Emergent methods for inactivation of Cronobacter sakazakii in foods: A systematic review and meta-analysis

Cronobacter sakazakii is a potentially pathogenic bacterium that is resistant to osmotic stress and low aw, and capable of persisting in a desiccated state in powdered infant milks. It is widespread in the environment and present in various products. Despite the low incidence of cases, its high mortality rates of 40 to 80 % amongst neonates make it a microorganism of public health interest. This current study performed a comparative assessment between current reduction methods applied for C. sakazakii in various food matrices, indicating tendencies and relevant parameters for process optimization. A systematic review and meta-analysis were conducted, qualitatively identifying the main methods of inactivation and control, and quantitatively evaluating the effect of treatment factors on the reduction response. Hierarchical clustering dendrograms led to conclusions on the efficiency of each treatment. Review of recent research trend identified a focus on the potential use of alternative treatments, with most studies related to non-thermal methods and dairy products. Using random-effects meta-analysis, a summary effect-size of 4-log was estimated; however, thermal methods and treatments on dairy matrices displayed wider dispersions - of τ2 = 8.1, compared with τ2 = 4.5 for vegetal matrices and τ2 = 4.0 for biofilms. Meta-analytical models indicated that factors such as chemical concentration, energy applied, and treatment time had a more significant impact on reduction than the increase in temperature. Non-thermal treatments, synergically associated with heat, and treatments on dairy matrices were found to be the most efficient.

Microbiological survey and genomic analysis of Cronobacter sakazakii strains isolated from US households and retail foods

Cronobacter species are opportunistic pathogens that are capable of causing morbidity and mortality, particularly in infants. Although the transmission dynamics involved in Cronobacter infections remain largely unknown, contaminated powdered infant formula (PIF) has been linked to 30% of Cronobacter sakazakii cases involving invasive illness in infants. As several lines of evidence have implicated the domestic environment in PIF contamination, we undertook a microbiological survey of homes (N = 263) across the US. Cronobacter spp. and C. sakazakii were isolated from 36.1% and 24.7% of US homes, respectively, with higher recovery rates observed for floor and kitchen surfaces. Multi-locus sequence typing indicated that the dominant strain was C. sakazakii ST4, the sequence type most commonly associated with neonatal meningitis. For comparison purposes, retail foods (N = 4,009) were also surveyed, with the highest contamination frequencies (10.1%-26.3%) seen for nut products, seeds, and grains/baked goods/flours. The sequence type profile of isolates recovered from homes mirrored that of isolates recovered from retail foods, with increased representation of ST1, ST4, ST13, ST17, and ST40. Analysis of 386 whole genomic sequences revealed significant diversity. Redundancies were only observed for isolates recovered from within the same domicile, and there were no identical matches with sequences archived at the NCBI pathogen database. Genes coding for putative virulence and antibiotic resistance factors did not segregate with clinically significant sequence types. Collectively, these findings support the possibility that contamination events occurring within the home should not be overlooked as a contributor to community-onset Cronobacter infections.

IMPORTANCE

Cronobacter sakazakii is an opportunistic pathogen that can cause significant morbidity and mortality in neonates. Its transmission dynamics are poorly understood, though powered infant formula (PIF) is thought to be the major transmission vehicle. How the PIF becomes contaminated remains unknown. Our survey shows that roughly 1/4 of US homes are contaminated with Cronobacter sakazakii, particularly in the kitchen setting. Our analyses suggest that the domestic environment may contribute to contamination of PIF and provides insights into mitigating the risk of transmission.

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.

Underestimated Risks of Infantile Infectious Disease from the Caregiver's Typical Handling Practices of Infant Formula

The impact on infant caregiver as a reservoir of pathogens has not been exploited with perspective to powdered infant formula (PIF). Here we reveal novel route of pathogen transfer through hand-spoon-PIF unexpectedly occurred by even typical practices of caregivers, handling of PIF and storage of feeding-spoon in PIF container. Hand-spoon-PIF contamination route was simulated to analyze the transfer and subsequent survival of pathogens. Major pathogens associated with infantile fatal diseases (Cronobacter sakazakii, Salmonella enterica, Staphylococcus aureus) were readily transmitted to PIF from skin (3−6 log CFU/hand) via spoons following long-term survival of transferred pathogens (3 weeks; use-by date of PIF) as the excessive level of infectious dose, highlighting direct onset of diseases. Low bacterial load on skin (ca. 1 log CFU/hand) could prevent cross-contamination of PIF, however, at least 72 h survival of transferred pathogen on spoons demonstrated the probability on re-contamination of PIF. To our knowledge, this is the first study to investigate the cross-contamination of utensils in contact with powdered-foods. Bacterial load on hands is the key determinant of pathogen transfer and the extent of risk are species-dependent. These evidential results redefine risk of caregivers’ practices and facilitate incorporation of cross-contamination into risk-assessment as underestimated route of infection.

Draft genomes of Cronobacter sakazakii strains isolated from dried spices bring unique insights into the diversity of plant-associated strains

Cronobacter sakazakii is a Gram-negative opportunistic pathogen that causes life- threatening infantile infections, such as meningitis, septicemia, and necrotizing enterocolitis, as well as pneumonia, septicemia, and urinary tract and wound infections in adults. Here, we report 26 draft genome sequences of C. sakazakii, which were obtained from dried spices from the USA, the Middle East, China, and the Republic of Korea. The average genome size of the C. sakazakii genomes was 4393 kb, with an average of 4055 protein coding genes, and an average genome G + C content of 56.9%. The genomes contained genes related to carbohydrate transport and metabolism, amino acid transport and metabolism, and cell wall/membrane biogenesis. In addition, we identified genes encoding proteins involved in osmotic responses such as DnaJ, Aquaproin Z, ProQ, and TreF, as well as virulence-related and heat shock-related proteins. Interestingly, a metabolic island comprised of a variably-sized xylose utilization operon was found within the spice-associated C. sakazakii genomes, which supports the hypothesis that plants may serve as transmission vectors or alternative hosts for Cronobacter species. The presence of the genes identified in this study can support the remarkable phenotypic traits of C. sakazakii such as the organism's capabilities of adaptation and survival in response to adverse growth environmental conditions (e.g. osmotic and desiccative stresses). Accordingly, the genome analyses provided insights into many aspects of physiology and evolutionary history of this important foodborne pathogen.

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

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

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.

Evaluation of Whole Genome Mapping as a Fast and Automated Molecular Epidemiological Tool for the Study of Cronobacter spp. in Powdered Infant Formula Processing Facilities

Cronobacter has been identified as the causative agent of outbreaks or sporadic cases of meningitis, necrotizing enterocolitis, and septicemia associated with powdered infant formula. Food processing environments may provide a possible contamination route. The purpose of this study was to evaluate whole genome mapping (WGM) as a fast and automated molecular epidemiological method for characterizing Cronobacter spp. in the processing environment. This is the first study indicating the applicability of WGM to Cronobacter. WGM was compared with ribotyping, which is often used as an automated typing tool, and with pulsed-field gel electrophoresis, which is a well-known and highly discriminating tool that is also based on restriction site analysis. The comparison of the three tools was carried out on a subset of Cronobacter isolates collected from 2011 to 2014 through a monitoring program. The performance characteristics of WGM have not yet been described; therefore, in the current study its performance was evaluated based on five criteria: typeability, reproducibility, stability, epidemiological concordance, and the discrimination power. WGM was shown to produce typeable, reproducible, and stable results. With a similar cut-off of 98%, WGM was shown to have a discriminatory power equivalent to pulsed-field gel electrophoresis and higher than ribotyping. Future studies are needed to confirm the indicated cut-off level of 98%.

Cronobacter spp

The Cronobacter group of pathogens, associated with severe and potentially life-threatening diseases, until recently were classified as a single species, Enterobacter sakazakii. The group was reclassified in 2007 into the genus Cronobacter as a member of the Enterobacteriaceae. This chapter outlines the history behind the epidemiology, analyzes how our understanding of these bacteria has evolved, and highlights the clinical significance the Cronobacter spp. have for neonatal and elderly patient populations and treatment of the associated infections.

The Prevalence and Control of Bacillus and Related Spore-Forming Bacteria in the Dairy Industry

Milk produced in udder cells is sterile but due to its high nutrient content, it can be a good growth substrate for contaminating bacteria. The quality of milk is monitored via somatic cell counts and total bacterial counts, with prescribed regulatory limits to ensure quality and safety. Bacterial contaminants can cause disease, or spoilage of milk and its secondary products. Aerobic spore-forming bacteria, such as those from the genera Sporosarcina, Paenisporosarcina, Brevibacillus, Paenibacillus, Geobacillus and Bacillus, are a particular concern in this regard as they are able to survive industrial pasteurization and form biofilms within pipes and stainless steel equipment. These single or multiple-species biofilms become a reservoir of spoilage microorganisms and a cycle of contamination can be initiated. Indeed, previous studies have highlighted that these microorganisms are highly prevalent in dead ends, corners, cracks, crevices, gaskets, valves and the joints of stainless steel equipment used in the dairy manufacturing plants. Hence, adequate monitoring and control measures are essential to prevent spoilage and ensure consumer safety. Common controlling approaches include specific cleaning-in-place processes, chemical and biological biocides and other novel methods. In this review, we highlight the problems caused by these microorganisms, and discuss issues relating to their prevalence, monitoring thereof and control with respect to the dairy industry.

Occurrence and Characterization of Cronobacter spp. in Dehydrated Rice Powder from Chinese Supermarket

Cronobacter spp. are emerging food-borne pathogens and have been identified as causative agents of meningitis and necrotizing enterocolitis in infants. Dehydrated rice is popular with a wide range of people and it is frequently used as a substitute for infant milk powder to baby older than four months. The occurrence of Cronobacter spp. was investigated in 1,012 samples of dehydrated rice powder collected from 14 manufacturers in China during 2010 to 2012. The isolates were identified using fusA allele sequencing and subtyped using pulsed-field gel electrophoresis. Seventy-six samples (7.5%) contained Cronobacter spp. The prevalence among manufacturers ranged from 0-28.8%. The 76 isolates included 4 species [Cronobacter sakazakii (52 isolates) Cronobacter malonaticus (14 isolates), Cronobacter dublinensis (7 isolates), and Cronobacter muytjensii (3 isolates)]. Twenty-three unique fusA alleles and sixty-six PFGE-patterns were detected. All isolated strains were observed to be sensitive or to show intermediate susceptibility to eight tested antimicrobial agents. The study revealed serious contamination of dehydrated rice powder by Cronobacter spp., with prevalence varying among manufacturers in China. Identified Cronobacter species, fusA alleles, and subtypes were diverse.

Novel approaches to improve the intrinsic microbiological safety of powdered infant milk formula

Human milk is recognised as the best form of nutrition for infants. However; in instances where breast-feeding is not possible, unsuitable or inadequate, infant milk formulae are used as breast milk substitutes. These formulae are designed to provide infants with optimum nutrition for normal growth and development and are available in either powdered or liquid forms. Powdered infant formula is widely used for convenience and economic reasons. However; current manufacturing processes are not capable of producing a sterile powdered infant formula. Due to their immature immune systems and permeable gastro-intestinal tracts, infants can be more susceptible to infection via foodborne pathogenic bacteria than other age-groups. Consumption of powdered infant formula contaminated by pathogenic microbes can be a cause of serious illness. In this review paper, we discuss the current manufacturing practices present in the infant formula industry, the pathogens of greatest concern, Cronobacter and Salmonella and methods of improving the intrinsic safety of powdered infant formula via the addition of antimicrobials such as: bioactive peptides; organic acids; probiotics and prebiotics.

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

The genus Cronobacter consists of a diverse group of Gram-negative bacilli and comprises seven species: Cronobacter sakazakii, Cronobacter malonaticus, Cronobacter muytjensii, Cronobacter turicensis, Cronobacter dublinensis, Cronobacter universalis and Cronobacter condimenti. Cronobacter are regarded as opportunistic pathogens, and have been implicated in newborn and infant infections, causing meningitis, necrotizing enterocolitis and bacteraemia or sepsis. Cronobacter virulence is believed to be due to multiple factors. Some strains were found to produce diarrhoea or cause significant fluid accumulation in suckling mice. Two iron acquisition systems (eitCBAD and iucABCD/iutA), Cronobacter plasminogen activator gene (cpa), a 17 kb type VI secretion system (T6SS), and a 27 kb filamentous haemagglutinin gene (fhaBC) and associated putative adhesins locus are harboured on a family of RepFIB-related plasmids (pESA3 and pCTU1), suggesting that these are common virulence plasmids; 98% of 229 tested Cronobacter strains possessed these plasmids. Even though pESA3 and pCTU1 share a common backbone composed of the repA gene and eitCBAD and iucABCD/iutA gene clusters, the presence of cpa, T6SS and FHA loci depended on species, demonstrating a strong correlation with the presence of virulence traits, plasmid type and species. Other factors were observed, in that Cronobacter form biofilms, and show unusual resistance to heat, dry and acid stress growth conditions. The outer-membrane protein A is probably one of the best-characterized virulence markers of Cronobacter. Furthermore, it was reported that Cronobacter employ phosphatidylinositide 3-kinase/Akt signalling, which activates protein kinase C-α and impairs the host cell's mitogen-activated protein kinase pathway, in order to invade cells. Cronobacter can also use immature dendritic cells and macrophages to escape the immune response. This review addresses the various virulence and environmental-adaptive characteristics possessed by members of the genus Cronobacter.

Complete genome sequence and phenotype microarray analysis of Cronobacter sakazakii SP291: a persistent isolate cultured from a powdered infant formula production facility

Outbreaks of human infection linked to the powdered infant formula (PIF) food chain and associated with the bacterium Cronobacter, are of concern to public health. These bacteria are regarded as opportunistic pathogens linked to life-threatening infections predominantly in neonates, with an under developed immune system. Monitoring the microbiological ecology of PIF production sites is an important step in attempting to limit the risk of contamination in the finished food product. Cronobacter species, like other microorganisms can adapt to the production environment. These organisms are known for their desiccation tolerance, a phenotype that can aid their survival in the production site and PIF itself. In evaluating the genome data currently available for Cronobacter species, no sequence information has been published describing a Cronobacter sakazakii isolate found to persist in a PIF production facility. Here we report on the complete genome sequence of one such isolate, Cronobacter sakazakii SP291 along with its phenotypic characteristics. The genome of C. sakazakii SP291 consists of a 4.3-Mb chromosome (56.9% GC) and three plasmids, denoted as pSP291-1, [118.1-kb (57.2% GC)], pSP291-2, [52.1-kb (49.2% GC)], and pSP291-3, [4.4-kb (54.0% GC)]. When C. sakazakii SP291 was compared to the reference C. sakazakii ATCC BAA-894, which is also of PIF origin, the annotated genome data identified two interesting functional categories, comprising of genes related to the bacterial stress response and resistance to antimicrobial and toxic compounds. Using a phenotypic microarray (PM), we provided a full metabolic profile comparing C. sakazakii SP291 and the previously sequenced C. sakazakii ATCC BAA-894. These data extend our understanding of the genome of this important neonatal pathogen and provides further insights into the genotypes associated with features that can contribute to its persistence in the PIF environment.

Cronobacter: an emerging opportunistic pathogen associated with neonatal meningitis, sepsis and necrotizing enterocolitis

Members of the genus Cronobacter are an emerging group of opportunist Gram-negative pathogens. This genus was previously thought to be a single species, called Enterobacter sakazakii. Cronobacter spp. typically affect low-birth-weight neonates, causing life-threatening meningitis, sepsis and necrotizing enterocolitis. Outbreaks of disease have been associated with contaminated infant formula, although the primary environmental source remains elusive. Advanced understanding of these bacteria and better classification has been obtained by improved detection techniques and genomic analysis. Research has begun to characterize the virulence factors and pathogenic potential of Cronobacter. Investigations into sterilization techniques and protocols for minimizing the risk of contamination have been reviewed at national and international forums. In this review, we explore the clinical impact of Cronobacter neonatal and pediatric infections, discuss virulence and pathogenesis, and review prevention and treatment strategies.

Behavior of Enterobacter pulveris in amorphous and crystalline powder matrices treated with supercritical carbon dioxide

The resistance of an Enterobacter pulveris strain to combined heat and supercritical carbon dioxide (scCO(2)) treatments in different powder matrices was examined. The strain proved resistant to scCO(2) treatment up to 50 MPa pressure at temperatures >73 °C for at least 20 min in a commercial infant formula. Water availability was shown to be important for the observed thermotolerance, because introduction of water in the scCO(2) gas flow during treatment resulted in a 1 log(10) cfu/g reduction of the initial inoculum. Interestingly, similar tolerance to heat and scCO(2) treatment was observed in a less complex matrix, a maltodextrin powder. In contrast, the bacterial strain proved sensitive to lower temperatures (55-65 °C) over shorter times (≤10 min) in a dextrose powder composed of crystalline particles. Therefore, the microorganism demonstrates heat sensitivity in the crystalline powder matrix closer to that of nonpowder liquid matrices. These data demonstrate the increased heat tolerance of the bacterium specifically in amorphous powders and indicate that this characteristic is not dependent on fat and other components commonly found in infant formula. The information is important in designing strategies to deal with contamination of powders with Enterobacteriacae, including pathogenic Cronobacter spp.

Cronobacter species (formerly known as Enterobacter sakazakii) in powdered infant formula: a review of our current understanding of the biology of this bacterium

Cronobacter species (formerly known as Enterobacter sakazakii) are opportunistic pathogens that can cause necrotizing enterocolitis, bacteraemia and meningitis, predominantly in neonates. Infection in these vulnerable infants has been linked to the consumption of contaminated powdered infant formula (PIF). Considerable research has been undertaken on this organism in the past number of years which has enhanced our understanding of this neonatal pathogen leading to improvements in its control within the PIF production environment. The taxonomy of the organism resulted in the recognition of a new genus, Cronobacter, which consists of seven species. This paper presents an up-to-date review of our current knowledge of Cronobacter species. Taxonomy, genome sequencing, current detection protocols and epidemiology are all discussed. In addition, consideration is given to the control of this organism in the manufacturing environment, as a first step towards reducing the occurrence of this pathogen in PIF.

Cronobacter spp. in powdered infant formula

Cronobacter species are opportunistic pathogens, and a mortality rate of 40 to 80% is associated with infections. This pathogen can cause a range of serious diseases such as meningitis, septicemia, necrotizing enterocolitis, and brain abscesses and has been responsible for a variety of sequelae such as quadriplegia. Although Cronobacter can cause disease in both adults and infants, infant infections associated with powdered formula are the focus of this review. Since the first reported Cronobacter infection outbreak in 1958, powdered infant formula has been identified as a major source of these outbreaks, resulting in many recalls of powdered infant formula worldwide. This contamination has created an immense problem for the powdered infant formula industry. In this review, we discuss the taxonomy of Cronobacter species, the natural habitat of Cronobacter and its presence in foods, the physiology, pathogenicity, and virulence of Cronobacter species, and available detection methods. We also discuss reported cases of Cronobacter infection linked to powdered infant formula consumption and then focus specifically on the official World Health Organization guidelines for preparation of powdered infant formula.

Human isolates of Cronobacter sakazakii bind efficiently to intestinal epithelial cells in vitro to induce monolayer permeability and apoptosis

BACKGROUND

Cronobacter sakazakii (CS) is an emerging opportunistic pathogen that causes life-threatening infections in infants. This pathogen has been implicated in the outbreaks of necrotizing enterocolitis (NEC) with associated rates of high mortality and morbidity. In this study, we compared the abilities of CS strains isolated from human and environmental sources to bind to intestinal epithelial cells and trigger apoptosis.

MATERIALS AND METHODS

CS strains were isolated from human and environmental sources and their abilities to bind to intestinal epithelial cells were determined. Monolayer permeability was determined by transepithelial electrical resistance (TEER) and horseradish peroxidase (HRP) leakage. Apoptosis was examined by ApoTag and AnnexinV-7AAD staining. PKC activation was evaluated by non-radioactive PepTag assay.

RESULTS

Human isolates of CS bind to rat and human enterocytes more efficiently than environmental strains. Additionally, these strains induced increased enterocyte monolayer permeability as indicated by a decrease in TEER and an increase in transcellular leakage of exogenously added HRP. Human isolates also caused tight junction disruption and significant apoptosis of enterocytes compared with environmental strains due to increased production of inducible nitric oxide. We also observed that human CS isolates caused 2-fold increase in the activation of phosphokinase C (PKC) than environmental strains. Blocking the PKC activity in enterocytes by an inhibitor, Gö 6983, suppressed CS-mediated tight junction disruption, monolayer permeability, and apoptosis of the cells.

CONCLUSION

These results suggest that human isolates of CS more efficiently bind to and cause damage to intestinal epithelial cells compared with environmental strains.

Analysis of the DNA region mediating increased thermotolerance at 58°C in Cronobacter sp. and other enterobacterial strains

Cronobacter spp. are opportunistic pathogens associated with serious infections in neonates. The increased stress tolerance, including thermoresistance, of some Cronobacter strains can promote their survival in production facilities and thus raise the possibility of contamination of dried infant milk formula, which has been identified as a potential source of infection. In this study, we characterized a DNA region which is present in some Cronobacter strains and which contributes to their prolonged survival at 58°C. The 18 kbp long region containing 22 open reading frames was sequenced in Cronobacter sakazakii ATCC 29544. The major feature of the region contained a cluster of conserved genes, most of them having significant homologies with bacterial proteins involved in some type of stress response, including heat, oxidation and acid stress. The same thermoresistance DNA region was detected in strains belonging to the genera Cronobacter, Enterobacter, Citrobacter and Escherichia and its presence positively correlated with increased thermotolerance.