Mathematical modeling to predict the fitness cost associated with triclosan tolerance in Salmonella enterica serovars

Triclosan is a broad spectrum biocide that is incorporated in a wide variety of products for food industry, medical applications and domestic use to reduce microbial load and to improve hygiene. Despite the extended use of the biocide, bacterial tolerance to triclosan is still infrequent. Here, we support the hypothesis that the acquisition of a triclosan tolerance-mediating mutation in the target site for triclosan, the gene fabI, is associated with a fitness cost in Salmonella enterica. Growth competition experiments with mutants exhibiting the Gly₉₃-Val mutation in fabI and their wild-type strains revealed overall decreases in the relative proportions of mutants. For all four serovars investigated, the log₁₀ difference values increased linearly over the experimental time of 96 h. Therefore, a linear regression model was used to characterize the changes in log ratios of wild-type strains and mutants over time. The calculated regression coefficients allowed an estimation of the fitness cost of triclosan tolerance in Salmonella mutants in comparison to their wild-type strains.     

Prediction and modeling of microbial growth in minimally processed fresh-cut apples packaged in a modified atmosphere: A review

Minimally processed fresh-cut (MPFC) fruit products are an important source of functional ingredients, and increased consumers’ demand boosted an expansion of this segment of food industry. Apples (Malus sp.) are commonly cultivated fruits and processed to MPFC products. Their low shelf life is the main obstacle for gaining maximum nutritive and economic benefits. Enzymatic, metabolic, and other physiological processes induce changes that render the product spoiled and decrease the storage and marketability life of MPFC fruits. Such spoilage can be controlled by modified atmosphere packaging (MAP), but intrinsic influences of numerous MAP factors are not clearly elucidated. Microbial growth adds another layer of complexity to MAP. Mathematical modeling can successfully predict microbial growth and spoilage, hence saving production cost and provide better control over the production chain. In this sense, this review provides an overview of MAP’s factors that influence the quality of stored MPFC products. Focus was placed on apples and development of mathematical models that can be useful for prediction of their spoilage during storage and subsequently their shelf-life.     

Incidence of Salmonella spp. in raw vegetables in Selangor,Malaysia

A total of 43 samples of ‘selom’ (Oenanthe stolonifera), 26 samples of ‘pegaga’ (Centella asiatica), 25 samples of ‘kangkong’ (Ipomoea aquatica) and 18 samples of ‘kesum’ (Polygonum minus) were examined for the presence of Salmonella spp. Salmonellae were detected from 40 (35%) of the vegetables samples examined. The most common serotypes isolated were S. weltevreden (23.5%), S. agona (16.2%), S. senftenberg (10.1%) and S. albany (6.7%). The other 27 Salmonella serovars were isolated at frequencies from 0.6% to 3.4%. Several of the Salmonella serotypes isolated in this study have been implicated in human infections in other countries. Although Salmonella species are frequently detected in foods of animal origin, the detection of 31 Salmonella serovars in four local salad vegetables in this study is not very encouraging, and supported the notion that these vegetables can be potential health hazards.     

A case of spoilage in wurstel sold in an Italian supermarket

In the current study, the shelf-life and the spoilage of Italian wurstel sold in a local supermarket was investigated. The analysis included identifying the causative microorganisms and the variations in physical-chemical parameters (pH, a_W, lactic acid, and ammonia). The spoilage consisted of a white surface coating or slime that appeared after the thirtieth day of storage. The cause of the spoilage was the uncontrolled growth of thermoduric heterofermentative lactic acid bacteria (LAB) that occurred during storage. The LAB, including Leuconostocs and Brochothrix thermosphacta organisms, can survived the pasteurisation process. Due to the deacidifying action of B. thermosphacta and the production of ammonia, there was no evidence of off-odour or off-flavour and no change in pH. Furthermore, no loss of the vacuum seal was observed in the spoiled wurstel.     

Plant essential oils and components on growth of spoilage yeasts in microbiological media and a model salad dressing

Essential oils (EOs) and EO components have been widely tested for their antimicrobial properties against microorganisms. However, less is known about the inhibitory properties of essential oil components against microorganisms in foods and, more specifically, spoilage yeasts in a food matrix. Clove bud, cinnamon bark, and thyme oils, and the EO components, trans-cinnamaldehyde, cinnamic acid, eugenol, carvacrol, and thymol first were evaluated for their antimicrobial activity against yeasts in microbiological media. The yeasts tested included Torulaspora delbrueckii, Candida krusei, Schizosaccharomyces pombe, and Zygosaccharomyces bailii. The most efficacious EO components in media were applied to a model mayonnaise-based salad dressing as a food model to determine the effect on spoilage yeast growth. Trans-cinnamaldehyde and cinnamon bark oil were the most effective against yeasts in microbiological media among the compounds tested with minimum inhibitory concentrations (MICs) of 50 mg/L. Thymol and carvacrol had the next most inhibitory activity against yeasts with MICs of 200 mg/L. In a model salad dressing at pH 4.2, trans-cinnamaldehyde at 500 mg/L was most effective among the EO components inhibiting S. pombe and Z. bailii during 4- and 5-day storage, respectively, at 22 °C.     

Comparison of microbial transfer rates from Salmonella spp. biofilm growth on stainless steel to selected processed and raw meat

Salmonella biofilm cells can serve as a serious source of cross-contamination, both in the home and at food production sites. The objectives of this study were to determine the transfer rates (RTs) of Salmonella biofilm cells and to model the transfer process of biofilm cells from stainless steel surfaces to raw meat. The results showed that the RTs were significantly influenced by the types of meat products, with bacon and emulsified sausage showing higher RTs and roast pork showing lower RTs. Higher RTs of biofilm grown in a meat-based medium, Meat Thawing-Loss Broth (MTLB), were observed as compared to that in a standard growth medium (TSB). The logistic, exponential and multi-roots models could be used to satisfactorily describe the transfer of biofilm cells as demonstrated by use of MSE, F-test and R². There was no difference in attachment strength (reflected by the coefficients of transfer models) of biofilm grown in TSB or MTLB, as shown by the coefficients of r, D and B in three models. Compared with the exponential and the multi-roots models, the logistic model was able to more accurately fit the whole transfer process of biofilm cells. Our findings highlight the occurrence of cross-contamination with biofilm cells, and the models may provide useful tools in quantitative microbiological risk assessment of meat products.     

Detection and CRISPR subtyping of Salmonella spp. isolated from whole raw chickens in Yangzhou from China

This study was undertaken to acquire data on Salmonella contamination of whole raw chickens, eggs, and vegetables available to consumers in Yangzhou city, China, between April 2011 and March 2012. In total, 240 chicken carcasses were tested, and the overall contamination rate for Salmonella was 33.8%. While the prevalence of Salmonella in 100 eggs and 155 vegetable samples was 7.0% and 3.2%, respectively. The 84 isolated strains were identified in 19 different serotypes with Salmonella enterica serovar Indiana (S. Indiana) (25.0%), S. Typhimurium (21.4%) and S. Enteritidis (17.9%) as the predominant serovars. Moreover, the median load of the contaminated chicken samples reached 6.4 MPN/100 g with 3.6 MPN/100 g as the 25th percentile and 15.0 MPN/100 g as the 75th percentile. Chicken carcasses collected in October had not only the highest prevalence of Salmonella (70%), but also the highest median load (33 MPN/100 g) and 75th percentile load (460 MPN/100 g), while the lowest prevalence (10%) was in April. The clustered regularly interspaced short palindromic repeats (CRISPR) subtyping method was then used to identify serotypes of Salmonella and distinguish strains from the same Salmonella serotypes. We found that 85.7% of strains were distributed in 11 serotypes speculated by CRISPR typing, which corresponded to the identified serotypes by O and H antiserum. The speculated serotypes of 7.1% of the strains by CRISPR typing are very close to the identified ones, as they belong to the same O group with a small difference in the O or H antigen. All of the above findings implied that CRISPR typing could be applied to serotyping of Salmonella. In addition, CRISPR typing method could be used to subtype different strains from the same serotype, specifically S. Hadar.     

油田开发动态色谱指纹监测技术的数学模拟研究

在油气藏的勘探阶段,对油气藏流体的认识只是静态的,宏观的,油气藏一旦投入开发,地下流体就处于运动状态,注水开发油气藏是如此,随着流体不断采出,地下温度压力条件不断变化,由于储集层本身的厚度,孔隙度,渗透度等非均质性的差异,各开采单层的产液贡献也不相同,即井口产出流体的种类,多少以及来源和物理化学性质的变化直接影响着油气的采油率,因此在油井的正常生产过程中就要对油气藏的生产动态进行监测,利用各种井下测试仪器定量解释每个小层的压力,温度,流体密度,体积流量,含水率等各种参数变化,研究油井产液动态,油气运动规律和剩余油分布特征。     

Detection of Salmonella spp. in spices and herbs

The detection of microbial contaminations in spices and herbs is a challenging task due to their strong antimicrobial effects, which potentially increase the risk for false-negative results. Therefore, the present study mainly focuses on the detection of Salmonella spiked to cinnamon and oregano. Both condiments completely inhibited the proliferation of Salmonella at a 1:10 (w/w) dilution. Consequently, the supplementation of the buffered peptone water with K₂SO₃ as well as the application of higher initial dilutions was investigated. While no detrimental effect of K₂SO₃ was observed during the growth of 14 different Salmonella isolates, it even improved their detection in condiments. An effect, which was also determined with increased dilution ratios. For detection, a quantitative approach via enumeration of the colony-forming units (CFUs), and qualitative approaches via the culture-based detection according to ISO 6579 and via the nucleic acid-based detection with the 3M Molecular Detection System (MDS) were performed. Subsequently, the limit of detection (LOD) was determined, which was <5 CFU 25 g⁻¹ for both qualitative approaches. Furthermore, the persistence of Salmonella DNA spiked to parsley was determined with the MDS. Despite of the modifications, the LOD for Salmonella spiked to oregano was significantly lower prior than after enrichment, pointing to the requirement for further improvements. Last but not least, a ring trial was performed, which emphasized the importance for a reliable detection.     

Inactivation behaviors of foodborne microorganisms in multi-frequency power ultrasound-treated orange juice

This study established the inactivation kinetic parameters of some pathogenic bacteria including Escherichia coli O157:H7, Salmonella enterica serotypes, and Listeria monocytogenes; and spoilage yeasts namely, Debaryomyces hansenii, Clavispora lusitaniae, Torulaspora delbrueckii, Pichia fermentans, and Saccharomyces cerevisiae in orange juice subjected to multi-frequency Dynashock power ultrasound treatment. All test organisms exhibited a biphasic inactivation behavior with a sigmoidal inactivation curve consisted of an initial inactivation lag, followed by logarithmic linear inactivation. Injury accumulation in the inactivation lag phase was established in acid-adapted bacteria. The time necessary to reduce initial inoculated populations by 5 log cycles (99.999%), T_5D values, significantly increased with acid adaptation. The T_5D of E. coli, S. enterica, and L. monocytogenes increased from 37.64, 36.87, and 34.59 respectively; to 54.72, 40.38, and 37.83 min respectively after acid exposure. Temperature increase due to sensible heat propagation during ultrasound treatment decreased the resistance of the test bacteria. The cocktail of E. coli O157:H7 had significantly greater resistance towards ultrasound treatment (T_5D = 54.72 min) than any of the individual strain (T_5D = 41.48–47.48 min) in the mix. Similar results were found in the composited (T_5D = 60.02 min) and individual species (T_5D = 20.31–59.04 min). The results established in this work provide baseline information on microbial behavior in multi-frequency ultrasound-treated orange juice for establishment of pasteurization process schedules.     

Impact of Clostridium spp. on cheese characteristics: Microbiology,color, formation of volatile compounds and off-flavors

The impact of autochthonous and type-strains of Clostridium tyrobutyricum, Clostridium butyricum, Clostridium beijerinckii and Clostridium sporogenes on spoilage (late blowing defect, LBD), physico-chemical characteristics and volatile profile of cheese has been investigated. Five semi-hard cheeses were produced from ewe milk inoculated with 10⁴ spores/mL of five Clostridium strains and ripened for 60 d. One cheese without clostridial spores served as control. C. tyrobutyricum CECT 4011 and INIA 68 resulted potent cheese spoilers, and caused the appearance of the earliest and greatest symptoms of LBD, affecting cheese pH and color, and leading to accumulation of volatile compounds like butyric, propionic and pentanoic acids and some aldehydes, alcohols and esters associated with cheese rancid and pungent off-odors. Cheeses contaminated with C. beijerinckii INIA 63 and C. sporogenes INIA 71 showed milder and late LBD symptoms, and a volatile profile characterized by higher levels of 2-butanone, 2,3-butanedione and 2-butanol than the rest of cheeses. Despite cheese inoculated with C. butyricum CECT 361 presented a slight blown-pack at the end of ripening, it showed physico-chemical characteristics and a volatile profile similar to control cheese. The first two axes of a principal component analysis (PCA) performed for the 21 significant volatile compounds out of 38, accounting for 91% of the variability between cheeses, separated cheeses made with C. tyrobutyricum CECT 4011 and INIA 68, with severe LBD symptoms, from the rest of cheeses, and also differentiated control cheese and cheese made with C. butyricum CECT 361, from cheeses with milder LBD symptoms made with C. beijerinckii INIA 63 and C. sporogenes INIA 71.     

Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the growth kinetics of C. sporogenes in cooked beef under different temperature conditions.Ground beef samples, inoculated with C. sporogenes spores, were incubated at temperatures between 8 and 47 °C to examine the growth of this microorganism. Two primary models (Huang and Baranyi models) were used to analyze the growth data. The Ratkowsky square-root model was used as the secondary model to evaluate the effect of temperature on bacterial growth rate and lag time. The USDA IPMP 2013, a free data analysis tool for predictive microbiology, was used in data analysis.No growth of C. sporogenes was observed at temperatures below 15 °C for up to 25 days. At temperatures between 20 and 47 °C, C. sporogenes grew in cooked beef. The growth curves could be analyzed by both Huang and Baranyi models. The root mean squared error (RMSE) was 0.375 for the Huang model, and 0.441 for the Baranyi model with a global h₀ of 10.46. The nominal minimum growth temperature (T₀) estimated from the Huang model was 15.5 °C, which was 12.7 °C for the Baranyi model. The maximum growth temperature was 48.0 and 48.3 °C for the Baranyi and Huang models, respectively. The lag times and specific growth rates of C. sporogenes observed in this study were reasonably close to the data reported in the literature for C. botulinum under comparable conditions, suggesting that C. sporogenes may be used as a potential surrogate for evaluating the growth of C. botulinum in cooked meats during cooling. However, a direct comparison of growth kinetics between the two microorganisms is needed to confirm the suitability of C. sporogenes as a surrogate of C. botulinum.     

水平井泡沫分流酸化数学模型及其数值解法

由于钻井过程中钻井液对储层的伤害,水平井的产能受到影响。酸化是一种常用的水平井增产措施,常规酸化存在地层进酸不均的问题;而泡沫酸化能有效地封堵高渗透储层,提高低渗透储层的渗透性,达到更有效的酸化增产效果。通过研究泡沫流体在水平井段流动和在油藏中的渗流特性,建立了水平井泡沫分流酸化数学模型,并对模型进行求解,得到了沿水平井段酸液的流量和压力的变化关系,以及沿水平井段流入地层泡沫酸量的变化规律。结果表明,沿水平井段流入地层的酸液量变化不大。因此,泡沫酸化能够解决地层进酸不均、解堵不均的问题,提高酸液利用效率,均匀改善受污染储层,提高受污染储层的渗透性,达到良好的均匀酸化的效果。     

In vitro evaluation of Lactobacillus animalis SB310, Lactobacillus paracasei subsp. paracasei SB137 and their mixtures as potential bioprotective agents for raw meat

Lactobacillus animalis SB310 and Lactobacillus paracasei subsp. paracasei SB137, isolated from the gut of veal calves, were investigated in terms of antimicrobial activity for a possible application as bioprotective agents in vacuum-packed raw meat. In the first trial, cultures of single strains and their mixture obtained adding the two strains before the incubation, their cell-free supernatants and buffered cell-free supernatants were tested in vitro against a wide range of spoilage or potentially pathogenic bacteria. In the second trial different mixtures were evaluated for the same tests (L. animalis: L. paracasei rates = 1:2, 1:5, 1:10, 2:1, 5:1, 10:1 and 1:1 obtained mixing the two cultures grown separately). An evident inhibitory activity exerted by the single Lactobacillus strains and the mixtures was observed for all the target bacteria tested. In almost all the cases, the inhibition halos produced by the mixtures were significantly higher than those produced by the single strains, especially if L. paracasei subsp. paracasei SB317 was predominant in the mixture. Among the target bacteria, Pseudomonas fluorescens and Pseudomonas putida were clearly the most susceptible; a high variability in Enterobacteriaceae was detected, depending on the species. Serratia marcescens and Escherichia coli O157:H7 resulted as the less susceptible strains. A very limited activity of the cell-free supernatants was found for all the 12 strains tested, compared with the action of viable Lactobacilli, highlighting that the antimicrobial action originated from a combination of bacterial competition and the production of extracellular compounds. The absence of effects by the buffered cell-free supernatants suggests that these compounds are organic acids. Further studies are necessary to clarify the effects of these strains when applied to raw meat.     

采油微生物在多孔介质中的迁移滞留机制

采油微生物在多孔介质迁移过程中的滞留特征明显。以2株典型采油微生物Pseudomonas aeruginosa WJ-1和Bacillus subtilis SLY-3为研究对象,通过等温吸附实验和流动实验研究了其迁移滞留规律。研究结果表明:多孔介质的比表面积越大,吸附位点越多,菌体的吸附量越大。菌体和多孔介质表面的疏水性关系影响菌体在多孔介质表面的吸附量。采油微生物在油藏多孔介质环境中的总菌浓度一般低于3.5×108cfu/mL,在此条件下,采油微生物在油藏多孔介质中的吸附符合Freundlich吸附等温线。体积较大的微生物运移速度超前,说明采油微生物在多孔介质运移过程中存在不可及孔隙体积。采油微生物在多孔介质运移过程中受到平衡吸附和架桥筛分的共同作用,且架桥筛分的作用相比于平衡吸附更加突出。基于实验研究确定了微生物的迁移滞留机制,并在此基础上修改完善了微生物迁移数学模型。研究成果为微生物采油数值模拟软件的研发与优化提供了实验依据及理论基础。     

Effect of Anisakis simplex (sl) larvae on the spoilage rate and shelf-life of fish mince products under laboratory conditions

Wild caught marine fish are commonly infected with anisakid nematodes lodging in the intestinal linings or in the fish muscle. One of the most commonly found nematode parasites in marine fish is Anisakis simplex. During production of mince from the muscle of wild caught Anisakis-infected fish, the larvae would be disrupted during mince production. Any bacteria within or on the surface of such larvae are during the mincing process evenly distributed throughout the mince, and could thus possibly affect the spoilage rate of the final products. To explore if or how any bacteria associated with muscle-invading Anisakis larvae may affect the spoilage rate of fish mince, a controlled storage trial was conducted. Fillets of farmed Atlantic cod (Gadus morhua), exclusively fed on dried and heat-treated compound feed and hence expectably free from Anisakis larvae, were aseptically collected and homogenised. Fish mince aliquots were added different volumes of Anisakis homogenate based on larvae which were freshly sampled from the visceral cavity of NE Atlantic blue whiting (Micromesistius poutassou). The volumes of added parasite homogenate (parasite(+)-samples) reflected different infection intensities from 15 (low) to 50 (high) larvae per 100 g fish fillet, representing an actual Anisakis intensity range in the flesh of blue whiting. The samples were kept at 4 °C for 15 days and subjected to microbiological, sensory and chemical evaluation at 3 days intervals. Upon visual examination and plate count measurements (PC) on Iron Agar Lyngby (IAL), the samples without any parasite additives (no[parasite]) spoiled differently and more rapidly than any of the parasite(+)-samples. However, H₂S-producing bacteria were only recorded in the latter samples, which were also the only ones that showed increased levels of the spoilage indicator substance trimethylamine (TMA). Moreover, the parasite(+)-samples changed their sensory characteristics at a later stage compared to the no[parasite]-samples. Although some cultures of H₂S-producing bacteria were found on IAL, molecular identification by PCR-DGGE of the actual bacteria was not conclusive. Psychrobacter sp. which has no or only little spoilage activity, was identified in all samples until trial day 9, but was probably outgrown by the stronger spoilers Pseudomonas fluorescence/fragi and Photobacterium phosphoreum. Thus, and somewhat unexpected, our findings indicate that – under the present trial conditions – fish mince contaminated with bacteria which originate from Anisakis larvae, spoiled less rapidly than samples without any parasite-related bacteria present. Moreover, the shelf-life of fish mince was apparently not reduced by the presence of bacteria transferred to the mince by Anisakis larvae.     

Prevalence of L. monocytogenes and Salmonella spp. in Tulum cheese

Tulum cheese, which is produced from raw milk, is one of the most popular semi-hard cheeses in Turkey. The growth of some food pathogens such as Listeria monocytogenes and Salmonella spp. in cheese and other dairy products may cause serious health problems for consumers. The aim of this study was to assess the presence of L. monocytogenes and Salmonella spp. in Tulum cheese sold in Istanbul. During the period March 2004–March 2005, a total of 250 Tulum cheese samples were obtained from various markets located in Istanbul and the presence of L. monocytogenes and Salmonella spp. was analyzed according to “The US Food and Drug Administration” (FDA) methods. The results were positive for L. monocytogenes and Salmonella spp. in 12 (4.8%) and 6 (2.4%) samples respectively.     

Development of a multiplex real-time PCR method for simultaneous detection of Vibrio parahaemolyticus,Listeria monocytogenes and Salmonella spp. in raw shrimp

Vibrio parahaemolyticus, Listeria monocytogenes and Salmonella spp. are important pathogens contaminating seafood in China. In this study, we developed an efficient multiplex real-time PCR for the simultaneous detection of V. parahaemolyticus, L. monocytogenes and Salmonella spp. in raw shrimp without a prior enrichment step. In a test using 28 target and non-target strains only the targets were detected and two calibration curves, for pure cultures and artificially contaminated samples, were used to evaluate the efficiencies of this method. Amplification efficiencies of this multiplex real-time PCR were excellent in pure cultures and artificially contaminated shrimps. The limits of detection in artificially contaminated shrimps were 112 CFU/g for V. parahaemolyticus, 158 CFU/g for L. monocytogenes and 103 CFU/g for Salmonella spp. We validated this multiplex real-time PCR method on 48 commercial samples and the results were comparable to standard culture methods. This efficient multiplex real-time PCR, where each test takes only 50 min after DNA extraction, is a useful tool for high-throughput surveillance of V. parahaemolyticus, L. monocytogenes and Salmonella spp. in seafood products.     

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井下循环温度不但直接水泥浆的稠化时间、流变性等性能，而且与井内压力平衡、井壁稳定、井内工作液体系选择、套管和钻柱强度设计等方面有关。文章根据传热学的基本原理，针对井内热传递特点，建立了井下循环温度的二维瞬态数学模型，并用无条件稳定的全隐式有 差臾法数值求解数学模型。最后用塔里木油田的3口井的实测井底钻井液循环温度对模型预测结果进行了验证，并对理论模型和简易法计算的循环温度与实测值进行了对比分析。该模型可用于计算实际循环条件下的管内液体、管壁、环空液体与地层的温度分布，为水泥浆、泥浆与管柱强度设计等提供基础。