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.     

铀和铅对大肠杆菌毒性的研究

采用3种方法研究了铀和铅对大肠杆菌的毒性:1)试纸法测抑菌圈的直径;2)血球计数板测细菌菌数;3)高倍显微镜下观察细菌形态和密度的变化。得到铀和铅对大肠杆菌的致死质量浓度均为1 000 mg/L,最大无作用剂量均为小于1 mg/L,并将这2种重金属对大肠杆菌的毒性大小进行了比较。     

Rates of experimental microbiological contamination of fish exposed to polluted water

Fish inhabiting fecally polluted bodies of water are often used for human consumption. Such fish can be contaminated by enteric human pathogens and may pose a potential risk to public health. Controlled experiments with 132 fish of 100 g average weight were conducted to evaluate the rate of contamination of various tissues of fish (tilapia hybrids). The fish were exposed to E. coli introduced into the ambient water at concentrations of up to 10⁶ cfu/ml. Additional experiments were conducted with diluted wastewater containing Aeromonas, enterococci, fecal coliform and F+ coliphages. In another experiment poliovirus I was also added. The highest bacterial concentrations were recovered from the digestive tract (DT), some 5–24 h following exposure, with DT levels essentially similar to those in the inoculated water. In the E. coli experiments, geometric mean levels of about 10² cfu/cm² were recovered from the skin, 26 cfu/g in the spleen and 10² cfu/g in the liver. Most of the muscle samples were not contaminated. Greater contamination was not found under conditions of stress such as high organic load, a water temperature of 37°C or low levels of dissolved oxygen.     

Comparison of the efficacy of an existing versus a locally developed metabolic fingerprint database to identify non-point sources of faecal contamination in a coastal lake

A comparison of the efficacy of an existing large metabolic fingerprint database of enterococci and Escherichia coli with a locally developed database was undertaken to identify the sources of faecal contamination in a coastal lake, in southeast Qld., Australia. The local database comprised of 776 enterococci and 780 E. coli isolates from six host groups. In all, 189 enterococci and 245 E. coli biochemical phenotypes (BPTs) were found, of which 118 and 137 BPTs were unique (UQ) to host groups. The existing database comprised of 295 enterococci UQ-BPTs and 273 E. coli UQ-BPTs from 10 host groups. The representativeness and the stability of the existing database were assessed by comparing with isolates that were external to the database. In all, 197 enterococci BPTs and 179 E. coli BPTs were found in water samples. The existing database was able to identify 62.4% of enterococci BPTs and 64.8% of E. coli BPTs as human and animal sources. The results indicated that a representative database developed from a catchment can be used to predict the sources of faecal contamination in another catchment with similar landuse features within the same geographical area. However, the representativeness and the stability of the database should be evaluated prior to its application in such investigation.     

Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions

Escherichia coli and thermotolerant coliforms are of major importance as indicators of fecal contamination of water. Due to its negative surface charge and relatively low die-off or inactivation rate coefficient, E. coli is able to travel long distances underground and is therefore also a useful indicator of fecal contamination of groundwater. In this review, the major processes known to determine the underground transport of E. coli (attachment, straining and inactivation) are evaluated. The single collector contact efficiency (SCCE), eta0, one of two parameters commonly used to assess the importance of attachment, can be quantified for E. coli using classical colloid filtration theory. The sticking efficiency, alpha, the second parameter frequently used in determining attachment, varies widely (from 0.003 to almost 1) and mainly depends on charge differences between the surface of the collector and E. coli. Straining can be quantified from geometrical considerations; it is proposed to employ a so-called straining correction parameter, alpha(str). Sticking efficiencies determined from field experiments were lower than those determined under laboratory conditions. We hypothesize that this is due to preferential flow mechanisms, E. coli population heterogeneity, and/or the presence of organic and inorganic compounds in wastewater possibly affecting bacterial attachment characteristics. Of equal importance is the inactivation or die-off of E. coli that is affected by factors like type of bacterial strain, temperature, predation, antagonism, light, soil type, pH, toxic substances, and dissolved oxygen. Modeling transport of E. coli can be separated into three steps: (1) attachment rate coefficients and straining rate coefficients can be calculated from Darcy flow velocity fields or pore water flow velocity fields, calculated SCCE fields, realistic sticking efficiency values and straining correction parameters, (2) together with the inactivation rate coefficient, total rate coefficient fields can be generated, and (3) used as input for modeling the transport of E. coli in existing contaminant transport codes. Areas of future research are manifold and include the effects of typical wastewater characteristics, including high concentrations of organic compounds, on the transport of E. coli and thermotolerant coliforms, and the upscaling of experiments to represent typical field conditions, possibly including preferential flow mechanisms and the aspect of population heterogeneity of E. coli.     

浊度对紫外灭活大肠杆菌和MS-2噬茵体的影响

以大肠杆菌和MS-2噬菌体为细菌和病毒的替代指标，考察了浊度及颗粒物分布对紫外线灭活大肠杆菌和MS-2噬菌体的影响。结果表明，紫外线对大肠杆菌的灭活率高于对MS-2噬菌体的灭活率，当紫外线剂量为10mJ／cm^2时，对大肠杆菌的灭活率为4．66个对数级，而对MS-2的灭活率仅为0．45个对数级；浊度对紫外线灭活大肠杆菌的效果有一定的影响，当浊度〈4NTU时对灭活效果的影响较小，而当浊度〉4NTU时，会对灭活效果产生明显的影响；颗粒物对紫外线灭活大肠杆菌的影响与其粒径有关，粒径〉5μm的颗粒物对消毒效果的影响较为明显，而粒径〈5μm的颗粒对紫外线消毒效果的影响较小。综合不同粒径颗粒物对消毒效果的影响可以认为，就试验水样而言，浊度对紫外线消毒效果的影响主要是由粒径〉5μm的颗粒造成的；而浊度及颗粒物的粒径分布对紫外线灭活MS-2噬菌体的效果没有显著影响。     

Escherichia coli, enterococci, and Bacteroides thetaiotaomicron qPCR signals through wastewater and septage treatment

Fecal indicators such as Escherichia coli and enterococci are used as regulatory tools to monitor water with 24 h cultivation techniques for possible input of sewage or feces and presence of potential enteric pathogens yet their source (human or animal) cannot be determined with routine methods. This critical uncertainty has furthered water pollution science toward new molecular approaches. Members of Bacteroides genus, such as Bacteroides thetaiotaomicron are found to have features that allow their use as alternative fecal indicators and for Microbial Source Tracking (MST). The overall aim of this study was to evaluate the concentration and fate of B. thetaiotaomicron, throughout a wastewater treatment facility and septage treatment facility. A large number of samples were collected and tested for E. coli and enterococci by both cultivation and qPCR assays. B. thetaiotaomicron qPCR equivalent cells (mean: 1.8 × 10⁷/100 mL) were present in significantly higher concentrations than E. coli or enterococci in raw sewage and at the same levels in raw septage. The removal of B. thetaiotaomicron target qPCR signals was similar to E. coli and enterococci DNA during the treatment of these wastes and ranged from 3 to 5 log₁₀ for wastewater and was 7 log₁₀ for the septage. A significant correlation was found between B. thetaiotaomicron marker and each of the conventional indicators throughout the waste treatment process for both raw sewage and septage. A greater variability was found with enterococci when compared to E. coli, and CFU and equivalent cells could be contrasted by various treatment processes to examine removal and inactivation via septage and wastewater treatment. These results are compared and contrasted with other qPCR studies and other targets in wastewater samples providing a view of DNA targets in such environments.     

Effects of primary sludge particulate (PSP) entrapment on ultrasonic (20 kHz) disinfection of Escherichia coli

The role of primary sludge particulates (PSPs) in ultrasonic disinfection of Escherichia coli (E. coli) was investigated. Entrapment of E. coli by PSP was directly observed through scanning electron microscope (SEM) after E. coli and PSP were incubated together in water for 24 h at 35 °C. Entrapment coefficient was proposed for the first time to reflect the ability of PSP to entrap E. coli and was estimated as 1.4 × 10³ CFU/mg PSP under our experimental conditions. Ultrasonication (20 kHz) of different E. coli-PSPs solutions showed that the entrapped E. coli cells were protected by PSP from ultrasonication and the unentrapped cells were not. However, the protection of entrapped E. coli cells gradually decreased as ultrasonication proceeded, suggesting the ability of power ultrasonication to deprotect the entrapped E. coli cells. SEM studies suggested a two-step mechanism for ultrasonic (20 kHz) disinfection of entrapped E. coli: breakdown of the protective PSP refugia and disinfection of the exposed E. coli cells. This research will enable more informed decisions about disinfection of aqueous samples where porous PSP are present.     

Predicting faecal indicator fluxes using digital land use data in the UK's sentinel Water Framework Directive catchment: the Ribble study

The Ribble drainage basin is the single UK sentinel study area chosen for examining the implementation of the EU Water Framework Directive (WFD 20/60/EC). The study which has generated the data for this paper was initiated to quantify 'catchment-derived' fluxes of faecal indicators originating from both point and diffuse sources to inform the competent authorities on the potential for, and prioritization of, further options for reducing the faecal indicator loadings to this crucial coastal environment. It represents the first UK drainage basin-scale 'profile' of faecal indicator sources as recommended by WHO [1999. Health Based Monitoring of Recreational Waters: The Feasibility of a New Approach; the "Annapolis Protocol". World Health Organisation Geneva, Switzerland; 2003. Guidelines for Safe Recreational-Water Environments Volume 1: Coastal and Fresh-Waters. World Health Organisation Geneva, Switzerland] and incorporated into current drafts of the revised Bathing Water Directive [Anon, 2004. Council of the European Communities Amended proposal for a Directive of the European Parliament and of the Council concerning the management of bathing water quality. Brussels 23rd June]. This paper focuses on the relationships between land use and faecal indicator organism concentrations in surface waters within this very large drainage basin (1583 km2) containing some extensive urban areas. A geographical information system comprising readily available digital elevation, remotely sensed land cover and digital map data was used to generate the land use variables for subcatchments draining to 41 locations across the study area. Presumptive concentrations of coliforms, Escherichia coli and enterococci (colony forming unit (cfu) 100 ml(-1)) were measured at each location on at least 20 occasions over a 44-day period within the 2002 bathing season. The sampling programme targeted hydrograph events. Hydrometric records were used to allocate results as either base flow or high flow. At each site, geometric mean faecal indicator organism concentrations were significantly elevated at high flow compared to base flow. Stepwise regression modelling produced statistically significant models predicting geometric mean base and high-flow faecal indicator organism concentrations from land use variables (r2: 49.5-68.1%). The dominant predictor variable in each case was the proportion of built-up land in subcatchments, suggesting that this land use type, with associated sewage-related inputs, is a critical source of faecal indicator organisms in this drainage basin.     

2017—2019年郴州市食源性疾病主动监测病原学特征及耐药分析

目的 了解郴州市食源性疾病的病原学特征和流行规律,为食源性疾病预防控制措施提供科学依据。方法 收集2017—2019年郴州市2家哨点医院主动监测的病例信息、粪便或肛拭子标本,依据《国家食源性疾病监测工作手册》中的方法对标本开展病原学检验、病原体分型以及药敏试验。结果 采集腹泻病例标本825份,病原体总检出率为30.18%（249/825）,其中沙门菌16.24%（134/825）、诺如病毒11.76%（97/825）、致泻大肠埃希菌3.52%（29/825）、副溶血性弧菌0.73%（6/825）、志贺菌0.12%（1/825）;第二、第三季度细菌检出率高,第一、第四季度病毒检出率高;不同年龄段病原体检出率以2～6岁年龄段最高（40.79%,31/76）;可疑暴露食品主要为乳及乳制品、粮食类及其制品和水果类及其制品;检出的沙门菌中以鼠伤寒沙门菌占比最高（74.63%,100/134）,致泻大肠埃希菌中以肠黏附型（EAEC）和产肠毒素型（ETEC）占比最高（34.48%,10/29）,诺如病毒以GⅡ型为主（85.57%,83/97）;沙门菌对四环素（TET）耐药率最高达88.71%（110/124）,沙门菌多重耐药率达85.48%（106/124）;致泻大肠埃希菌对氨苄西林（AMP）耐药率较高（79.31%,23/29）,致泻大肠埃希菌多重耐药率为62.07%（18/29）。结论 郴州市食源性疾病腹泻病例的主要病原体为沙门菌和诺如病毒,沙门菌和致泻大肠埃希菌耐药严重,应针对性地开展食品安全监管,强化抗生素耐药监测,严防抗生素滥用。