A chromogenic plating medium for the isolation and identification of Enterobacter sakazakii from foods, food ingredients, and environmental sources

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.

Draft Genome Sequence of Cronobacter sakazakii H05, Sequence Type 156, Isolated from a Spiced Ground Beef Dish, Kitfo

Cronobacter sakazakii is a foodborne pathogen that causes severe illness in neonates and the elderly. Here, we present the genome sequence of C. sakazakii H05 sequence type 156 (ST156), CC21 strain from Kitfo, resulting in a genome size of 4,495,386 bp, with 4,340 coding sequences and a G+C content of 56.85% after assembly and annotation.

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

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

Comparison of Chromogenic Selective Media for the Detection of Cronobacter spp. (Enterobacter sakazakii)

　The four types of chromogenic selective media that are commercially available in Japan were compared for establishing a Japanese standard method for detecting Cronobacter spp. based on ISO/TS 22964:2006. When assessed using 9 standard Cronobacter spp. strains and 29 non-Cronobacter strains, Enterobacter sakazakii isolation agar, Chromocult^TM Enterobacter sakazakii agar, CHROMagar^TM E. sakazakii, and XM-sakazakii agar demonstrated excellent inclusivity and exclusivity. Using the ISO/TS 22964:2006 method, the recovered numbers of 38 Cronobacter spp. strains, including 29 C. sakazakii isolates obtained from each medium, were equivalent, indicating that there was no significant difference (p > 0.05) among the four types of chromogenic selective media. Thus, we demonstrated that these four chromogenic selective media are suitable alternatives when using the standard method for detecting Cronobacter spp. in Japan, based on the ISO/TS 22964:2006.

Novel Method for Reliable Identification of Siccibacter and Franconibacter Strains: from "Pseudo-Cronobacter" to New Enterobacteriaceae Genera

In the last decade, strains of the genera Franconibacter and Siccibacter have been misclassified as first Enterobacter and later Cronobacter Because Cronobacter is a serious foodborne pathogen that affects premature neonates and elderly individuals, such misidentification may not only falsify epidemiological statistics but also lead to tests of powdered infant formula or other foods giving false results. Currently, the main ways of identifying Franconibacter and Siccibacter strains are by biochemical testing or by sequencing of the fusA gene as part of Cronobacter multilocus sequence typing (MLST), but in relation to these strains the former is generally highly difficult and unreliable while the latter remains expensive. To address this, we developed a fast, simple, and most importantly, reliable method for Franconibacter and Siccibacter identification based on intact-cell matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Our method integrates the following steps: data preprocessing using mMass software; principal-component analysis (PCA) for the selection of mass spectrum fingerprints of Franconibacter and Siccibacter strains; optimization of the Biotyper database settings for the creation of main spectrum projections (MSPs). This methodology enabled us to create an in-house MALDI MS database that extends the current MALDI Biotyper database by including Franconibacter and Siccibacter strains. Finally, we verified our approach using seven previously unclassified strains, all of which were correctly identified, thereby validating our method.IMPORTANCE We show that the majority of methods currently used for the identification of Franconibacter and Siccibacter bacteria are not able to properly distinguish these strains from those of Cronobacter While sequencing of the fusA gene as part of Cronobacter MLST remains the most reliable such method, it is highly expensive and time-consuming. Here, we demonstrate a cost-effective and reliable alternative that correctly distinguishes between Franconibacter, Siccibacter, and Cronobacter bacteria and identifies Franconibacter and Siccibacter at the species level. Using intact-cell MALDI-TOF MS, we extend the current MALDI Biotyper database with 11 Franconibacter and Siccibacter MSPs. In addition, the use of our approach is likely to lead to a more reliable identification scheme for Franconibacter and Siccibacter strains and, consequently, a more trustworthy epidemiological picture of their involvement in disease.

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.

Isolation of Cronobacter spp. (Enterobacter Sakazakii) from Artisanal Mozzarella

Cronobacter spp. (Enterobacter sakazakii) is an opportunistic bacterial pathogen capable of causing disease and even fatalities in newborn infants within the first weeks of life if consumed as part of the diet. Premature and immunocompromised newborn infants are at particular risk. The microorganism has been isolated from a variety of foods including contaminated infant milk formula powder and milk powder substitute. The study aimed to evaluate the level of microbiological contamination in 47 samples of mozzarella cheese made with cow's milk collected from artisan cheese producers in Southern Italy. Samples were collected from commercial sales points and underwent qualitative and quantitative microbiological analyses to test for the bacterial contaminants most commonly found in milk and cheese products. The 47 samples underwent qualitative and quantitative microbiological tests according to ISO UNI EN standards. Analyses focused on Staphylococcus aures, Salmonella spp., Listeria monocytogenes, Pseudomonas spp., E. coli, Yersinia spp., total coliforms and Cronobacter sakazakii. The ISO/TS 22964:2006 method was used to investigate possible contamination by C. sakazakii. Biochemical identification was carried out using an automated system for identification and susceptibility tests. None of the samples examined resulted positive for Salmonella spp. or Listeria spp. Only one sample resulted positive for Staphylococcus aureus. Pseudomonas spp. was isolated in 10 (21%) of 47 samples. High levels of total coliforms were found in 10 of 47 samples. Cronobacter spp. (Enterobacter sakazakii) was isolated in one sample. This is the first study to confirm isolation of C. sakazakii in artisan mozzarella cheese made from cow's milk. The presence of C. sakazakii could be related to external contamination during the phases of production or to the use of contaminated milk. Since mozzarella is recommended in the diet of children and adults of all ages, this present study helps define it as a potential vehicle for C. sakazakii in subjects at particular risk.

Cronobacter: an emergent pathogen causing meningitis to neonates through their feeds

The recognition of Cronobacter as a public health concern was raised when powdered infant formula (PIF) was linked to several neonatal meningitis outbreaks. It is an opportunistic pathogen that causes necrotising enterocolitis, infantile septicaemia, and meningitis which carries a high mortality rate among neonates. It has been also linked with cases of infection in adults and elderly. Over the past decade, much focus has been made on developing sensitive and specific characterisation, detection, and isolation methods to ascertain the quality of foods, notably contamination of PIF with Cronobacter and to understand its ability to cause disease. Whole genome sequencing has unveiled several putative virulence factors, yet the full capacity of the pathogenesis of Cronobacter has not yet been elucidated.

Low-water activity foods: increased concern as vehicles of foodborne pathogens

Foods and food ingredients with low water activity (a(w)) have been implicated with increased frequency in recent years as vehicles for pathogens that have caused outbreaks of illnesses. Some of these foodborne pathogens can survive for several months, even years, in low-a(w) foods and in dry food processing and preparation environments. Foodborne pathogens in low-a(w) foods often exhibit an increased tolerance to heat and other treatments that are lethal to cells in high-a(w) environments. It is virtually impossible to eliminate these pathogens in many dry foods or dry food ingredients without impairing organoleptic quality. Control measures should therefore focus on preventing contamination, which is often a much greater challenge than designing efficient control measures for high-a(w) foods. The most efficient approaches to prevent contamination are based on hygienic design, zoning, and implementation of efficient cleaning and sanitation procedures in the food processing environment. Methodologies to improve the sensitivity and speed of assays to resuscitate desiccated cells of foodborne pathogens and to detect them when present in dry foods in very low numbers should be developed. The goal should be to advance our knowledge of the behavior of foodborne pathogens in low-a(w) foods and food ingredients, with the ultimate aim of developing and implementing interventions that will reduce foodborne illness associated with this food category. Presented here are some observations on survival and persistence of foodborne pathogens in low-a(w) foods, selected outbreaks of illnesses associated with consumption of these foods, and approaches to minimize safety risks.

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.

[Microbiological quality of wheat flour consumed in Morocco]

Cereal products (soft and hard wheat) are a basic staple food in the Moroccan diet. A total of 60 samples of two types of wheat flours used for human consumption were collected; 30 samples among this collection were obtained from various households using Moroccan varieties of wheat produced in traditional flour mills. The rest of the samples were purchased from retail wheat flour sources in the Rabat and Sale city markets. Standard plate counts (SPC), total and faecal coliforms, Clostridium, Salmonella spp., Shigella spp., Staphylococcus aureus, Listeria monocytogenes, yeast, lactic acid bacteria, and molds, were carried out to assess the microbiological quality of wheat flour. Microbiological interpretation of the criteria was performed according to standards implemented by the Codex Alimentarius Commission. Most frequent counts, in traditional and industrial wheat flour, were total aerobic mesophilic bacteria with an average 4 × 104 and 2.5 × 104 cfu/g, respectively. The results showed higher coliform and fungi counts in house than in commercial samples. Pathogenic flora as Salmonella spp., Shigella spp., S. aureus, L. monocytogenes, and Clostridium were not detected in all investigated samples. Bacterial strains isolated from both flours belong to the following genera: Enterobacter spp., Serratia spp., Klebsiella spp., Pantoea spp., Leclercia spp., Proteus spp. The most frequent genus of the investigated isolates was Aspergillus (81 %). Microbial counts were lower than the limit laid down in the Codex Alimentarius, attributing to these flours a satisfactory microbiological quality.

Efficacy of the thin agar layer method for the recovery of stressed Cronobacter spp. (Enterobacter sakazakii)

Cronobacter spp. (Enterobacter sakazakii) are emerging opportunistic pathogens for all age groups, and are of particular concern when it comes to infants. Prior to contaminating food, the organism may be exposed to a variety of stresses, leading to a generation of sublethally injured cells that may not be detected by selective media unless a protracted recovery period is included in the isolation procedure. This study evaluated the efficacy of the thin agar layer (TAL) method for the recovery of Cronobacter cells that had been exposed to various stress conditions. Five strains of C. sakazakii and C. muytjensii were exposed to starvation, heat, cold, acid, alkaline, chlorine, or ethanol, with or without further exposure to desiccation stress. The recovery of the stressed cells was determined on tryptone soy agar (TSA; nonselective control medium), violet red bile glucose agar (VRBGA; selective agar), Druggan-Forsythe-Iversen (DFI; selective agar), and TAL media (viz., VRBGA overlaid with TSA, and DFI overlaid with TSA). Regardless of stress type, there were no significant differences among the recoveries of stressed desiccated Cronobacter spp. cultures on TSA, DFI+TSA, and VRBGA+TSA, but there was significantly less recovery on VRBGA. The recovery of prestressed desiccated Cronobacter spp. on DFI+TSA was similar to that on TSA, whereas the recovery on VRBGA+TSA was lower. DFI+TSA performed better than VRBGA+TSA did in differentiating Cronobacter spp. within mixed bacterial cultures. The results of this study suggest the use of the TAL method DFI+TSA as an improved method for the direct recovery of stressed Cronobacter spp.

Rapid and sensitive detection of Enterobacter sakazakii by cross-priming amplification combined with immuno-blotting analysis

Enterobacter sakazakii is a widespread and life-threatening bacterium especially in polluted powdered infant milk formula. Several methods have been developed for detection of E. sakazakii such as physiological and biochemical methods, PCR and loop-mediated isothermal amplification. However, these procedures were disadvantages due to a long assay time, low sensitivity or the use of toxic reagents. Our method of cross-priming amplification (CPA) under isothermal conditions combined with immuno-blotting analysis made the whole detection procedure more sensitivity and lower time-consuming. A set of specific displacement primers, cross primers and testing primers were designed based on six specific sequences in E. sakazakii 16S-23S rDNA internal transcribed spacer. Under isothermal condition at 63 °C for 60 min, the specific amplification and hybridization steps were processed simultaneously. The specificity of the CPA was tested in panel of 54 different bacterial strains and 236 milk powder products. Two red signal lines were developed on the BioHelix Express strip in all of positive E. sakazakii strains, and only one signal line was demonstrated by non- E. sakazakii bacterial strains. The limit of decetion of CPA was 6.3 ± 2.7277 fg for the genomic DNA, 88 ± 8.7892 cfu/ml for pure bacterial culture, and 3.2 ± 2.0569 cfu per 100 g milk powder with pre-enrichment. The current study demonstrated that the assay method of CPA combined with immuno-blotting analysis was a specific and sensitive detection for the rapid detection of E. sakazakii.

Cronobacter (Enterobacter sakazakii): an opportunistic foodborne pathogen

Cronobacter spp. (Enterobacter sakazakii) are a recently described genus that is comprised of six genomospecies. The classification of these organisms was revised based on a detailed polyphasic taxonomic study. Cronobacter spp. are regarded as ubiquitous organisms having been isolated from a wide variety of foods. These bacteria are opportunistic pathogens and are linked with life-threatening infections in neonates. Clinical symptoms of Cronobacter infection include necrotizing enterocolitis, bacteremia, and meningitis, with case fatality rates of 50-80% being reported. Contaminated powdered infant formula has been epidemiologically linked with infections. Recently, infections among immunocompromised adults, mainly the elderly, have also been reported. A high tolerance to osmotic stress and elevated temperatures contribute to the survival of Cronobacter spp. in dried foods such as powdered infant formula. Controlling the organism in the production environment, thereby reducing dissemination, necessitates the provision of suitable diagnostic tools. Studies demonstrated that a high degree of variability exists amongst the phenotypic-based methods used to identify Cronobacter spp. However, advances in molecular detection and subtyping techniques have significantly improved the identification and characterization of Cronobacter spp. The dose required to induce infection has yet to be determined. In vitro virulence studies have shown that Cronobacter spp. may survive in macrophage cells and efficiently attach to and invade epithelial cell lines. The production of exopolysaccharide may contribute to the formation of biofilm and active efflux pumps promote resistance to antimicrobial agents such as bile salts and disinfectants. A holistic approach combining techniques such as comparative genome analysis, proteomics, and in vivo challenges could help unravel the complex interactions between this pathogen and its host. These data would help identify those properties in Cronobacter spp. which enable the bacterium to survive in the production environment and infect vulnerable neonates via the food chain.

Development of an improved protocol for the isolation and detection of Enterobacter sakazakii (Cronobacter) from powdered infant formula

Enterobacter sakazakii causes severe maladies and, in some cases, is fatal among infants. Powdered infant formula (PIF) contaminated with E. sakazakii has been documented as a potential cause of several outbreaks involving infants. This study describes the development of a method for the isolation and detection of E. sakazakii from PIF. It combines Taqman real-time PCR, Brilliance E. sakazakii and R&F chromogenic agars, and RAPID ID 32E biochemical tests. This method provides an expedient analysis within 1 to 2 days depending on the amount and stress status of E. sakazakii organisms and competing microorganisms in PIF. The real-time PCR has bifunctional applications, including both screening and culture confirmation of E. sakazakii.

Isolation of Cronobacter spp. (formerly Enterobacter sakazakii) from infant food, herbs and environmental samples and the subsequent identification and confirmation of the isolates using biochemical, chromogenic assays, PCR and 16S rRNA sequencing

Background

Cronobacter spp. (formerly Enterobacter sakazakii), are a group of Gram-negative pathogens that have been implicated as causative agents of meningitis and necrotizing enterocolitis in infants. The pathogens are linked to infant formula; however, they have also been isolated from a wide range of foods and environmental samples.

Results

In this study, 233 samples of food, infant formula and environment were screened for the presence of Cronobacter spp. in an attempt to find its source. Twenty nine strains were isolated from samples of spices, herbs, infant foods, and dust obtained from household vacuum cleaners. Among the 76 samples of infant food, infant formula, milk powder and non-milk dairy products tested, only one sample of infant food contained Cronobacter spp. (1.4%). The other Cronobacter spp. isolates recovered include two from household vacuum dust, and 26 from 67 samples of herbs and spices. Among the food categories analyzed, herbs and spices harbored the highest number of isolates, indicating plants as a possible reservoir of this pathogen. Initial screening with API 20E test strips yielded 42 presumptive isolates. Further characterization using 3 chromogenic media (α-MUG, DFI and EsPM) and 8 sets of PCR primers detecting ITS (internal transcribed spacer sequences), 16S rRNA, zpx, gluA, gluB, OmpA genes followed by nucleotide sequencing of some PCR amplicons did not confirm the identity of all the isolates as none of the methods proved to be free of both false positives or false negatives. The final confirmation step was done by 16S rRNA sequence analysis identifying only 29 of the 42 isolates as Cronobacter spp.

Conclusion

Our studies showed that Cronobacter spp. are highly diverse and share many phenotypic traits with other Enterobacteriaceae members highlighting the need to use several methods to confirm the identity of this pathogen. None of the biochemical, chromogenic or PCR primers proved to be a reliable method for confirmation of the identity of the isolates as all of them gave either false positives or false negatives or both. It is therefore concluded that 16S rRNA sequencing is pivotal to confirm the identity of the isolates.

[Enterobacter sakazakii in powdered infant food formulas]

Species of the Cronobacter genus ("Enterobacter sakazakii" s. l.) are emergent food-borne pathogens that can cause rare but severe neonatal meningitis, bacteriaemia, and necrotizing enterocolitis. Preterm, low-birth-weight, and immuno-compromised infants exposed to these bacterial species are at particular risk. Over the last 50 years, the literature has reported, mainly in newborn children, more than one hundred cases of infection due to these pathogens. The objective of this review was to synthesize the recent advances in knowledge of species of the Cronobacter genus, in particular with regards to taxonomy, physiology, pathogenicity, clinical cases, the methods for detection, isolation, and characterization, and their presence in powdered formulae for infants and young children, which were identified as the main infection vector. Researchers and international public health authorities have explored the ways contamination occur to better control the risks of pathogen development. Appropriate analysis and control measures were implemented in areas processing powdered formulae for infants and young children, and caregivers and families were informed to undertake good hygienic practices.

Enzymatic substrates in microbiology

Enzymatic substrates are powerful tools in biochemistry. They are widely used in microbiology to study metabolic pathways, to monitor metabolism and to detect, enumerate and identify microorganisms. Synthetic enzymatic substrates have been customized for various microbial assays, to detect an expanding range of both new enzymatic activities and target microorganisms. Recent developments in synthetic enzymatic substrates with new spectral, chemical and biochemical properties allow improved detection, enumeration and identification of food-borne microorganisms, clinical pathogens and multi-resistant bacteria in various sample types. In the past 20 years, the range of synthetic enzymatic substrates used in microbiology has been markedly extended supporting the development of new multi-test systems (e.g., Microscan, Vitek 2, Phoenix) and chromogenic culture media. The use of such substrates enables an improvement in time to detection and specificity over conventional tests that employ natural substrates. In the era of intense developments in molecular biology, phenotypic tests involving enzymatic substrates remain useful to analyse both simple and complex samples. Such tests are applicable to diagnostic and research laboratories all over the world.

Desiccation resistance and persistence of Cronobacter species in infant formula

Cronobacter is a newly described genus which includes opportunistic pathogens formerly known as 'Enterobacter sakazakii'. These organisms have been isolated from a wide variety of sources, including powdered infant formula (PIF). This review focuses on the desiccation survival of Cronobacter, and its relevance to vehicles of infection. Due to its probable natural habitat of plant material, the organism has an array of survival mechanisms which includes resistance to desiccation and osmotic stresses. The organism can survive for long periods of time (>2years) in the desiccated state, and can be recovered from a large number of powdered foods in addition to powdered infant formula. On reconstitution, the organism may rapidly multiply and present a risk to immunocompromised infants. It is expected that an improved understanding of the nature of Cronobacter persistence may aid in further improved control measures and eliminate the bacterium from the critical food production environments.

Cronobacter ('Enterobacter sakazakii'): current status and future prospects

The genus Cronobacter accommodates the 16 biogroups of the emerging opportunistic pathogen known formerly as Enterobacter sakazakii. Cronobacter spp. are occasional contaminants of milk powder and, consequently, powdered infant formula and represent a significant health risk to neonates. This review presents current knowledge of the food safety aspects of Cronobacter, particularly in infant formula milk powder. Sources of contamination, ecology, disease characteristics and risk management strategies are discussed. Future directions for research are indicated, with a particular focus on the management of this increasingly important bacterium in the production environment.

Enterobacter sakazakii in dried infant formulas and milk kitchens of maternity wards in São Paulo, Brazil

This study was the first conducted in Brazil to evaluate the presence of Enterobacter sakazakii in milk-based powdered infant formula manufactured for infants 0 to 6 months of age and to examine the conditions of formula preparation and service in three hospitals in São Paulo State, Brazil. Samples of dried and rehydrated infant formula, environments of milk kitchens, water, bottles and nipples, utensils, and hands of personnel were analyzed, and E. sakazakii and Enterobacteriaceae populations were determined. All samples of powdered infant formula purchased at retail contained E. sakazakii at <0.3 [corrected] most probable number (MPN)/100 g. In hospital samples, E. sakazakii was found in one unopened formula can (0.3 MPN/100 g) and in the residue from one nursing bottle from hospital A. All other cans of formula from the same lot bought at a retail store contained E. sakazakii at <0.3 [corrected] MPN/100 g. The pathogen also was found in one cleaning sponge from hospital B. Enterobacteriaceae populations ranged from 10(1) to 10(5) CFU/g in cleaning aids and <5 CFU/g in all formula types (dry or rehydrated), except for the sample that contained E. sakazakii, which also was contaminated with Enterobacteriaceae at 5 CFU/g. E. sakazakii isolates were not genetically related. In an experiment in which rehydrated formula was used as the growth medium, the temperature was that of the neonatal intensive care unit (25 degrees C), and the incubation time was the average time that formula is left at room temperature while feeding the babies (up to 4 h), a 2-log increase in levels of E. sakazakii was found in the formula. Visual inspection of the facilities revealed that the hygienic conditions in the milk kitchens needed improvement. The length of time that formula is left at room temperature in the different hospitals while the babies in the neonatal intensive care unit are being fed (up to 4 h) may allow for the multiplication of E. sakazakii and thus may lead to an increased health risk for infants.

[Enterobacter sakazakii in powdered infant formula]

Under inadequate hygienic conditions, opportunistic bacteria may multiply in powdered infant formula (PIF) and cause severe, often fatal neonatal infections. Enterobacter sakazakii has obtained Public Health relevance causing neonatal meningitis (often fatal), bacteremia and necrotizing enterocolitis. At highest risk are neonates up to two months of age. The new genus designation Cronobacter spp. nov. has been proposed to replace Enterobacter sakazakii. Enterobacter sakazakii is relatively resistant to osmotic and dry stress and may survive in PIF more than 2 years. (Inter)national organisations (EFSA, FAO, WHO, ESPGHAN, DGKJ, OGKJ, ISO) published their opinions recently. Manufacturers can minimize the risk of contamination of PIF by continuously improving technologies and by microbiological surveillance. Institutional and private consumers may reduce the risk of infection by using appropriate hygienic procedures.

Occurrence of Listeria and Enterobacteriaceae in domestic refrigerators

Consumers' refrigeration practices have a significant impact on the safety and quality of foods. To determine the prevalence and the identity of microorganisms in domestic refrigerators, swab samples were taken from various locations in the refrigerators from 137 households in middle Tennessee. The swabs were inoculated into different media, and standard procedures were used to characterize the isolates. API 20E and API Listeria were used for identification of Enterobacteriaceae and Listeria spp., respectively. The Kirby-Bauer technique was used to test resistance of the isolates. Actual counts for aerobic and Enterobacteriaceae ranged from not detected to 8.53 and 8.39 log CFU per sample, respectively. Klebsiella pneumoniae (23.4%), Klebsiella oxytoca (6.8%), Klebsiella terrigena (4.0%), Enterobacter sakazakii (2.2%), and Yersinia enterocolitica (0.7%) were some of the bacteria of concern that were isolated from domestic refrigerators. Resistance to antibiotics was most common in erythromycin (39.9%), followed by ampicillin (33.8%), cefoxitin (12.8%), tetracycline (5%), streptomycin (4.0%), nalidixic acid (2.1%), kanamycin (1.4%), and colistin (0.7%). None of the isolates tested was resistant to ciprofloxacin or gentamycin. Listeria spp. were also detected in six refrigerators. These findings underline the need for greater consumer education regarding proper refrigerator cleaning and safe food handling practices.

Tracing of Enterobacter sakazakii isolates in infant milk formula processing by BOX-PCR genotyping

AIMS

Enterobacter sakazakii is an emerging food-borne pathogen that can cause rare but severe neonatal meningitis, bacteraemia and necrotizing enterocolitis. Contaminated powder infant formulae (PIF) have been identified as one of various infection routes. In this study, E. sakazakii was monitored in the processing environment of a PIF factory to identify possible dissemination routes.

METHODS AND RESULTS

The BOX-polymerase chain reaction (PCR), a fingerprinting technique which targets the repetitive BOX sequences, was used in routine to identify points of contamination and investigate clonal persistence. Two hundred E. sakazakii isolates were collected and typed. Most (70%) showed the same fingerprint that revealed the persistence of resident E. sakazakii strains in the processing environment. This method allowed to detect contamination of some PIF by dry-blending ingredients.

CONCLUSIONS

Environment was the major cause for contamination of PIF and facilities. Some raw materials delivered as powder were also implicated.

SIGNIFICANCE AND IMPACT OF THE STUDY

Routine BOX-PCR genotyping was very useful to trace and investigate in real-time dissemination of micro-organisms in the PIF plant and to implement a series of additional control measures to reduce the risk of final product contamination by E. sakazakii.

Development of a novel screening method for the isolation of "Cronobacter" spp. (Enterobacter sakazakii)

A differential medium, "Cronobacter" screening broth, has been designed to complement agars based on hydrolysis of chromogenic alpha-glucopyranoside substrates. The broth was evaluated using 329 Enterobacteriaceae strains (229 target isolates), spiked/naturally contaminated samples, and a parallel comparison with current methods for raw materials, line/end products, and factory environment samples.

A new chromogenic agar medium for detection of potentially virulent Yersinia enterocolitica

Several outbreaks of foodborne yersiniosis have been documented and this disease continues to be source of infections transmitted through foods. The selective agars most commonly used to isolate Yersinia enterocolitica in clinical, food and environmental samples, cefsulodin-irgasan-novobiocin (CIN) and MacConkey (MAC) agars, lack the ability to differentiate potentially virulent Y. enterocolitica from other Yersinia that may be present as well as some other bacterial spp. This study proposes the use of an agar medium, Y. enterocolitica chromogenic medium (YeCM), for isolation of potentially virulent Y. enterocolitica. This agar contains cellobiose as the fermentable sugar, a chromogenic substrate and selective inhibitors for suppression of colony formation by many competing bacteria. All strains of potentially virulent Yersinia of biotypes 1B, and biotypes 2-5 formed convex, red bulls-eye colonies on YeCM that were very similar to those described for CIN agar. However, Y. enterocolitica biotype 1A and other related Yersinia formed colonies that were purple/blue on YeCM while they formed typical red bulls-eye colonies on CIN agar. When a mixture of potentially virulent Y. enterocolitica biotype 1B, Y. enterocolitica biotype 1A and 5 other bacterial species was used to artificially contaminate tofu and then spread-plated on three selective agars, Y. enterocolitica biotype 1B colonies were easily distinguished from other strains on YeCM. However, Y. enterocolitica biotype 1B colonies were indistinguishable from many other colonies on CIN and only distinguishable from those of C. freundii on MAC. When colonies were picked and identified from these agars, typical colonies from YeCM were confirmed only as Y. enterocolitica biotype 1B. Typical colonies on CIN and MAC were found to belong to several competing species and biotypes.