Modeling the effect of simultaneous use of allyl isothiocyanate and cinnamaldehyde on high hydrostatic pressure inactivation of Uropathogenic and Shiga toxin-producing Escherichia coli in ground chicken

BACKGROUND

A combination of high-pressure processing (HPP) and antimicrobials is a well-known approach for enhancing the microbiological safety of foods. However, few studies have applied multiple antimicrobials simultaneously with HPP, which could be an additional hurdle for microbial inactivation. The present study applied a full factorial design to investigate the impact of HPP (225-325 MPa; 10-20 min), allyl isothiocyanate (AITC) (0.3-0.9 g kg^-1 ) and trans-cinnamaldehyde (tCinn) (1.0-2.0 g kg^-1 ) on the inactivation of Shiga toxin-producing Escherichia coli (STEC) O157:H7 and uropathogenic E. coli (UPEC) in ground chicken meat.

RESULTS

The regulatory requirement of 5-log reduction was achieved at 305 MPa, 18 min, 0.8 g kg^-1 AITC and 1.7 g kg^-1 tCinn for STEC O157:H7 and at 293 MPa, 16 min, 0.6 g kg^-1 AITC and 1.6 g kg^-1 tCinn for UPEC, as specified by response surface analysis and verified via experiments. The surviving population was eliminated by post-treatment storage of 9 days at 10 °C. The developed linear regression models showed r²  > 0.9 for the E. coli inactivation. The developed dimensionless non-linear regression models covered a factorial range slightly wider than the original experimental limit, with probability P_r  > F (< 0.0001).

CONCLUSION

Simultaneous use of AITC and tCinn reduced not only the necessary concentration of each compound, but also the intensity of high-pressure treatments, at the same time achieving a similar level of microbial inactivation. STEC O157:H7 was found to be more resistant than UPEC to the HPP-AITC-tCinn stress. The developed models may be applied in commercial application to enhance the microbiological safety of ground chicken meat. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Characterization of Shiga toxin-producing Escherichia coli in raw beef from informal and commercial abattoirs

Shiga toxin-producing Escherichia coli are foodborne pathogens that are mostly associated with beef products and have been implicated in human illness. E.coli-associated illness range from asymptomatic conditions of mild diarrhoea to haemorrhagic colitis which can progress into life threatening haemolytic uremic syndrome (HUS). Beef from cattle are regarded as the main reservoir of Shiga toxin-producing E. coli (STEC) pathogen. The aim of this study was to assess the level and sources of contamination of raw beef with STEC, and determine the incidences of STEC strains in raw beef from informal and commercial abattoirs in Windhoek, Namibia. A total of 204 raw beef samples, 37 equipment and 29 hand swabs were collected and tested for STEC. The meat samples were first enriched with pre-warmed buffered peptone water, cultured on Tryptone Bile X-Glucuronide and CHROMagar STEC, and then sub-cultured on nutrient agar. The presence of E.coli in the samples was confirmed by using VITEK 2 E.coli identification cards and PCR. The overall prevalence of STEC in the meat samples from both the abattoirs was 41.66% raw beef samples; 5.40% equipment swabs; and none of the hand swabs was STEC positive. From the STEC positive meat samples 29.41% contained one of the major STEC strains. Moreover, 52% of the 25 samples that contained the major STECs were characterised by eae and stx1, 8% characterised by eae and stx2 while 40% were characterised by eae, stx1 and stx2 virulence genes. This study has revealed the necessity for proper training on meat safety (for meat handlers) as well as the development, implementation and maintenance of effective sanitary dressing procedures at abattoirs to eliminate beef contamination by STECs thereby ensuring the production of wholesome meat, and to prevent the occurrences of STEC infections.

Metabolic Traits of Bovine Shiga Toxin-Producing Escherichia Coli (STEC) Strains with Different Colonization Properties

Cattle harbor Shiga toxin-producing Escherichia coli (STEC) in their intestinal tract, thereby providing these microorganisms with an ecological niche, but without this colonization leading to any clinical signs. In a preceding study, genotypic characterization of bovine STEC isolates unveiled that their ability to colonize cattle persistently (STEC^per) or only sporadically (STEC^spo) is more closely associated with the overall composition of the accessory rather than the core genome. However, the colonization pattern could not be unequivocally linked to the possession of classical virulence genes. This study aimed at assessing, therefore, if the presence of certain phenotypic traits in the strains determines their colonization pattern and if these can be traced back to distinctive genetic features. STEC^spo strains produced significantly more biofilm than STEC^per when incubated at lower temperatures. Key substrates, the metabolism of which showed a significant association with colonization type, were glyoxylic acid and L-rhamnose, which were utilized by STEC^spo, but not or only by some STEC^per. Genomic sequences of the respective glc and rha operons contained mutations and frameshifts in uptake and/or regulatory genes, particularly in STEC^per. These findings suggest that STEC^spo conserved features leveraging survival in the environment, whereas the acquisition of a persistent colonization phenotype in the cattle reservoir was accompanied by the loss of metabolic properties and genomic mutations in the underlying genetic pathways.

Influence of Plant Species, Tissue Type, and Temperature on the Capacity of Shiga-Toxigenic Escherichia coli To Colonize, Grow, and Be Internalized by Plants

Contamination of fresh produce with pathogenic Escherichia coli, including Shiga-toxigenic E. coli (STEC), represents a serious risk to human health. Colonization is governed by multiple bacterial and plant factors that can impact the probability and suitability of bacterial growth. Thus, we aimed to determine whether the growth potential of STEC for plants associated with foodborne outbreaks (two leafy vegetables and two sprouted seed species) is predictive of the colonization of living plants, as assessed from growth kinetics and biofilm formation in plant extracts. The fitness of STEC isolates was compared to that of environmental E. coli isolates at temperatures relevant to plant growth. Growth kinetics in plant extracts varied in a plant-dependent and isolate-dependent manner for all isolates, with spinach leaf lysates supporting the highest rates of growth. Spinach extracts also supported the highest levels of biofilm formation. Saccharides were identified to be the major driver of bacterial growth, although no single metabolite could be correlated with growth kinetics. The highest level of in planta colonization occurred on alfalfa sprouts, though internalization was 10 times more prevalent in the leafy vegetables than in sprouted seeds. Marked differences in in planta growth meant that the growth potential of STEC could be inferred only for sprouted seeds. In contrast, biofilm formation in extracts related to spinach colonization. Overall, the capacity of E. coli to colonize, grow, and be internalized within plants or plant-derived matrices was influenced by the isolate type, plant species, plant tissue type, and temperature, complicating any straightforward relationship between in vitro and in planta behaviors.IMPORTANCE Fresh produce is an important vehicle for STEC transmission, and experimental evidence shows that STEC can colonize plants as secondary hosts, but differences in the capacity to colonize occur between different plant species and tissues. Therefore, an understanding of the impact that these plant factors have on the ability of STEC to grow and establish is required for food safety considerations and risk assessment. Here, we determined whether growth and the ability of STEC to form biofilms in plant extracts could be related to specific plant metabolites or could predict the ability of the bacteria to colonize living plants. Growth rates for sprouted seeds (alfalfa and fenugreek) but not those for leafy vegetables (lettuce and spinach) exhibited a positive relationship between plant extracts and living plants. Therefore, the detailed variations at the level of the bacterial isolate, plant species, and tissue type all need to be considered in risk assessment.

Shiga toxigenic Escherichia coli incidence is related to small area variation in cattle density in a region in Ireland

Shiga toxigenic Escherichia coli (STEC) are pathogenic E. coli that cause infectious diarrhoea. In some cases infection may be complicated by renal failure and death. The incidence of human infection with STEC in Ireland is the highest in Europe. The objective of the study was to examine the spatial incidence of human STEC infection in a region of Ireland with significantly higher rates of STEC incidence than the national average and to identify possible risk factors of STEC incidence at area level. Anonymised laboratory records (n = 379) from 2009 to 2015 were obtained from laboratories serving three counties in the West of Ireland. Data included location and sample date. Population and electoral division (ED) data were obtained from the Irish 2011 Census of Population. STEC incidence was calculated for each ED (n = 498) and used to map hotspots/coldspots using the Getis-Ord Gi* spatial statistic and significant spatial clustering using the Anselin's Local Moran's I statistic. Multivariable regression analysis was used to consider the importance of a number of potential predictors of STEC incidence. Incidence rates for the seven-year period ranged from 0 to 10.9 cases per 1000. A number of areas with significant local clustering of STEC incidence as well as variation in the spatial distribution of the two main serogroups associated with disease in the region i.e. O26 and O157 were identified. Cattle density was found to be a statistically significant predictor of STEC in the region. GIS analysis of routine data indicates that cattle density is associated STEC infection in this high incidence region. This finding points to the importance of agricultural practices for human health and the importance of a "one-health" approach to public policy in relation to agriculture, health and environment.

Simple Purification of Nicotiana benthamiana-Produced Recombinant Colicins: High-Yield Recovery of Purified Proteins with Minimum Alkaloid Content Supports the Suitability of the Host for Manufacturing Food Additives

Colicins are natural non-antibiotic bacterial proteins with a narrow spectrum but an extremely high antibacterial activity. These proteins are promising food additives for the control of major pathogenic Shiga toxin-producing E. coli serovars in meats and produce. In the USA, colicins produced in edible plants such as spinach and leafy beets have already been accepted by the U. S. Food and Drug Administration (FDA) and U. S. Department of Agriculture (USDA) as food-processing antibacterials through the GRAS (generally recognized as safe) regulatory review process. Nicotiana benthamiana, a wild relative of tobacco, N. tabacum, has become the preferred production host plant for manufacturing recombinant proteins-including biopharmaceuticals, vaccines, and biomaterials-but the purification procedures that have been employed thus far are highly complex and costly. We describe a simple and inexpensive purification method based on specific acidic extraction followed by one chromatography step. The method provides for a high recovery yield of purified colicins, as well as a drastic reduction of nicotine to levels that could enable the final products to be used on food. The described purification method allows production of the colicin products at a commercially viable cost of goods and might be broadly applicable to other cost-sensitive proteins.

Intestinal organoids model human responses to infection by commensal and Shiga toxin producing Escherichia coli

Infection with Shiga toxin (Stx) producing Escherichia coli O157:H7 can cause the potentially fatal complication hemolytic uremic syndrome, and currently only supportive therapy is available. Lack of suitable animal models has hindered study of this disease. Induced human intestinal organoids (iHIOs), generated by in vitro differentiation of pluripotent stem cells, represent differentiated human intestinal tissue. We show that iHIOs with addition of human neutrophils can model E. coli intestinal infection and innate cellular responses. Commensal and O157:H7 introduced into the iHIO lumen replicated rapidly achieving high numbers. Commensal E. coli did not cause damage, and were completely contained within the lumen, suggesting defenses, such as mucus production, can constrain non-pathogenic strains. Some O157:H7 initially co-localized with cellular actin. Loss of actin and epithelial integrity was observed after 4 hours. O157:H7 grew as filaments, consistent with activation of the bacterial SOS stress response. SOS is induced by reactive oxygen species (ROS), and O157:H7 infection increased ROS production. Transcriptional profiling (RNAseq) demonstrated that both commensal and O157:H7 upregulated genes associated with gastrointestinal maturation, while infection with O157:H7 upregulated inflammatory responses, including interleukin 8 (IL-8). IL-8 is associated with neutrophil recruitment, and infection with O157:H7 resulted in recruitment of human neutrophils into the iHIO tissue.

Anti-bacterial effect of essential oil from Xanthium strumarium against shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) serotype O157:H7 is one of the most important human pathogenic microorganisms, which can cause life-threatening infections. Xanthium strumarium L. is a plant with anti-bacterial activity against gram-negative and gram-positive bacteria. This study aims to demonstrate in vitro efficacy of the essential oil (EO) extracted from Xanthium strumarium L. against E. coli O157:H7. Using the agar test diffusion, the effect of Xanthium strumarium L. EO (5, 10, 15, 30, 60, and 120 mg/mL) was verified at each of the four different growth phases of E. coli O157:H7. Cell counts of viable cells and colony forming unit (CFU) were determined at regular time points using Breed's method and colony counting method, respectively. No viable cell was detectable after the 1 hour-exposure to X. strumarium EO at 30, 60, and 120 mg/mL concentrations. No bacterial colony was formed after 1 h until the end of the incubation period at 24 h. At lower concentrations, the number of bacteria cells decreased and colonies could be observed only after incubation. At the exponential phase, the EO at 15 mg/mL was only bacteriostatic, while from 30 mg/mL started to be bactericidal. X. strumarium EO antibacterial activity against Shiga toxin-producing E. coli O157:H7 is dependent on EO concentration and physiological state of the microorganisms tested. The best inhibitory activity was achieved during the late exponential and the stationary phases.

Influence of Extracellular Cellulose and Colanic Acid Production on the Survival of Shiga Toxin-Producing Escherichia coli on Spinach and Lettuce after Chlorine Treatment

Shiga toxin-producing Escherichia coli (STEC) strains produce extracellular cellulose and colanic acid, which may influence stress tolerance. This study investigates the role of these extracellular polymers on the tolerance of STEC to chlorine treatment after attachment to lettuce and spinach. Four STEC strains, two wild-type cellulose-producing and their cellulose-deficient derivatives, were used. One strain pair produced colanic acid in addition to cellulose. Spinach and lettuce with attached cells were treated with chlorinated water (50 and 150 ppm of free chlorine). The production of the extracellular polymers by the planktonic cells had small, but significant, effects on the survival of the attached pathogen when subjected to chlorine treatment. On the lettuce surface, the colanic acid-producing, cellulose-negative mutant (49d) was most susceptible to the treatment, declining significantly (P < 0.05) in population by 0.9 and 1.4 log units after treatment with 50 and 150 ppm of chlorine, respectively. Chlorine treatment reduced populations of cellulose-deficient cells on the intact spinach surface 1.2 log units more than the wild type when treated with 150 ppm of chlorine (P < 0.05). However, populations of cellulose-producing cells were reduced by 1.5 log units more than their mutant counterparts when the cells also produced colanic acid (P < 0.05). A greater proportion of cells attached to the spinach leaf edge were injured by chlorine treatment compared with attached to the leaf surface. These results indicate that extracellular polymers do not generally increase the ability of STEC to survive chlorine treatment and that any effects on survival are influenced by location of attachment, type of leafy green, and concentration of chlorine.

Male-specific coliphages for source tracking fecal contamination in surface waters and prevalence of Shiga-toxigenic Escherichia coli in a major produce production region of the Central Coast of California

To provide data for traditional trace-back studies from fork to farm, it is necessary to determine the environmental sources for Shiga-toxigenic Escherichia coli. We developed SYBR green based reverse-transcriptase PCR methods to determine the prevalence of F+ RNA coliphages (FRNA) as indicators of fecal contamination. Male-specific coliphages, determined using a single-agar overlay method, were prevalent in all surface waters sampled for 8 months. F+ DNA coliphages (FDNA) were predominant compared to FRNA in water samples from majority of sampling locations. Most (90%) of the FRNA were sourced to humans and originated from human-impacted sites. Members of genogroup III represented 77% of FRNA originated from human sources. Furthermore, 93% of FRNA sourced to animals were also detected in water samples from human-impacted sites. Eighty percent of all FRNA were isolated during the winter months indicating seasonality in prevalence. In contrast, FDNA were more prevalent during summer months. E. coli O157:H7 and Shiga-toxigenic E. coli were detected in water samples from locations predominantly influenced by agriculture. Owing to their scarcity, their numbers could not be correlated with the prevalence of FRNA or FDNA in water samples. Both coliform bacteria and generic E. coli from agricultural or human-impacted sites were similar in numbers and thus could not be used to determine the sources of fecal contamination. Data on the prevalence of male-specific coliphages may be invaluable for predicting the sources of fecal contamination and aid in developing methods to prevent enteric pathogen contamination from likely sources during produce production.

Behavior of Shiga toxigenic Escherichia coli relevant to lettuce washing processes and consideration of factors for evaluating washing process surrogates

Postharvest processes for fresh produce commonly include washing in water containing antimicrobial chemicals, such as chlorine; however, if the antimicrobials are not present in sufficient levels, washing can promote the spread of contamination that might be present. To understand cross-contamination risk during washing, we tested a collection of Shiga toxigenic Escherichia coli (STEC), including O157:H7 and other non-O157 strains, for certain traits during washing of fresh-cut lettuce, i.e., sensitivity to sublethal chlorine levels and ability to cross-contaminate (detach from and attach to) lettuce in the presence of sublethal chlorine levels. Nonpathogenic E. coli Nissle 1917 (EcN) and Pediococcus pentosaceus lactic acid bacterial species (LAB) were included as potential washing process validation surrogates. As measured by extension of the lag phase of growth in media containing 0.15 ppm of chlorine, chlorine sensitivity varied among the STECs. Cross-contamination was assessed by evaluating transfer of bacteria from inoculated to uninoculated leaves during washing. Without chlorine, similar transfer to wash water and uninoculated leaves was shown. In 1 ppm of chlorine, cross-contamination was not detected with most strains, except for the substantial transfer by a STEC O111 strain and EcN in some replicates. Strain O111 and EcN showed less inactivation in 0.25 ppm of chlorine water compared with O157 (P < 0.05). LAB showed similar transfer and similar chlorine inactivation to O157. Considering together the sublethal chlorine sensitivity and detachment/attachment traits, neither EcN nor LAB displayed optimal characteristics as washing process surrogates for the STEC strains, although further evaluation is needed. This work demonstrated a range of behaviors of STEC strains during lettuce washing and may be helpful in hazard characterization, identifying factors to consider for evaluating washing process efficacy, and identifying phenotypic traits to select surrogates to validate washing processes.

Presence of non-O157 Shiga toxin-producing Escherichia coli, enterotoxigenic E. coli, enteropathogenic E. coli and Salmonella in fresh beetroot (Beta vulgaris L.) juice from public markets in Mexico

BACKGROUND

Unpasteurized juice has been associated with foodborne illness outbreaks for many years. Beetroot is a vegetable grown all over the world in temperate areas. In Mexico beetroot is consumed cooked in salads or raw as fresh unpasteurized juices. No data about the microbiological quality or safety of unpasteurized beetroot juices are available. Indicator bacteria, diarrheagenic Escherichia coli pathotypes (DEP) and Salmonella frequencies were determined for fresh unpasteurized beetroot juice from restaurants.

RESULTS

One hundred unpasteurized beetroot juice samples were collected from public markets in Pachuca, Mexico. Frequencies in these samples were 100%, 75%, 53%, 9% and 4% of positive samples, for coliform bacteria, fecal coliforms, E. coli, DEP and Salmonella, respectively. Identified DEP included enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC) and non-O157 Shiga toxin-producing E. coli (STEC). Identified Salmonella serotypes included Typhimurium and Enteritidis.

CONCLUSION

This is the first report of microbiological quality and atypical EPEC, ETEC, non-O157 STEC and Salmonella isolation from fresh raw beetroot juice in Mexico. Fresh raw beetroot juice from markets is very probably an important factor contributing to the endemicity of atypical EPEC, ETEC, non-O157 STEC and Salmonella-related gastroenteritis in Mexico.

Interactive effects of temperature, pH, and water activity on the growth kinetics of Shiga toxin-producing Escherichia coli O104:H4 3

The risk of non-O157 Shiga toxin-producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw ; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and temperature of the growth medium. Increasing temperature resulted in a concomitant decrease in LPD. Regression analysis suggests that temperature, pH, and aw significantly affect the LPD, exponential growth rate, generation time, and MPD of E. coli O104:H4. A comparison between the observed values and those of E. coli O157:H7 predictions obtained by using the U. S. Department of Agriculture Pathogen Modeling Program indicated that E. coli O104:H4 grows faster than E. coli O157:H7. The developed models were validated with alfalfa and broccoli sprouts. These models will provide risk assessors and food safety managers a rapid means of estimating the likelihood that the pathogen, if present, would grow in response to the interaction of the three variables assessed.

Shiga toxin-producing Escherichia coli distribution and characterization in a pasture-based cow-calf production system

Shiga toxin-producing Escherichia coli (STEC) strains are commonly found in cattle gastrointestinal tracts. In this study, prevalence and distribution of E. coli virulence genes (stx1, stx2, hlyA, and eaeA) were assessed in a cow-calf pasture-based production system. Angus cows (n = 90) and their calves (n = 90) were kept in three on-farm locations, and fecal samples were collected at three consecutive times (July, August, and September 2011). After enrichment of samples, stx1, stx2, eaeA, and hlyA were amplified and detected with a multiplex PCR (mPCR) assay. Fecal samples positive for stx genes were obtained from 93.3% (84 of 90) of dams and 95.6% (86 of 90) of calves at one or more sampling times. Age class (dam or calf), spatial distribution of cattle (farm locations B, H, K), and sampling time influenced prevalence and distribution of virulence genes in the herd. From 293 stx-positive fecal samples, 744 E. coli colonies were isolated. Virulence patterns of isolates were determined through mPCR assay: stx1 was present in 41.9% (312 of 744) of the isolates, stx2 in 6.5% (48 of 744), eaeA in 4.2% (31 of 744), and hlyA in 2.4% (18 of 744). Prevalence of non-O157 STEC was high among the isolates: 33.8% (112 of 331) were STEC O121, 3.6% (12 of 331) were STEC O103, and 1.8% (6 of 331) were STEC O113. One isolate (0.3%) was identified as STEC O157. Repetitive element sequence-based PCR (rep-PCR) fingerprinting was used to study genetic diversity of stx-positive E. coli isolates. Overall, rep-PCR fingerprints were highly similar, supporting the hypothesis that strains are transmitted between animals but not necessarily from a dam to its calf. Highly similar STEC isolates were obtained at each sampling time, but isolates obtained from dams were more diverse than those from calves, suggesting that strain differences in transference may exist. Understanding the transfer of E. coli from environmental and animal sources to calves may aid in developing intervention strategies to reduce E. coli colonization of young cattle.

Detection of verotoxin producing Escherichia coli in marine environments of the Caribbean

The goal of this study was to determine the potential for Enterohemorrhagic Escherichia coli O157:H7 (EHEC) contamination in tropical marine waters. Samples were collected from urban, suburban, and rural sites around the islands of Puerto Rico and The Republic of Trinidad and Tobago. Quantification of E. coli and EHEC was evaluated using MI plates and qPCR. EHEC was detected in six sites in Puerto Rico: West of La Parguera Town, Boquilla, Oro Creek, Fishers Association, Joyuda Lagoon, and Boqueron Wetland Creek and in two rural sites in Trinidad: Balandra Bay and Quinam Bay. Plate count enumeration of E. coli was not a reliable indicator for the presence of EHEC. The sites where EHEC was detected on both islands are used for recreational bathing, water sports and recreational/commercial fisheries and therefore pose a public potential health risk.

Evaluation of eight agar media for the isolation of shiga toxin-Producing Escherichia coli

The growth characteristics of 96 shiga toxin-producing Escherichia coli (STEC) strains representing 36 different O-types (including priority O types O26, O45, O103, O111, O121, O145 and O157) on commercial and in-house agar media were studied. The ability of the strains to grow on agar media with varying selective supplement formulations was evaluated using MacConkey Agar (MAC); Rainbow® Agar O157 (RBA); Rainbow® Agar O157 with manufacturer-recommended selective supplements (RBA-NT); Rainbow® Agar O157 with USDA-recommended selective supplements (RBA-USDA); CHROMagar STEC™ (CH STEC); Tryptone Bile agar containing cefixime and tellurite (TBA-CT); Tryptone Bile agar containing cefixime, tellurite, eosin and methylene blue (TBA-EM); and VTEC agar. All of the strains were able to grow on MAC, RBA and VTEC agar, whereas a number of strains (including some non-O157 priority O types) were unable to grow on the highly selective media CH STEC, RBA-NT, RBA-USDA, TBA-EM and TBA-CT. Only RBA-NT and CH STEC exhibited significant inhibition of background flora from ground beef enrichment. Significant inhibition of background flora from beef trim enrichment was observed with RBA-NT, RBA-USDA, CH STEC, TBA-EM and VTEC agar. With exception of E. coli O157, several different colony morphologies were observed on the differential plating media among strains of the same O type, indicating that this colony morphology is not a reliable means of identifying target STEC. These results suggest that an approach to maximize the recovery of target STEC from beef enrichment cultures is dual plating on lesser (RBA, MAC, VTEC agar) and more highly (RBA-NT, CH STEC) selective agars.

Behavior of different Shiga toxin-producing Escherichia coli serotypes in various experimentally contaminated raw-milk cheeses

Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness. The public health implication of the presence of STEC in dairy products remains unclear. Knowledge of STEC behavior in cheeses would help to evaluate the human health risk. The aim of our study was to observe the growth and survival of experimentally inoculated STEC strains in raw-milk cheeses manufactured and ripened according to five technological schemes: blue-type cheese, uncooked pressed cheese with long ripening and with short ripening steps, cooked cheese, and lactic cheese. Cheeses were contaminated with different STEC serotypes (O157:H7, O26:H11, O103:H2, and O145:H28) at the milk preparation stage. STEC growth and survival were monitored on selective media during the entire manufacturing process. STEC grew (2 to 3 log(10) CFU · g(-1)) in blue-type cheese and the two uncooked pressed cheeses during the first 24 h of cheese making. Then, STEC levels progressively decreased in cheeses that were ripened for more than 6 months. In cooked cheese and in lactic cheese with a long acidic coagulation step (pH < 4.5), STEC did not grow. Their levels decreased after the cooking step in the cooked cheese and after the coagulation step in the lactic cheese, but STEC was still detectable at the end of ripening and storage. A serotype effect was found: in all cheeses studied, serotype O157:H7 grew less strongly and was less persistent than the others serotypes. This study improves knowledge of the behavior of different STEC serotypes in various raw-milk cheeses.

[Construction of the XZ113 delta eaeA, XZ113 delta stx2 and XZ113 delta ehxA mutants of STEC O18 XZ113 and their pathogenicity in mice]

OBJECTIVE

To study the contribution of virulence genes of STEC O18 XZ113 isolate to the pathogenicity in mice.

METHODS

The eaeA, stx2 and ehxA knock-out mutants of STEC strain XZ113 were generated using lambda-Red recombination system.

RESULTS

Bacterial adherence test showed that the eaeA mutant adhered to HEp-2 cells in a diffuse manner with no microcolony formation. Vero cells assay showed that the stx mutant had no cytotoxicity to Vero cells. Enterohemolytic activity test showed that the ehxA mutant lost the ability to express the enterohemolytic activity. Competition assay between the wild-type strain XZ113 and its mutants in vivo and in vitro showed that all mutants were mildly attenuated in vitro, but in vivo, XZ113 delta eaeA was moderate attenuated, XZ113 delta stx2 and XZ113 delta ehxA were all highly attenuated.

CONCLUSIONS

These results indicate that the virulence factors encoded by the stx2 and ehxA genes were important for the pathogenesis of STEC O18 in mice.

Rapid and sensitive detection of Shiga toxin-producing Escherichia coli directly from stool samples by real-time PCR in comparison to culture, enzyme immunoassay and Vero cell cytotoxicity assay

BACKGROUND

From May until July 2011 a large outbreak of infections with Shiga toxin (Stx)-producing Escherichia coli (STEC) occurred in Germany. More than 800 patients suffered from hemolytic uremic syndrome (HUS), and 49 fatal cases were reported. Obviously, a mandatory requirement for such a clinical situation is the availability of rapid and reliable STEC tests from the investigating laboratory. The standard methods like enzyme immunoassay (EIA), vero cell cytotoxicity assay (VCA), and microbiological culture are, however, hampered by a lack of sensitivity and specificity unless a prior, time consuming broth enrichment step is employed. In order to acelerate the laboratory diagnosis, we evaluated an in-house real-time PCR assay for the detection of the Stx genes (stx1 and stx2) directly from stool specimens without the need of broth enrichment procedures.

METHODS

754 faecal samples were collected from 481 predominantly hospitalised patients with diarrhea from May 23 to June 10, 2011 at the Medical Laboratory Bremen, Germany. The samples were analysed with a direct stx real-time PCR and compared to EIA, VCA and culturing on enterohemolysin, ESBL, and CPS agar after broth enrichment. In addition, artificial samples (n = 12) from three official EHEC/STEC PCR quality proficiency panels (INSTAND, Germany, September 2006, September 2007, and April 2008) were analysed by real-time PCR only.

RESULTS

The real-time PCR produced reliable, distinct melting profiles with characteristic peaks for the stx1 and stx2 PCR products. The quality proficiency panels revealed a detection limit of 10 CFU/PCR per reaction. 112, 86, 99, and 122 of 754 clinical samples were positive for culture, EIA, VCA, and real-time PCR, respectively. 121 of 122 PCR samples were positive only for stx2. Compared to culture as the gold standard, sensitivities of EIA, VCA, and real-time PCR were 76.8 %, 83.9%, and 96.4% and specificities were 99.4%, 99.2%, and 97.8%, respectively.

CONCLUSIONS

The direct fecal stx real-time PCR proved superior to enrichment based VCA and EIA and can be recommended as a quick and sensitive tool for the early diagnosis of STEC infection in addition to microbiological culture.

Do camels (Camelus dromedarius) play an epidemiological role in the spread of Shiga Toxin producing Escherichia coli (STEC) infection?

In the present work, faecal and serum samples from 400 camels were investigated for the presence of Shiga Toxin producing E.coli (STEC) and Anti-Shiga Toxin (Anti-Stx) antibodies, respectively. The used samples were obtained from adult male camels of five east African countries (Egypt, Somalia, Djibouti, Kenya and Sudan) between the years 2002-2004. One E.coli isolate per camel was randomly selected to be cultured on Gassner, Chromocult and sorbit agar for the detection of O157:H7 strains. In the same time, a Stx-specific PCR screening was performed for the isolates using the shiga toxin specific primers Mk1-Mk2. Vero cells were also used for shiga toxin neutralization assay. None of the investigated isolates reacted positively with the Stx-specific primers. Also, none of the studied sera could neutralize the Stx on tissue culture. The obtained results indicate that camels do not play any significant epidemiological role in STEC infection and transmission. The possible reasons for the absence of STEC in the investigated samples are discussed in brief.

The effect of intramuscular administration of colistin on the development and course of experimentally induced oedema disease in weaned piglets

Shiga-toxigenic E. coli (STEC) strains that produce Shiga toxin Stx2e cause oedema disease in weaned piglets. The purpose of the present study was to investigate the impact of Stx2e released in mesenteric lymph nodes on disease pathogenesis. Colistin and ampicillin were intramuscularly administered to piglets of the experimental group simultaneously challenged with STEC strain, type O139:F18ab, Stx2e+. Piglets of the control group were challenged with STEC only. The strain was naturally resistant to ampicillin and susceptible to colistin. After the challenge, colonisation of the intestines was observed in both antibiotic-treated piglets and control piglets without antibiotic treatment. Histochemistry and scanning electron microscopy revealed sporadic colonisation of the small intestine in the piglets. STEC was detected in the mesenteric lymph nodes of untreated piglets. The clinical manifestations of oedema disease were observed in both groups. In the antibiotic-treated group (11 piglets), oedema disease developed in 10 piglets, eight of which died or were euthanized ante finem. In the untreated group (11 piglets), oedema disease developed in five piglets, four of which died or were euthanized ante finem. We therefore propose that the STEC lysed by colistin suddenly released the toxin from bacterial cells immediately after their passage through the intestinal wall. That could explain a more severe course of oedema disease in the treated piglets. Even though high amounts of STEC were present in the lymph nodes of untreated piglets, the toxin was not released abruptly because the bacterial cells were not damaged.