Expression of stress regulator and virulence genes of Cronobacter sakazakii strain Yrt2a as a response to acid stress

Probiotic Saccharomyces boulardii Against Cronobacter sakazakii Infection: In Vitro and In Vivo Studies

Cronobacter sakazakii is an opportunistic foodborne pathogen causing intestinal and extra-intestinal diseases in humans, especially young children, and is regarded as one of the main concerns in public health. Saccharomyces boulardii is a well-known probiotic yeast widely used to treat and prevent antibiotic-associated diarrheal infections in infants and neonates. This study evaluated the preventive effects and potential of probiotic S. boulardii against C. sakazakii intestinal infections in humans. Viability, bacterial virulence factor, cellular pro-inflammatory gene expression, and nanomechanical properties of the cytoplasmic membrane of caco-2 cells were evaluated using MTT, real-time PCR, and AFM methods, respectively. Using histopathological analysis, S. boulardii treatment was evaluated on infected newborn C57 BL/6 mice. We found that S. boulardii inoculation significantly (P < 0.05) increased the viability and downregulated the cellular pro-inflammatory genes (IL-8 and NFkB) and bacterial virulence factor genes (ompA and hfq) in infected intestinal cells while also decreasing the morphological alterations. We also observed that S. boulardii treatment reduced the intestinal damage induced by C. sakazakii infection. In conclusion, our findings demonstrate that S. boulardii effectively protects against C. sakazakii infections. This probiotic yeast holds promise as a potential preventive and therapeutic agent for intestinal diseases associated with C. sakazakii.

RecA deletion disrupts protein homeostasis, leading to deamidation, oxidation, and impaired glycolysis in Cronobacter sakazakii

Cronobacter sakazakii is a foodborne pathogen linked to severe infections in infants and often associated with contaminated powdered infant formula. The RecA protein, a key player in DNA repair and recombination, also influences bacterial resilience and virulence. This study investigated the impact of recA deletion on the pathogenicity and environmental stress tolerance of C. sakazakii BAA-894. A recA knockout mutant displayed impaired growth, desiccation tolerance, and biofilm formation. In a rat model, the mutant demonstrated significantly reduced virulence evidenced by higher host survival rates and lower bacterial loads in blood and tissues compared to the wild-type strain. Proteomic analysis revealed extensive disruptions in protein expression, particularly downregulation of carbohydrate metabolism and respiration-related proteins, alongside increased protein deamidation and oxidation. Functional assays identified fructose-bisphosphate aldolase as a target of oxidative and deamidative damage, resulting in reduced enzymatic activity and glycolytic disruption. These findings highlight the critical role of RecA in maintaining protein homeostasis, environmental resilience, and pathogenicity in C. sakazakii, providing valuable insights for developing targeted interventions against this pathogen.IMPORTANCECronobacter sakazakii poses significant risks due to its ability to persist in low-moisture environments and cause severe neonatal infections. This study identifies RecA as a key factor in environmental resilience and virulence, making it a promising target for mitigating infections and contamination. Inhibiting RecA function could sensitize C. sakazakii to stress during production and sterilization processes, reducing its persistence in powdered infant formula. Future research on RecA-specific inhibitors may lead to innovative strategies for enhancing food safety and preventing infections caused by this pathogen.

γ-Aminobutyric Acid (GABA) Metabolic Bypass Plays a Crucial Role in Stress Tolerance and Biofilm Formation in C. sakazakii ATCC 29544

Cronobacter sakazakii is a foodborne pathogen characterized by its robust stress tolerance and ability to form biofilms, which facilitates its survival in powdered infant formula (PIF) processing environments for prolonged periods. Gamma-aminobutyric acid (GABA) is a kind of non-protein amino acid that acts as an osmoprotectant. This study aimed to elucidate the effects of the gabT gene on the survival of C. sakazakii, GABA accumulation, and biofilm formation under desiccation, osmotic stress, and acid exposure. A gabT knockout strain of C. sakazakii was developed using gene recombination techniques. The GABA content and survival rates of both the wild-type and knockout strains were compared under various stress conditions. Scanning electron microscopy (SEM) was used to observe cellular damage and biofilm formation. Statistical analysis was performed using a one-way analysis of variance (ANOVA). The deletion of gabT resulted in enhanced GABA accumulation under different stress conditions, improving the bacterium's tolerance to desiccation, osmotic pressure, and acid treatment. SEM images revealed that under identical stress conditions, the gabT knockout strain exhibited less cellular damage compared to the wild-type strain. Both strains were capable of biofilm formation under low osmotic pressure stress, but the gabT knockout strain showed higher GABA content, denser biofilm formation, and increased biofilm quantity. Similar trends were observed under acid stress conditions. The gabT gene plays a key role in modulating GABA accumulation, which enhances the stress tolerance and biofilm formation of C. sakazakii. These findings provide new insights into the role of GABA in bacterial survival mechanisms and highlight the potential for targeting GABA pathways to control C. sakazakii in food processing environments.

VBNC Cronobacter sakazakii survives in macrophages by resisting oxidative stress and evading recognition by macrophages

Survival in host macrophages is an effective strategy for pathogenic bacterial transmission and pathogenesis. Our previous study found that viable but non-culturable (VBNC) Cronobacter Sakazakii (C. sakazakii) can survive in macrophages, but its survival mechanism is not clear. In this study, we investigated the possible mechanisms of VBNC C. sakazakii survival in macrophages in terms of environmental tolerance within macrophages and evasion of macrophages recognition. The results revealed that VBNC C. sakazakii survived under oxidative conditions at a higher rate than the culturable C. sakazakii. Moreover, the stringent response gene (relA and spoT) and the antioxidant-related genes (sodA, katG, and trxA) were up-regulated, indicating that VBNC C. sakazakii may regulate antioxidation through stringent response. On the other hand, compared with culturable C. sakazakii, VBNC C. sakazakii caused reduced response (Toll-like receptor 4) in macrophages, which was attributed to the suppression of biosynthesis of the lipopolysaccharides (LPS). Furthermore, we found that ellagic acid can reduce the survival rate of bacteria in macrophages by improving the immune TLR4 recognition ability of macrophages. In conclusion, VBNC C. sakazakii may survive in macrophages by regulating oxidative tolerance through stringent response and altering LPS synthesis to evade TLR4 recognition by macrophages, which suggests the pathogenic risk of VBNC C. sakazakii.

The viable but non-culturable (VBNC) status of Shewanella putrefaciens (S. putrefaciens) with thermosonication (TS) treatment

Although thermosonication (TS) treatment has been widely used in food sterilization, the viable but non-culturable (VBNC) of bacteria with TS treatment has still concerned potential food safety and public health. The molecular mechanism of VBNC status of bacteria with TS treatment is not clearly known. Therefore, in this study, we used Shewanella putrefaciens, which was a common putrefactive bacteria in aquatic products, to study the VBNC state of bacteria with TS treatment. Firstly, our results revealed that S. putrefaciens still could enter the VBNC state after TS treatments: 50 kHz, 300 W, 30 min ultrasonic treatment and 70 °C heating; Subsequently, we found the VBNC state of S. putrefaciens can resist the damage of TS treatment, such as cell wall break, DNA degradation, etc; Finally, four-dimensional data-independent acquisition-based proteomics showed that under VBNC state, S. putrefaciens upregulated functional proteins to resist TS treatment, such as: ribosomal proteins to accelerate the synthesis of stress proteins to counteract TS treatments, ornithine decarboxylase SpeF and MraY to repair TS treatment-induced damage, etc. Meanwhile, S. putrefaciens downregulates metabolic and transport functional proteins such as dehydrogenase to reduce the metabolism. Importantly, among those proteins, the ribosomal transcriptional regulatory protein family, such as rpsB, etc, may be the key proteins for S. putrefaciens entering VBNC state. This finding can provide some new strategies for preventing VBNC status of bacteria with TS treatment, such as: inhibition of key proteins, etc.

EnvZ/OmpR Controls Protein Expression and Modifications in Cronobacter sakazakii for Virulence and Environmental Resilience

Cronobacter sakazakii is a notorious foodborne opportunistic pathogen, particularly affecting vulnerable populations such as premature infants, and poses significant public health challenges. This study aimed to elucidate the role of the envZ/ompR genes in environmental tolerance, pathogenicity, and protein regulation of C. sakazakii. An envZ/ompR knockout mutant was constructed and assessed for its impact on bacterial growth, virulence, environmental tolerance, and protein regulation. Results demonstrate that deletion of envZ/ompR genes leads to reduced growth rate and attenuated virulence in animal models. Additionally, the knockout strain exhibited compromised environmental tolerance, particularly in desiccation and oxidative stress conditions, along with impaired adhesion and invasion abilities in epithelial cells. Proteomic analysis revealed significant alterations in protein expression and phosphorylation patterns, highlighting potential compensatory mechanisms triggered by gene deletion. Furthermore, investigation into protein deamidation and glucose metabolism uncovered a link between envZ/ompR deletion and energy metabolism dysregulation. Interestingly, the downregulation of MalK and GrxC proteins was identified as contributing factors to altered desiccation tolerance and disrupted redox homeostasis, respectively, providing mechanistic insights into the phenotypic changes observed. Overall, this study enhances understanding of the multifaceted roles of envZ/ompR in C. sakazakii physiology and pathogenesis, shedding light on potential targets for therapeutic intervention and food safety strategies.

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.

Survival and Expression of rpoS and grxB of Cronobacter sakazakii in Powdered Infant Formula Under Simulated Gastric Conditions of Newborns

Cronobacter sakazakii can cause severe illnesses in infants, predominantly in preterm newborns, with consumption of contaminated powdered infant formula (PIF) being the major vehicle of infection. Using a dynamic human gastrointestinal simulator called the SHIME, this study examined the effects of gastric acidity and gastric digestion time of newborns on the survival and expression of stress genes of C. sakazakii. Individual strains, inoculated at 7 log CFU/mL into reconstituted PIF, were exposed to gastric pH values of 4.00, 5.00 and 6.00 for 4 h with gradual acidification. The survival results showed that C. sakazakii grew in the stomach portion of the SHIME during a 4-h exposure to pH 4.00, 5.00 and 6.00 by 0.96-1.05, 1.02-1.28 and 1.11-1.73 log CFU/mL, respectively. The expression of two stress genes, rpoS and grxB, throughout gastric digestion was evaluated using reverse transcription qPCR. The upregulation of rpoS and grxB during the 4-h exposure to simulated gastric fluid at pH 4.00 showed that C. sakazakii strains may be experiencing the most stress in the pH 4.00 treatment. The gene expression results also suggest that C. sakazakii strains appeared to develop an acid adaptation response during the 4-h exposure that may facilitate their survival. Altogether, this study highlights that a combination of low gastric acidity, long digestion time in the presence of reconstituted PIF, created a favorable environment for the adaptation and survival of C. sakazakii in the simulation of a newborn's stomach. This study gives directions for future research to further advance our understanding of the behavior of C. sakazakii in the GI tract of newborns.

Comprehensive Genomic Characterization of Cronobacter sakazakii Isolates from Infant Formula Processing Facilities Using Whole-Genome Sequencing

Cronobacter sakazakii is an opportunistic pathogen linked to outbreaks in powdered infant formula (PIF), primarily causing meningitis and necrotizing enterocolitis. Whole-genome sequencing (WGS) was used to characterize 18 C. sakazakii strains isolated from PIF (powdered infant formula) manufacturing plants (2011-2015). Sequence Type (ST) 1 was identified as the dominant sequence type, and all isolates carried virulence genes for chemotaxis, flagellar motion, and heat shock proteins. Multiple antibiotic resistance genes were detected, with all isolates exhibiting resistance to Cephalosporins and Tetracycline. A significant correlation existed between genotypic and phenotypic antibiotic resistance. The plasmid Col(pHAD28) was identified in the isolates recovered from the same PIF environment. All isolates harbored at least one intact phage. All the study isolates were compared with a collection of 96 publicly available C. sakazakii genomes to place these isolates within a global context. This comprehensive study, integrating phylogenetic, genomic, and epidemiological data, contributes to a deeper understanding of Cronobacter outbreaks. It provides valuable insights to enhance surveillance, prevention, and control strategies in food processing and public health contexts.

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.

DnaK-Mediated Protein Deamidation: a Potential Mechanism for Virulence and Stress Adaptation in Cronobacter sakazakii

Cronobacter sakazakii is a Gram-negative bacterium that causes infections in individuals of all ages, with neonates being the most vulnerable group. The objective of this study was to explore the function of the dnaK gene in C. sakazakii and to elucidate the impact of alterations in the protein composition regulated by dnaK on virulence and stress adaptation. Our research demonstrates the critical role of the dnaK gene in various key virulence factors, including adhesion, invasion, and acid resistance in C. sakazakii. Through the use of proteomic analysis, we discovered that deletion of the dnaK gene in C. sakazakii leads to an upregulation of protein abundance and increased levels of deamidated posttranscriptional modifications, suggesting that DnaK may play a role in maintaining proper protein activity by reducing protein deamidation in bacteria. These findings indicate that DnaK-mediated protein deamidation may be a novel mechanism for virulence and stress adaptation in C. sakazakii. These findings suggest that targeting DnaK could be a promising strategy for developing drugs to treat C. sakazakii infections. IMPORTANCE Cronobacter sakazakii can cause disease in individuals of all ages, with infections in premature infants being particularly deadly and resulting in bacterial meningitis and sepsis with a high mortality rate. Our study demonstrates that dnaK in Cronobacter sakazakii plays a critical role in virulence, adhesion, invasion, and acid resistance. Using proteomic analysis to compare protein changes in response to dnaK knockout, we found that dnaK knockout significantly upregulates the abundance of some proteins but also results in the deamidation of many proteins. Our research has identified a connection between molecular chaperones and protein deamidation, which suggests a potential future drug development strategy of targeting DnaK as a drug target.

Bacterial Stress Responses as Potential Targets in Overcoming Antibiotic Resistance

Bacteria can be adapted to adverse and detrimental conditions that induce general and specific responses to DNA damage as well as acid, heat, cold, starvation, oxidative, envelope, and osmotic stresses. The stress-triggered regulatory systems are involved in bacterial survival processes, such as adaptation, physiological changes, virulence potential, and antibiotic resistance. Antibiotic susceptibility to several antibiotics is reduced due to the activation of stress responses in cellular physiology by the stimulation of resistance mechanisms, the promotion of a resistant lifestyle (biofilm or persistence), and/or the induction of resistance mutations. Hence, the activation of bacterial stress responses poses a serious threat to the efficacy and clinical success of antibiotic therapy. Bacterial stress responses can be potential targets for therapeutic alternatives to antibiotics. An understanding of the regulation of stress response in association with antibiotic resistance provides useful information for the discovery of novel antimicrobial adjuvants and the development of effective therapeutic strategies to control antibiotic resistance in bacteria. Therefore, this review discusses bacterial stress responses linked to antibiotic resistance in Gram-negative bacteria and also provides information on novel therapies targeting bacterial stress responses that have been identified as potential candidates for the effective control of Gram-negative antibiotic-resistant bacteria.

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.