Prevalence and characterization of Escherichia coli O157:H7 from samples along the production line in Chinese beef-processing plants

This work investigated the prevalence of Escherichia coli O157:H7 and the antibiotic susceptibility, genetic diversity and virulence genes of isolated strains from four beef slaughter plants in China. A total of 510 samples (feces, hide, carcasses and raw meat) were tested for E. coli O157:H7 using enrichment, immunomagnetic separation, and plating on selective media. The prevalence of E. coli O157:H7 in the feces, hide, pre-evisceration carcass, post-evisceration carcass, post-washing carcass, chilled carcass, and raw meat samples was 1.43%, 1.43%, 0%, 0%, 0%, 1.25%, and 0%, respectively. Multiplex PCR assays were used for serotype confirmation and virulence gene detection. stx₂, eaeA and EHEC-hlyA genes were present in all six of the strains, and the stx₁ gene was not present. Fluorescence amplified fragment length polymorphism (FAFLP) was used to determine the genetic diversity of E. coli O157:H7 and revealed a high similarity between the strains isolated from feces and those isolated from carcasses. None of the isolated strains were found to be resistant to sixteen commonly used antimicrobial agents. The results of this study indicate that although E. coli O157:H7 contamination in the Chinese beef industry is sporadic and not as common as reported in other counties, all of the isolates contained three major virulence genes, presenting a high risk of disease for humans. The current research provides baseline information on E. coli O157:H7 prevalence and character profiles in Chinese beef-processing plants that can be used for future studies.     

Occurrence,serotypes and virulence genes of non-O157 Shiga toxin-producing Escherichia coli in fresh beef,ground beef,and beef burger

This study determined the prevalence, serotypes and virulence genes distribution of non-O157 Shiga toxin-producing Escherichia coli in meat products collected from butchers shops and supermarkets in Mansoura city, Egypt. We have characterized 18 non-O157 STEC strains among the identified 100 E. coli isolates recovered from the examined 87 meat product samples. The prevalence of non-O157 STEC strains in fresh beef, ground beef and beef burger samples were 11.1% (3/27), 16.7% (5/30), and 33.3% (10/30), respectively. The eighteen non-O157 STEC isolated strains were serotyped into seven (38.9%) O111:H8, six (33.3%) O26:H11, two (11.1%) O111:H–, and one (5.56%) for each of O55:H7, O126:H5 and O128:H2. PCR assays for different virulence genes showed that nine (50%), eleven (61.1%), and nine (50%) strains carry stx1, stx2, and eae genes, respectively. The distribution of shiga toxin genes among the isolated strains indicated that seven (38.9%) strains harbored stx1 only, nine (50%) strains harbored stx2 only, and two (11.1%) strains harbored both stx1 and stx2. The eae gene was present in association with five (27.8%), three (16.7%), and one (5.6%) strains that harbored stx1 only, stx2 only, and both stx1 and stx2, respectively. This study concluded that the examined meat products, particularly beef burger, consumed in Egypt are considerably contaminated with a variety of non-O157 STEC serotypes, and hence consumption of such products may constitute a potential health risk for consumers.     

Detection of Escherichia coli O157:H7 in ground beef using immunomagnetic separation and multiplex PCR

In the study 251 fresh ground beef samples sold in Ankara were analyzed to evaluate the prevalence of Escherichia coli O157:H7 by immunomagnetic separation (IMS) based cultivation technique. Virulence factors of the isolates were determined by multiplex PCR. Nineteen (7.6%) of 251 ground beef samples were found as contaminated with E. coli O157. By PCR analyse in two of the isolates fliC_h7 gene was detected and identified as E. coli O157:H7. According to the multiplex PCR one of the isolate has all stx₁, stx₂, eaeA, hly and fliC_h7 genes and the other has stx₁, eaeA, hly and fliC_h7 genes.     

Detection of verocytotoxin-producing Escherichia coli (VTEC) in minced beef and raw milk by colony blot hybridization

Verocytotoxin-producing Escherichia coli (VTEC) are foodborne pathogens that cause outbreaks linked to consumption of meat and raw milk. In this note the authors report results obtained from a survey conducted on minced beef and raw bovine milk samples using a Multiplex PCR (M-PCR) for the detection of eae, stx₁, stx₂ and hlyA genes as a screening step followed by a colony blot hybridization (CBH) technique for the isolation of the VTEC. Of 100 minced beef and 123 raw milk samples, 13 (13%) and 7 (5.7%) were positive in the M-PCR and among these 9 and 3 strains were isolated using CBH, respectively. All isolates showed the presence of the stx₂ gene, single or in association with the other investigated genes. None of the isolates belonged to the O157, O26, O91, O103, O111 and O145 serogroups. The study showed that the use of M-PCR for the screening of samples coupled with a sensitive and specific detection technique, could improve the possibility of detection of VTEC strains in foods. Moreover, the presence of VTEC in minced beef and in raw milk confirms their important role as putative vehicles of infection to humans. Stringent control of these foodstuffs is essential for food safety purposes.     

Inactivation of Shiga toxin-producing and nonpathogenic Escherichia coli in non-intact steaks cooked in a radio frequency oven

This study evaluated the thermal inactivation of Shiga toxin-producing Escherichia coli (O157:H7, O26:H11 and O111) (STEC) and non-pathogenic E. coli in non-intact beefsteaks (NIBS) cooked by radio frequency (RF). Blade tenderized steaks were inoculated with nalidixic (Nal) acid resistant E. coli strains, vacuum packaged in thermal pouches and cooked using pre-determined cooking times to 60 °C (rare) or 65 °C (medium-rare) inside a RF oven. Log reduction ranged from 0.99, 3.08, 2.85 and 5.0 for O157:H7, O26:H11, O111 and non-pathogenic E. coli respectively at 60 °C and a 5.0 log reduction at 65 °C for all strains. Non-pathogenic E. coli strains selected for the present study did not behave similar to the pathogenic strains being significantly more sensitive; therefore, they were not considered for testing at 63 °C. A second part of the study focused on the extent of thermal inactivation of STEC when NIBS were cooked to 63 °C (minimum safe cooking temperature recommended by USDA-FSIS). There was a 5.0 log reduction for E. coli O157:H7 and E. coli O111; but not for E. coli O26:H11. The results indicated that cooking steaks to 65 °C with a holding time at room temperature of 5 min before refrigeration would be enough to reduce numbers of E. coli O157:H7, O26:H11 and O111 using RF. The cooking protocol developed on the present study, has a practical relevance for the industry since the experiments were carried on a pilot-scale RF oven and also pathogens were tested under realistic processing conditions.     

Effects of mild and pasteurizing heat treatments on survival of generic and verotoxigenic Escherichia coli from beef enrichment cultures

At many North American beef packing plants, hot water washes and pasteurizing treatments are used to clean and decontaminate carcasses. The aim of this study was to determine whether reduction in numbers of total Escherichia coli found on beef could be regarded as indicative of the reduction in numbers of verotoxigenic E. coli (VTEC) resulting from the same heat treatment. Swab samples were collected from hide-on beef carcasses and were enriched for E. coli in E. coli broth supplemented with novobiocin. Suspensions containing cells in the stationary phase were mixed with equal volumes of meat juice medium and the mixtures were not heated or were heated at temperatures between 55 and 70 °C. All preparations were treated with deoxycholate and propidium monoazide (PMA), then DNA was extracted. Real-time PCR was performed using primers targeting the uidA gene for total E. coli, the stx₁ and stx₂ genes for VTEC, and the eae gene for O157. For samples that were not subjected to heat treatment, cycle threshold (Ct) values were from 13.53 to 17.93 for uidA, 17.94 to 26.77 for stx₁, 21.57 to 29.36 for stx₂, and 23.53 to 28.31 for eae. Ct values for all genes were higher for heat treated than for not treated portions of samples. Differences between Ct values for not treated and heat treated portions of each sample were 5.06–7.57 for uidA, 4.35 to 7.03 for stx₁, 4.49 to 7.12 for stx₂ and 4.75 to 6.77 for eae. Differences between the increases of Ct values for pairs of genes in the sample were 0.32–0.83 for uidA and stx₁, 0.19–0.57 for uidA and stx₂ and 0.31–0.80 for uidA and eae. The maximum change in the ratio of Ct values for uidA and stx₁, stx₂ or eae as a result of heating corresponded to a change of 0.3 log units, which is less than the 0.5 log units generally considered to be microbiologically significant. Therefore, the findings indicate that reductions as a result of mild or pasteurizing heat treatments of total E. coli populations derived from beef can be regarded as indicative of the reductions in sub-populations of O157-VTEC and total VTEC resulting from the treatments.     

Genotypic characterization of Shiga toxin-producing Escherichia coli O157:H7 isolates in food products from china between 2005 and 2010

Shiga toxin-producing Escherichia coli (STEC) O157 is an important foodborne pathogen. The aims of this study were to determine genetic relatedness of STEC O157 isolated from foods in China. STEC O157 isolates from food were characterized by virulence gene typing, antibiotyping, Multi-locus sequence typing (MLST), pulsed-field gel electrophoresis analysis (PFGE), Multi-locus variable number tandem repeat analysis (MLVA), and the single nucleotide polymorphism (SNP) clade typing. Of the 30 STEC O157 isolates analyzed, all isolates harbored eae, exhA, stx1 and/or stx2 genes with stx2c subtype predominating. By MLST, they were relatively homogenous with only 4 STs. PFGE and MLVA generated 22 pulsotyples and 23 patterns, respectively, which showed considerable diversity. Only one clade 8 isolate was detected. These results indicate that STEC O157 isolates from foods in China were heterogeneous. There was no correlation between genotypic characteristics and sources of isolates. Since different subtyping methods often give different discriminatory powers, the use of more than one subtyping approach is necessary in providing a more accurate picture of the genetic diversity of STEC O157. Four isolates were from ready-to-eat meat or salads, underscores the risk of infections. There is a need for surveillance of STEC O157 in foods and clinically and implementation of prevention strategies to prevent outbreaks of STEC O157 infections in China.     

Presence of indicator bacteria,Salmonella and diarrheagenic Escherichia coli pathotypes on mung bean sprouts from public markets in Pachuca,Mexico

Coliform bacteria (CB), fecal coliforms (FC), Escherichia coli, diarrheagenic E. coli pathotypes (DEP) and Salmonella frequencies were determined for mung bean (Vigna radiata) sprouts. One hundred sprout samples were collected from markets in Pachuca, Hidalgo state, Mexico. Of these samples, 100% were positive for CB, 98% for FC, 95% for E. coli, 10% for DEP and 5% for Salmonella. Identified DEP included enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC) and Shiga toxin-producing E. coli (STEC). The ETEC and EIEC were each isolated from 2% of samples, and the STEC from 6% of samples. No E. coli O157:H7 were detected in any STEC-positive samples. Positive correlations were observed between FC and E. coli and between E. coli and DEP. A negative correlation occurred between CB and DEP, and between CB and Salmonella. Neither FC nor E. coli correlated with Salmonella presence in the sprout samples. This is the first report of ETEC, EIEC and STEC isolated from sprouts in Mexico and the first report of Salmonella isolation from mung bean in Mexico. Mung bean sprouts are very probably an important factor contributing to the endemicity of ETEC, EIEC and STEC and Salmonella-related gastroenteritis in Mexico.     

Comparison of effects of mild heat combined with lactic acid on Shiga toxin producing Escherichia coli O157:H7, O103, O111, O145 and O26 inoculated to spinach and soybean sprout

The aim of the present study was to investigate the effect of lactic acid against Shiga toxin producing Escherichia coli (O157:H7 and non-O157 serogroups including O103, O111, O145 and O26) at different conditions. Soybean sprouts and spinach leaves inoculated with each serogroup of E. coli (∼7.00 + 1.00 log₁₀ cfu/g) were treated with the lactic acid solutions at different concentrations (0% (control), 1.5%, 2.0%, or 2.5%) and at different temperatures (20, 40, or 50 °C) for 3 min. Results indicated that regardless of the treatment temperature, no significant reduction in the numbers of any serogroup occurred in the control group (0%) (p > 0.05). However, lactic acid at concentration of 1.5%, 2% and 2.5% was found to be effective against all organisms tested. There was no significant difference (p > 0.05) between E. coli O157:H7 and non-O157 STEC serogroups at any treatment group. The highest reductions (ca. 4.00 log₁₀ cfu/g) of all serotypes in both produces were observed after immersing into 2.5% lactic acid at 50 °C. The results of this study showed that decontamination of fresh produces such as spinach and soybean sprout with lactic acid solutions prepared at mild temperatures (40 °C and 50 °C) might be an effective safety measure in preventing public health risks associated with these products contaminated with STEC.     

Bacterial quality of raw milk investigated by Escherichia coli and isolates analysis for specific virulence-gene markers

The bacterial quality and safety of raw milk sources in Taif region (Western Saudi Arabia) were analyzed for the natural contamination of fecal coliform and Escherichia coli by standard most probable number method. The E. coli isolates were identified to species identity using API 20E and screened for markers of STEC (Stx1, Stx2), ETEC (ST, LT), (EaeA) and ExPEC (CNF1, CNF2, SfaS, PapA, CdtB, IutA, FyuA, TraT) using PCR assays. Thirty-three E. coli strains were recovered from raw milk sample sources, which were contaminated by fecal coliform. None of the investigated isolates reacted positively with the PapA, SfaS and CdtB, ST and LT-specific primers. Markers of STEC and EPEC were each detected in three strains. NTEC was detected in four strains. The most frequent virulence markers were TraT (17 strains), IutA (11 strains) and FyuA (8 strains). Results suggested a possibility of potential public health threat of E. coli originating from raw milk sources.     

Prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) in whole-muscle beef cuts sold at retail markets in Costa Rica

The present study sought to determine the prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) serogroups O26, O45, O103, O111, O121, O145, and O157 in whole-muscle beef cuts sold at retail in urban and semi-rural areas of Costa Rica. A total of 279 (171 urban, 108 semi-rural) samples were purchased from 93 butcher shops between August of 2012 and August of 2013 and tested for the presence of molecular markers characteristic of Salmonella and STEC using the DuPont Qualicon BAX^® System. The overall prevalence of Salmonella and STEC markers was 3.6% (10/279) and 4.7% (13/279), respectively. Salmonella markers were more frequently found in semi-rural (6.5%; 7/108) than in urban (1.8%; 3/171) areas. Similarly, STEC markers were more commonly detected in semi-rural (7.4%; 8/108) than in urban (2.9%; 5/171) areas. A marginal association was found between Salmonella markers and sampling location (P = 0.0496), whereas the presence of STEC markers and sampling location were considered independent (P = 0.1416). Among the 13 positive samples for STEC, 38 O-antigen gene fragments were amplified, with serogroups O45 and O121 being the predominant (28.9 and 21.1%, respectively). Markers for somatic antigens O111 and O157 were not detected in any of the samples. The present investigation is the first of its kind in Central America and shows that both Salmonella and STEC may be commonly present in whole-muscle raw beef cuts sold at retail markets in Costa Rica. Consequently, consumers may be directly at risk of foodborne illness due if meat products are not adequately cooked and handled in food service or domestic settings. Future work should emphasize continuous monitoring of the presence of these and other zoonotic pathogens in meat and meat products and on the implementation and validation of adequate food safety controls along the farm-to-table continuum.     

Antimicrobial activity of ascorbic acid alone or in combination with lactic acid on Escherichia coli O157:H7 in laboratory medium and carrot juice

The antimicrobial effects of ascorbic acid alone and in combination with lactic acid, against Escherichia coli O157:H7 in Brain Heart Infusion (BHI) broth and in carrot juice as a food model was investigated. In control samples, E. coli O157:H7 continued to growth from 3.98 ± 0.2 log CFU and reached to 8.88 ± 0.1 log₁₀ CFU after 8 h at 37° C; however, bacterial population was undetectable level in BHI in the presence of 0.4% ascorbic acid and 0.2% lactic acid. In carrot juice, E. coli O157:H7 continue to grow from initial population count of 4.41 ± 0.9 log₁₀ CFU to 8.75 ± 0.07 log₁₀ CFU at 37 °C for 24 h. Similarly, the bacteria population was undetectable when 0.2 or 0.4% ascorbic acid and 0.2% lactic acid applied. Our findings suggest the application of ascorbic acid, in combination with lactic acid, may have potential as preservative to inhibit the growth of E. coli O157:H7 in food.     

Development of a controlling method for Escherichia coli O157:H7 and Salmonella spp. in fresh market beef by using polylysine and modified atmosphere packaging

Escherichia coli O157:H7 and Salmonella spp. often contaminate fresh beef. In Japan, an E coli outbreak caused by raw beef made 181 people ill and 5 individuals dead in 2011. Responding to this outbreak, an effective sterilization method for fresh beef is expected to be developed. In this study, ε-polylysine combined with CO₂-packaging method was examined for controlling these pathogens in fresh beef. At an incubation temperature of 4 °C, approximately 4.3 log and 2.4 log reduction in bacterial numbers were observed after 7-day incubation for E. coli O157:H7 and Salmonella, respectively, in ε-polylysine-added beef. When effectiveness of CO₂-packaging combined with ε-polylysine was investigated, CO₂ did not have additional inhibiting effect on bacterial growth compared to only-ε-polylysine-treated samples when incubated at 4 °C. However, effectiveness of CO₂ was observed when incubated at 10 °C where approximately 2.9 log and 4.4 log reduction in E. coli cell numbers were observed in only-ε-polylysine-treated samples and polylysine- and CO₂-treated group, respectively, and approximately 1.7 log and 3.5 log reduction in Salmonella cell numbers were observed in only-ε-polylysine-treated samples and polylysine and CO₂-treated group, respectively. This study confirmed that ε-polylysine or ε-polylysine combined with CO₂ packaging are effective in preventing foodborne diseases caused by raw beef.     

Inhibitory effect of Cinnamomum cassia oil on non-O157 Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) have caused numerous foodborne outbreaks. Compared with the most well-known STEC E. coli O157:H7, importance of non-O157 STEC has been underestimated and they have gained far less attention till increasing outbreaks recently. Using natural plant materials as antimicrobial agents is a heated area. Therefore in this study, Cinnamomum cassia, a widely used spice in cuisine, was tested for its antibacterial efficacy on CDC “top six” non-O157 STECs including O26, O45, O103, O111, O121, O145. Gas chromatography-mass spectrometry analysis showed that the major component of C. cassia oil was cinnamaldehyde (59.96%). The disk diffusion assay indicated that 20 μL 4% (v/v) C. cassia oil per disk resulted in inhibition zones of 15.0 mm, 18.5 mm, 15.7 mm, 19.3 mm, 18.8 mm, and 25.3 mm for O26:H11, O45:NM, O103:H2, O111:H2, O121:H19, and O145:NT, respectively. Minimum inhibitory concentration for all tested non-O157 STECs were 0.025% (v/v). Minimum bactericidal concentration was strain dependent, which was 0.05% (v/v) for O26:H11, O121:H19, O145:NT, while 0.1% (v/v) for O45:NM, O103:H2 and O111:H2. Growth kinetics showed that at the low inoculation of approximate 2.5 × 10⁵ CFU/mL, C. cassia oil at the concentration of 0.01875% (v/v) completely inhibited the growth of O26:H11 and O145:NT for at least 24 h, and increased the duration of lag phase of O45:NM, O103:H2, O111:H2, O121:H19 by18, 12, 6, and 16 h, respectively. Including 0.025% (v/v) C. cassia oil completely inhibited the growth of all tested non-O157 STECs for at least 24 h. At high inoculation of 5 × 10⁶ CFU/mL, inhibition effect of C. cassia oil decreased. Death curve showed that including as low as 0.05% (v/v) C. cassia oil could kill non-O157 STECs. 0.1% (v/v) C. cassia oil showed bactericidal effects on all tested non-O157 STECs within 15 min. C. cassia oil at the concentration of 0.15% (v/v) killed all O26:H11, O121:H19 and O145:NT within 30 min, while O45:NM, O103:H2 and O111:H2 at 120, 60, and 60 min, respectively. In conclusion, C. cassia oil can effectively inhibit the growth of non-O157 STECs at concentration as low as 0.025% (v/v). Our data suggest that C. cassia oil has the potential to be used as a natural antibacterial agent in food industry.     

Development of a real-time PCR procedure for quantification of viable Escherichia coli in populations of E. coli exposed to lactic acid,and the acid tolerance of verotoxigenic E. coli (VTEC) from cattle hides

The aims of this study were to develop a real-time PCR procedure for determining the effects on Escherichia coli of treatment for decontaminating beef carcasses with lactic acid solution, and determining if there were differences in the acid tolerance of E. coli generally and verotoxigenic E. coli (VTEC). Suspensions of E. coli were incubated with 4% lactic acid at pH 3.6. The numbers of surviving E. coli at different incubation times were determined from plate counts and from quantification by real-time PCR of the uidA gene in DNA preparations. The numbers of viable E. coli progressively declined, by about 4 log units during incubation for 6 h. The mean cycle threshold (Ct) values for uidA in DNA from samples collected at different times and treated or not treated with propidium monoazide (PMA) before DNA extraction were similar. Treatment with 1% sodium deoxycholate (SD) before PMA treatment resulted in an increase of >6 Ct when the reduction in viable cell number was around 1 log. When E. coli incubated with 4% lactic acid solutions of pH 2.4, 2.8, 3.2 or 3.6 were resuscitated in half strength brain heart infusion (BHI) for 2 h before treatments with SD and PMA, the slope of the plot relating Ct values to the numbers of viable E. coli was 1.85 Ct log cfu⁻¹ with the correlation coefficient (R²) being 0.80. The findings indicate that while the membranes of E. coli inactivated by 4% lactic acid were largely impermeable to PMA, the membranes of both dead and injured cells were rendered permeable to PMA by treatment with 1% SD. Resuscitation in BHI restored the membrane barrier properties of the injured cells. Treatment with lactic acid resulted in increases in Ct values of 4.1, 3.7, 2.5 and 1.5 for the uidA, stx₁, stx₂ and eae genes, respectively; and the increases in Ct values for the latter two genes were significantly different (p < 0.05) from that for the uidA gene. This indicates that VTEC carrying stx₂ and/or eae were more acid resistant than other E. coli. Thus, caution should be exercised when using generic E. coli as an indicator for VTEC for assessment of the antimicrobial efficacy of organic acid decontaminating treatments at abattoirs.     

Development of an immunomagnetic separation method for efficient enrichment of Escherichia coli O157:H7

Immunomagnetic separation uses antibody-coated paramagnetic particles to selectively bind and purify the target organisms from a comprehensive range of complex food matrices. Aim of this study was to develop and optimize an immunomagnetic separation method based on monoclonal antibody for efficient isolation of Escherichia coli O157:H7 in food samples. The key parameters for preparing the immunomagnetic beads; the coupling rate between monoclonal antibody and magnetic beads, additive amount of immunomagnetic beads, and magnetic separation times were optimized with different concentrations of E. coli O157:H7. Under optimized conditions, the capture efficiency (CE) was greater than 98% against 10¹–10⁶ cells of E. coli O157:H7 with 0.05 mg immunomagnetic beads. The immunomagnetic beads exhibited high specific binding with E. coli O157:H7 strains (CE > 98%), and low binding with non-target bacteria (CE < 2%) except for S. aureus (CE = 23.6%). The capture efficiency of immunomagnetic beads against E. coli O157:H7 in ground beef and milk samples were 94.4% and 99.8%, respectively.     

Antimicrobial efficacy of grape seed extract against Escherichia coli O157:H7 growth,motility and Shiga toxin production

Escherichia coli O157:H7 produces Shiga toxin (Stx) which is heat stable and causes Hemolytic Uremic Syndrome (HUS), a serious disease associated with bloody diarrhea and even death. To ensure food safety, both live E. coli O157:H7 and its toxin production in food products need to be controlled. Natural ingredients with inhibitory effects on E. coli O157:H7 growth and toxin production are top choices of antimicrobials for the food industry. The objectives of this study were to evaluate efficacy of grape seed extract (GSE) against the growth, swimming motility and Stx production of E. coli O157:H7. The disc diffusion assay indicated that 3.2 mg GSE per disc resulted in an inhibition zone of 14.8 ± 0.21 mm. The minimal inhibitory concentration of GSE against E. coli O157: H7 was 4.0 mg/ml. At high inoculation level (1 × 10⁷ CFU/ml), including GSE at 0.25–2.0 mg/ml reduced Stx production without inhibiting E. coli O157:H7 growth. At 5 × 10⁵ CFU/ml inoculation level, 2.0 and 4.0 mg/ml GSE effectively inhibited the growth of E. coli O157:H7 for at least 72 h, however, a low level of GSE (0.125–1.0 mg/ml) enhanced E. coli O157:H7 growth and Stx2 production. At 4 mg/ml, GSE completely abolished Stx2 production in addition to it bactericidal effect against E. coli O157:H7. In addition, GSE at concentration as low as 0.125% blocked the swimming motility, which is important for E. coli O157:H7 surface adherence. In conclusion, GSE is effective in inhibiting the motility of E. coli O157:H7, GSE shows potential to be used as a natural antimicrobial to control E. coli O157:H7.     

Prevalence,identification and molecular characterization of Cronobacter sakazakii isolated from retail meat products

Cronobacter sakazakii is an opportunistic foodborne pathogen predominantly in neonates with reported incidences in adults especially immunocompromised and the elderly. The current study was carried out to determine the prevalence of these organisms on meat products sold at Mansoura city, Egypt; besides its ability to compete with E. coli O157:H7 and Salmonella on their media. Suspected colonies were phenotypically-identified using API 20E system, additional biochemical tests, besides production of yellow-pigmented colonies; and genotypically-identified using species-specific PCR assays to detect the gene responsible for α-glucosidase activity, 16S rRNA gene and internal transcriber spacer sequence between 16S and 23S rRNA. Out of the 93 tested isolates, 14 isolates were confirmed as C. sakazakii with contamination rates of 16% (8/50) and 15% (6/40) of ground beef and beef burger samples, respectively and overall contamination rate of 15.6% (14/90) of all tested samples. The isolates were distributed among 7 different biogroups. These results added new epidemiological evidence about the widespread occurrence of these pathogens on tested meat products and such occurrence is an indicator for potential contamination with pathogens and so a health risk for consumers. Furthermore, C. sakazakii is an important competitor to E. coli O157:H7 and Salmonella on their selective media.