Thermal inactivation of Yersinia enterocolitica in milk

Graphene Quantum Dots as Nanozymes for Electrochemical Sensing of Yersinia enterocolitica in Milk and Human Serum

The genus Yersinia contains three well-recognized human pathogens, including Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis. Various domesticated and wild animals carry Yersinia in their intestines. Spread to individuals arises from eating food or water contaminated by infected human or animal faeces. Interaction with infected pets and domestic stock may also lead to infection. Yersinia is able to multiply at temperatures found in normal refrigerators; hence, a large number of the bacteria may be present if meat is kept without freezing. Yersinia is also rarely transmitted by blood transfusion, because it is able to multiply in stored blood products. Infection with Yersinia can cause yersiniosis, a serious bacterial infection associated with fever, abdominal pain and cramps, diarrhea, joint pain, and symptoms similar to appendicitis in older children and adults. This paper describes a novel immunosensor approach using graphene quantum dots (GQDs) as enzyme mimics in an electrochemical sensor set up to provide an efficient diagnostic method for Y. enterecolitica. The optimum assay conditions were initially determined and the developed immunosensor was subsequently used for the detection of the bacterium in milk and human serum. The GQD-immunosensor enabled the quantification of Y. enterocolitica in a wide concentration range with a high sensitivity (LODmilk = 5 cfu mL-1 and LODserum = 30 cfu mL-1) and specificity. The developed method can be used for any pathogenic bacteria detection for clinical and food samples without pre-sample treatment. Offering a very rapid, specific and sensitive detection with a label-free system, the GQD-based immunosensor can be coupled with many electrochemical biosensors.

Main Groups of Microorganisms of Relevance for Food Safety and Stability

Microbiology is important to food safety, production, processing, preservation, and storage. Microbes such as bacteria, molds, and yeasts are employed for the foods production and food ingredients such as production of wine, beer, bakery, and dairy products. On the other hand, the growth and contamination of spoilage and pathogenic microorganisms is considered as one of the main causes to loss of foodstuff nowadays. Although technology, hygienic strategies, and traceability are important factors to prevent and delay microbial growth and contamination, food remains susceptible to spoilage and activity of pathogen microorganisms. Food loss by either spoilage or contaminated food affects food industry and consumers leading to economic losses and increased hospitalization costs. This chapter focuses on general aspects, characteristics, and importance of main microorganisms (bacteria, yeasts, molds, virus, and parasites) involved in food spoilage or contamination: known and recently discovered species; defects and alterations in foodstuff; most common food associated with each foodborne disease; resistance to thermal processing; occurrence in different countries; outbreaks; and associated symptoms.

Prevalence of Yersinia enterocolitica in raw cow's milk collected from stables of Mexico City

Yersinia enterocolitica has been isolated from a batch of pork-derived products, from healthy and diseased animals, and from different types of milk and dairy products, among others. We studied the prevalence and diversity of Y. enterocolitica isolated from raw cow's milk collected from stables in Mexico City. Of the 1,300 samples analyzed, Y. enterocolitica was isolated in 454, with an average of 25% positive samples for each stable. Of the total isolated bacteria of the Yersinia genus, 44.25% were Y. enterocolitica, 18.28% were Y. kristensenii, 13.65% were Y. intermedia, 14.85% were Y. frederiksenii, and 9.14% were Y. aldovae. Among the different strains of Y. enterocolitica, biotype 1A was present in 70%, biotype 2 in 13.2%, biotype 3 in 8.54%, and biotype 4 in 8.15% of samples. Serotypes O:5, O:3, O:2, and O:9 were found in all biotypes identified. There were no statistically significant differences in the isolation of this bacterium with respect to the stables where they were found, although there was significant difference regarding the time of year. The data obtained in this work show the need to protect public health in Mexico against infections transmitted by raw cow's milk.

Prevalence and survival of potential pathogens in source-segregated green waste compost

Composting of source-separated green waste (SSGW) is essential to meet the EU Landfill Directive target and agricultural land is considered a significant market for the resulting composts. A critical review of the literature was performed to evaluate the potential for pathogens to enter the composting process via SSGW feedstocks and the likelihood of their survival of the composting process and subsequent application to land. This is discussed in the context of application of other organic wastes to land. It was concluded that zoonoses such as verotoxigenic Escherichia coli and Salmonella spp. are unlikely to survive and effective composting process, whereas spore forming organisms are more resistant to composting but are also ubiquitous in the environment. Adherence to existing guidelines, such as those for farm yard manures, is likely to provide a rational degree of health protection for humans and livestock.

Behavior of Yersinia enterocolitica in Foods

Yersinia enterocolitica are ubiquitous, being isolated frequently from soil, water, animals, and a variety of foods. They comprise a biochemically heterogeneous group that can survive and grow at refrigeration temperatures. The ability to propagate at refrigeration temperatures is of considerable significance in food hygiene. Virulent strains of Yersinia invade mammalian cells such as HeLa cells in tissue culture. Two chromosomal genes, inv and ail, were identified for cell invasion of mammalian. The pathogen can cause diarrhoea, appendicitis and post-infection arthritis may occur in a small proportion of cases. The most common transmission route of pathogenic Y. enterocolitica is thought to be fecal-oral via contaminated food. Direct person-to-person contact is rare. Occasionally, pathogenic Y. enterocolitica has been detected in vegetables and environmental water; thus, vegetables and untreated water are also potential sources of human yersiniosis. However, the isolation rates of pathogenic Y. enterocolitica have been low, which may be due to the limited sensitivity of the detection methods. To identify other possible transmission vehicles, different food items should be studied more extensively. Many factors related to the epidemiology of Y. enterocolitica, such as sources, transmission routes, and predominating genotypes remain obscure because of the low sensitivity of detection methods.

Development of associations and kinetic models for microbiological data to be used in comprehensive food safety prediction software

The objective of this study was to use an existing database of food products and their associated processes, link it with a list of the foodborne pathogenic microorganisms associated with those products and finally identify growth and inactivation kinetic parameters associated with those pathogens. The database was to be used as a part of the development of comprehensive software which could predict food safety and quality for any food product. The main issues in building such a predictive system included selection of predictive models, associations of different food types with pathogens (as determined from outbreak histories), and variability in data from different experiments. More than 1000 data sets from published literature were analyzed and grouped according to microorganisms and food types. Final grouping of data consisted of the 8 most prevalent pathogens for 14 different food groups, covering all of the foods (>7000) listed in the USDA Natl. Nutrient Database. Data for each group were analyzed in terms of 1st-order inactivation, 1st-order growth, and sigmoidal growth models, and their kinetic response for growth and inactivation as a function of temperature were reported. Means and 95% confidence intervals were calculated for prediction equations. The primary advantage in obtaining group-specific kinetic data is the ability to extend microbiological growth and death simulation to a large array of product and process possibilities, while still being reasonably accurate. Such simulation capability could provide vital ''what if'' scenarios for industry, Extension, and academia in food safety.

Inactivation of Salmonella serovars in liquid whole egg by heat following irradiation treatments

Salmonella is a frequent contaminant on eggs and is responsible for foodborne illnesses in humans. Ionizing radiation and thermal processing can be used to inactivate Salmonella in liquid whole egg, but when restricted to doses that do not affect egg quality, these technologies are only partially effective in reducing Salmonella populations. In this study, the effect of ionizing radiation in combination with thermal treatment on the survival of Salmonella serovars was investigated. Of the six Salmonella serovars tested, Salmonella Senftenberg was the most resistant to radiation (Dgamma = 0.65 kGy) and heat (D(55 degrees C) = 11.31 min, z = 4.9 degrees C). Irradiation followed by thermal treatment at 55 or 57 degrees C improved the pasteurization process. Radiation doses as low as 0.1 kGy prior to thermal treatments synergistically reduced the D(55 degrees C) and D(57 degrees C) of Salmonella Senftenberg 3.6- and 2.5-fold, respectively. The D(55 degrees C) and D(57 degrees C) of Salmonella Typhimurium were reduced 2- and 1.4-fold and those of Salmonella Enteritidis were reduced 2- and 1.6-fold, respectively. Irradiation prior to thermal treatment would enable the reduction of heat treatment times by 86 and 30% at 55 and 57 degrees C, respectively, and would inactivate 9 log units of Salmonella serovars.

Inactivation of Salmonella Senftenberg 775W by ultrasonic waves under pressure at different water activities

The inactivation of Salmonella Senftenberg 775W by ultrasonic waves (20 kHz, 117 microm) under pressure (175 kPa) treatments at sublethal (manosonication; MS) and lethal temperatures (manothermosonication; MTS) in media of different water activities has been investigated. Heat decimal reduction time values increased up to eighteen fold when the water activity was decreased from >0.99 to 0.93 at 65 degrees C, but hardly increased the MS resistance. In reduced water activity media (a(w) of 0.96 and 0.93) a synergistic lethal effect was observed between heat and ultrasound under pressure, being the inactivation rate of Salmonella Senftenberg 775W three times faster than the expected additive rate considering an effect of both bacterial lethal processes. An empirical mathematical equation enabled to predict the D(MS) and D(MTS) values obtained at different temperatures and a(w) in the ranges investigated of Salmonella serovars and also the microbial level of inactivation due to the synergistic lethal effect of MTS treatments in media of reduced a(w). This work could be useful for improving sanitation and preservation treatments of foods, especially those in which components protect microorganisms to heat.

Heat resistance in liquids of Enterococcus spp., Listeria spp., Escherichia coli, Yersinia enterocolitica, Salmonella spp. and Campylobacter spp

The aim of the work was to collect, evaluate, summarize and compare heat resistance data reported for Campylobacter, Enterococcus, Escherichia, Listeria, Salmonella and Yersinia spp. The work was limited to resistance in liquids with pH values 6-8. Results obtained under similar experimental conditions were sought. Thermal destruction lines for the various bacterial groups studied were constructed using log10 D values and treatment temperatures. There was a good linear relationship between log10 D and temperature with Escherichia coli, listerias and salmonellas. For campylobacters, enterococci and yersinias the relationships were weaker but, nevertheless, present. Using the slopes of the lines and their 95% confidence limits, z values and their 95% confidence limits were calculated. z values were compared with z values obtained from reports. The equations for the lines were also used for calculation of predicted means of D values at various treatment temperatures. 95% confidence limits on predicted means of D values and on predicted individual D values were also calculated. Lines and values are shown in figures and tables. Differences in heat resistance noted between and within the bacterial groups studied are discussed.

Inactivation of Salmonella enterica serovar enteritidis by ultrasonic waves under pressure at different water activities

The inactivation of Salmonella enterica serovar Enteritidis by ultrasonic waves (20 kHz; 117- microm wavelength) under pressure (175 kPa) at nonlethal temperatures (manosonication [MS]) and lethal temperatures (manothermosonication [MTS]) in media of different water activities has been investigated. Heat decimal reduction time values increased 30 times when the water activity was decreased from nearly 1 to 0.96, but the MS resistance was increased only twofold. The inactivation of Salmonella serovar Enteritidis by ultrasound under pressure at low water activities was a phenomenon of the "all-or-nothing" type. A synergistic lethal effect was observed between heat and ultrasound in media with reduced water activity; the lower the water activity, the greater the synergistic effect. This work could be useful for improving sanitation and preservation treatments of foods, especially those which are sensitive to temperature and those in which components protect microorganisms to heat. It also contributes to our knowledge of microbial inactivation mechanisms by MS and MTS treatments.

Heat resistance of Yersinia enterocolitica grown at different temperatures and heated in different media

In the range of 4-20 degrees C, growth temperature did not influence the heat resistance at 54-66 degrees C for Yersinia enterocolitica at pH 7 in citrate phosphate buffer. However, when cells were grown at 37 degrees C. the D62 increased from 0.044 to 0.17 min. This increase was constant at all heating temperatures tested (z = 5.7-5.8). Growth temperature did not influence the proportion of heat-damaged cells after a heat treatment, as measured by their response to a 2% of sodium chloride added to the recovery medium. The sensitivity of heat treated cells to nisin or lysozyme depended on growth temperature: Whereas the number of cells grown at 4 degrees C surviving heat treatment was the same regardless of the presence of 100 IU/ml of nisin or 100 microg/ml of lysozyme in the recovery medium, that of cells grown at 37 degrees C was, in these media, lower. The pH of maximum heat resistance in citrate phosphate buffer was pH 7 for cells grown at 37 degrees C, but pH 5 for those grown at 4 degrees C. In both suspensions the magnitude of the effect of pH on heat resistance was constant at all heating temperatures. For cells grown at 4 degrees C the heat resistance at 54-66 degrees C, in skimmed milk or pH 7 buffer, was the same. For cells grown at 37 degrees C this also applied for heat treatment at 66 degrees C but at 56 degrees C the heat resistance in skimmed milk was higher.

Model of the influence of time and mild temperature on Listeria monocytogenes nonlinear survival curves

Heat treatment has long been regarded as one of the most widely used and most effective means of destroying pathogens in food. Up to now the linear relationship between the death rate and the temperature has been used when choosing the best heat treatment to apply. However, the information given by this linear relationship is no longer sufficient when nonlinear survival curves are observed. Consequently, the agri-food industry needs a tool to choose the best mild heat treatment to apply in the case of nonlinear survival curves. This study deals with the temperature-induced death of Listeria monocytogenes CIP 7831 in the stationary phase of growth. Eleven temperatures were tested. With the proposed primary and secondary models good fits of our data were obtained. A model describing both the effect of the duration of treatment and the temperature on the logarithm of the number of survivors was then built. A clear increase in the precision of the estimation of the parameters was obtained with this model. Moreover, with this model a new graphical strategy to choose a mild heat increase regarding a maximal survivor number has been proposed.

Influence of temperature and pressure on the lethality of ultrasound

A specially designed resistometer was constructed, and the lethal effect on Yersinia enterocolitica of ultrasonic waves (UW) at different static pressures (manosonication [MS]) and of combined heat-UW under pressure treatments (manothermosonication [MTS]) was investigated. During MS treatments at 30 degrees C and 200 kPa, the increase in the amplitude of UW of 20 kHz from 21 to 150 mum exponentially decreased decimal reduction time values (D(MS)) from 4 to 0.37 min. When pressure was increased from 0 to 600 kPa at a constant amplitude (150 mum) and temperature (30 degrees C), D(MS) values decreased from 1.52 to 0.20 min. The magnitude of this decrease in D(MS) declined progressively as pressure was increased. The influence of pressure on D(MS) values was greater with increased amplitude of UW. Pressure alone of as much as 600 kPa did not influence the heat resistance of Y. enterocolitica (D(60) = 0.094; z = 5.65). At temperatures of as much as 58 degrees C, the lethality of UW under pressure was greater than that of heat treatment alone at the same temperature. At higher temperatures, this difference disappeared. Heat and UW under pressure seemed to act independently. The lethality of MTS treatments appeared to result from the added effects of UW under pressure and the lethal effect of heat. The individual contributions of heat and of UW under pressure to the total lethal effect of MTS depended on temperature. The inactivating effect of UW was not due to titanium particles eroded from the sonication horn. The addition to the MS media of cysteamine did not increase the resistance of Y. enterocolitica to MS treatment. MS treatment caused cell disruption.

Psychrotrophs in dairy products: their effects and their control

Health concerns and technological effects of psychrotrophic bacteria in dairy products are reviewed, as well as methods to control their presence and development. The various Gram-negative and Gram-positive psychrotrophic species are listed and, with respect to pathogenic psychrotrophs, emphasis is given on Listeria monocytogenes, Yersinia enterocolitica, and Bacillus cereus. The influence of psychrotrophic bacteria on the quality of raw milk, pasteurized and UHT milks, butter, ice cream, cheese, and powders is examined. Public health considerations of Listeria monocytogenes, Yersinia enterocolitica, and Bacillus cereus of these various dairy products are also presented. Methods that can be used to eliminate or control the development of psychrotropic bacteria include low or high temperatures, chemicals, gases, the lactoperoxidase system, lactic acid bacteria, microfiltration, bactofugation, lactoferrin-related proteins, sanitation, flavors, and naturally occurring spore germinants.

The source of Yersinia spp. in pasteurized milk: an investigation at a dairy

Pasteurized bottled milk supplied by a single dairy was frequently found to be contaminated with Yersinia spp. Investigations were carried out at the dairy in an effort to pinpoint the source of these organisms. Viable counts obtained from milk bottle rinses indicated that bottle washing was often unsatisfactory, and on one occasion Y. frederiksenii was isolated from the pooled rinse water of six bottles. Samples of milk were taken on arrival at the dairy and at various stages following pasteurization. Heat resistance tests carried out on strains of yersinia isolated from pasteurized milk indicated that they would not survive the pasteurization process. However two strains of yersinia were isolated from a sample of milk taken immediately after pasteurization but before bottling. The thermograph indicated that the time/temperature conditions applied during pasteurization were adequate. The presence of yersinia strains in the milk at this stage therefore suggests that undetectable levels of raw milk were being allowed to contaminate the pasteurized milk. The absence of yersinia in cartoned samples produced on the same day as contaminated bottled samples indicated that environmental contamination of the bottle filler valve also may have occurred at times. Results of this investigation indicate that increased vigilance is required to ensure proper operation of pasteurizers and bottle washers.

Heat resistance of Campylobacter and Yersinia strains by three methods

Two methods of determining the heat resistance of bacteria, a glass cup and a test tube method, were compared with a method using capillary tubes. Three strains of Yersinia enterocolitica, one of Campylobacter jejuni and two of C. coli were tested in physiological saline. The differences between the results obtained by the glass cup method and the reference method were not statistically significant for five strains and were small also for the other, a Yersinia strain. D values obtained by the glass cup method at 58, 60 and 62 degrees C were 1.4-1.8, 0.40-0.51 and 0.15-0.19 min (zeta values 4.00-4.52 degrees C) for the Yersinia strains, and 0.42, 0.13 and 0.07 min (zeta value 5.07 degrees C) for one C. coli strain. For the other Campylobacter strains, D values of 0.71-0.78, 0.24-0.28 and 0.12-0.14 min (zeta values 4.94 and 5.60 degrees C) were recorded at 56, 58 and 60 degrees C. D values obtained at 60 degrees C by the test tube method were 2.7-5.0 min and were considered to be unrealistic.

Thermal inactivation of Campylobacter species, Yersinia enterocolitica, and hemorrhagic Escherichia coli O157:H7 in fluid milk

Heat treatment of raw milk in an HTST pasteurizer operated at 60.0 to 72.0 degrees C for a minimum holding time of 16.2 s rapidly inactivated mixtures of hemorrhagic Escherichia coli O157:H7, Yersinia enterocolitica and Campylobacter spp. (C. fetus, C. coli, and C. jejuni). Each of the three genera in the mixture was inoculated at a level of approximately 1.0 x 10(5) cfu/ml. At 60.0 degrees C, hemorrhagic E. coli showed a maximum 2 log10 reduction in counts and no viability at greater than or equal to 64.5 degrees C. Yersinia enterocolitica and Campylobacter spp. showed greater heat sensitivity with a 4 log10 reduction in counts at 60.0 degrees C and absence of viable cells at greater than or equal to 63.0 degrees C. These findings reiterate the need for stringent control of thermal processes in the manufacture of dairy products from raw or heat-treated (non-pasteurized) milk.

Yersinia enterocolitica in milk and dairy products

Yersinia enterocolitica was first recognized during the 1960's as an important human enteropathogen. The species as later redefined includes both pathogenic and nonpathogenic forms. Pathogenic strains that retain the virulence plasmid can be identified in several animal models and four indirect tests (calcium dependency, autoagglutination, Congo red uptake, serological detection of outer membrane antigen) and by tissue culture assay, serotype, and biotype. Y. enterocolitica and related bacteria have frequently been isolated from raw milk, but none of the isolates, with the possible exception of serotype 05,27, are recognizable as pathogens. Under normal circumstances Y. enterocolitica does not survive pasteurization. If introduced into pasteurized milk, it can grow well at refrigeration temperatures. Two outbreaks of yersiniosis have occurred that involved pasteurized milk. Pigs, which frequently carry pathogenic Y. enterocolitica in their throat, were the probable source in one of these outbreaks. The most rapid enrichment procedure available for isolation of Y. enterocolitica requires 6 d. No isolation method is available for selective isolation of pathogenic Y. enterocolitica in the presence of related bacteria common in milk and other foods.

The incidence of Yersinia enterocolitica and Yersinia enterocolitica-like organisms in raw and pasteurized milk in Northern Ireland

Yersinia enterocolitica and Y. enterocolitica-like bacteria were frequently isolated from samples of both raw bulked milk (34/150) and farm bottled (raw) milk (5/20). These bacteria were also found to contaminate creamery pasteurized milk (6/100 samples) and farm pasteurized milk (4/50 samples). Although Y. enterocolitica was the most commonly isolated species, Y. intermedia and Y. frederiksenii were also frequently obtained (52, 31 and 15% of isolates, respectively). Also, one atypical strain was identified as Y. aldovae. The Y. enterocolitica strains were largely biotype 1 (20/27) including five strains which could ferment lactose. One third of the Y. enterocolitica strains were not typable, but of those which were, the serotypes were 0:34 (18.5%), 0:5.27 (18.5%), 0:6.3 (15%), 0:4 (11%) and 0:7 (4%). Pre-enrichment in trypticase-soy broth (TSB) (at 22 degrees C for 24 h) followed by selective enrichment in bile-oxalate-sorbose broth (at 22 degrees C for 6 d) allowed the recovery of 92.3% of all isolates, as compared with 15.4% using cold enrichment in TSB at 4 degrees C for 21 d.

A comparison of media and methods for the recovery of Yersinia enterocolitica and Yersinia enterocolitica-like bacteria from milk containing simulated raw milk microfloras

A number of plating and enrichment media proposed for the isolation of Yersinia enterocolitica from foodstuffs were examined for their ability to recover the type strains of Y. enterocolitica sensu stricto, Y. intermedia, Y. frederiksenii and Y. kristensenii. Nine selective plating media were evaluated for the quantitative recovery of the type strains in pure culture, and their inhibition of other organisms typical of both milk and enteric microfloras. Cefsulodin-irgasan-novobiocin (CIN) agar, incubated for 48 h at 25 degrees C, allowed a high recovery of all the Yersinia spp. and was the most selective medium. The same four type strains were added to UHT milk that had been previously inoculated with bacteria to simulate either freshly drawn or cold stored milk microfloras. Twenty-six enrichment procedures (including cold enrichment, selective enrichment at higher temperatures, two-step procedures and a post-enrichment alkali treatment) were assessed for the efficiency of recovery of the Yersinia spp. Pre-enrichment in trypticase-soy broth (TSB) for 24 h at 22 degrees C followed by selective enrichment in bile-oxalate-sorbose (BOS) medium for 5 d at 22 degrees C and plating on CIN agar (48 h at 25 degrees C) allowed the greatest increase in the numbers of Yersinia spp. and maximum inhibition of the competing microflora.

Significance of milk as a possible source of infection for human yersiniosis. I. Incidence of Yersinia organisms in raw milk in Shimane Prefecture, Japan

Twelve strains of Yersinia enterocolitica and 4 strains of a Y. enterocolitica-like organism (Y. intermedia) were isolated from 374 pooled raw milk samples. Growth occurred in a cold enrichment system using phosphate buffer solution (7 strains), peptone solution (5 strains) and yeast extract-casein-cystine broth (5 strains). Serovar 13,7 was most frequently isolated (8 strains) followed by serovars 5,27 (2 strains), 6,31, 7,8, 14 and 22 (each one strain). Two strains were untypable, serologically. Seasonal variation was of little consequence, but the regional incidence was an important feature of the bacteriological findings. Autoagglutination tests gave negative results with all isolates. Although so-called "clinical strains" were not identified, the relationship of the strains of Yersinia to milk-borne infections in humans cannot be excluded.