Influence of SARS-CoV-2 inactivation by different chemical reagents on the humoral response evaluated in a murine model

Viral inactivation for antibody induction purposes, among other applications, should ensure biosafety, completely avoiding the risk of infectivity, and preserving viral immunogenicity. β-propiolactone (BPL) is one of the most used reagents for viral inactivation, despite its high toxicity and recent difficulties related to importation, experienced in Brazil during the SARS-CoV-2 pandemic. In this context, the main objectives of this work were to test different inactivation procedures for SARS-CoV-2 and to evaluate the induction of neutralizing antibodies in mice immunized with antigenic preparations obtained after viral treatment with formaldehyde (FDE), glutaraldehyde (GDE), peroxide hydrogen (H₂O₂), as well as with viral proteins extract (VPE), in parallel with BPL. Verification of viral inactivation was performed by subsequent incubations of the inactivated virus in Vero cells, followed by cytopathic effect and lysis plaques observation, as well as by quantification of RNA load using reverse transcription-quantitative real time polymerase chain reaction. Once viral inactivation was confirmed, cell culture supernatants were concentrated and purified. In addition, an aliquot inactivated by BPL was also subjected to viral protein extraction (VPE). The different antigens were prepared using a previously developed microemulsion as adjuvant, and were administered in a four-dose immunization protocol. Antibody production was comparatively evaluated by ELISA and Plaque Reduction Neutralization Tests (PRNT). All immunogens evaluated showed some level of IgG anti-SARS-CoV-2 antibodies in the ELISA assay, with the highest levels presented by the group immunized with FDE-inactivated viral antigen. In the PRNT results, except for VPE-antigen, all other immunogens evaluated induced some level of neutralizing anti-SARS-CoV-2 antibodies, and the FDE-antigen stood out again with the most expressive values. Taken together, the present work shows that FDE can be an efficient and affordable alternative to BPL for the production of inactivated SARS-CoV-2 viral antigen.

Visceral leishmaniasis: a practical strategy for quantitative molecular diagnosis in naturally infected dogs

The diagnosis of canine visceral leishmaniasis (CVL) has been a problem for public health services due to the variety of clinical signs similar to other diseases and low sensitivity and specificity of available tests. In this sense, our main objective was to develop a simple, rapid, and accurate quantitative real-time PCR (qPCR) diagnosis for CVL. Thus, low-invasive samples from bone marrow (BM), popliteal lymph nodes (PLN), and conjunctival swabs (CS) were selected from negative and VL-positive dogs, using as gold standard, immunological and parasitological tests performed with different tissues. Oligonucleotides for Leishmania infantum kDNA were designed and the limit of quantification and amplification efficiency of the qPCR were determined using tissue-specific standards produced with DNA from those different tissues, mixed with DNA from a known amount of L. infantum promastigotes. Endogenous control was used to validate a comparative Ct method, and tissue parasite concentrations were estimated by comparison with tissue-specific reference standard samples. The overall analysis of the qPCR data suggests the following ranking for tissue choice: PLN > BM > CS. Finally, we have concluded that this molecular approach simplifies and accelerates the quantitative diagnostic process because it is easy to perform, requiring no DNA dosing or standard curve application, and it shows good diagnostic parameters, especially when using popliteal lymph node samples.

The effect of benznidazole dose among the efficacy outcome in the murine animal model. A quantitative integration of the literature

Despite more than 100 years since it was firstly described Chagas disease, only two drugs are available to treat Chagas disease: Nifurtimox launched by Bayer in 1965 and benznidazole launched by Roche in 1971. Drug discovery initiatives have been looking for new compounds as an alternative to these old drugs. Although new platforms have been used with the latest technologies, a critical step on that process still relies on the in vivo model. Unfortunately, to date, available animal models have limited predictive value and there is no standardization. With the aim to better understand the role of benznidazole, the current standard of care of Chagas disease, we performed this review. We intend to analyze the influence of the experimental design of the most used animal model, the murine model, in the assessment of the efficacy endpoint.

Benznidazole, itraconazole and their combination in the treatment of acute experimental Chagas disease in dogs

Chagas disease (CD) is a serious public health problem in Latin America and its treatment remains neglected. Benznidazole (BZ) available in Brazil, presents serious side effects and low therapeutic efficacy at chronic phase. This study evaluated the therapeutic efficacy of BZ, itraconazole (ITZ) and BZ + ITZ in dogs infected with VL-10 T. cruzi strain in the acute phase (Ethic protocol number 2013/28). Twenty young mongrel dogs were inoculated with 2.0 × 103 blood trypomastigotes/kg and divided into four groups: treated with BZ, ITZ and BZ + ITZ for 60 days, and control group (INT-infected not treated). The parasitemia of the BZ + ITZ and BZ groups were similar and showed significant reduction compared to the INT group. The ITZ group also showed significant parasitemia reduction compared to the INT group. For cure control the global analysis of hemoculture (HC), blood PCR, conventional serology (CS-ELISA), heart qPCR and histopathology revealed that BZ + ITZ lead to more reduction of parasitemia during the acute phase and heart qPCR positivity, less cardiac damage and total survival than BZ or ITZ. Moreover, two other dogs, one treated with ITZ and other treated with BZ + ITZ, were always negative in all parasitological tests what indicates parasitological cure or that these dogs are in process of cure. •BZ + ITZ lead to more reduction of parasitemia, total survival, less heart qPCR positivity and cardiac damage.•According to the classic cure criterion cure was observed only in one dog submitted to BZ + ITZ treatment.•Two dogs, one treated with ITZ and other treated with BZ + ITZ were always parasitologically negative.

Therapeutic Hypothermia in Brazil: A MultiProfessional National Survey

OBJECTIVE

To determine the rate of therapeutic hypothermia (TH) use, current practices, and long-term follow-up.

STUDY DESIGN

Prospective cross-sectional national survey with 19 questions related to the assessment of hypoxic-ischemic encephalopathy (HIE) and TH practices. An online questionnaire was made available to health care professionals working in neonatal care in Brazil.

RESULTS

A total of 1,092 professionals replied, of which 681 (62%) reported using TH in their units. Of these, 624 (92%) provided TH practices details: 136 (20%) did not use any neurologic score or amplitude-integrated electroencephalogram (aEEG) to assess encephalopathy and 81(13%) did not answer this question. Any specific training for encephalopathy assessment was provided to only 81/407 (19%) professionals. Infants with mild HIE are cooled according to 184 (29%) of the respondents. Significant variations in practice were noticed concerning time of initiation and cooling methods, site of temperature measurements and monitoring, and access to aEEG, electroencephalogram (EEG), and neurology consultation. Only 19% could perform a brain magnetic resonance imaging (MRI), and 31% reported having a well-established follow-up program for these infants.

CONCLUSION

TH has been implemented in Brazil but with significant heterogeneity for most aspects of hypothermia practices, which may affect safety or efficacy of the therapy. A step forward toward quality improvement is important.

Increasing phenolic and aromatic compounds extraction and maximizing liking of lemon verbena (Aloysia triphylla) infusions through the optimization of steeping temperature and time

Herbal infusions are a new emerging trend among consumers, appearing in the market in many different forms. Due to intense competition, the commercial success of herbal infusions largely depends on flavour. The identification of the best combinations of steeping time and water temperature for the preparation of Aloysia triphylla infusions using a central composite design and response surface methodology was performed. The procedure aimed to maximize its antioxidant activity, phenolic and aromatic compounds, and consumers' liking of the infusions. The antioxidant activity and phenolic content were evaluated using the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical cation) method and the Folin-Ciocalteu procedure. The analysis of aromatic compounds was performed based on the method of terpenic compounds. Sensory evaluation encompassed overall liking using a 9-point hedonic scale. Antioxidant activity and extraction of most phenolic compounds was higher for longer steeping times and higher temperatures, with some presenting a contrasting effect due to degradation at higher temperatures for longer steeping times. Results for terpenic compounds showed similar contrasting patterns. Based on the quadratic response surface, it was possible to predict the maximum overall liking for lemon verbena infusions prepared by brewing for 6 min at 96 ℃. Under such conditions, extraction of bioactive compounds was kept at a high level, close to the maximum attainable, while reducing the extraction of bitter compounds. These results are considered of great importance for the development of premium infusions from organic lemon verbena leaves.

Benznidazole, itraconazole and their combination in the treatment of acute experimental chagas disease in dogs

Chagas disease (CD) is a serious public health problem in Latin America and its treatment remains neglected. Benznidazole (BZ), the only drug available in Brazil, presents serious side effects and low therapeutic efficacy, especially at the chronic phase. The last clinical trials demonstrated that the first generation of azole compounds were less successful than BZ in CD chemotherapy, which stimulated studies of these compounds associated to BZ and nifurtimox (NF). This study evaluated the therapeutic efficacy of BZ, itraconazole (ITZ) and their combination (BZ + ITZ) in dogs infected with the VL-10 T. cruzi strain in the acute phase of the disease. Twenty young mongrel dogs were inoculated with 2.0 × 10³ blood trypomastigotes/kg and divided into four groups: treated with BZ, ITZ and BZ + ITZ for 60 days, and control group (INT). The parasitemia of the BZ + ITZ and BZ groups were similar and showed significant reduction compared to the INT group. The group treated with ITZ also showed significant parasitemia reduction compared to the INT group. The global analysis of hemoculture (HC), blood PCR, conventional serology (CS-ELISA), heart qPCR and histopathology techniques, used in the post-treatment evaluation, revealed that BZ + ITZ combination lead to a more reduction of parasitemia during the acute phase and heart qPCR positivity, less cardiac damage (inflammation and fibrosis in the left ventricle) and total survival. According to the classical cure criteria one animal treated with BZ + ITZ can be considered cured in its final evaluation and two other dogs, one of this group and one treated with ITZ were in process of cure. At least for BZ-resistant T. cruzi strains such as VL-10, BZ + ITZ was not effective to induce parasitological cure or a profound and sustained reduction of the parasite burden in blood and infected organs.

Synanthropic diptera affecting layer poultry farms: a review

ABSTRACT: The poultry farm of posture is an economic activity of great relevance to Brazil. Health aspects of flocks of laying chickens, such as the occurrence of infestations by parasites and poultry pests, influence significantly the productivity indicators. In this context, the control of synanthropic diptera is one of the challenges of the poultry farmers and professionals of this area. In Brazil, the control of flies in poultry environments is based mainly on the use of pesticides, while other alternatives are less frequent. Among the flies’ species most regularly found in poultry farms are the Musca domestica, Chrysomya spp., Fannia spp., and others. This review aims at compiling the literature on the occurrence, impact on poultry systems, biology, epidemiology and control of the species of synanthropic flies considered important for the Brazilian poultry industry.

Epidemiological Characterization and Risk Assessment Associated with the Presence of Diptera Order in Laying Poultry Farms

Background: Health aspects of flocks of laying chickens, such as the occurrence of infestations by parasites and poultry pests, influence significantly the productivity indicators. In recent years, Brazilian poultry has gone through a scientific and technological evolution which resulted in high density poultry hens in the laying sheds and an increase of the occurrence of ectoparasites such as Diptera. The presence of these flies have caused negative impacts for poultry farming, since these may be responsible for the increase of stress and disease emergence and, in addition, reduction of productivity. In this context, the control of synanthropic Diptera is one of the challenges of the poultry farmers and professionals of this area. This study was carried to assess and characterize the risks for the presence of flies in chicken houses of laying farms in the state of Minas Gerais.Materials, Methods & Results: Was used a secondary database and adapted for this study, with information from 402 chicken houses of 42 laying hens commercial properties. The variables used to compose the correspondence model were selected through chi-square tests (P ≤ 0.05). A risk index was built to the presence of flies from variables considered as risk factors for these ectoparasites. In addition, a study of the spatial analysis was carried to evaluate the intensity of chicken houses of poultry farms with the presence of flies. For this, a Kernel map was produced using the QGIZ 2.18.1 software, georreferencing the regions of state of Minas Gerais that have these ectoparasites. It was observed the presence of flies in 253 chicken houses evaluated, which corresponds to a frequency of 62.9%, with the most present flies were Chrysomya spp. 37.3%, M. domestica 34.3%, Fannia spp. 16% and Stomoxys spp. 14%. The graph of the correspondence analysis produced for the epidemiological characterization of the presence of flies presented an accumulated chi-square value of 56.05%. There was an association of the risk index with removal interval and the humidity of the manure and with the type of installation of chicken houses. Farms with chicken houses that create their birds on the ground present a lower risk for the presence of Diptera. In addition, when the removal of the manure is performed manually and is not done periodically, the presence of flies in the chicken houses is observed. It was verified that clusters located in the messoregion south/southwest of Minas Gerais and between the west and metropolitan mesoregion of Belo Horizonte with chicken houses that have the presence of flies.Discussion: The accumulation and permanence of manure can occur in less technical farms that have laying hens kept in confinement with high densities. In the case of Diptera, the greater the interval of removal of the manure below cages, the greater the risk for their presence, combined with the high densities of the birds that contribute to a faster accumulation of manure. The humidity of the manure is another important factor for the development of flies. The risk is high when chicken feces are liquefied, due to the fact that larvaes of flies need a moist substrate for survival. These results provide knowledge about the epidemiology of flies, in addition to demonstrate the profile of laying farms in the state of Minas Gerais. The implementation of certain management measures and the investment in technification of the chicken houses could reduce the risks of possible infestations in the flocks, besides the negative effects resulting from this ectoparasitism.

Epidemiological aspects of lice (Menacanthus species) infections in laying hen flocks from the State of Minas Gerais, Brazil

The epidemiology of chicken lice species such as Menacanthus stramineus, M. cornutus and M. pallidulus were studied during an observational, analytical and sectional survey, to determine predisposing factors for their occurrence in laying hen farms in the State of Minas Gerais, Brazil. A total of 431 houses on 43 farms were visited in 2012. M. cornutus, M. stramineus and M. pallidulus occurred in 20.9%, 11.6% and 11.6% of farms, respectively. The frequencies of occurrence of M. cornutus, M. stramineus and M.pallidulus in poultry houses were 10.4%, 8.8% and 3.7%, respectively. The epidemiological determinants for the occurrence of these species were investigated using Poisson or logistic regression models. The region of the farm, the recent use of acaricides and the presence of birds, such as saffron finch (Sicalis flaveola), feral pigeon (Columba livia) and Guira cuckoo (Guira guira) around the farms were related to the epidemiology of M. cornutus. Infestation by M. stramineus was associated with age of birds, number of birds per cage and the presence of Guira cuckoo and Chopi blackbird (Gnorimopsar chopi) near the poultry houses. The occurrence of M. pallidulus was influenced by the type of facilities, presence of cattle egret (Bubulcus ibis) and free-range domestic hens around the farm. The use of wire mesh nets in the houses and of forced moulting did not influence lice infestation.

Epidemiology of Megninia spp. in laying flocks from the State of Minas Gerais, Brazil

Aspects related to the epidemiology of Megninia ginglymura were studied, in order to determine predisposing factors for the occurrence in layer chicken houses of commercial farms in the State of Minas Gerais, Brazil. An observational, cross-sectional, analytical survey was conducted for identifying major risks or protection factors for infestations. Four hundred thirty-one houses located in forty-three farms were visited in 2012. Regarding the farms, 17 (39.53%) had chickens infested by M. ginglymura and 1 (2.32%) presented Megninia cubitalis. The epidemiological aspects of the occurrence of M. ginglymura were investigated using multiple logistic regression models. The chicken house organization was an important protection factor involved in the occurrence of M. ginglymura (odds ratio [OR] = 0.85). The presence of subsistence breedings of poultry within the premises or at the proximity of a farm was characterized as a risk factor for the occurrence of infestations (OR = 3.92). The use of mineral oil (OR = 0.16) was considered protective against new infestations. Some regions of the state were characterized by a higher risk for mite infestation than others.

Análise de diferentes métodos de avaliação do estado nutricional de pacientes em hemodiálise

<p><strong>Introdução: </strong>O paciente em diálise deve ser avaliado nutricionalmente e monitorado periodicamente desde o início do tratamento dialítico, possibilitando melhores propostas de intervenções e adequações dietéticas eficazes. Objetivo:<strong> </strong>Comparar estado nutricional de pacientes com Doença Renal Crônica em hemodiálise, classificados entre desnutridos e não desnutridos, por diferentes parâmetros clínicos, antropométricos, laboratoriais e verificar o nível de concordância dessas formas avaliativas. <strong>Materiais e Métodos: </strong>Estudo transversal, realizado em 2010, com 90 pacientes de uma clínica de diálise em Belo Horizonte/MG. Foram coletados dados pessoais, socioeconômicos, nutricionais, clínicos, bioquímicos e antropométricos. <strong>Resultados e Discussão: </strong>Houve variação de 12,2% a 86,7% de indivíduos desnutridos conforme diferentes parâmetros avaliativos. Nas análises antropométricas, homens apresentaram pregas cutâneas menores que mulheres. Quanto à circunferência muscular do braço, quase 40% apresentaram classificação de desnutrição, sendo aproximadamente 30% destes do sexo masculino. Os valores médios Índice de Massa Corporal encontraram-se dentro da classificação de normalidade. Quanto à ingestão calórica e ingestão protéica, as proporções de pacientes com ingestão inferior ao desejado foram de 86,7% e 57,8% respectivamente. A média dos valores de albumina foi de 3,9g/dL e a classificação de desnutrição variou entre 25,6% e 50% dependendo da referência utilizada. <strong>Conclusões: </strong>A grande variação de classificação dos pacientes como desnutridos obtida, sugere a necessidade de padronização de rotinas, observação e acompanhamento cautelosos das referências e a necessidade de comitês de avaliação para determinação de novos pontos de corte para melhor classificação nutricional desta população.</p><p><strong><em>Cómo citar este artículo: </em></strong><em>Ribeiro M, Araújo ML, Cunha L, Ribeiro D, Pena G</em><em>. Análise de diferentes métodos de avaliação do estado nutricional de pacientes em hemodiálise</em>.<strong> </strong><em>Rev Cuid. 2015; 6(1): 932-40.</em><em> <a href="http://dx.doi.org/10.15649/cuidarte.v6i1.163">http://dx.doi.org/10.15649/cuidarte.v6i1.163</a></em><em> </em><em></em></p>

Influence of acute exercise on the osmotic stability of the human erythrocyte membrane

This study evaluated the effects of 2 different types of acute aerobic exercise on the osmotic stability of human erythrocyte membrane and on different hematological and biochemical variables that are associated with this membrane property. The study population consisted of 20 healthy and active men. Participants performed single sessions of 2 types of exercise. The first session consisted of 60 min of moderate-intensity continuous exercise (MICE). The second session, executed a week later, consisted of high-intensity interval exercise (HIIE) until exhaustion. The osmotic stability of the erythrocyte membrane was represented by the inverse of the salt concentration (1/H50) at the midpoint of the sigmoidal curve of dependence between the absorbance of hemoglobin and the NaCl concentration. The values of 1/H50 changed from 2.29±0.1 to 2.33±0.09 after MICE and from 2.30±0.08 to 2.23±0.12 after HIIE. During MICE mean corpuscular volume increased, probably due to in vivo lysis of older erythrocytes, with preservation of cells that were larger and more resistant to in vitro lysis. The study showed that a single bout of acute exercise affected erythrocyte stability, which increased after MICE and decreased after HIIE.

Nutritional and epidemiological aspects of patients with chronic renal failure undergoing hemodialysis from Brazil, 2010

INTRODUCTION

The Nutrition Committee of the Brazilian Society of Nephrology (SBN) held in 2010 the first Brazilian Nutrition Census in hemodialysis patients. Multicenter data contribute to clinical development and nutritional intervention.

OBJECTIVE

To describe epidemiological and nutritional aspects of hemodialysis patients.

METHOD

Cross-sectional study in 36 dialysis clinics and 2,622 randomly selected participants. Socio-demographical, clinical, biochemical and anthropometric records were collected.

RESULTS

60.45% of the patients lived in the Brazilian Southeast. 13.53% came from Northeast region, while 12.81% from South, 10.33% from Midwest and 2.86% from North regions. Approximately 58% were male and 63.1% were below 60 years old. 58.5% of patients were married or in cohabitation. Around 80% of them depended on the government Unified Health System. Smoking showed a difference between gender and age. Presumptive etiologies were Hypertensive Nephrosclerosis (26.4%), Diabetic Nephropathy (24.6%), unknown/undiagnosed causes (19.9%), Glomerulopathies (13.6%) and others (11.2%). Both Hypertension and Diabetes Mellitus affect approximately 30% of patients, especially over 60 years. Body Mass Index did not differ between genders, although it differed between age groups and when used different evaluation criteria. Men and women average waist circumference were respectively 90.5 and 88.0 cm. Lipid profile did not differ between age groups, but it did between genders. Albumin values were lower in women and in patients older than 60 years.

CONCLUSION

This study characterized Brazilian hemodialysis patients in 2010, and may support further studies to monitor nutrition and epidemiological transitions of the population.

Effects of customary dinner on dietetical profile of patients undergoing hemodialysis

INTRODUCTION

To assess the effects of the habit of having evening dinner on the dietary macro- and micronutrient profile of chronic kidney failure patients on hemodialysis.

METHODS

Cross-sectional study carried out at a dialysis clinic at the city of Belo Horizonte, state of Minas Gerais. The study comprised 90 patients undergoing hemodialysis. Personal, clinical, and dietary (three-day food record) data were collected. The habit of having dinner was considered as having a complete evening meal, and the lack of that habit was considered as not having it or replacing it by a fast meal. The amounts of nutrient intake were estimated in the specific software Dietwin®.

RESULTS

The carbohydrate, thiamine, riboflavin, ascorbic acid, calcium, and selenium intake values showed no difference between the group having a complete evening meal and that not having it (p > 0.05). Both groups did not differ in the following: body mass index, and energy, protein, lipid, niacin, pantothenic acid, pyridoxine, folic acid, cobalamin, potassium, phosphorus, zinc, and magnesium intake values (p < 0.05). Regarding nutrient adequacy, the complete evening meal group performed better than the other group, except for carbohydrates, lipids, pantothenic acid, ascorbic acid, potassium, calcium, and zinc (p < 0.05). None of the patients showed the adequate pyridoxine, folic acid, and selenium intake values. Few patients in both groups showed adequate energy, pantothenic acid, and zinc intake values.

CONCLUSION

The habit of having a complete evening meal influenced positively the micro and macronutrient intakes in chronic kidney failure patients on hemodialysis.

Amblyomma rotundatum (Koch, 1844) (Acari: Ixodidae) two-host life-cycle on Viperidae snakes

Amblyomma rotundatum is an ixodid tick that infests ectothermic animals and reproduces exclusively by parthenogenesis. This tick has been frequently reported to infest reptiles and amphibians, under natural conditions and sometimes in captivity. It was described in Brazil and several other countries of South, Central and North America. Although many studies have reported aspects of its biology, none of them has used regularly either ophidian as hosts, or controlled temperature, humidity and luminosity for parasitic stages. The objective of this experiment was to study the life cycle of A. rotundatum feeding on Viperidae snakes under room controlled conditions at 27 ± 1 ºC temperature, 85 ± 10% relative humidity and 12:12 hours photoperiod for parasitic stages, and under B.O.D incubator conditions at 27 ± 1 ºC temperature, 85 ± 10% relative humidity and scotophase for non-parasitic stages. The total duration of the life cycle ranged from 56 to 163 days (mean of 105 days). Two-host life cycle was observed for most of the ixodid population studied.

Changes in the pro-inflammatory cytokine production and peritoneal macrophage function in rats with chronic heart failure

Chronic heart failure (CHF) is a state of immune activation, and pro-inflammatory cytokines play an important role in its development and progression. Macrophages (Mphis), when activated, are the main source of pro-inflammatory cytokines. We measured interleukin-6 (IL-6), interleukin (IL-1beta) and tumor necrosis factor - alpha (TNF-alpha) production after lipopolysaccharide (LPS)-stimulation, as well as peritoneal Mphis migration, phagocytic capacity, chemotaxis index, and hydrogen peroxide production, in an attempt to clarify the role of this cell in an animal model of CHF. Ligature of the left coronary artery or sham operation was performed in adult Wistar rats. After 12 weeks, resident and total cell number, phagocytic capacity, chemotaxis index, and hydrogen peroxide production in Mphis were significantly higher in CHF than in control rats. The production of IL-6 and TNF- alpha was similarly significantly enhanced in CHF as compared with controls. Mphis obtained from CHF rats were more responsive to LPS, suggesting the existence, in vivo, of possible factor(s) modulating the production of pro-inflammatory cytokines. The results demonstrated that there is modification of peritoneal Mphis function along CHF development, possibly contributing to the pathophysiological process in the establishment of CHF.

Improved model based on the Weibull distribution to describe the combined effect of pH and temperature on the heat resistance of Bacillus cereus in carrot juice

The effect of pH and temperature on the thermal inactivation of different strains of Bacillus cereus was modeled. Inactivation tests were carried out in carrot broth, following a full factorial design at four levels for temperature (from 90 to 105 degrees C, depending on the strain) and pH (6.2, 5.8, 5.2, and 4.7). Individual inactivation curves were analyzed by applying the Weibull model function (with percent discrepancy close to 20% for most cases), and the effects of pH and temperature on the scale parameter (designated D(beta)) and the shape parameter (beta) were also studied. Temperature and pH did not have a significant effect on the shape parameter (beta). The effect of temperature on the scale parameter was modeled by the zeta concept. The scale parameter decreased with pH, although the behavior of the strains was not homogeneous. Two global models with a small number of parameters were developed, providing a satisfactory description of the thermal inactivation of B. cereus, with percent discrepancy ranging from 18 to 25%.

Empirical model building based on Weibull distribution to describe the joint effect of pH and temperature on the thermal resistance of Bacillus cereus in vegetable substrate

A mathematical model based on Weibull parameters was built to describe the joint effect of temperature and pH on thermal inactivation of Bacillus cereus spores (strain INRA TZ415). The effect of these factors on Weibull model parameters (beta, 1/alpha) was also studied. Heat inactivation tests were carried out in acidified carrot broth as vegetable substrate, following a full factorial design at four levels for temperature (80, 85, 90 and 95 degrees C) and pH (6.2, 5.8, 5.2 and 4.7). The Weibull distribution model provided good individual fits for the different combinations of temperature-pH tested, with discrepancy factors, Df, coming close to 25% for most cases. The temperature and pH did not have a significant effect on the shape parameter (beta), which yielded a mean value of 0.88. The scale parameter (alpha) decreased with pH, and its inverse (1/alpha) followed an Arrhenius-type relationship with temperature. A global model was built, including the dependence of the alpha parameter on temperature and pH, and the model parameters were estimated by using a one-step nonlinear least-squares regression to improve the precision of the estimates. Results indicated that the global model provides a satisfactory description of the thermal inactivation of B. cereus spores, with R2 equal to 0.983.