Inhibition of Escherichia coli O157:H7 in ripening dry fermented sausage by ground yellow mustard

Compounds generated by the enzymatic hydrolysis of glucosinolates naturally present in mustard powder are potently bactericidal against Escherichia coli O157:H7. Because E. coli O157:H7 can survive the dry fermented sausage manufacturing process, 2, 4, and 6% (wt/wt) nondeheated (hot) mustard powder or 6% (wt/wt) deheated (cold) mustard powder were added to dry sausage batter inoculated with E. coli O157:H7 at about 7 log CFU/g to evaluate the antimicrobial effectiveness of the powders. Reductions in E. coli O157:H7 populations, changes in pH and water activity (aw), effects on starter culture (Pediococcus pentosaceus and Staphylococcus carnosus) populations, and effects of mustard powder on sausage texture (shear) were monitored during ripening. Nondeheated mustard powder at 2, 4, and 6% in dry sausage (0.90 aw) resulted in significant reductions in E. coli O157:H7 (P < 0.05) of 3.4, 4.4, and 6.9 log CFU/g, respectively, within 30 days of drying. During fermentation and drying, mustard powder did not affect P. pentosaceus and S. carnosus activity in any of the treatments. Extension of drying to 36 and 48 days reduced E. coli O157:H7 by >5 log CFU/g in the 4 and 2% mustard powder treatments, respectively. The 6% deheated mustard powder treatment provided the most rapid reductions of E. coli O157:H7 (yielding <0.20 log CFU/g after 24 days) by an unknown mechanism and was the least detrimental (P < 0.05) to sausage texture.     

Survival of Escherichia coli O157:H7 in dry sausage fermented by probiotic lactic acid bacteria

Probiotic Lactobacillus rhamnosus GG, L rhamnosus E‐97800, L rhamnosus LC‐705 and commercial Pediococcus pentosaceus were studied for their ability to inhibit the growth of Escherichia coli O157:H7 in dry sausage. The strains were able to produce technologically high‐quality dry sausage. The number of E coli O157:H7 decreased from approximately 5 to approximately 2 log cfu g⁻¹ It was concluded that the above‐mentioned strains and the commercial culture were equally effective in inhibiting E coli O157:H7. © 2000 Society of Chemical Industry     

Predicting survival of Escherichia coli O157:H7 in dry fermented sausage using artificial neural networks

The Canadian Food Inspection Agency required the meat industry to ensure Escherichia coli O157:H7 does not survive (experiences > or = 5 log CFU/g reduction) in dry fermented sausage (salami) during processing after a series of foodborne illness outbreaks resulting from this pathogenic bacterium occurred. The industry is in need of an effective technique like predictive modeling for estimating bacterial viability, because traditional microbiological enumeration is a time-consuming and laborious method. The accuracy and speed of artificial neural networks (ANNs) for this purpose is an attractive alternative (developed from predictive microbiology), especially for on-line processing in industry. Data from a study of interactive effects of different levels of pH, water activity, and the concentrations of allyl isothiocyanate at various times during sausage manufacture in reducing numbers of E. coli O157:H7 were collected. Data were used to develop predictive models using a general regression neural network (GRNN), a form of ANN, and a statistical linear polynomial regression technique. Both models were compared for their predictive error, using various statistical indices. GRNN predictions for training and test data sets had less serious errors when compared with the statistical model predictions. GRNN models were better and slightly better for training and test sets, respectively, than was the statistical model. Also, GRNN accurately predicted the level of allyl isothiocyanate required, ensuring a 5-log reduction, when an appropriate production set was created by interpolation. Because they are simple to generate, fast, and accurate, ANN models may be of value for industrial use in dry fermented sausage manufacture to reduce the hazard associated with E. coli O157:H7 in fresh beef and permit production of consistently safe products from this raw material.     

Process control and sampling for Escherichia coli O157:H7 in beef trimmings

Raw beef producers currently face the problem of Escherichia coli O157:H7 surface contamination of beef carcasses that can lead to product adulteration. Although carcass interventions are in place, elimination of E. coli O157:H7 from every potential hiding place on the surfaces of a beef carcass is not technologically feasible. Therefore, E. coli O157:H7 on beef carcasses might further contaminate the surfaces of beef trimmings. With the use of case scenarios from nine commercial processing facilities, we present a process control and statistical sampling approach for monitoring beef trimmings to divert contaminated lots of the trimmings from the raw ground beef supply chain.     

Survival ofEscherichia coliO157:H7,Listeria monocytogenesandSalmonella kentuckyin Norwegian fermented,dry sausage

Raw, newly produced sausages containing a mixed starter culture of lactobacilli and micrococci were each inoculated at separate locations (using a syringe) with low (10³–10⁴cfu) and high (10⁵–10⁷cfu) numbers of eitherEscherichia coliO157:H7, Listeria monocytogenes orSalmonella kentucky. Three identically prepared sausages were analysed at each sampling day during fermentation, maturation and storage at 4 and 20°C. In the low-inoculum samples, growth was observed initially (2 days) during fermentation forE. coliO157:H7 (3log₈increase in cfu) andL. monocytogenes(five-fold increase in cfu) but not forS. kentuckywhich decreased below the detection limit (150cfu sample^–1). None of the pathogens was detected after 5.5 months, neither at 4 nor 20°C. In the high-inoculum samples there was a decrease during fermentation and maturation for all the pathogens. After 5.5-months storage at 4°C, there was only about 90% reduction of the original inoculate ofL. monocytogenes, whereasE. coliO157:H7 survived at a low number (500cfu sample^–1) andS. kentuckydisappeared below the detection limit. After 5.5-months storage at 20°C, all the pathogens had disappeared below the detection limit. These results indicate that, from a safety point of view, it may be better to store these kinds of sausages at room temperature than in the cold, provided that the sensory qualities are retained and that similar results are obtained with other food pathogens.     

Elimination of Escherichia coli O 157 : H7 and Listeria monocytogenes from raw beef sausage by gamma-irradiation

The effectiveness of low gamma-irradiation doses in the destruction of Escherichia coli O 157 : H7 and Listeria monocytogenes in raw beef sausages was investigated. Raw samples of fresh manufactured beef sausage were subjected to gamma-irradiation at doses of 0, 1, 2, and 3 kGy. Then samples were cold-stored (4 +/- 1 degrees C) for 12 days and the effects of irradiation and storage on the counts of these harmful bacteria were studied. Moreover, the effects of irradiation and storage on the percentages of free fatty acids (FFAs) in lipids, on the p-anisidine values of lipids, solubility of sarcoplasmic and myofibrilar proteins, and water-holding capacity (WHC) were also determined. The results showed that gamma-irradiation at 1 and 2 kGy significantly reduced the counts of E. coli O 157 : H7 and L. monocytogenes, while 3 kGy dose effectively eliminated these bacteria by more than 4 log and 3 log units, respectively, and could keep their counts below the detection level during storage. Gamma-irradiation had no significant effects on the percentages of FFAs in lipids, solubility of sarcoplasmic and myofibrilar proteins, and WHC of samples, while it significantly increased the p-anisidine value of lipids. During storage, significant increases in the percentages of FFAs and p-anisidine values were observed for lipids of irradiated and nonirradiated sausages, while the solubility of sarcoplasmic and myofibrilar proteins showed no significant changes. Moreover, samples of irradiated and nonirradiated sausages showed significant decreases in their WHC during the first 6 days of storage at 4 +/- 1 degrees C, then showed no significant changes. Finally, gamma-irradiation at a dose of 3 kGy appeared to be sufficient to improve the microbiological safety of raw beef sausages without adverse effects on their chemical properties.     

Modeling the survival of Escherichia coli O157:H7 in uncooked, semidry, fermented sausage

The data collected from studies to monitor inactivation of Escherichia coli O157:H7 in uncooked fermented salami were used to develop models to describe survival of the organism. Three models were developed that included different variables to best describe E. coli O157:H7 reduction. Model A included the variables water activity (a(w)), pH, time, and quadratic variables pH and time. Model B separated the processing stages into fermentation and drying. The fermentation included the variables pH and temperature x time (ttarea) and interaction between the two variables. The drying stage was modeled using the variables time and a(w) and interaction between the two. Model C looked at variables a(w) and the time at pH 5.3 to achieve a 2-D log reduction of E. coli O157:H7 and the interaction between the variables. The variables selected for inclusion in all the models were significant at the P < 0.0001 level. The predicted values for all models correlated well to the observed values with R2 of 0.888, 0.828, 0.836, and 0.818 for models A. Bferm, Bdrying, and C, respectively. The models were validated using data from a trial not used to develop the model. In general the predicted reduction in E. coli O157:H7 count in uncooked fermented salami was greater than for the observed E. coli O157:H7 log reductions for all models, but the relation between the two was linear. The results demonstrate that modeling can be a useful tool in assessing manufacturing practices for uncooked fermented salami processes.     

Multiplex PCR for simultaneous detection of Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7 in meat samples

A multiplex PCR method was developed for simultaneous detection of Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7 in meat samples. DNA detection sensitivity for this method was 10(3) CFU/ml for each pathogen. When this protocol was used for the detection of each of the above pathogenic bacteria in spiked pork samples, 1 cell per 25 g of inoculated sample could be detected within 30 h. In the samples of naturally contaminated meat, Salmonella spp., L. monocytogenes, and E. coli O157:H7 were detected over the same time period. Excellent agreement was obtained for the results of multiplex PCR and the conventional culture method, which suggests that the multiplex PCR is a reliable and useful method for rapid screening of meat products for Salmonella spp., L. monocytogenes, and E. coli O157:H7 contamination.     

A note on the incidences of Salmonella spp., Listeria spp. and Escherichia coli O157:H7 serotypes in Turkish sausage (Soudjouck)

The incidence of Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 was determined in 100 Turkish sausage (soudjouck) samples collected from shops and markets in the Afyon province, Turkey. Salmonella spp. were detected in 7% of the samples. All of the isolates were S. enterica Paratyphi B. In addition, Listeria spp. were detected in 9% of the samples. Its distribution was 7% L. monocytogenes and 1% each of L. ivanovii and L. innocua. Serological study of the seven L. monocytogenes isolates showed that three of these were 1/2 ab, three were 5/6 ab and one was 1 ab. E. coli O157:H7 was not detected in any of the samples. The pH values of the samples ranged from 4.8 to 6.5. In conclusion, increasing number of listeriosis and salmonellosis cases in Turkey and the contamination levels found indicate that risk assessment and improved preventive measures are required for these sausages.     

Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries

For maximum shelf life, fresh strawberries are harvested directly without washing into retail containers. Frozen berries are usually hulled in the field and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surfaces of fresh strawberries were spot inoculated with five- or six-strain cocktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in closed containers at 5 or 24 degrees C. Sliced strawberries with or without added 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degrees C. An initial population reduction of approximately 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degrees C for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degrees C for up to 7 days, populations of both pathogens remained constant on cut surfaces but decreased by 1 - to 2-log cycles on intact surfaces. After 30 days of frozen storage, the population of E. coli O157:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, respectively). Results of this study indicate that E. coli O157:H7 and Salmonella are capable of survival but not growth on the surface of fresh strawberries throughout the expected shelf life of the fruit and can survive in frozen strawberries for periods of greater than 1 month.     

Survival and detection of Escherichia coli O157:H7 and Listeria monocytogenes during the manufacture of dry sausage using two different starter cultures

A sausage batter (35% pork, 35% beef, 30% fat) was inoculated with high (5·46–5·68), medium (3·78–4·54) or low (2·30–2·60 log₁₀cfug⁻¹) levels of Escherichia coli O157:H7 and with high (5·05–5·41) or medium (2·92–3·35 log₁₀cfug⁻¹) levels of Listeria monocytogenes serovar 4b and fermented using starter cultures A (Staphylococcus xylosus DD-34 with bacteriocin-producingPediococcusacidilactici PA-2 and Lactobacillus bavaricus MI-401) and B(S. carnosus MIII withLb. curvatus Lb3). Sausages were manufactured (fermented and dried) in a smoke chamber at 17–23°C for 15 days and further stored at 15–17°C for 34 days. The numbers of E. coli O157:H7 decreased more using starter B than starter A (first experiment P<0·0015, second experiment P<0·0002) but the organism was not eliminated. Small numbers of E. coli O157:H7 were more often detected after enrichment for 18–24 h than for 6 h (P=0·0044) when tested after deep freezing. By contrast, L. monocytogenes decreased more rapidly in the high-inoculum sausages produced with starter A (P<0·0001) but no significant difference was detected between the starters in the medium-inoculum sausages. L. monocytogenes was eliminated from the medium-inoculum sausages after 49 days.     

Viability of Escherichia coli O157:H7 during manufacturing and storage of a fermented,semidry soudjouk-style sausage

Soudjouk-style batter was inoculated with a five-strain mixture of Escherichia coli O157:H7 at about 7.6 log10 CFU/g in each of two trials. The sticks were fermented and dried at 22 degrees C and 50% relative humidity (RH) for 3 days and then at 9 degrees C and 40% RH for 18 h. After being flattened to about 1.25 cm, the sticks were conditioned at 38 degrees C and 70% RH or at 22 degrees C and 50% RH for about 3 days. After the latter conditioning treatment, sticks either were cooked to an internal temperature of 63 degrees C or received no heat treatment. Final mean pH values after conditioning at 22 degrees C and 50% RH for soudjouk manufactured with a starter culture and dextrose (1.0%) and for soudjouk manufactured without a starter culture were about 4.9 and 6.0, respectively. For soudjouk produced with a starter culture, pathogen numbers were reduced by 4.53 and 0.88 log10 CFU/g after conditioning at 38 degrees C and 70% RH and at 22 degrees C and 50% RH, respectively. For soudjouk produced via natural fermentation, pathogen numbers were reduced by 1.39 and 0.09 log10 CFU/g after conditioning at 38 degrees C and 70% RH and at 22 degrees C and 50% RH, respectively. Cooking reduced pathogen numbers to below the levels detectable by direct plating (<1.0 log10 CFU/g) and by enrichment for soudjouk produced with a starter culture and also reduced pathogen numbers by 6.28 log10 CFU/g for soudjouk produced via natural fermentation. However, cooking also resulted in an unacceptable product. In general, the reduction in pathogen numbers achieved by storage at ambient temperature (25 degrees C) was greater than that achieved by storage at cooler temperatures (4 and 15 degrees C), particularly for soudjouk prepared with a starter culture (for which a final pH value of 4.8 and a 6.4-log10 reduction were obtained after 21 days at 25 degrees C) rather than for that prepared without a starter culture (for which a final pH value of 6.1 and a 2.6-log10 reduction were obtained after 21 days at 25 degrees C). These results indicate that naturally fermented old-country-type sausage may allow the survival of E. coli O157:H7 in the absence of controlled fermentation, postfermentation cooking, and/or an ambient-storage processing step.     

Effects on Escherichia coli O157:H7 and meat starter cultures of bovine lactoferrin in broth and microencapsulated lactoferrin in dry sausage batters

The effects of lactoferrin (LF) alone or with various chelating agents on the growth of 5 strains of Escherichia coli O157:H7 and 7 meat starter cultures were evaluated. E.coli O157:H7 and starter cultures were grown at 13 or 26 degrees C in Lauria (LB) or All Purpose Tween (APT) broths, respectively, with both broths being supplemented with 2.9% NaCl. LF alone prevented the growth of E. coli O157:H7 strains 0627 and 0628 but other strains grew. The antimicrobial effectiveness of LF was enhanced by EDTA but LF alone did not affect the growth of meat starter cultures in broth. However, when LF plus EDTA and sodium bicarbonate (SB) were used the growth of all meat starter cultures except Lactobacillus curvatus was reduced. During dry sausage manufacture with L. curvatus and Staphylococcus carnosus starter cultures the effects of LF, unencapsulated or microencapsulated in paste-like and dried powder forms, in sausage batters with or without EDTA and SB, on the viability of E. coli O157:H7 were examined. The reduction of E. coli O157:H7 during sausage manufacture was significantly enhanced (p<0.05) by all LF treatments. The largest reduction (4.2 log units) was obtained with unencapsulated LF. However, some of the apparent reduction in E.coli O157:H7 numbers with all treatments was due to cell injury rather than lethality, since significantly greater numbers were recovered on APT agar overlaid with the selective medium cefixime-tellurite Sorbitol McConkey agar (ct-SMAC) than on ct-SMAC alone. The narrow spectrum of LF activity and induction of injury rather than inactivation of E. coli O157:H7 limit the effectiveness of this agent against the pathogen in fermented meats.     

Use of deodorized yellow mustard powder to control Escherichia coli O157:H7 in dry cured Westphalian ham

Dry cured (uncooked) hams with low water activity and pH ≥5.6 seem a likely food vehicle for Escherichia coli O157:H7. In previous work, isothiocyanates produced from mustard glucosinolates by bacterial myrosinase-like activity converted deodorized mustard into a potent antimicrobial in dry sausage. In this study its value in controlling E. coli O157:H7 survival in Westphalian ham was investigated. Hams were inoculated with a 7.5 log cfu g(-1) cocktail of E. coli O157:H7, 4% or 6% (w/w) deodorized yellow mustard powder was surface applied and monitored 80 d for pathogen survival. In one trial to accelerate formation of isothiocyanate, a Staphylococcus (S.) carnosus meat starter culture was added to hams at 45 d (after salt equilibration). At 21 d, E. coli O157:H7 was reduced by 3 log cfu g(-1) on hams treated with mustard powder compared to only a 1 log cfu g(-1) reduction in the control. By 45 d, mustard powder caused a reduction of >5 log cfu g(-1)E. coli O157:H7, whereas it took 80 d for numbers in control hams to be similarly reduced. Although the commercial process used caused a 5 log cfu g(-1) reduction of E. coli O157:H7 in 80 d, 4% or 6% deodorized mustard accelerated this reduction and the S. carnosus starter culture may have contributed to the maintenance of this effect.     

Survival of Escherichia coli O157:H7 in dry fermented sausages containing micro-encapsulated probiotic lactic acid bacteria

Escherichia coli O157:H7 is capable of surviving the rigorous processing steps during the manufacture of dry fermented sausages. The effect of adding two probiotic organisms, Lactobacillus reuteri and Bifidobacterium longum as co-cultures with the meat starter cultures Pediococcus pentosaceus and Staphylococcus carnosus on the viability of E. coli O157:H7 in dry fermented sausages was studied. A 5 strain cocktail of E. coli O157:H7 was added at 7.4 log cfu/g to the sausage batter and challenged with either or both Lb. reuteri or B. longum before or after they were micro-encapsulated. Sausages were fermented at < or = 26 degrees C and 88% relative humidity (RH) followed by drying at 75% RH and 13 degrees C for 25 d. The pH, water activity (aw), protein, moisture, and numbers of all inoculated organisms were monitored during processing. The pH and aw decreased from 5.7 and 0.98 to 4.9 and 0.88 at the end of fermentation and drying, respectively. These processes reduced E. coli O157:H7 by 1.0 and 0.7 log cfu/g at the end of fermentation and drying, respectively. Unencapsulated Lb. reuteri with or without B. longum reduced E. coli O157:H7 by 3.0 log cfu/g and B. longum caused a 1.9 log cfu/g reduction. While micro-encapsulation increased survival of Lb. reuteri and B. longum, it reduced their inhibitory action against E. coli O157:H7.     

Survival of Listeria monocytogenes and Escherichia coli O157:H7 during sauerkraut fermentation

Sauerkraut was produced from shredded cabbage, as is typical in the United States, and from whole head cabbages, which is a traditional process in parts of Eastern Europe. The sauerkraut was inoculated with five strain mixtures of Escherichia coli O157:H7 and Listeria monocytogenes, and the populations of these bacteria, as well as lactic acid bacteria, pH, and titratable acidity, were monitored over the course of fermentation. Fermentation variables were temperature (18 and 22 degrees C) and salt concentration (1.8, 2.25, and 3%). For most of the analyses, the type of cabbage processing was a significant factor, although within cabbage type, neither salt nor fermentation temperature had significant effects. The final pH of the whole-head sauerkraut was lower than the shredded sauerkraut, but the titratable acidity was significantly higher in the shredded sauerkraut. E. coli O157:H7 and L. monocytogenes persisted in the brines for most of the fermentation, although at the end of the fermentations (15 days for shredded, 28 days for whole head), neither pathogen had detectable populations. E. coli populations decreased more rapidly in the shredded sauerkraut even though the pH was higher because of the higher total acidity in the shredded sauerkraut. Acid-tolerant strains of E. coli and L. monocytogenes were isolated from both shredded and whole-head sauerkraut at different salt concentrations and temperatures after 15 days of fermentation and could be detected at 35 days in the wholehead sauerkraut.     

Metabiotic effects of Fusarium spp. on Escherichia coli O157:H7 and Listeria monocytogenes on raw portioned tomatoes

The metabiotic effects of Fusarium proliferatum, F. avenaceum, and F. oxysporum on Escherichia coli O157:H7 and Listeria monocytogenes in fresh tomatoes were investigated. Tomatoes were preinoculated with the molds and incubated at 15 degrees C for 7 days; then they were inoculated separately with the pathogens, packaged in air and modified atmosphere (5% O2, 30% CO2, and 65% N2), and stored at 4, 8, and 12 degrees C for 9 days. The cell loads of pathogens and lactic acid bacteria and the pH were evaluated periodically. The data were modeled through some different mathematical models to assess the shoulder length, i.e., the time before the beginning of the exponential death phase, the 1-log reduction time (s), and the pathogen death time (deltastand). The preinoculation of tomatoes with the molds enhanced the survival of E. coli O157:H7 by prolonging shoulder length and 8 parameters; this effect, however, was not observed for L. monocytogenes. pH values did not undergo significant changes within the storage time, and the lactic acid bacteria increased from 5 to 7 log CFU/g, without significant differences among the storage temperatures or the packaging atmospheres. The results of this research showed that the use of fresh tomatoes colonized by fusaria (even if the contamination is not visible) could increase significantly the risk of outbreaks due to some pathogens that could be on the surface of fruits and vegetables as a result of cross-contamination at home or incorrect postharvest operations.     

Reduction of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 During Processing of Country-cured Hams

ABSTRACT: The country-cured ham process, including curing, equalization, cold-smoked or nonsmoked, and aging up to 6 mo, was validated and showed its effectiveness in achieving a 6-log reduction of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7. The viable counts of L. monocytogenes populations decreased to below detection levels after 206 d, Salmonella populations required 122 d, and E. coli O157:H7 required 66 d. However, L. monocytogenes -inoculated hams were positive and Salmonella spp-inoculated and E. coli O157:H7-inoculated hams were negative following enrichment procedures at the end of the aging process. Therefore, the survival of L. monocytogenes on country-cured ham represents a risk.     

Impact of pH enhancement on populations of Salmonella,Listeria monocytogenes,and Escherichia coli O157:H7 in boneless lean beef trimmings

Boneless lean beef trimmings were inoculated with multiple strains of salmonellae, Listeria monocytogenes, and Escherichia coli O157:H7 at levels of ca. 6 log10 CFU/g. pH enhancement with ammonia gas was then used to increase the pH of the trimmings to ca. 9.6. The product was then frozen, chipped, and compressed into blocks. pH enhancement reduced the populations of salmonellae, L. monocytogenes, and E. coli O157:H7 by approximately 4, 3, and 1 log10 cycles, respectively. After the product had been frozen and compressed into blocks, no salmonellae or E. coli O157:H7 were detectable by enumeration or after enrichment and isolation. The final populations of L. monocytogenes were reduced by ca. 3 log10 cycles relative to the initial populations. When uninoculated pH-enhanced lean boneless trimmings were blended with inoculated ground beef to a final concentration of 15% (wt/wt), pathogen populations in the ground beef were reduced by approximately 0.2 log10 cycles.     

A note on Escherichia coli O157:H7 serotype in Turkish meat products

255 minced beef, 101 soudjouk and 50 uncooked hamburger samples were analyzed for the presence of Escherichia coli O157:H7 serotype. m-EC and LST broths were used as selective enrichment media and SMAC agar was used as a selective isolation medium. A total of 3 E. coli O157 were isolated by conventional culture techniques; one from each of minced beef, uncooked hamburger and soudjouk but none were identified as the H7 serotype. For determination of selective media-growing cohabitant bacteria, 2645 isolates were obtained from SMAC agar. Results showed that E. coli type 1, Hafnia alvei and Citrobacter freundii were dominant competitive flora. As selective enrichment broth-growing cohabitant microflora existed at higher levels, it was too difficult to isolate E. coli O157 from these mixed flora. Therefore, conventional methods are not suitable for these types of products, because of isolation difficulties and failure to confirm.