Sorbitol MacConkey Agar Research Articles

Impact of Management Practices and Distillers' Grains Feeding on the Prevalence ofEscherichia coliO157 in Feedlot Cattle in Minnesota

Escherichia coli O157 is a foodborne pathogen that can be transmitted by contaminated ground beef and is shed naturally in cattle feces. Recent reports indicated that feeding distillers' grains (DG) to cattle increased fecal shedding and prevalence of E. coli O157. In Minnesota, feeding DG with solubles (DGS) to livestock became widespread within the last 10 years, but there is no report about the prevalence of E. coli O157 in beef cattle in this state. This study was undertaken to survey the fecal prevalence of E. coli O157 in cattle fed diets containing DG and its association with environmental conditions and management practices. Fecal samples were collected from three feedlots during a 1-year period. All animals in those feedlots were fed different DGS levels. E. coli O157 presence was determined using a combination of enrichment, immunomagnetic separation, plating onto sorbitol MacConkey agar, and confirmation of isolates by immunoassay and multiplex virulence genes polymerase chain reaction analysis. Overall, E. coli O157 was confirmed in 9.7% of samples. Prevalence during summer was 30% and declined to less than 10% the rest of the year. In animals grouped by dietary DGS concentration, no significant difference in prevalence (12.0 and 5.5%) was detected between the low and the high average groups (less and more than 20%). Previous feeding of DGS before arriving to the feedlot also had no influence on fecal prevalence. The presence of several interacting variables, uncontrolled in a real-life feedlot environment, was the likely reason for our observation and suggested that at the levels studied, DGS had no effect on the STEC O157 prevalence in cattle populations.

Enumeration of Sublethally Injured Escherichia coli O157:H7 ATCC 43895 and Escherichia coli Strain B-41560 Using Selective Agar Overlays versus Commercial Methods

Quality control procedures during food processing may involve direct inoculation of food samples onto appropriate selective media for subsequent enumeration. However, sublethally injured bacteria often fail to grow, enabling them to evade detection and intervention measures and ultimately threaten the health of consumers. This study compares traditional selective and nonselective agar-based overlays versus two commercial systems (Petrifilm and Easygel) for recovery of injured E. coli B-41560 and O157:H7 strains. Bacteria were propagated in tryptic soy broth (TSB), ground beef slurry, and infant milk formula to a density of 10(6) to 10(8) CFU/ml and then were stressed for 6 min either in lactic acid (pH 4.5) or heat shocked for 3 min at 60°C. Samples were pour plated in basal layers of either tryptic soy agar (TSA), sorbitol MacConkey agar (SMAC), or violet red bile agar (VRB) and were resuscitated for 4 h prior to addition of agar overlays. Other stressed bacteria were plated directly onto Petrifilm and Easygel. Results indicate that selective and nonselective agar overlays recovered significantly higher numbers (greater than 1 log) of acid- and heat-injured E. coli O157:H7 from TSB, ground beef, and infant milk formula compared with direct plating onto selective media, Petrifilm, or Easygel, while no significant differences among these media combinations were observed for stressed E. coli B-41560. Nonstressed bacteria from TSB and ground beef were also recovered at densities significantly higher in nonselective TSA-TSA and in VRB-VRB and SMAC-SMAC compared with Petrifilm and Easygel. These data underscore the need to implement food safety measures that address sublethally injured pathogens such as E. coli O157:H7 in order to avoid underestimation of true densities for target pathogens.

Study on Carcass Contaminating Escherichia coli in Apparently Healthy Slaughtered Cattle in Haramaya University Slaughter House with Special Emphasis on Escherichia coli O157:H7, Ethiopia

A cross sectional study was conducted from October 2010 to March 2011, on apparently healthy slaughtered cattle in Haramaya University Slaughter House to determine prevalence of Escherichia coli, with special emphasis on Escherichia coli O157:H7, and its antimicrobial susceptibility pattern. Carcass swab samples were collected and pre-enriched in buffered peptone water and plated on MacConkey agar plate. Presumptive colonies were confirmed by biochemical tests. Further identification of Escherichia coli O157:H7 was done by plating the isolatedm bacteria on Sorbitol MacConkey agar; and then colorless colonies were subjected to Escherichia coli O157:H7 Latex agglutination test. From a total of 113 samples collected, Escherichia coli was isolated from 35 (30.97%) and out of these, 3 (2.65%) were found to be Escherichia coli O157:H7. The difference in prevalence was not statistically significant (P>0.05) between local and cross breeds (χ2=0.11, df =4), among age group of animals (χ2=2.56, df=1) and origin of animals (χ2=2.56, df=2). The isolated bacteria were subjected to antimicrobial susceptibility testing and the majority were found to be susceptible to Chloramphenicol (30 μg), Kanamycin (30 μg), Spectinomycin (SH, 100 μg). The presence of E. coli O157:H7 in raw meats reaching to consumers indicated possible risks of infection to people through the consumption of raw (undercooked) meat and cross contamination of other food products. Therefore, control measures at all stages of food chain was recommended.

Membrane Damage and Viability Loss of E. coli O157:H7 and Salmonella spp in Apple Juice Treated with High Hydrostatic Pressure and Thermal Death Time Disks

Differences in membrane damage including leakage of intracellular UV-materials and loss of viability of Salmonella spp. and Escherichia coli O157:H7 bacteria in apple juice following thermal-death-time (TDT) disk and high hydrostatic pressure treatments were investigated. Salmonella spp. and E. coli O157H:H7 bacteria were inoculated in apple juice to a final 7.8 log10 CFU/ml and were thermally treated with TDT disks at 25, 35, 45, 50, 55 and 60°C for 4 min or pressurized at 350, 400 and 450 MPa at 25, 35, 45, 50, 55 and 60°C for 20 min. Sublethal injury, leakage of UV- materials and viability loss as a function of membrane damage of these bacterial pathogens was investigated by plating 0.1 ml of treated and untreated samples on non selective Trypticase Soy Agar (TSA) and selective Xylose Lysine Sodium Tetradecylsufate (XLT4) for Salmonella and Cefixime Potassium Tellurite Sorbitol-MacConkey (CT-SMACK) agar plates for E. coli bacteria with incubation at 36°C for 48 h. Sub-lethal injury occurred in Salmonella spp. and E. coli populations thermally treated with TDT disk at 55°C and above and at a pressure treatments of 25°C and above. Leakage of intracellular UV-materials and ATP of TDT disk injured cells was lower than the values determined from pressurized cells. Similarly, recovery of TDT injured cells occurred faster than pressurized cells during storage of treated samples at 22°C. The results of this study indicate that pressure treatment of 350 MPa at 35°C for 20 min and thermal treatments of 55 and 60°C and immediate storage of treated samples at 5°C will inhibit recovery and complete inactivation of injured bacteria in apple juice and therefore, will enhance the microbial safety of the treated juice.

PREVALENCE AND ANTIMICRIBIAL SUSCEPTIBILITY OF ESCHERICHIA COLI O157:H7 ISOLATED FROM HUMAN AND ANIMAL SOURCES IN BASRAH PROVINCE

The present study assessed the prevalence of Escherichia coli O157 in diarrhea patients ,beef, and raw milk. A total of 675 samples were inoculated in trypticase soy broth to enhance the growth of E. coli O157:H7. Out of total samples 73.5% isolated as E. coli then cultured on Sorbitol MacConkey agar ,31.8% non fermenting sorbitol (NSF) E. coli colonies were isolated and confirmed by specific biochemical tests . From NSFEC 13.7% were diagnosed as E.coli O157:H7 by serological test ,the result revealed no significant differences in the level of contamination with E. coli O157:H7 between beef ,stool and milk .The isolated bacteria were tested for antibiotic susceptibility test which showed resistance 100% to cephalothin ,cefoxitin , cefixime, trimethoprim , amoxicillin, azithromycin, and amoxicillin/clavulanic acid and sensitive 100% to ciprofloxacin ,imepenim ,nitrofurantion gentamycin and amikacin . No major differences in antibiotic susceptibility patterns among the isolates were observed.

Factors affecting the occurrence of Escherichia coli O157 contamination in irrigation ponds on produce farms in the Suwannee River Watershed

Outbreaks of enteritis caused by Escherichia coli O157 associated with fresh produce have resulted in questions about the safety of irrigation water; however, associated risks have not been systematically evaluated. In this study, the occurrence and distribution of the human pathogen E. coli O157 from vegetable irrigation ponds within the Suwannee River Watershed in Georgia were investigated, and the relationship to environmental factors was analyzed. Surface and subsurface water samples were collected monthly from 10 vegetable irrigation ponds from March 2011 to February 2012. Escherichia coli O157 was isolated from enriched filtrates on CHROMagar and sorbitol MacConkey agar media and confirmed by an agglutination test. Presence of virulence genes stx1, stx2 , and eae was tested by polymerase chain reaction. In addition, 27 environmental variables of the sampled ponds were measured. Denaturing gradient gel electrophoresis was conducted for the analysis of bacterial communities in the water samples. Biserial correlation coefficients were calculated to evaluate the log10 colony-forming unit per millilitre correlations between the environmental factors and the occurrence of E. coli O157. Stepwise and canonical discriminant analyses were used to determine the factors that were associated with the presence and absence of E. coli O157 in water samples. All 10 ponds were positive for E. coli O157 some of the time, mainly in summer and fall of 2011. The temporal distribution of this bacterium differed among the 10 ponds. Temperature, rainfall, populations of fecal coliform, and culturable bacteria were positively correlated with the occurrence of E. coli O157 (P < 0.05), while the total nitrogen concentration, oxidation-reduction potential, and dissolved oxygen concentration were negatively correlated with the occurrence of this pathogen (P < 0.05). Temperature and rainfall were the most important factors contributing to the discrimination between samples with and without E. coli O157, followed by bacterial diversity and culturable bacteria population density. Bacterial numbers and diversity, including fecal coliforms and E. coli O157, increased after rainfall (and possibly runoff from pond margins) in periods with relatively high temperatures, suggesting that prevention of runoff may be important to minimize the risk of enteric pathogens in irrigation ponds.

Comparison of Three Different Methods for Detection of Shiga Toxin-Producing Escherichia coli in a Tertiary Pediatric Care Center

Shiga toxin-producing Escherichia coli (STEC) is a well-known cause of sporadic and epidemic food-borne gastroenteritis. A low infectious dose, approximately 10 microorganisms, is sufficient to cause disease that may lead to hemolytic-uremic syndrome. The objective of this study was to compare the performances of an in-house real-time PCR, a commercial enzyme immunoassay (EIA) (Premier EHEC; Meridian Bioscience), and culture on sorbitol MacConkey agar for the detection of STEC in a tertiary care pediatric hospital. Of 632 stool samples tested, 21 were positive for STEC. All were detected by PCR, 6 were detected by EIA, and only 5 O157 STEC isolates were identified by culture. Among the 15 specimens falsely negative by EIA, there were 9 Stx1, 2 Stx2, and 4 Stx1 and Stx2 STEC isolates. The latter group included 2 O157 STEC isolates that would have been missed if only EIA had been performed. To our knowledge, this is the first prospective study performed in a pediatric hospital which demonstrates the superiority of PCR over EIA for the detection of STEC. We conclude that PCR is specific and more sensitive than EIA. PCR should be considered for routine use in clinical settings where molecular detection facilities are available. Its lower limit of detection, equivalent to the infectious dose, is an obvious advantage for patient care and public health surveillance.

Detection of rfbO157 and fliCH7 Genes in Escherichia coli Isolated from Human and Sheep in Basrah Province

This study aimed to detect Escherichia coli O157:H7 in samples from patients with diarrhea, sheep milk, and sheep drinking water by growth on selective media, biochemical tests, latex agglutination test, and PCR technique. During the period from November 2008 to May 2009, a total of 340 samples were collected; stools diarrhoeic patients (125), healthy sheep feces (125), milk (45), and sheep drinking water samples (45). Samples were screened for the presence of non-sorbitol fermenting colonies (NSF) on sorbitol MacConkey agar supplemented with cefixime and potassium tellurite (CT-SMAC). Out of the 340 samples, 58 (46.4%) stool from diarrhea, 98 (78.4%) from sheep feces, 19 (42.2%) milk, and 17 (37.7%) drinking water were nonsorbitol fermenting. E. coli isolates were serotyped as E. coli O157:H7 by latex agglutination test, 3 (5.7%) isolates of stool from diarrhea patients, 7 (7.3%) isolates of sheep feces, 2 (11.1%) isolates of milk, and none of drinking water samples were positive. All latex agglutination positive isolates were positive to PCR test except one isolate from sheep feces. PCR positive isolates were produced enterohemolysin on sheep blood agar, and were found resistant to at least 3 antibiotics. The highest rate of E. coli O157:H7 isolation was observed in April (7.6%) followed by December (4.7%) , while those of sheep feces showed the highest rate in March (10%) followed by April (8.6%).

The Effect of Regions of Interest and Spectral Pre-Processing on the Detection of Non-0157 Shiga-Toxin Producing Escherichia Coli Serogroups on Agar Media by Hyperspectral Imaging

Foodborne infection caused by Shiga toxin-producing Escherichia coli (STEC) is a major worldwide health concern. The best known and highly virulent STEC serogroup is E. coli 0157:H7, which can be easily identified when cultured on sorbitol-MacConkey (SMAC) agar. Recently, six non-0157 STEC serogroups have been found to cause human illnesses. These non-0157 serogroups ferment sorbital and form pink colonies; therefore SMAC agar cannot be used to differentiate non-0157 serogroups from each other and other flora growing on the plate. This study investigated the potential of visible and near infrared hyperspectral imaging and chemometrics to spectrally differentiate six representative non-0517 STEC serogroups (026, 045, 0103, 0111, 0121 and 0145) grown as spots on Rainbow agar media. Mahalanobis distance classifiers were developed with spectra obtained from ground truth regions of interest (ROIs) of each serogroup colony. The ROIs were selected as a doughnut-like open-ellipse to only include the leading edge of growth and as a closed-ellipse covering the entire colony. For each ROI type, the Mahalanobis distance classifiers were developed with log (1/Reflectance), first derivative and standard normal variate and detrending (SNVD) pre-processing treatments. Serogroups 045 and 0121 were consistently classified over 98% accurate, regard less of the classification algorithm used. The lowest classification accuracies were from classifiers developed with only log (1/ R) ROI spectra. First derivative and SNVD spectra helped to increase the detection accuracies of the other serogroups. The classification accuracy for serogroups 026, 0111, 0103 and 0145 with the closed-ellipse and open-ellipse classification algorithms showed varying results from 8% to 87% and 57% to 100%, respectively. The lower accuracies with closed ellipse spectra were due to greater spectral variation in the centre pixels on a per-pixel basis. Practical implications of this study are the demonstrated potential of hyperspectral imaging for presumptive-positive screening of non-0157 serogroups on Rainbow agar and the extensibility of the developed sampling methods and classification models for future research to identify the target bacteria in the presence of background flora grown on spread plates.

Effects of Preparation and Storage of Agar Media on the Sensitivity of Bacterial Forward Scattering Patterns

Recent worldwide foodborne outbreaks emphasize the need for the development of rapid and accurate method for pathogen detection. To address such issues, a new colony based label-free detection method working on the principles of elastic light scattering was introduced. In order to build libraries of scattering images for bacterial pathogens, it is pertinent to determine the effect of preparation and storage of the agar media on the scatter patterns. Scatter patterns of three Escherichia coli serovars (O26, O111 and O157) were studied and used in a model system, after growth on Sorbitol-MacConkey agar plates that were prepared and stored at different conditions in the laboratory. Quantitative image processing software was used to analyze variation in scatter patterns of the same serovar on media prepared under various standard laboratory conditions and to generate a cross-validation matrix for comparison. Based on the results, it was determined that attention should be given during preparation of media so that the agar plates are not air-dried more than 10 - 20 min after solidification at room temperature. The plates could be stored in sealed bags in cold room (4oC - 10oC) for up to a month before use. The findings of this study should provide guidelines in preparation, storage, and handling of media for generation of reproducible scatter patterns of bacterial colonies with the light scattering sensor for pathogen detection.

Inactivation and injury of pathogens on intact beef treated with hydrodynamic pressure

Abstract The effect of hydrodynamic pressure (HDP) treatment on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes attached to beef surface was evaluated. Irradiated beef cubes were inoculated with these individual pathogens (ca. 4 log CFU.g −1 ) and treated with HDP. Surviving populations of E. coli O157:H7, S . Typhimurium, and L. monocytogenes were determined by spiral-plating on Sorbitol MacConkey agar (SMAC), XLT4 agar, and modified Oxford (MOX) agar, respectively. The HDP treatment significantly reduced E. coli O157:H7 (0.75 log CFU.g −1 ), S. Typhimurium (1.09 log CFU.g −1 ), and L. monocytogenes (0.55 log CFU.g −1 ) from beef surfaces. HDP-induced injury as determined by plating on non-selective media revealed that ca. 0.5 log CFU.g −1 of E. coli O157:H7 and S. Typhimurium cells were injured. Most cell injury occurred at the cell membrane level as observed by transmission electron microscopy (TEM). Industrial relevance Results obtained in the present study show that HDP treatment, primarily evaluated for meat tenderness improvement, also reduces the number of viable pathogens attached to beef surface. Additional hurdle treatment will be helpful to further reduce pathogens on beef surface.

Sorbitol-Fermenting, β-Glucuronidase–Positive, Shiga Toxin–Negative Escherichia coli O157:H7 in Free-Ranging Red Deer in South-Central Spain

We investigated the prevalence of Escherichia coli O157:H7 in free-ranging red deer in south-central Spain, to assess their potential as reservoir hosts of sorbitol-fermenting (SF) E. coli O157:H7 strains, which are emerging causes of hemolytic uremic syndrome in Europe. Fecal samples from 264 hunter-harvested Iberian red deer (Cervus elaphus) were collected in 25 different game estates and examined for E. coli O157:H7 by culture and PCR. E. coli O157:H7 was detected and isolated in 4 of the 25 game estates sampled (16%) and the isolates obtained (four in total) were further phenogenotypically characterized. One of them was biochemically typical of E. coli O157:H7, that is, neither fermented sorbitol nor exhibited β-glucuronidase (GUD) activity, and carried genes encoding Shiga toxins (Stx) 1 and 2, the intimin subtype γ1, the enterohemorrhagic E. coli (EHEC)-hemolysin, and the ter gene cluster. The rest of the isolates (three of four) fermented sorbitol, exhibited GUD activity after 18-24 h incubation, and carried genes encoding the intimin subtype γ1 and the EHEC-hemolysin, although no Stx-encoding genes were detected. All these atypical isolates carried the sfp gene cluster, lacked the ter gene cluster, and were unable to grow on cefixime tellurite sorbitol MacConkey agar, which are typical features of SF E. coli O157:H7 strains isolated from patients. In total, SF, GUD-positive, Stx-negative E. coli O157:H7 strains were isolated in 3 of the 25 game estates sampled (12%), with an overall sample-level prevalence of 1.1% (3/264). Our findings indicate that free-ranging red deer may be one of the possible reservoir hosts of Stx-negative derivatives of SF E. coli O157:H7.

Prevalence of Escherichia coli O157:H7 on hides and faeces of ruminants at slaughter in two major abattoirs in Nigeria

To determine the occurrence of Escherichia coli O157: H7 in hides and faeces of slaughtered ruminants in Nigeria. A total number of 320 animals were sampled from January to December covering the wet and harmattan seasons. Samples were obtained from the hides and faeces of animals at slaughter. The ISO (ISO 16654:2001, Microbiology of food and animal feedingstuffs--horizontal method for the detection of Escherichia coli O157) method for enrichment and isolation of E. coli O157 incorporating selective enrichment using modified tryptone soya broth with novobiocin (mTSBn),immunomagnetic separation and plating on sorbitol-MacConkey agar with cefixime tellurite (CT-SMAC) was used. Overall cattle had a prevalence rate of 49.4% followed by sheep and goats with rates of 6.3% and 2.5%, respectively. There was a significant difference in carriage of E. coli O157 among two different cattle breeds. The prevalence of E. coli O157: H7 is substantial from two abattoirs in the country. The carriage and shedding of E. coli O157: H7 did not differ with season but differed among groups of ruminants and among breeds of cattle in a tropical country. This is the first study on E. coli O157: H7 from abattoir operations in Nigeria. The study emphasizes the risk of E. coli O157: H7 along the meat chain and the need for concerted effort to limit it through best hygiene practices.

Identification of shiga toxin producing Escherichia coli O157:H7 in raw cow milk samples from dairy farms in Mashhad using multiplex PCR assay

Summary In this study 130 bulk tank milk samples which were delivered to the Pegah Pasturisation Factory in Mashhad were collected randomly during the summer months. Samples were firstly enriched in modified trypticase soy broth containing novobiocin, followed by plating onto sorbitol MacConkey agar supplemented with cefixime and potassium tellurite for isolation of Escherichia coli O157:H7. Consequently the suspected non-sorbitol fermenting (NSF) colonies were confirmed by biochemical tests as Escherichia coli and then were used for multiplex-PCR assay, using primers specific for O157 and H7 antigens genes and then primers specific for stx1 and stx2 genes. NSF Escherichia coli colonies were recovered from 8 samples, and in multiplex-PCR assay one sample (0.77%) was confirmed as Escherichia coli O157:H7. The second multiplex PCR assay showed that the isolate was harboring the stx2 gene. The PCR assay used in this study may be a possible alternative to immunological assays which detect somatic and flagellar antigens. Besides, this procedure determines the potential of isolates for toxin production.

Hydrophobic and Electrostatic Interaction Chromatography for Estimating Changes in Cell Surface Charge ofEscherichia coliCells Treated with Pulsed Electric Fields

Pulsed electric field (PEF) treatments, a nonthermal process, have been reported to injure and inactivate bacteria in liquid foods. However, the effect of this treatment on bacterial cell surface charge and hydrophobicity has not been investigated. Apple juice (pH 3.8) purchased from a wholesale distributor was inoculated with cocktail of Escherichia coli O157:H7 at 7.4 log CFU/mL, processed with a PEF at a field strength of 18.4 kV/cm and 32.2 kV/cm at 25°C, 35°C, and 45°C with a treatment time of 160 μs and a flow rate of 120 mL/min. Bacterial cell surface charge and hydrophobicity of untreated and PEF-treated E. coli O157:H7 were determined immediately and after storage at 5°C and 23°C using hydrophobic and electrostatic interaction chromatography. Similarly, the populations surviving the PEF treatments including injured cells were determined by plating 0.1 mL of the sample on sorbitol MacConkey agar and tryptic soy agar (TSA) plates. The surviving populations of E. coli cells after PEF treatment varied depending on field strength and treatment temperature used. Percent injury in the surviving populations was high immediately after PEF treatment and varied among treatment temperatures. Cell surface charge of E. coli bacteria before PEF treatment averaged 32.10±8.12. PEF treatments at 25°C, 35°C, and 45°C reduced the above surface charge to 26.34±1.24, 14.24±3.30, and 6.72±2.82, respectively. Similarly, the surface hydrophobicity of untreated E. coli cells at 0.194±0.034 was increased to an average of 0.268±0.022, 0.320±0.124, and 0.586±0.123 after PEF treatments at 25°C, 35°C, and 45°C, respectively. The results of this study indicate that PEF treatment affects the outer cell envelope of E. coli bacteria as evidenced by the changes in surface hydrophobicity and cell surface charge leading to injury and subsequent inactivation of the cells.

Development and validation of a culture-based method suitable for monitoring environmental survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in developing countries

A non-GMO culture-based method suitable for studying the fate of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in an agricultural environment in developing countries was developed and validated. This method is based on the use of spontaneous rifampicin-resistant mutants of non-toxigenic variants of E. coli O157:H7 and S. Typhimurium combined with counting of colony-forming units (CFU) on selective media, i.e., Cefixime–Tellurite–Sorbitol MacConkey agar containing 100 μg/ml rifampicin, 50 μg/ml cycloheximide and 50 μg/ml nystatin for E. coli O157:H7 and Xylose–Lysine–Tergitol-4 agar containing the same antimicrobials for S. Typhimurium. Validation experiments using gfp- and ds-red-labelled derivatives of the rifampicin-resistant mutants in a non-sterile manure-soil matrix demonstrated that the new culture method was effective in the selection and recovery of the test strains without any detectable interference from background contaminants both in the short and long term. The rifampicin-resistant-based culture method designed provides a feasible low-cost option to study environmental survival of E. coli O157:H7 and Salmonella spp. in developing countries.

The occurrence of Escherichia coli O157:H7 in market and abattoir meat in Plateau State, Nigeria

Escherichia coli O157:H7 is a newly emerging pathogen frequently associated with the consumption of foods of bovine origin. The severity of the infections caused by this food borne pathogen in the young and the elderly has had a tremendous impact on human health and food industry. The present study evaluated the occurrence of E. coli O157:H7 in abattoir and market meat in seven selected sites in Plateau State, Nigeria. One hundred and forty samples of each of the various meat parts including muscle, liver, heart, kidney and intestine were collected to give a total of 700 meat samples. The samples were aseptically collected at monthly intervals from December 2008 to November 2009 after which they were transported to the laboratory for bacteriological analysis. Enrichment medium Tryptone Soya Broth (TSB) and selective agar media, namely; sorbitol MacConkey agar (SMAC)and cefixime tellurite-sorbitol MacConkey agar (CT-SMAC) were used for the isolation of E. coli O157:H7 from the various meat samples. The results of this study indicated that the intestinal samples had the highest percentage occurrence of the organism (3.39%), while muscle tissue had the lowest (0.43%). The organ meats had comparable percentage occurrence of the organism, with 1.0% for liver, 0.86% for kidney and 0.71% for heart samples. Significant difference (P 0.05) existed in the occurrence of the organism with respect to the sampling sites and the sources (abattoir and market). The presence of E. coli O157:H7 in beef should be regarded as being highly hazardous to consumers and handlers alike because of the severity of the infections associated with the organism. Thus, hygienic and good management of meats and meat environments are very essential.

Frequency of Detection ofEscherichia coli,Salmonellaspp., andCampylobacterspp. in the Faeces of Wild Rats (Rattusspp.) in Trinidad and Tobago

The study was conducted to determine the frequency of isolation of Salmonella, Campylobacter and E. coli O157 in the faecal samples of rats trapped across the regional corporations in Trinidad and to assess their resistance to antimicrobial agents. A total of 204 rats were trapped for the detection of selected bacteria. Standard methods were used to isolate Salmonella, Campylobacter and E. coli O157. Characterization of E. coli was done on sorbitol MacConkey agar to determine non-sorbitol fermentation, blood agar to determine haemolytic and mucoid colonies and by using E. coli O157 antiserum to determine O157 strain. The disc diffusion method was used to determine resistance to nine antimicrobial agents. Of the 204 rats, 4 (2.0%), 7 (3.4%) and 171 (83.8%) were positive for Salmonella spp., Campylobacter spp. and E. coli, respectively. Of the 171 isolates of E. coli tested 0 (0.0%), 25 (14.6%) and 19 (11.1%) were haemolytic, mucoid and non-sorbitol fermenters, respectively. All isolates were negative for the O157 strain. The frequency of resistance to the 9 antimicrobial agents tested was 75% (3 of 4) for Salmonella, 85.7% (6 of 7) of Campylobacter spp. and 36.3% (62 of 171) for E. coli (P < .05; χ2).

Shiga Toxin-Producing Escherichia coli in Children: Diagnosis and Clinical Manifestations of O157:H7 and Non-O157:H7 Infection

Shiga toxin-producing Escherichia coli (STEC), a cause of food-borne colitis and hemolytic-uremic syndrome in children, can be serotype O157:H7 (O157) or other serotypes (non-O157). E. coli O157 can be detected by culture with sorbitol-MacConkey agar (SMAC), but non-O157 STEC cannot be detected with this medium. Both O157 and non-O157 STEC can be detected by immunoassay for Shiga toxins 1 and 2. The objectives of this study were first to compare the diagnostic utility of SMAC to that of the Premier EHEC enzyme immunoassay (Meridian Diagnostics) for detection of STEC in children and second to compare the clinical and laboratory characteristics of children with serotype O157:H7 STEC and non-O157:H7 STEC infections. Stool samples submitted for testing for STEC between April 2004 and September 2009 were tested by both SMAC culture and the Premier EHEC assay at Children's Hospital Boston. Samples positive by either test were sent for confirmatory testing and serotyping at the Hinton State Laboratory Institute (HSLI). Chart review was performed on children with confirmed STEC infection. Of 5,110 children tested for STEC, 50 (0.9%) had STEC infection confirmed by culture; 33 were O157:H7 and 17 were non-O157:H7. The Premier EHEC assay and SMAC culture detected 96.0% and 58.0% of culture-confirmed STEC isolates (any serotype), respectively, and 93.9% and 87.9% of STEC O157:H7 isolates, respectively. There were no significant differences in disease severity or laboratory manifestations of STEC infection between children with O157:H7 and those with non-O157 STEC. The Premier EHEC assay was significantly more sensitive than SMAC culture for diagnosis of STEC, and O157:H7 and non-O157:H7 STEC caused infections of similar severity in children.

Reduction of Escherichia coli O157:H7 viability on leafy green vegetables by treatment with a bacteriophage mixture and trans-cinnamaldehyde

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been recognized as a major foodborne pathogen responsible for frequent gastroenteritis outbreaks. Phages and essential oils can be used as a natural antimicrobial method to reduce bacterial pathogens from the food supply. The objective of this study was to determine the effect of a bacteriophage cocktail, BEC8, alone and in combination with the essential oil trans-cinnameldehyde (TC) on the viability of a mixture of EHEC O157:H7 strains applied on whole baby romaine lettuce and baby spinach leaves. The EHEC O157:H7 strains used were Nal R mutants of EK27, ATCC 43895, and 472. Exponentially growing cells from tryptic soy (TS) broth cultures were spot inoculated on leaves and dried. EHEC cells were placed at low, medium, and high inoculum levels (10 4, 10 5, and 10 6 CFU/mL, respectively). Appropriate controls, BEC8 (approx. 10 6 PFU/leaf), and TC (0.5% v/v) were applied on treated leaves. The leaves were incubated at 4, 8, 23, and 37 °C in Petri dishes with moistened filter papers. EHEC survival was determined using standard plate count on nalidixic acid (50 μg/mL) Sorbitol MacConkey agar. No survivors were detected when both leaves were treated with BEC8 or TC individually at low inoculum levels after 24 h at 23 and 37 °C. When the EHEC inoculum size increased and/or incubation temperature decreased, the efficacy of BEC8 and TC decreased. However, when the two treatments were combined, no survivors were detected after 10 min at all temperatures and inoculum levels on both leafy greens. These results indicated that the BEC8/TC combination was highly effective against EHEC on both leafy greens. This combination could potentially be used as an antimicrobial to inactivate EHEC O157:H7 and reduce their incidence in the food chain.