The occurrence and distribution characteristics of Cronobacter in diverse cereal kernels, flour, and flour-based products

Occurrence, molecular characterization and tolerance of Cronobacter spp. isolated from fermented corn products in China

Cronobacter spp. is an opportunistic pathogen that cause serious infections in all age groups. The organism has frequently been isolated from plant-based foods, especially cereals. Therefore, this study determined the occurrence, molecular characterization and tolerance of Cronobacter in fermented corn products (FCP) in China. Isolates were speciated and genotyped according to multilocus sequence typing (MLST), which included the pathogenicity associated allele ompA, as well as serotyping. Twenty-two strains of Cronobacter (20 C. sakazakii and 2 C. muytjensii) were isolated from 216 FCP samples, such as fermented corn noodles, fermented corn doughs, fermented corn vermicelli, fermented corn flour paste, fermented corn beverage, and fermented corn bread. All Cronobacter isolates were divided into 8 sequence types (STs), 4 serotypes and 4 ompA genotypes. The dominant type (10/22) was C. sakzakii ST8, C. sakazakii serotypes O:2, and ompA5, mainly in fermented corn noodle and fermented corn dough. Of all the strains, Cronobacter strains with ST770 had a stronger ability to tolerate acid, osmotic stress and cold, while Cronobacter strains with ST8 had a weaker tolerance to acid, osmotic stress and cold. Eight isolates exhibited strong biofilm-forming ability (OD595 > 1), among which the ST770, ST771, and ST556 strains showed more pronounced abilities. All Cronobacter isolates were sensitive to amoxicillin/clavulanic acid, ceftazidime, aztreonam, meropenem, tetracycline, ciprofloxacin, trimethoprim/sulfamethoxazole, polymyxin B, and chloramphenicol, while 77.27% of isolates were resistant to cefotaxime. This study supports the concern of Cronobacter transmission through plant-based foods, and provides a theoretical basis for the prevention and control of this pathogen in FCP.

Occurrence, genetic characterization, and antibiotic susceptibility of Cronobacter spp. isolated from low water activity functional foods in Brazil

Cronobacter spp. are bacterial pathogens isolated from a wide variety of foods. This study aims at evaluating the occurrence of Cronobacter spp. in low water activity functional food samples, detect the presence of virulence genes, and determine the antibiotic susceptibility of strains. From 105 samples, 38 (36.2%) were contaminated with Cronobacter spp. The species identified by polymerase chain reaction (PCR) and sequencing analyses (rpoB and fusA genes, respectively) were C. sakazakii (60.3%), C. dublinensis (25.4%), C. turincensis (9.5%), and C. malonaticus (4.8%). Nineteen fusA alleles were identified, including four new alleles. The virulence genes were identified by PCR and all isolates were positive for ompX and sodA genes, 60.3% to cpa gene, and 58.7% to hly gene. Using the disk diffusion method, antibiotic susceptibility to twelve antibiotics was assessed twice, separated by a 19-month period. In the first test, the isolates showed diverse antibiotic susceptibility profiles, with nineteen isolates (30.2%) being multi-drug resistant (resistant to three or more antibiotic classes), in the second, the isolates were susceptible to all antibiotics. Cronobacter spp. in functional foods demonstrates the need for continued investigation of this pathogen in foods, and further research is needed to clarify the loss of resistance of Cronobacter strains.

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.

Global and regional prevalence of Cronobacter sakazakii in powdered milk and flour

Cronobacter sakazakii (Cz) infections linked with powdered milk/flour (PMF) are on the increase in recent times. The current study aimed at assessing worldwide and regional prevalence of Cz in PMF. Cz-PMF-directed data were conscientiously mined in four mega-databases via topic-field driven PRISMA protocol without any restriction. Bivariate analysis of datasets was conducted and then fitted to random-intercept logistic mixed-effects regressions with leave-one-study-out-cross-validation (LOSOCV). Small-study effects were assayed via Egger's regression tests. Contributing factors to Cz contamination/detection in PMF were determined using 1000-permutation-bootstrapped meta-regressions. A total of 3761 records were found out of which 68 studies were included. Sample-size showed considerable correlation with Cz positivity (r = 0.75, p = 2.5e-17), Milkprod2020 (r = 0.33, p = 1.820e-03), and SuDI (r = - 0.30, p = 4.11e-03). The global prevalence of Cz in PMF was 8.39% (95%CI 6.06-11.51, PI: 0.46-64.35) with LOSOCV value of 7.66% (6.39-9.15; PI: 3.10-17.70). Cz prevalence in PMF varies significantly (p < 0.05) with detection methods, DNA extraction method, across continents, WHO regions, and world bank regions. Nation, detection method, world bank region, WHO region, and sample size explained 53.88%, 19.62%, 19.03%, 15.63%, and 9.22% of the true differences in the Cz prevalence in PMF, respectively. In conclusion, the results indicated that national will power in the monitoring and surveillance of Cz in PMF matched with adequate sample size and appropriate detection methods will go a long way in preventing Cz contamination and infections.

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

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

The Genotyping Diversity and Hemolytic Activity of Cronobacter spp. Isolated from Plant-Based Food Products in Poland

The present study aimed to determine the genotyping diversity and hemolytic properties of 24 strains of Cronobacter spp. (15 Cronobacter sakazakii, 6 Cronobacter malonaticus, 2 Cronobacter turicensis, and 1 Cronobacter condimenti) isolated from commercial ready-to-eat leaf vegetables, sprouts, nuts, and dried fruits. The multilocus sequence typing (MLST) method was used to determine the sequence types (ST) and clonal complexes (CC) of these strains. The study demonstrated the high genotypic diversity of the Cronobacter genus bacteria isolated from plant-based foods. Five novel sequence types (804, 805, 806, 807, and 808) and the presence of novel alleles in the ppsA, gltB, gyrB, and infB loci were detected. In total, 16 of the 24 strains were assigned to the sequence types ST99, ST258, ST17, ST648, ST21, ST494, and ST98. One C. sakazakii strain (s12) isolated from alfalfa sprouts was assigned to the clonal complex CC4, which encompasses strains often associated with severe infections leading to meningitis in infants. In addition, 87.5% and 16.7% of the Cronobacter spp. strains showed β-hemolysis of equine and sheep red blood cells, respectively. The presence of the pathogenic species C. sakazakii, C. malonaticus, and C. turicensis in ready-to-eat plant-derived food products shows they are potential sources of infection, especially to those with compromised immunity, which substantiates their further multi-faceted characterization. The significance of this study may prove useful not only in epidemiological investigations, but also in assessing the risk of infections caused by the presence of Cronobacter.

Cronobacter spp. Isolated from Quick-Frozen Foods in China: Incidence, Genetic Characteristics, and Antibiotic Resistance

Cronobacter spp. are emerging foodborne pathogens that cause severe diseases. However, information on Cronobacter contamination in quick-frozen foods in China is limited. Therefore, we studied the prevalence, molecular characterization, and antimicrobial susceptibility of Cronobacter in 576 quick-frozen food samples collected from 39 cities in China. Cronobacter spp. were found in 18.75% (108/576) of the samples, and the contamination degree of the total positive samples was 5.82 MPN/g. The contamination level of frozen flour product samples was high (44.34%). Among 154 isolates, 109 were C. sakazakii, and the main serotype was C. sakazakii O1 (44/154). Additionally, 11 serotypes existed among four species. Eighty-five sequence types (STs), including 22 novel ones, were assigned, indicating a relatively high genetic diversity of the Cronobacter in this food type. Pathogenic ST148, ST7, and ST1 were the main STs in this study. ST4, epidemiologically related to neonatal meningitis, was also identified. All strains were sensitive to cefepime, tobramycin, ciprofloxacin, and imipenem, in which the resistance to cephalothin was the highest (64.94%).Two isolates exhibited multidrug resistance to five and seven antimicrobial agents, respectively. In conclusion, these findings suggest that the comparatively high contamination level of Cronobacter spp. in quick-frozen foods is a potential risk warranting public attention.

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.

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.

Effects of radio frequency heating on microbial populations and physicochemical properties of buckwheat

Microbial contamination is a persistent problem for grain industry. Many studies have shown that radio frequency (RF) heating can effectively reduce pathogens populations in low moisture foods, but there is a lack on the efficacy to decontaminate natural microbiome. The main objectives of this study were to investigate the effects of different RF heating conditions on natural microbial populations and physicochemical properties of buckwheat. In this study, 30 buckwheat samples collected from 10 different Provinces in China were analyzed for their microbial loads, and the samples with the highest microbial populations were used for further study to select the suitable RF heating conditions. The results showed that microbial loads in tested buckwheat kernels were in the range of 3.4-6.2 log CFU/g. Samples from Shanxi (SX-3) had significantly higher microbial counts than other samples. The selected four temperature-time combinations: 75 °C-20 min, 80 °C-10 min, 85 °C-5 min, and 90 °C-0 min of RF heating could reduce microbial counts to <3.0 log CFU/g in buckwheat kernels at 16.5% w.b. moisture content. Furthermore, the reduction populations of the inoculated pathogens (Salmonella Typhimurium, Escherichia coli, Cronobacter sakazakii, and Bacillus cereus) reached 4.0 log CFU/g under the above conditions, and almost 5.0 log CFU/g especially at high temperature-short holding time combinations (85 °C-5 min and 90 °C-0 min). Besides, physicochemical properties evaluation also showed the insignificant color changes and nutrients loss after RF treatment at 90 °C-0 min. Therefore, the RF heating at 90 °C-0 min holds greater potential than the other lower temperature-longer holding time combinations for applications in buckwheat pasteurization.

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

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

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.

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

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

Natural Compounds With Antibacterial Activity Against Cronobacter spp. in Powdered Infant Formula: A Review

Bacteria from the genus Cronobacter are opportunistic foodborne pathogens capable of causing severe infections in neonates, the elderly and immunocompromised adults. The majority of neonatal infections have been linked epidemiologically to dehydrated powdered infant formulas (PIFs), the majority of which are manufactured using processes that do not ensure commercial sterility. Unfortunately, the osmotolerance, desiccation resistance, mild thermotolerance and wide-ranging minimum, optimum and maximum growth temperatures of Cronobacter spp. are conducive to survival and/or growth during the processing, reconstitution and storage of reconstituted PIFs. Consequently, considerable research has been directed at the development of alternative strategies for the control of Cronobacter spp. in PIFs, including approaches that employ antimicrobial compounds derived from natural sources. The latter include a range of phytochemicals ranging from crude extracts or essential oils derived from various plants (e.g., thyme, cinnamon, clove, marjoram, cumin, mint, fennel), to complex polyphenolic extracts (e.g., muscadine seed, pomegranate peel, olive oil, and cocoa powder extracts), purified simple phenolic compounds (e.g., carvacrol, citral, thymol, eugenol, diacetyl, vanillin, cinnamic acid, trans-cinnamaldehyde, ferulic acid), and medium chain fatty acids (monocaprylin, caprylic acid). Antimicrobials derived from microbial sources (e.g., nisin, other antibacterial peptides, organic acids, coenzyme Q0) and animal sources (e.g., chitosan, lactoferrin, antibacterial peptides from milk) have also been shown to exhibit antibacterial activity against the species. The selection of antimicrobials for the control of Cronobacter spp. requires an understanding of activity at different temperatures, knowledge about their mode of action, and careful consideration for toxicological and nutritional effects on neonates. Consequently, the purpose of the present review is to provide a comprehensive summary of currently available data pertaining to the antibacterial effects of natural antimicrobial compounds against Cronobacter spp. with a view to provide information needed to inform the selection of compounds suitable for control of the pathogen during the manufacture or preparation of PIFs by end users.