found to be remarkably reduced compared with that in the wild-type and the others were also affected excepted ompX. In summary, bcsR is a negative regulator of cellulose biosynthesis but positively regulates biofilm formation and the adhesion/invasion ability of C. sakazakii.

Cronobacter sakazakii ATCC 29544 Autoaggregation Requires FliC Flagellation, Not Motility

Cronobacter sakazakii is an opportunistic nosocomial and foodborne pathogen that causes severe infections with high morbidity and mortality rates in neonates, the elderly, and immunocompromised individuals. Little is known about the pathogenesis mechanism of this pathogen and if there are any consequences of C. sakazakii colonization in healthy individuals. In this study, we characterized the mechanisms of autoaggregation in C. sakazakii ATCC 29544 (CS29544). Autoaggregation in CS29544 occurred rapidly, within 30 min, and proceeded to a maximum of 70%. Frameshift mutations in two flagellum proteins (FlhA and FliG) were identified in two nonautoaggregating CS29544 clonal variant isolates. Strategic gene knockouts were generated to determine if structurally intact and functional flagella were required for autoaggregation in CS29544. All structural knockouts (ΔflhA, ΔfliG, and ΔfliC) abolished autoaggregation, whereas the functional knockout (ΔmotAB) did not prevent autoaggregation. Complementation with FliC (ΔfliC/cfliC) restored autoaggregation. Autoaggregation was also disrupted by the addition of exogenous wild-type CS29544 filaments in a dose-dependent manner. Finally, filament supercoils tethering neighboring wild-type CS29544 cells together were observed by transmission electron microscopy. In silico analyses suggest that direct interactions of neighboring CS29544 FliC filaments proceed by hydrophobic bonding between the externally exposed hypervariable regions of the CS29544 FliC flagellin protein. Further research is needed to confirm if flagella-mediated autoaggregation plays a prominent role in C. sakazakii pathogenesis.

Inhibition of Cronobacter sakazakii Virulence Factors by Citral

Cronobacter sakazakii is a foodborne pathogen associated with fatal forms of necrotizing enterocolitis, meningitis and sepsis in neonates and infants. The aim of this study was to determine whether citral, a major component of lemongrass oil, could suppress putative virulence factors of C. sakazakii that contribute to infection. Sub-inhibitory concentrations of citral significantly decreased motility, quorum sensing, biofilm formation and endotoxin production. Citral substantially reduced the adhesion and invasion of C. sakazakii to Caco-2 cells and decreased bacterial survival and replication within the RAW 264.7 macrophage cells. Citral also repressed the expression of eighteen genes involved in the virulence. These findings suggest that citral has potential to be developed as an alternative or supplemental agent to mitigate the infections caused by C. sakazakii.

Biofilms in bioremediation and wastewater treatment: characterization of bacterial community structure and diversity during seasons in municipal wastewater treatment process

The bacterial community structure and diversity were assessed at the scale of rotating biodisk procedure (RB) in a semi-industrial pilot plant. As well, the Salmonella community was particularly monitored, and the effects of ultraviolet (UV-C₂₅₄) on the bacterial community were studied. The identification of dominant bacteria revealed the presence of beneficial and useful species that could play an important role in the process of wastewater purification. Several species as Enterobacter agglomerans, Cronobacter sakazakii, and Pantoea agglomerans known for their bioremediation activities were revealed in the majority of biofilm samples. Common detection of Salmonella community provides evidence that the RB system did not seriously affect Salmonella. Furthermore, the investigation on the (UV)-C₂₅₄ inactivation of the whole bacterial community, in secondary treated wastewater, showed variable UV resistance results. No Salmonella detection was registered at a dose of around 1440 mW s cm^-2 since a total disappearance of Salmonella was recorded.

Screening of genes involved in interactions with intestinal epithelial cells in Cronobacter sakazakii

Cronobacter sakazakii possesses a significant ability to adhere to and invade epithelial cells in its host. However, the molecular mechanisms underlying this process are poorly understood. In the current study, the adhesive and invasive capabilities of 56 C. sakazakii strains against human epithelial cells were evaluated, and one of them was selected for construction of a mutant library using the Tn5 transposon. In a systematic analysis of the adhesive and invasive capabilities of 1084 mutants, 10 mutants that showed more than a 50 % reduction in adhesion or invasion were obtained. Tail-PCR was used to sequence the flanking regions of the inserted transposon and 8 different genes (in 10 different mutants) were identified that encoded an exonuclease subunit, a sugar transporter, a transcriptional regulator, two flagellar biosynthesis proteins, and three hypothetical proteins. Raman spectroscopy was used to analyze variations in the biochemical components of the mutants, and the results showed that there were fewer amide III proteins, protein -CH deformations, nucleic acids and tyrosines and more phenylalanine, carotenes, and fatty acids in the mutants than in the wild type strain. Real-time PCR was used to further confirm the involvement of the genes in the adhesive and invasive abilities of C. sakazakii, and the results indicated that the expression levels of the 8 identified genes were upregulated 1.2- to 11.2-fold. The results of this study provide us with insight into the mechanism by which C. sakazakii infects host cells at molecular level.

Transcriptome analysis of Cronobacter sakazakii ATCC BAA-894 after interaction with human intestinal epithelial cell line HCT-8

Cronobacter spp. are opportunistic pathogens that are responsible for infections including severe meningitis, septicemia, and necrotizing enterocolitis in neonates and infants. To date, questions still remain regarding the mechanisms of pathogenicity and virulence determinants for each bacterial strain. In this study, we established an in vitro model for Cronobacter sakazakii ATCC BAA-894 infection of HCT-8 human colorectal epithelial cells. The transcriptome profile of C. sakazakii ATCC BAA-894 after interaction with HCT-8 cells was determined using high-throughput whole-transcriptome sequencing (RNA sequencing (RNA-seq)). Gene expression profiles indicated that 139 genes were upregulated and 72 genes were downregulated in the adherent C. sakazakii ATCC BAA-894 strain on HCT-8 cells compared to the cultured bacteria in the cell-free medium. Expressions of some flagella genes and virulence factors involved in adherence were upregulated. High osmolarity and osmotic stress-associated genes were highly upregulated, as well as genes responsible for the synthesis of lipopolysaccharides and outer membrane proteins, iron acquisition systems, and glycerol and glycerophospholipid metabolism. In sum, our study provides further insight into the mechanisms underlying C. sakazakii pathogenesis in the human gastrointestinal tract.

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

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

The DSF type quorum sensing signalling system RpfF/R regulates diverse phenotypes in the opportunistic pathogen Cronobacter

Several bacterial pathogens produce diffusible signal factor (DSF)-type quorum sensing (QS) signals to control biofilm formation and virulence. Previous work showed that in Burkholderia cenocepacia the RpfF_Bc/RpfR system is involved in sensing and responding to DSF signals and that this signal/sensor gene pair is highly conserved in several bacterial species including Cronobacter spp. Here we show that C. turicensis LMG 23827^T possesses a functional RpfF/R system that is involved in the regulation of various phenotypes, including colony morphology, biofilm formation and swarming motility. In vivo experiments using the zebrafish embryo model revealed a role of this regulatory system in virulence of this opportunistic pathogen. We provide evidence that the RpfF/R system modulates the intracellular c-di-GMP level of the organism, an effect that may underpin the alteration in phenotype and thus the regulated phenotypes may be a consequence thereof. This first report on an RpfF/R-type QS system of an organism outside the genus Burkholderia revealed that both the underlying molecular mechanisms as well as the regulated functions show a high degree of conservation.

A Novel Bacteriophage Targeting Cronobacter sakazakii Is a Potential Biocontrol Agent in Foods

Cronobacter sakazakii is an important pathogen that causes high mortality in infants. Due to its occasional antibiotic resistance, a bacteriophage approach might be an alternative effective method for the control of this pathogen. To develop a novel biocontrol agent using bacteriophages, the C. sakazakii-infecting phage CR5 was newly isolated and characterized. Interestingly, this phage exhibited efficient and relatively durable host lysis activity. In addition, a specific gene knockout study and subsequent complementation experiment revealed that this phage infected the host strain using the bacterial flagella. The complete genome sequence analysis of phage CR5 showed that its genome contains 223,989 bp of DNA, including 231 predicted open reading frames (ORFs), and it has a G+C content of 50.06%. The annotated ORFs were classified into six functional groups (structure, packaging, host lysis, DNA manipulation, transcription, and additional functions); no gene was found to be related to virulence or toxin or lysogen formation, but >80% of the predicted ORFs are unknown. In addition, a phage proteomic analysis using SDS-PAGE and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) revealed that seven phage structural proteins are indeed present, supporting the ORF predictions. To verify the potential of this phage as a biocontrol agent against C. sakazakii, it was added to infant formula milk contaminated with a C. sakazakii clinical isolate or food isolate, revealing complete growth inhibition of the isolates by the addition of phage CR5 when the multiplicity of infection (MOI) was 10(5).