Analysis and mathematical modelling of the behaviour of Escherichia coli in the mascarpone cheese during cold storage

The aim of this work was to study the behaviour of E. coli in mascarpone cheese during storage at the temperatures ranging from 3 to 15 °C, as well as application of predictive microbiology to describe the experimental data. The Baranyi, Gompertz and logistic models were fitted at the stage of primary modelling. Although all applied primary models described the growth of micro‐organisms accurately, the most accurate goodness of fit was obtained for the Gompertz model and the growth rates generated by this model were used for secondary modelling. The polynomial model predicted accurately the influence of temperature on the growth rate of E. coli, reaching the adjusted coefficient of linear regression 0.99. Generated predictive model that describes the growth of E. coli in mascarpone cheese constitutes a valuable tool in assessing the microbiological stability of the food product with similar physicochemical properties.     

Detection and quantification of Escherichia coli and Pseudomonas aeruginosa in cow milk by near‐infrared spectroscopy

This work investigated the potential of NIR technology to be applied in the dairy industry for the detection of micro‐organisms. To this end, two types of cow milk samples were studied, one in which only bacterial biomass was considered and the other in which bacteria were cultured and grown in milk for 24 h. The study was carried out using two micro‐organisms Escherichia coli and Pseudomonas aeruginosa. Both types of samples with different counts of both micro‐organisms were analysed by a NIR analyser in the range 10 000–4000 cm^?1 based on transmittance measurements. Multivariate models indicated that a better discrimination between micro‐organisms was attained in those milk samples in which micro‐organisms have been grown.     

Occurrence and antibiotic resistance of Escherichia coli,Staphylococcus aureus and Bacillus cereus in raw milk and dairy products in Turkey

In this survey, 150 samples of raw milk, white cheese and ice cream from three different dairy‐processing plants in Ankara were analysed to find out if they were contaminated with Escherichia coli, Staphylococcus aureus or Bacillus cereus. The highest contamination percentages were found in raw milk samples as follows: B. cereus (90%), E. coli (74%) and S. aureus (56%) followed by cheese (70% B. cereus, 60% E. coli, and 48% S. aureus) and ice cream (56% E. coli, 36% S. aureus and 20% B. cereus). The survey showed that 2% of cheese samples were contaminated with E. coli O157. It was also found that the numbers of S. aureus and E. coli in raw milk, cheese and ice cream samples exceeded the numbers permitted under the Turkish Food Codex (TFC). The number of B. cereus in raw milk, cheese and ice cream samples was lower than the limit given in the TFC standards. The study also showed that E. coli and S. aureus exhibit resistance to ampicillin, penicillin, tetracycline, erythromycin, gentamicin and trimethoprim/sulfamethoxazole. Escherichia coli isolates also showed resistance to chloramphenicol and ciprofloxacin but none of them exhibited resistance to cefotaxime. All S. aureus isolates were found to be susceptible to cefotaxime, chloramphenicol, and ciprofloxacin. Bacillus cereus isolates were found to be resistant to ampicillin, penicillin and trimethoprim/sulfamethoxazole and sensitive to cefotaxime, chloramphenicol, ciprofloxacin erythromycin, gentamicin and tetracycline.     

Antibacterial effects of chitosan coating containing Mentha aquatica L. essence against Escherichia coli,Staphylococcus aureus and Listeria monocytogenes in Iranian white cheese

The effect of a chitosan coating and Mentha aquatica L. essence on Iranian white cheese was investigated. Results showed 100% inhibition of Escherichia coli growth using 1.5% essence after 10 days. After 15 days of incubation, the Staphylococcus aureus population was reduced by 44.2%, 70.0%, and 88.5% using 0.5, 1.0 and 1.5% essence, respectively. After 15 days, Listeria monocytogenes growth was inhibited by 63.84%, 70.12%, and 85.9% using 0.5, 1.0, and 1.5% essence, respectively. Inhibition zone diameter studies also confirmed the antibacterial effects of applied coating against all the above‐mentioned bacteria in Iranian white cheese.     

应用基因芯片技术检测食源性腹泻致病大肠杆菌

目的基因芯片技术在食源性致病大肠杆菌检测中的建立与应用。方法对菌株进行预处理,通过溴化十六烷基三甲铵(cetyltrime thylammonium ammonium bromide,CTAB)方法提取细菌中的基因组DNA并去除其中的杂质,利用提取的基因组设计引物序列和探针序列,设计完成后对致病大肠杆菌致病大肠杆就基因芯片进行杂交与洗涤,使用扫描仪对处理过的基因芯片进行扫描实现食源性致病大肠杆菌的检测。结果在病原菌按不同程度稀释的情况下,与传统的病原分离鉴定检测方法相比,将基因芯片技术应用在食源性致病大肠杆菌致检测中,能够明显的检测出荧光标记的病原菌。结论该方法的灵敏度更高,可以解决传统的致病大肠杆菌检测方法灵敏度较低,病原处于较低的感染状态时难以检出的问题。     

Caseinoglycomacropeptide inhibits adhesion of pathogenic Escherichia coli strains to human cells in culture

Caseinoglycomacropeptide (CGMP) derived from κ-casein was investigated for its ability to inhibit the adhesion of 3 strains of verotoxigenic Escherichia coli (VTEC) and 3 strains of enteropathogenic Escherichia coli (EPEC) to human HT29 tissue cell cultures. Effects on adhesion of Desulfovibrio desulfuricans, Lactobacillus pentosus, Lactobacillus casei, Lactobacillus acidophilus, and Lactobacillus gasseri were also investigated. Generally, CGMP exerted effective anti-adhesive properties at a dose of 2.5 mg/mL, albeit with a high degree of strain specificity. The CGMP reduced adhesion of VTEC strains to <50% of the control and reduced adhesion of EPEC strains to between 80 and 10% of the control. The CGMP also reduced the adhesion of L. pentosus and L. casei to 44 and 42%, respectively. A slight but significant reduction of L. acidophilus, to 81%, was observed, but no significant effects were detected with either Dsv. desulfuricans or L. gasseri. Further investigation of the dose response relationships with the E. coli strains gave IC50 values ranging between 0.12 and 1.06 mg/mL.     

LAMP技术检测食品中产肠毒素大肠埃希氏菌

产肠毒素大肠埃希氏菌(Enterotoxigenic Escherichia coli,ETEC)是一种重要的引起人畜共患病的致病菌,能引起水样便及酸中毒,建立快速、准确的检测方法对预防和控制产肠毒素大肠埃希氏菌的感染具有重要意义。基于ETEC不耐热肠毒素LT基因序列,设计LAMP引物检测产肠毒素大肠埃希氏菌。结果表明:LAMP检测产肠毒素大肠埃希氏菌的检出限为32.9cfu/mL,人工污染生猪肉的检出限为55cfu/g。LAMP将可以成为替代PCR的核酸扩增新技术,为快速检测产肠毒素大肠埃希氏菌构建了一个技术平台。     

Bacterial inactivation and quality changes of fresh‐cut avocados as affected by intense light pulses of specific spectra

Intense light pulses (ILP) treatments have good prospects for becoming an alternative to traditional thermal methods for decontamination of food surfaces. The aim of this work was to evaluate which ranges of the light spectrum are responsible for bacterial inactivation and their effect on the quality of fresh‐cut avocado. Results show that the effectiveness of ILP treatment decreases when the ultraviolet (UV) spectral region is blocked (particularly UV‐C). ILP treatments without UV‐C light (305–1100 nm) and an overall fluence of 10.68 J cm^?2 caused reductions of 2.47 and 1.35 log CFU g^?1 in the initial counts of inoculated Escherichia coli and Listeria innocua, respectively, in comparison with those treated using only VIS–NIR light (0.83 and 0.68 log CFU g^?1, respectively). Treatments applying light of a wavelength between 305 and 1100 nm had a more pronounced impact on colour, texture and headspace gas composition than treatments that did not contain UV light (400–1100 nm).     

酶底物法快速检测食品中的大肠埃希氏菌

目的将水质检验的酶底物法用于食品检验,探索酶底物法是否能快速检测食品中的大肠埃希氏菌。方法测定食品样品,比较酶底物法与传统鉴定法结果的一致性。结果传统方法检出24份阳性和8份阴性,酶底物法检出25份阳性和7份阴性。实验结果进行X~2检验,结果无显著性差异(X~2=0.087,P0.05)。32份样品MPN值结果一致,8份样品MPN值有差异,其中7份样品酶底物法的MPN值大于传统法。结论酶底物法可用于食品中大肠埃希氏菌的快速检测,具有快捷简便、特异性高的优势。     

Microbial inactivation and quality improvement of tomatoes treated by package film with allyl isothiocyanate vapour

In‐package sanitisation was developed using polylactic acid (PLA) films with allyl isothiocyanate (AIT) vapour. Tomatoes were artificially inoculated with Escherichia coli, Geotrichum candidum and Fusarium oxysporum and stored in clamshell boxes with the film fixed to the underside of the lid. The changes in bacterial and fungal populations and the quality of tomatoes during storage at 4 and 10 °C were evaluated. The results revealed that the film treatment (4 × 8 cm² film in 1 L box) reduced the populations of inoculated bacteria and fungi on tomatoes by 2–3 log CFU g^?1, and then significantly (P < 0.05) inhibited their growth during the 21‐day storage period at both temperatures. Tomatoes subject to film treatment had fewer changes in quality (colour, firmness, contents of total soluble solid, titratable acids and vitamin C) than the control samples during storage. The antimicrobial PLA film can be used for in‐package sanitisation to extend the shelf‐life of packaged tomatoes or similar perishable vegetables.     

The ability of Schisandra chinensis fruit to inhibit the growth of foodborne pathogenic bacteria and the viability and heat resistance of Bacillus cereus spores

The objective of this study was to investigate the influence of Schisandra chinensis fruit on the growth of spoilage and pathogenic bacteria and on the viability and heat resistance of Bacillus cereus spores. Schisandra chinensis fruit was extracted with one of three different solvents (50% ethanol, 100% ethanol and distilled water), and the extracts exhibited antimicrobial activity against all the bacteria tested. Particularly, the ethanol extracts of S. chinensis fruit had the strongest activity, in a concentration‐dependent manner. Fractionation of extracts by ion chromatography revealed that the antimicrobial activity of S. chinensis fruit is mainly due to organic acids such as citric acid and malic acid. Meanwhile, S. chinensis fruit extract (10%) significantly reduced the viability and heat resistance of B. cereus spores. Therefore, this study suggests that S. chinensis fruit extract has potential as a natural food preservative and/or sanitising agent for the reduction of spoilage and pathogenic contamination.     

Development of multiplex PCR assays to identify Escherichia coli pathogenic genes in food

In order to rapidly screen for the virulence factor that produces pathogenic Escherichia coli in food, we have developed multiplex polymerase chain reaction (PCR) assays. The multiplex PCR assays detect 4 pathogenic genes of enterohaemorrhagic E. coli (EHEC), enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), and enteroinvasive E. coli (EIEC). This allows for the generation of specific fragments 150, 179, 218, 401, 465, 584, and 881 bp for VT1, ST, LT, 16S rRNA, inV, VT2, and eaeA genes, respectively. The detection limit of 3 log CFU/mL for eaeA, LT, VT1, VT2, 4 log CFU/mL for inV, 6 log CFU/mL for ST by single PCR, while 5 log CFU/mL for VT1, VT2, 6 log CFU/mL for eaeA, LT, 7 log CFU/mL for ST, inV by multiplex PCR. This optimized detection method of pathogenic E. coli can be used as supportive data to revise the microbiological analytical manuals for the Korean Food Code.     

Efficacy testing of teat dip solutions used as disinfectants for the dairy industry: Antimicrobial properties

The production of raw milk containing a limited number of bacterial contaminants, which retains its quality during storage, is the major task of the dairy industry. This can only be achieved with adequate regular cleaning and disinfection of the udder, milking equipment, the dairy parlour and animal housing areas. Studies were conducted to assess the efficacy of a range of dairy disinfectants on bacterial species isolated from cow udders as well as reference microbial strains (ATCC). Testing included the assessment of bacterial growth inhibition, biofilm inhibition or bacterial susceptibility to disinfection treatment. Findings show that Lir Analytical chemical disinfectants proved highly successful at inactivating a range of Gram‐positive (Bacillus, Enterococcus, Aeromonas) and Gram‐negative (Escherichia coli, Pseudomonas, Micrococcus) organisms, with up to 99.9% inactivation achieved. Additionally, test chemicals provided significant levels (P < 0.05) of biofilm inhibition for a number of test species. Furthermore, it was found that bacterial isolates from cow udders proved more sensitive to the test chemicals than their reference counterparts.     

广州某生猪养殖场大肠杆菌流行性及抗生素的耐药性

本研究采集广州某规模化养殖场腹泻仔猪、健康仔猪及环境样本共147份,据国标GB 4789.6-2016分离鉴定大肠杆菌,用K-B法分析分离株对12种抗生素的敏感性,并用PCR检测其对应的耐药基因。结果共检出大肠杆菌115株;分离菌株依次对复方新诺明,左氧氟沙星、加替沙星、环丙沙星呈高水平耐药,耐药率30%;对庆大霉素、头孢他啶、氨曲南也呈现一定水平耐药(20%~30%);对多粘菌素B、替加环素、亚胺培南耐药水平较低(15%),对美罗培南敏感;46.09%菌株呈现多重耐药(≥3种抗生素),且腹泻仔猪源菌株多重耐药率显著高于健康仔猪源及环境源菌(p0.05)。分离株耐药基因携带严重,其中ant(3')-Ⅰa、aac(3')-Ⅰb、sul1、aac(3)-Ⅱb,blaTEM、blaCTX、tet M基因检出率50%,因此,这可能是本研究菌株的主要耐药机制。研究结果表明该养殖场大肠杆菌污染严重,耐药水平高,有关部门需加强养殖中腹泻仔猪防治用药的监管与指导。     

First evidence of the presence of genomic islands in Escherichia coli P4, a mammary pathogen frequently used to induce experimental mastitis

Mastitis pathogens belonging to Escherichia coli species are often considered as environmental opportunistic pathogens that invade the udder and are rapidly killed by the immune system of cows. However, several studies have reported that some of these strains are able to persist in the udder for prolonged periods or to adhere and invade mammary epithelial cells, suggesting that they might possess some specific properties or genes that could be involved in their capacity to provoke mastitis. The aim of this work was to search for such specific genes in the E. coli strain P4, which was isolated from a case of severe mastitis and is often used to induce experimental mastitis. We established that this strain belongs to phylogenetic group A of the E. coli species, and that its core genome is very similar to that of the commensal nonpathogenic strain E. coli K-12 MG1655. Seventeen transfer RNA loci, known to be frequently associated with genomic islands, were screened and an altered structure was detected for 7 of them. The partial characterization of 5 of these loci (asnT, leuX, pheV, serU, and thrW) and the complete characterization of 1 (argW) revealed the presence of genomic islands that differ from those already described in pathogenic or nonpathogenic E. coli strains.     

新疆部分地区食源性大肠杆菌耐药性的研究

本研究对新疆乌鲁木齐、石河子、奎屯农贸市场以及超市的肉品、蔬菜、乳制品和即食食品中的大肠杆菌进行检测,从198份样品中分离出63株大肠杆菌。采用K-B法,对63株大肠杆菌进行17种抗生素敏感试验;采用PCR技术检测9种耐药基因。药敏结果表明,63株大肠杆菌对四环素(44.44%)、氨苄西林(39.68%)和萘啶酮酸(38.10%)耐药率较高,所有受试菌株对亚胺培南(0.00%)敏感性最强;肉品、蔬菜分离株对四环素(57.14%、52.94%)耐药性最强,乳源性分离株对氨苄西林(26.67%)耐药性最强,即食食品分离株对17种抗生素敏感;乌鲁木齐、奎屯、石河子分离株对四环素(65.00%、40.00%、32.14%)耐药率最高。PCR结果表明,耐药菌株中,sul2耐药基因检出率最高(75.00%),add B耐药基因的检出率最低(19.23%)。1重以上耐药菌株占总菌数的63.49%,3重以上耐药菌株占总菌数的39.68%。新疆地区食源性大肠杆菌多重耐药性比较严重。     

Growth promotion of Bifidobacterium and Lactobacillus species by proteinaceous hydrolysates derived from poultry processing leftovers

Bacterial growth media represent a high cost in industrial applications, and for this reason, it is economically important to find less expensive supplements to replace the traditional ones. In the present work, peptide hydrolysates obtained from poultry meat and bone residues (functional animal protein [FAP]) and from feathers (functional feather protein [FFP]) were studied to determine their ability for the production of microbial biomass with improved viability. The results obtained were compared with those obtained with other supplement nutritive compounds used in fermentation growth media. The molecular composition of the hydrolysates in terms of total and soluble nitrogen, molecular weight distribution, total and free amino acids, was determined. The growth and cellular state of Bifidobacterium and Lactobacillus strains were studied by turbidimetric measurements and direct count by fluorescence microscopy. Overall, this study suggested that by‐products from poultry industry provide a good alternative to substitute expensive supplements for growth of Lactobacillus and Bifidobacterium with a high level of viability.     

季铵盐类消毒剂及大肠杆菌对其耐药性研究进展

研究表明,食源性细菌消毒剂耐药严重,大肠杆菌是食品污染状况及耐药性监测的指示菌,对季铵盐类消毒剂表现出比革兰氏阳性菌更强的抗性,且大肠杆菌对消毒剂与抗生素耐药性可共传播。鉴于此,本文综述了季铵盐类消毒剂的结构与种类、作用机制、大肠杆菌消毒剂耐药产生、耐药基因、基因型与表型的关系以及与抗生素耐药共传播机制等的研究进展。食源性大肠杆菌对季铵盐类消毒剂抗性的耐药机制研究很少,研究大肠杆菌对季铵盐类消毒剂耐药性,可为消毒剂的规范使用以及食源性大肠杆菌的防控提供科学依据及理论基础。