Selective Enumeration Research Articles

Investigation of Medium Chain Fatty Acid Feed Supplementation for Reducing Salmonella Typhimurium Colonization in Turkey Poults.

Studies indicate that persistent Salmonella colonization occurs in poultry that are infected early in life, leading to both food safety and public health concerns. Development of improved preharvest Salmonella management strategies is needed to reduce poultry product contamination. The objective of this study was to evaluate the efficacy of a product containing medium chain fatty acids (MCFA) for reducing early Salmonella colonization in turkey poults. Day-of-hatch turkeys were provided a standard starter diet supplemented with MCFA at 0 (negative and positive controls), 1.5, 3, 4.5, or 6 lbs/ton of feed. Positive control and MCFA treated birds were also crop-gavaged with 108 colony forming units (CFU) of bioluminescent Salmonella Typhimurium. Gastrointestinal tissue samples were collected at 3 days postinoculation for bioluminescence imaging (Meckel's diverticulum to the cloaca) and selective enumeration (cecal contents). Quantification of bioluminescence indicated that the 4.5 and 6 lbs/ton MCFA groups had significantly less colonization than the positive control group (p = 0.0412 and p < 0.0001, respectively). Similarly, significantly lower numbers (1-log10 CFU/g reduction) of Salmonella were observed in the ceca of the 6 lbs/ton MCFA group compared to the positive control group (p = 0.0153). These findings indicate that incorporation of MCFA in turkey diets can significantly reduce early Salmonella colonization. In addition, this study highlights the utility of bioluminescence imaging as a screening methodology for assessing the efficacy of treatments that may reduce Salmonella in poultry.

Expanded Selective Bacterial Enumeration with the TEMPO Most Probable Number Technique for AATCC Test Method 100

Enumeration of bacteria is a large component in standard testing of antimicrobial textiles; however, there are multiple plating methods used that are tedious and labor intensive to perform. TEMPO is an instrument that automates much of the enumeration process using the most probable number (MPN) technique. Selective reagents for Staphylococcus aureus (salt) and Pseudomonas aeruginosa (cetrimide) were used to expand TEMPO capability. It was demonstrated that TEMPO had either the same or smaller variance than the traditional spread plating for cells in solution and on textiles tested using AATCC Test Method (TM) 100. TEMPO is a faster and more cost-effective method, and with expanded selective capabilities, can be used to improve enumeration efficiency.

Bounded Selective Spanning With Extended Fast Enumeration for MIMO-OFDM Systems Detection

Sphere decoders allow receivers in multiple-input multiple-output (MIMO) communications systems to detect QAM symbols with quasi-optimal accuracy and low complexity compared with the ideal maximum likelihood detector. However, their high complexity relative to simple linear detectors means that the latter are still usually adopted, despite their lower detection performance. Configurable sphere decoders, such as selective spanning fast enumeration (SSFE), allow complexity to be reduced at the cost of lower performance and are hence ideal for transceivers for Internet-of-Things equipment, where scale, operating context and resource, and energy budgets vary dramatically. However, SSFE still suffers performance limitations due to the internal heuristics employed for symbol selection and enumeration and real time, and software-defined realizations for even moderately demanding MIMO standards, such as 802.11n, have not been recorded. This paper presents a new variant of SSFE which, by employing novel fast symbol enumeration and modulation dictionary spanning heuristics, increases performance and computational efficiency to the point where very substantial reductions in resource can be achieved without impacting detection accuracy relative to SSFE. This is demonstrated via a series of field programmable gate array-based detectors $2 \times 2$ and $4 \times 4$ , 16-QAM 802.11n MIMO.

Incubation of premise plumbing water samples on Buffered Charcoal Yeast Extract agar at elevated temperature and pH selects for Legionella pneumophila

Worldwide, over 90% of the notified cases of Legionnaires' disease are caused by Legionella pneumophila. However, the standard culture medium for the detection of Legionella in environmental water samples, Buffered Charcoal Yeast Extract (BCYE) agar of pH 6.9 ± 0.4 with or without antimicrobial agents incubated at 36 ± 1 °C, supports the growth of a large diversity of Legionella species. BCYE agar of elevated pH or/and incubation at elevated temperature gave strongly reduced recoveries of most of 26 L. non-pneumophila spp. tested, but not of L. pneumophila. BCYE agar of pH 7.3 ± 0.1, incubated at 40 ± 0.5 °C (BCYE pH 7.3/40 °C) was tested for selective enumeration of L. pneumophila. Of the L. non-pneumophila spp. tested, only L. adelaidensis and L. londiniensis multiplied under these conditions. The colony counts on BCYE pH 7.3/40 °C of a L. pneumophila serogroup 1 strain cultured in tap water did not differ significantly from those on BCYE pH 6.9/36 °C when directly plated and after membrane filtration and showed repeatability's of 13–14%. By using membrane filtration L. pneumophila was detected in 58 (54%) of 107 Legionella-positive water samples from premise plumbing systems under one or both of these culture conditions. The L. pneumophila colony counts (log-transformed) on BCYE pH 7.3/40 °C were strongly related (r2 = 0.87) to those on BCYE pH 6.9/36 °C, but differed significantly (p < 0.05) by a mean of – 0.12 ± 0.30 logs. L. non-pneumophila spp. were detected only on BCYE pH 6.9/36 °C in 49 (46%) of the samples. Hence, BCYE pH 7.3/40 °C can facilitate the enumeration of L. pneumophila and their isolation from premise plumbing systems with culturable L. non-pneumophila spp., some of which, e.g. L. anisa, can be present in high numbers.

In Vitro Activity of Lactobacillus fermentum LF5 Against Different Candida Species and Gardnerella vaginalis

This study was undertaken to demonstrate the ability of Lactobacillus fermentum LF5 (DSM 32277) to inhibit in vitro different Candida species and Gardnerella vaginalis to weigh its potential effectiveness even in mixed vaginal infections. A wide female population is suffering from various vulvovaginal infections. These diseases are often associated with a decrease in the concentration of Lactobacilli in the vagina. Mixed vaginal infections represent >20% of women with vulvovaginal infection. LF5 strain was cocultured in De Man, Rogosa and Sharpe with Candida according to a 1:100 ratio in favor of the yeast. Each culture was sampled after 24 hours of incubation for the selective enumeration of the yeasts performed on yeast extract glucose chloramphenicol agar medium.The growth of Gardnerella alone (positive control) and in the presence of different concentrations of neutralized supernatants of L. fermentum LF5 ranging from 5% to 20% was quantified by means of optical density at 600 nm (OD600). L. fermentum LF5 demonstrated the ability to inhibit significantly the growth of the 5 species of Candida by at least 4 logarithms.Furthermore, L. fermentum LF5 showed a significant activity after both 24 and 48 hours (46% and 82% with 20% of neutralized supernatant, respectively). A significant dose-dependent growth inhibition was recorded in particular after 48 hours of incubation, even achieving a 80% inhibition of G. vaginalis growth. The biotherapeutic LF5 could be the only documented strain effective in mixed forms. For this purpose, a human clinical trial is in progress.

Growth differences and competition between Listeria monocytogenes strains determine their predominance on ham slices and lead to bias during selective enrichment with the ISO protocol

Listeria monocytogenes strains are widespread in the environment where they live well mixed, often resulting in multiple strains contaminating a single food sample. The occurrence of different strains in the same food might trigger strain competition, contributing to uneven growth of strains in food and to bias during selective procedures.We tested the growth of seven L. monocytogenes strains (C5, 6179, ScottA, PL24, PL25, PL26, PL27) on ham slices and on nutrient-rich agar at 10°C, singly and in combinations. Strains were made resistant to different antibiotics for their selective enumeration. In addition, growth of single strains (axenic culture) and competition between strains in xenic cultures of two strains was evaluated in enrichment broth and on selective agar. According to ISO 11290-1:1996/Amd 1:2004 standard protocol for detection of L. monocytogenes, two enrichment steps both followed by streaking on ALOA were performed. Strain cultures were directly added in the enrichment broth or used to inoculate minced beef and sliced hams which were then mixed with enrichment broth. 180–360 colonies were used to determine the relative percentage of each strain recovered on plates per enrichment step.The data showed a significant impact of co-cultivation on the growth of six out of seven strains on ham and a bias towards certain strains during selective enrichment. Competition was manifested by: (i) cessation of growth for the outcompeted strain when the dominant strain reached stationary phase, (ii) reduction of growth rates or (iii) total suppression of growth (both on ham and in enrichment broth or ALOA). Outgrowth of strains by their competitors on ALOA resulted in limited to no recovery, with the outcompeting strain accounting for up to 100% of the total recovered colonies. The observed bias was associated with the enrichment conditions (i.e. food type added to the enrichment broth) and the strain-combination. The outcome of growth competition on food or nonselective agar surface did not necessarily coincide with the results of competition during enrichment. The results show that certain strains present in foods may be missed during classical detection due to strain competition and such likelihood should be taken into consideration when resolving a listeriosis outbreak.

Effect of &lt;em&gt;Asparagus falcatus&lt;/em&gt; and &lt;em&gt;Taraxacum javanicum&lt;/em&gt; Inulins on growth of &lt;em&gt;L. acidophilus&lt;/em&gt; La-5 and &lt;em&gt;B. animalis&lt;/em&gt; subsp lactis Bb-12, co-cultured in skim milk

A study was conducted to evaluate the effect of inulin from Asparagus falcatus and Taraxacum javanicum on growth of Lactobacillus acidophilus (La-5) and Bifidobacterium animalis (Bb-12) in skim milk. Commercially available chicory inulin and chicory fructooligosaccharides (FOS) were used as positive controls. Skim milk (13% (w/v)) samples supplemented with different concentrations (0.5, 1, 2, 3 and 5%) of AF or TJ inulin, 5% Chicory inulin and 5% FOS, inoculated with mix culture of La-5 and Bb-12 (1:1), were incubated at 37 oC for 24 hours. The skim milk samples prepared the same way, but without adding inulin were used as negative controls. Optical density and pH of the milk samples were checked during 0, 6, 12 and 24 hours of incubation. Selective enumeration of La-5 and Bb-12, at 6 hours of incubation, was done using MRS-sorbitol agar and Beerens agar, respectively. The AF and TJ inulin showed enhanced bifidobacterial growth in skim milk, similar to chicory inulin. The growth promotion effect of AF and TJ inulin on bifidobacteria was maximal at 3% inulin concentration. None of the inulin types or FOS significantly influenced the La-5 growth in skim milk. The pH values of fermented milk samples were significantly (P<0.05) lower in inulin or FOS supplemented skim milks compared with the control. AF and TJ inulin showed clear bifidogenic properties in skim milk, indicating their potential use as alternative inulin sources for the Food Industry.

Quantification of Slackia and Eggerthella spp. in Human Feces and Adhesion of Representatives Strains to Caco-2 Cells.

Eggerthella and Slackia spp. are gut associated bacteria that have been suggested to play roles in host lipid and xenobiotic metabolism. A quantitative PCR method for the selective enumeration of bacteria belonging to either the genus Eggerthella or Slackia was developed in order to establish the numbers of these bacteria occurring in human feces. The primers developed for selective amplification of these genera were tested first in conventional PCR to test for their specificity. Representative species of Eggerthella and Slackia, as well as closely related genera of the Coriobacteriia, were included in the investigation. The selected primers were shown to be capable of specific amplification of species of the genera Eggerthella and Slackia, but not all species of the genera may be amplified by the respective primers. Their use in qPCR experiments to assess the levels of Slackia equolifaciens and Eggerthella lenta in the feces of 19 human volunteers showed they occurred at mean counts of 7 × 105 and 3.1 × 105 CFU/g for Eggerthella spp. and Slackia spp., respectively. Electron microscopy investigations showed that while E. lenta cells exhibited slender and very regular shaped rods, Slackia cells showed a remarkably pleomorphic phenotype. Both species did not appear to have fimbriae or pili. Some S. equolifaciens cells showed a characteristic “ribbon” of presumably extracellular material around the cells, particularly at the areas of cell division. The two species also differed markedly in their adhesion behavior to Caco-2 cells in cell culture, as E. lenta DSMZ 15644 showed a high adhesion capacity of 74.2% adherence of the bacterial cells added to Caco-2 cells, while S. equolifaciens DSM 24851T on the other hand showed only low adhesion capability, as 6.1% of bacterial cells remained bound. Speculatively, this may imply that the ecological compartments where these bacteria reside in the gut may be different, i.e., E. lenta may be associated more with the gut wall, while Slackia may be free living in the lumen.

Novel method based on chromogenic media for discrimination and selective enumeration of lactic acid bacteria in fermented milk products

Microbial analyses of fermented milk products require selective methods to discriminate between close species simultaneously present in high amounts. A culture-based method combining novel chromogenic agar media and appropriate incubation conditions was developed to enumerate lactic acid bacteria (LAB) strains in fermented milk. M1 agar, containing two chromogenic substrates, allowed selective enumeration of Lactobacillus rhamnosus, two strains of Lactobacillus paracasei subsp. paracasei and Streptococcus salivarius subsp. thermophilus based on differential β-galactosidase and β-glucosidase activities. Depending on the presence of some or all of the above strains, M1 agar was supplemented with l-rhamnose or vancomycin and incubations were carried out at 37 °C or 44 °C to increase selectivity. A second agar medium, M2, containing one chromogenic substrates was used to selectively enumerate β-galactosidase producing Lactobacillus delbrueckii subsp. bulgaricus at 47 °C. By contrast with the usual culture media, the chromogenic method allowed unambiguous enumeration of each species, including discrimination between the two L. paracasei, up to 109 CFU/g of fermented milk. In addition, the relevance of the method was approved by enumerating reference ATCC strains in pure cultures and fermented milk product. The method could also be used for enumerations on non-Danone commercial fermented milk products containing strains different from those used in this study, showing versatility of the method. To our knowledge, this is the first description of a chromogenic culture method applied to selective enumeration of LAB.

Test-Cost Modeling and Optimal Test-Flow Selection of 3-D-Stacked ICs

Three-dimensional (3-D) integration is an attractive technology platform for next-generation ICs. Despite the benefits offered by 3-D integration, test cost remains a major concern, and analysis and tools are needed to understand test flows and minimize test cost. We propose a generic cost model to account for various test costs involved in 3-D integration and present a formal representation of the solution space to minimize the overall cost. We present an algorithm based on A*—a best-first search technique—to obtain an optimal solution. An approximation algorithm with provable bounds on optimality is proposed to further reduce the search space. In contrast to prior work, which is based on explicit enumeration of test flows, we adopt a formal optimization approach, which allows us to select an effective test flow by systematically exploring an exponentially large number of candidate test flows. Experimental results highlight the effectiveness of the proposed method. Adopting a formal approach to solving the cost-minimization problem provides useful insights that cannot be derived via selective enumeration of a smaller number of candidate test flows.

Effectiveness of different methodologies for the selective enumeration of Lactobacillus acidophilus La5 from yoghurt and Prato cheese

Prior to the selective enumeration of probiotic microorganisms in fermented dairy products, a preliminary evaluation of different culture media and incubation conditions is required to choose a suitable culture medium. The objective of this study was to evaluate the effectiveness of different methodologies for the selective enumeration of Lactobacillus acidophilus in probiotic yoghurt and Prato cheese. For selective enumeration of L. acidophilus, four methods were investigated under anaerobic conditions, as follows: MRS agar containing bile solution; MRS agar containing clindamycin solution; and MRS agar containing sorbitol solution, each one incubated at 37 °C for 72 h, and MRS agar containing sorbitol incubated at 45 °C for 72 h. These methodologies were used for enumeration of both the pure cultures and the microorganisms from probiotic yoghurt and Prato cheese. The results showed that the best selective medium for enumeration of L. acidophilus from yoghurt was MRS agar containing bile incubated at 37 °C for 72 h under anaerobic conditions. For enumeration of this probiotics from Prato cheese, MRS agar containing sorbitol incubated at 45 °C for 72 h under anaerobic conditions was proven to be the best selective medium.

A new medium containing mupirocin, acetic acid, and norfloxacin for the selective cultivation of bifidobacteria

Various culture media have been proposed for the isolation and selective enumeration of bifidobacteria. Mupirocin is widely used as a selective factor along with glacial acetic acid. TOS (transgalactosylated oligosaccharides) medium supplemented with mupirocin is recommended by the International Dairy Federation for the detection of bifidobacteria in fermented milk products. Mupirocin media with acetic acid are also reliable for intestinal samples in which bifidobacteria predominate. However, for complex samples containing more diverse microbiota, the selectivity of mupirocin media is limited. Resistance to mupirocin has been demonstrated by many anaerobic bacteria, especially clostridia. The objective was to identify an antibiotic that inhibits the growth of clostridia and allows the growth of bifidobacteria, and to use the identified substance to develop a selective cultivation medium for bifidobacteria. The susceptibility of bifidobacteria and clostridia to 12 antibiotics was tested on agar using the disk diffusion method. Only norfloxacin inhibited the growth of clostridia and did not affect the growth of bifidobacteria. Using both pure cultures and faecal samples from infants, adults, calves, lambs, and piglets, the optimal concentration of norfloxacin in solid cultivation media was determined to be 200 mg/L. Our results showed that solid medium containing norfloxacin (200 mg/L) in combination with mupirocin (100 mg/L) and glacial acetic acid (1 mL/L) is suitable for the enumeration and isolation of bifidobacteria from faecal samples of different origins.

English

Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus are involved in the manufacture of yogurt, and Bifidobacterium spp. can be supplemented if probiotic properties are expected. In such products, enumeration of each bacterial component is a hard task since they have similar nutritional requirements. For this reason, there is still no official and reliable methodology for this purpose. The objectives of the present study were to evaluate the most appropriate culture medium for the enumeration of four different Bifidobacterium species in the presence of S. thermophilus and L. delbrueckii subsp. bulgaricus isolated from commercial cultures and investigate the influence of different strains of S. thermophilus on the choice of medium. Among 11 isolates of S. thermophilus obtained from these cultures, and which were submitted to repetitive element sequence-based PCR (rep-PCR), nine were found to be distinct strains. For selective enumeration of the Bifidobacterium species, results were influenced by the S. thermophilus strain used, but De Man, Rogosa and Sharpe (MRS) agar containing bile salts showed the best results for all of the Bifidobacterium species. Key words: Bifidobacterium spp., Streptococcus thermophilus, culture media, selectivity.

Enumeration of Bifidobacterium in powdered milk products: effect of suspension buffer and development of selective enumeration media

Enumeration of <i>Bifidobacterium</i> in powdered milk products: effect of suspension buffer and development of selective enumeration media

Comparison of mupirocin-based media for selective enumeration of bifidobacteria in probiotic supplements

An international standard already exists for the selective enumeration of bifidobacteria in milk products. This standard uses Transgalactosylated oligosaccharides (TOS) propionate agar supplemented with mupirocin. However, no such standard method has been described for the selective enumeration of bifidobacteria in probiotic supplements, where the presence of bifidobacteria is much more variable than in milk products. Therefore, we enumerated bifidobacteria by colony count technique in 13 probiotic supplements using three media supplemented with mupirocin (Mup; 100mg/l): TOS, Bifidobacteria selective medium (BSM) and modified Wilkins-Chalgren anaerobe agar with soya peptone (WSP). Moreover, the potential growth of bifidobacterial strains often used in probiotic products was performed in these media. All 13 products contained members of the genus Bifidobacterium, and tested mupirocin media were found to be fully selective for bifidobacteria. However, the type strain Bifidobacterium bifidum DSM 20456 and collection strain B. bifidum DSM 20239 showed statistically significant lower counts on TOS Mup media, compared to BSM Mup and WSP Mup media. Therefore, the TOS Mup medium recommended by the ISO standard cannot be regarded as a fully selective and suitable medium for the genus Bifidobacterium. In contrast, the BSM Mup and WSP Mup media supported the growth of all bifidobacterial species.

Selective Enumeration of Lactobacillus acidophilus for Probiotic Formulations

Probiotic microorganisms have been utilized for many years in food processing, preservations and for nutraceutical health benefits. There are a large number of pharmaceutical formulations containing probiotic microorganisms available in the market worldwide. Majority of these organisms are the members specifically from genera Lactobacillus, Lactococcus and Bifidobacterium. A number of media have been proposed for selective or differential enumeration of lactobacilli and bifidobacteria in mixed populations. The development of selective medium using different types of ingredients and antibiotic are well practiced. In the present study we have developed a selective medium for the enumeration of Lactobacillus acidophilus by utilizing the antibiotic ofloxacin resistance of the organism in Lactobacilli MRS-agar. Samples were analyzed by determining viable counts in reference Lactobacilli MRS agar and selective Lactobacilli MRS-ofloxacin agar media. The results were statistically analyzed to evaluate the precision, accuracy, reproducibility and selectivity of the method developed. Thus MRS containing ofloxacin medium can be used for selective enumeration of Lactobacillus acidophilus strains available in commercial formulations containing Bifidobacterium species.

Mikrobiologická detekce probiotických mikroorganismů ve fermentovaných mléčných výrobcích

A number of health benefits have been claimed for probiotic bacteria such as Lactobacillus acidophilus, Bifidobacterium spp. and Lactobacillus rhamnosus. Because of the potential health benefits, these organisms are increasingly incorporated into dairy foods. However, to reach health benefits, the concentration of probiotics have to be 106 CFU/g of a product. For assessing of required probiotic bacteria quantity, it is important to have a working method for selective enumeration of these probiotic bacteria. Five bacteriological media were evaluated to assess their suitability to selectively enumerate Streptococcus thermophilus, Lactobacillus rhamnosus, Lactobacillus acidophilus and Bifidobacterium spp. Bacteriological media evaluated included Streptococcus thermophilus agar, pH modified MRS agar, MRS-vancomycine agar and BSM (Bifidus selective medium) agar under different culture conditions.Seven selected fermented milk products with probiotic culture were analyzed for their bacterial populations using the described selective bacteriological media and culture conditions. All milk products contained probiotic microorganisms claimed to be present in declared quantity (106–107/g).

Evaluation of culture media for selective enumeration of bifidobacteria and lactic acid bacteria

The purpose of this study was to test the suitability of Transgalactosylated oligosaccharides-mupirocin lithium salt (TOS-MUP) and MRS-clindamycin-ciprofloxacin (MRS-CC) agars, along with several other culture media, for selectively enumerating bifidobacteria and lactic acid bacteria (LAB) species commonly used to make fermented milks. Pure culture suspensions of a total of 13 dairy bacteria strains, belonging to eight species and five genera, were tested for growth capability under various incubation conditions. TOS-MUP agar was successfully used for the selective enumeration of both Bifidobacterium animalis subsp. lactis BB-12 and B. breve M-16 V. MRS-CC agar showed relatively good selectivity for Lactobacillus acidophilus, however, it also promoted the growth of Lb. casei strains. For this reason, MRS-CC agar can only be used as a selective medium for the enumeration of Lb. acidophilus if Lb. casei is not present in a product at levels similar to or exceeding those of Lb. acidophilus. Unlike bifidobacteria and coccus-shaped LAB, all the lactobacilli strains involved in this work were found to grow well in MRS pH 5.4 agar incubated under anaerobiosis at 37 °C for 72 h. Therefore, this method proved to be particularly suitable for the selective enumeration of Lactobacillus spp.

Mupirocin-mucin agar for selective enumeration of Bifidobacterium bifidum

Bifidobacterium bifidum is a bacterial species exclusively found in the human intestinal tract. This species is becoming increasingly popular as a probiotic organism added to lyophilized products. In this study, porcine mucin was used as the sole carbon source for the selective enumeration of B. bifidum in probiotic food additives. Thirty-six bifidobacterial strains were cultivated in broth with mucin. Only 13 strains of B. bifidum utilized the mucin to produce acids. B. bifidum was selectively enumerated in eight probiotic food supplements using agar (MM agar) containing mupirocin (100mg/L) and mucin (20g/L) as the sole carbon source. MM agar was fully selective if the B. bifidum species was presented together with Bifidobacterium animalis subsp. lactis, Bifidobacterium breve, and Bifidobacterium longum subsp. longum species and with lactic acid bacteria (lactobacilli, streptococci). Isolated strains of B. bifidum were identified using biochemical, PCR, MALDI-TOF procedures and 16S rRNA gene sequencing. The novel selective medium was also suitable for the isolation of B. bifidum strains from human fecal samples.

A modified MacConkey agar for selective enumeration of necrotoxigenic E. coli O55 and probiotic E. coli Nissle 1917

An agar selective enumeration of necrotoxigenic Escherichia coli O55 (NTEC2) and probiotic E. coli Nissle 1917, using modified MacConkey agar, was developed to study bacterial interference between these E. coli strains in a gnotobiotic piglet model. Replacement of lactose with saccharose in the agar enables the direct visual enumeration of red colonies of E. coli O55 and yellow colonies of E. coli Nissle 1917 that are co-cultured in the same Petri dish. A total of 336 colonies (168 for each color) were subjected to strain-specific PCR identification with LNA probes. Sensitivity, specificity, and positive and negative predictive values were 96.43%, 95.83%, 95.86% and 96.41% respectively in E. coli O55, and 98.21%, 97.02%, 97.06% and 98.19% respectively in E. coli Nissle 1917. Color-based enumeration of both E. coli strains in colonic contents and mesenteric lymph nodes homogenates of gnotobiotic piglets demonstrated the applicability of this method for the gnotobiotic piglet model of enteric diseases.