Polymerase chain reaction and gene probe detection of the 2,4-dichlorophenoxyacetic acid degradation plasmid, pJP4.

Specific and sensitive detection of indigenous and introduced degradative organisms is an essential prerequisite to their use in remediation of toxic waste and soil systems. Procedures were employed for the use of polymerase chain reaction and gene probes for sensitive detection of the 2,4-dichlorophenoxyacetic-acid-degrading bacterium, Alcaligenes eutrophus JMP134(pJP4). Two 20-mer oligonucleotide primers were identified for amplification of a 205-bp region of the tfdB gene of pJP4, and optimum conditions for amplification were determined. Both the polymerase chain reaction amplification process and hybridization with the 5'-end-labelled probe were found to be specific to organisms containing plasmid pJP4 or its derivative pRO103. Detection limits were determined for the template supplied either as bacterial cells or purified plasmid DNA. The detection was sensitive up to an initial inoculum of 3,000 CFU or 156 pg of total plasmid DNA. However, when the amplified product was transferred to a nylon membrane and hybridized with the 5'-end-labelled probe, the detection sensitivity increased to 300 CFU or 15.6 pg of plasmid DNA. This sensitive detection method is more specific than use of traditional indicator media (M. A. Loos, Can. J. Microbiol. 21:104-107, 1975). An oligonucleotide (20 bases) complementary to a sequence internal to the 205-bp region was synthesized and utilized as a probe to confirm the specificity of the detection.     

Sensitive and specific detection of Listeria monocytogenes in milk and ground beef with the polymerase chain reaction.

A sensitive and specific method for detection of Listeria monocytogenes in milk and ground-beef samples is described. It consists of culturing samples in listeria enrichment broth (LEB) and subculturing them from LEB to listeria plating media, followed by DNA extraction and species-specific detection of the organism by using the polymerase chain reaction (PCR). In developing the L. monocytogenes PCR assay, five oligonucleotide primers complementary to the nucleotide sequence of the listeriolysin O gene were synthesized and used in amplification experiments. PCR products of the predicted size, based on nucleotide sequence information, were generated with DNA from all of 72 L. monocytogenes strains with five different primer pairs. DNA from Listeria ivanovii, Listeria innocua, Listeria seeligeri, Listeria welshimeri, Listeria grayi, and Listeia murrayi strains and a panel of 47 bacterial strains representing 17 genera did not generate PCR products with the primer pairs employed. As little as 1 pg of L. monocytogenes DNA could be detected with the assay. To determine the most sensitive culture protocol to use in conjunction with the PCR assay, milk (10 ml) and ground-beef (25 g) samples were inoculated with L. monocytogenes at concentrations ranging from 0 to 10(5) CFU ml-1 or g-1, as appropriate for the sample. PCR assays on DNA extracted from growth on listeria plating media, inoculated with 24-h LEB samples cultures, were most sensitive, allowing detection of as little as 0.1 CFU of L. monocytogenes ml-1 or g-1 of milk and ground beef, respectively.     

Specific detection and confirmation of Campylobacter jejuni by DNA hybridization and PCR.

Conventional detection and confirmation methods for Campylobacter jejuni are lengthy and tedious. A rapid hybridization protocol in which a 1,475-bp chromogen-labelled DNA probe (pDT1720) and Campylobacter strains filtered and grown on 0.22-micron-pore-size hydrophobic grid membrane filters (HGMFs) are used was developed. Among the environmental and clinical isolates of C. jejuni, Campylobacter coli, Campylobacter jejuni subsp. doylei, Campylobacter lari, and Arcobacter nitrofigilis and a panel of 310 unrelated bacterial strains tested, only C. jejuni and C. jejuni subsp. doylei isolates hybridized with the probe under stringent conditions. The specificity of the probe was confirmed when the protocol was applied to spiked skim milk and chicken rinse samples. Based on the nucleotide sequence of pDT1720, a pair of oligonucleotide primers was designed for PCR amplification of DNA from Campylobacter spp. and other food pathogens grown overnight in selective Mueller-Hinton broth with cefoperazone and growth supplements. All C. jejuni strains tested, including DNase-producing strains and C. jejuni subsp. doylei, produced a specific 402-bp amplicon, as confirmed by restriction and Southern blot analysis. The detection range of the assay was as low as 3 CFU per PCR to as high as 10(5) CFU per PCR for pure cultures. Overnight enrichment of chicken rinse samples spiked initially with as little as approximately 10 CFU/ml produced amplicons after the PCR. No amplicon was detected with any of the other bacterial strains tested or from the chicken background microflora. Since C. jejuni is responsible for 99% of Campylobacter contamination in poultry, PCR and HGMF hybridization were performed on naturally contaminated chicken rinse samples, and the results were compared with the results of conventional cultural isolation on Preston agar. All samples confirmed to be culture positive for C. jejuni were also identified by DNA hybridization and PCR amplification, thus confirming that these DNA-based technologies are suitable alternatives to time-consuming conventional detection methods. DNA hybridization, besides being sensitive, also has the potential to be used in direct enumeration of C. jejuni organisms in chicken samples.     

Detection of Xanthomonas campestris pv. citri by the polymerase chain reaction method.

pFL1 is a pUC9 derivative that contains a 572-bp EcoRI insert cloned from plasmid DNA of Xanthomonas campestris pv. citri XC62. The nucleotide sequence of pFL1 was determined, and the sequence information was used to design primers for application of the polymerase chain reaction (PCR) to the detection of X. campestris pv. citri, the causal agent of citrus bacterial canker disease. Seven 18-bp oligonucleotide primers were designed and tested with DNA from X. campestris pv. citri strains and other strains of X. campestris associated with Citrus spp. as templates in the PCR. Four primer pairs directed the amplification of target DNA from X. campestris pv. citri strains but not from strains of X. campestris associated with a different disease, citrus bacterial spot. Primer pair 2-3 directed the specific amplification of target DNA from pathotype A but not other pathotypes of X. campestris pv. citri. A pH 9.0 buffer that contained 1% Triton X-100 and 0.1% gelatin was absolutely required for the successful amplification of the target DNA, which was 61% G+C. Limits of detection after amplification and gel electrophoresis were 25 pg of purified target DNA and about 10 cells when Southern blots were made after gel electrophoresis and probed with biotinylated pFL1. This level of detection represents an increase in sensitivity of about 100-fold over that of dot blotting with the same hybridization probe. PCR products of the expected sizes were amplified from DNA extracted from 7-month-old lesions from which viable bacteria could not be isolated. These products were confirmed to be specific for X. campestris pv. citri by Southern blotting. This PCR-based detection protocol will be a useful addition to current methods of detection of this pathogen, which is currently the target of international quarantine measures.     

Rapid detection of Vibrio vulnificus in shellfish and Gulf of Mexico water by real-time PCR

In this paper we describe optimization of SYBR Green I-based real-time PCR parameters and testing of a large number of microbial species with vvh-specific oligonucleotide primers to establish a rapid, specific, and sensitive method for detection of Vibrio vulnificus in oyster tissue homogenate and Gulf of Mexico water (gulf water). Selected oligonucleotide primers for the vvh gene were tested for PCR amplification of a 205-bp DNA fragment with a melting temperature of approximately 87 degrees C for 84 clinical and environmental strains of V. vulnificus. No amplification was observed with other vibrios or nonvibrio strains with these primers. The minimum level of detection by the real-time PCR method was 1 pg of purified genomic DNA or 10(2) V. vulnificus cells in 1 g of unenriched oyster tissue homogenate or 10 ml of gulf water. It was possible to improve the level of detection to one V. vulnificus cell in samples that were enriched for 5 h. The standard curves prepared from the real-time PCR cycle threshold values revealed that there was a strong correlation between the number of cells in unenriched samples and the number of cells in enriched samples. Detection of a single cell of V. vulnificus in 1 g of enriched oyster tissue homogenate is in compliance with the recent Interstate Shellfish Sanitation Conference guidelines. The entire detection method, including sample processing, enrichment, and real-time PCR amplification, was completed within 8 h, making it a rapid single-day assay. Rapid and sensitive detection of V. vulnificus would ensure a steady supply of postharvest treated oysters to consumers, which should help decrease the number of illnesses or outbreaks caused by this pathogen.     

Multiplex PCR detection of clinical and environmental strains of Vibrio vulnificus in shellfish

In this study, we developed a PCR-based rapid detection method for clinically important pathogenic strains of Vibrio vulnificus. Positive amplification of the 504-bp viuB fragment was seen in all 22 clinical isolates tested but only in 8 out of 33 environmental isolates. The combination of the species-specific 205-bp vvh fragment along with viuB in a multiplexed PCR enabled us to confirm the presence of potentially pathogenic strains of V. vulnificus. No amplification of other Vibrio spp. or non-Vibrio bacteria was evidenced, suggesting a high specificity of detection by this method. The sensitivity of detection for both targeted genes was 10 pg of purified DNA, which correlated with 10(3) V. vulnificus CFU in 1 mL of pure culture or 1 g un-enriched seeded oyster tissue homogenate. This sensitivity was improved to 1 CFU per gram of oyster tissue homogenate in overnight-enriched samples. A SYBR Green I based real-time PCR method was also developed that was shown to produce results consistent with the conventional PCR method. Application of the multiplexed real-time PCR to natural oyster tissue homogenates exhibited positive detection of vvh in 51% of the samples collected primarily during the summer months; however, only 15% of vvh positive samples exhibited viuB amplicons. The rapid, sensitive, and specific detection of clinically important pathogenic V. vulnificus in shellfish would be beneficial in reducing illnesses and deaths caused by this pathogen.     

Identification of Aeromonas hydrophila hybridization group 1 by PCR assays.

Synthetic oligonucleotide primers of 24 and 23 bases were used in a PCR assay to amplify a sequence of the lip gene, which encodes a thermostable extracellular lipase of Aeromonas hydrophila. A DNA fragment of approximately 760 bp was amplified from both sources, i.e., lysed A. hydrophila cells and isolated DNA. The amplified sequence was detected in ethidium bromide-stained agarose gels or by Southern blot analysis with an internal HindIII-BamHI 356-bp fragment as a hybridization probe. With A. hydrophila cells, the sensitivity of the PCR assay was < 10 CFU, and with the isolated target, the lower detection limit was 0.89 pg of DNA. Primer specificity for A. hydrophila was determined by the PCR assay with cells of 50 strains of bacteria, including most of the 14 currently recognized DNA hybridization groups of Aeromonas spp. as well as other human and environmental Aeromonas isolates. Detection of A. hydrophila by PCR amplification of DNA has great potential for rapid identification of this bacterium because it has proved to be highly specific.     

Sensitive and specific detection of Listeria monocytogenes in milk and ground beef with the polymerase chain reaction.

A sensitive and specific method for detection of Listeria monocytogenes in milk and ground-beef samples is described. It consists of culturing samples in listeria enrichment broth (LEB) and subculturing them from LEB to listeria plating media, followed by DNA extraction and species-specific detection of the organism by using the polymerase chain reaction (PCR). In developing the L. monocytogenes PCR assay, five oligonucleotide primers complementary to the nucleotide sequence of the listeriolysin O gene were synthesized and used in amplification experiments. PCR products of the predicted size, based on nucleotide sequence information, were generated with DNA from all of 72 L. monocytogenes strains with five different primer pairs. DNA from Listeria ivanovii, Listeria innocua, Listeria seeligeri, Listeria welshimeri, Listeria grayi, and Listeia murrayi strains and a panel of 47 bacterial strains representing 17 genera did not generate PCR products with the primer pairs employed. As little as 1 pg of L. monocytogenes DNA could be detected with the assay. To determine the most sensitive culture protocol to use in conjunction with the PCR assay, milk (10 ml) and ground-beef (25 g) samples were inoculated with L. monocytogenes at concentrations ranging from 0 to 10(5) CFU ml-1 or g-1, as appropriate for the sample. PCR assays on DNA extracted from growth on listeria plating media, inoculated with 24-h LEB samples cultures, were most sensitive, allowing detection of as little as 0.1 CFU of L. monocytogenes ml-1 or g-1 of milk and ground beef, respectively.     

Biomonitoring of pJP4-carrying Pseudomonas chlororaphis with Trb protein-specific antisera

The transfer of catabolic genes on conjugative plasmids to indigenous organisms from which they may spread further into the community allows the introduction of new biodegradative pathways for metabolic conversion of pollutants to the community. Biomonitoring of IncP plasmid pJP4-carrying Pseudomonas chlororaphis from the rhizosphere of Arabidopsis thaliana was achieved using antisera specific for proteins from the plasmid transfer machinery. Antisera were generated that recognized TrbC and TrbF, the putative major and minor components of pJP4-determined pili, respectively, and the putative lipoprotein TrbH. Cell fractionation studies showed association of TrbC, TrbF and TrbH with the cells and suggested that TrbC and TrbF are part of extracellular pJP4-determined pili. TrbF and TrbH antisera allowed specific detection of IncP compared with IncN or IncW plasmid-carrying cells and even permitted differentiation between bacteria carrying IncPα plasmid RP4 and IncPβ plasmid pJP4. Immunofluorescence microscopy was applied to detect TrbF and TrbH signal at the cell periphery, allowing distinction from autofluorescing cells and soil debris. In situ experiments showed specific recognition of pJP4-carrying cells from laboratory cultures, as well as from the rhizosphere of A. thaliana grown in natural soil. After co-inoculation of donor P. chlororaphis pJP4 and recipient Ralstonia eutropha , a combination of immunofluorescence and oligonucleotide hybridization techniques permitted the detection of plasmid transfer between both organisms in the A. thaliana rhizosphere. This strategy may be generally applicable for the analysis of plasmid transfer in natural ecosystems.     

Detection of HIV-1 DNA in cells and tissue by fluorescent in situ 5'-nuclease assay (FISNA).

The critical aspects of successful in situ amplification include fixation, permeabilization, amplification and detection. We address these aspects and present a novel detection scheme that eliminates hybridization following amplification. We use the 5'-nuclease activity of Taq polymerase to cleave in situ a 5'-reporter dye from an oligonucleotide probe which hybridizes to the target amplicon during amplification. The 5'-reporter dye is disassociated from the 3'-quenching dye and remains localized by charge interactions. In addition, we describe probe design constraints for 5'-nuclease assays both in solution and in situ. Using this technique, we show the sensitive and specific detection of HIV-1 DNA in cells lines and tissue from HIV-1-infected individuals.     

A型肉毒神经毒素基因的PCR检测

目的:建立快速筛查A型肉毒毒素的PCR方法。方法:根据GenBank中报道的肉毒毒素基因序列,综合应用多种生物软件分析设计特异的检测引物,从提取的基因组DNA、热裂解产物和菌液等不同形式的模板中扩增大小为457bp的A型肉毒毒素特异基因片段,以肉毒梭菌其他血清型及破伤风梭菌为对照。结果:检测方法无交叉反应,灵敏度可达10pgDNA,3×103个菌。结论:建立的检测方法特异性强、灵敏度高,可以用于A型肉毒毒素基因的快速筛查。     

A comparison of substrates for quantifying the signal from a nonradiolabeled DNA probe.

A method for measuring the amount of a nonradiolabeled DNA probe using four detection substrates is described. In preliminary experiments, digoxygenin-labeled DNA was bound to neutral, nylon membranes and detected with anti-digoxygenin antibodies conjugated to alkaline phosphatase. Four substrates [4-nitrophenyl phosphate, 4-methylumbelliferyl phosphate, AttoPhos, and adamantyl 1, 2-dioxetane phosphate (AMPPD)] were assessed for use in a quantitative hybridization assay. Only AttoPhos and AMPPD were found to have detection limits in the low picogram range and to respond linearly to DNA concentrations ranging from 0 to 1250 pg. In subsequent experiments, a 200-bp DNA probe cloned from the marine bacterium Pseudomonas perfectomarina 23S rRNA gene was hybridized to P. perfectomarina genomic DNA and total RNA. The amount of hybridized probe was determined using AttoPhos. Finally, a digoxygenin-labeled oligonucleotide was probed against genomic DNA. Linearity with respect to DNA concentration was observed using both the 200-bp fragment and the oligonucleotide as probes with a final target detection limit of 166 fg. This study demonstrates the substrate AttoPhos can be used to quantify the amount of nonradiolabeled probe hybridized to target with sufficient sensitivity for very dilute samples, such as environmental samples.     

Isolation of a Pseudomonas solanacearum-specific DNA probe by subtraction hybridization and construction of species-specific oligonucleotide primers for sensitive detection by the polymerase chain reaction.

A subtraction hybridization technique was employed to make a library enriched for Pseudomonas solanacearum-specific sequences. One cloned fragment, PS2096, hybridized under stringent conditions to DNA of 82 P. solanacearum strains representing all subgroups of the species. Other plant-associated bacteria, including closely related species such as Pseudomonas capacia, Pseudomonas picketti, or Pseudomonas syzygii, did not hybridize to PS2096. A minimum number of between 4 x 10(5) and 4 x 10(6) P. solanacearum cells could routinely be detected with PS2096 labelled either with [32P]dCTP or with digoxigenin-11-dUTP. To improve the sensitivity of detection, PS2096 was sequenced to allow the construction of specific oligonucleotide primers to be used for polymerase chain reaction (PCR) amplification. After 50 cycles of amplification, 5 to 116 cells, depending on the strain, could reproducibly be detected by visualization of a 148-bp PCR product on an agarose gel. A preliminary field trial in Burundi with the probe and PCR primers has confirmed that they are sensitive tools for specifically detecting low-level infections of P. solanacearum in potato tubers.     

PCR和Southern Blot检测土拉弗氏菌气溶胶

为提高检测土拉弗氏菌的特异性和敏感性,建立了土拉菌ＰＣＲ及核酸杂交检测方法。运用平板计数、多聚酶链反应对土拉菌气溶胶稳定性进行了比较,结果表明ＰＣＲ具有较高灵敏度,并且在采样后３小时ＰＣＲ就可以得出定性结果,而平板计数则需要３～７天。采用ＰＣＲ法合成了土拉菌３７６－ｂｐ探针,分别对细菌菌液、５６８－ｂｐＰＣＲ产物和气溶胶样品进行杂交,结果表明菌悬液直接杂交可检出１０５ＣＦＵ左右的细菌,检测ＰＣＲ产物可达４０ｐｇ。ＰＣＲ和Ｓｏｕｔｈｅｒｎ印迹相结合有利于细菌的分离鉴定     

Rapid Detection of Vibrio vulnificus in Shellfish and Gulf of Mexico Water by Real-Time PCR

In this paper we describe optimization of SYBR Green I-based real-time PCR parameters and testing of a large number of microbial species with vvh-specific oligonucleotide primers to establish a rapid, specific, and sensitive method for detection of Vibrio vulnificus in oyster tissue homogenate and Gulf of Mexico water (gulf water). Selected oligonucleotide primers for the vvh gene were tested for PCR amplification of a 205-bp DNA fragment with a melting temperature of approximately 87°C for 84 clinical and environmental strains of V. vulnificus. No amplification was observed with other vibrios or nonvibrio strains with these primers. The minimum level of detection by the real-time PCR method was 1 pg of purified genomic DNA or 10² V. vulnificus cells in 1 g of unenriched oyster tissue homogenate or 10 ml of gulf water. It was possible to improve the level of detection to one V. vulnificus cell in samples that were enriched for 5 h. The standard curves prepared from the real-time PCR cycle threshold values revealed that there was a strong correlation between the number of cells in unenriched samples and the number of cells in enriched samples. Detection of a single cell of V. vulnificus in 1 g of enriched oyster tissue homogenate is in compliance with the recent Interstate Shellfish Sanitation Conference guidelines. The entire detection method, including sample processing, enrichment, and real-time PCR amplification, was completed within 8 h, making it a rapid single-day assay. Rapid and sensitive detection of V. vulnificus would ensure a steady supply of postharvest treated oysters to consumers, which should help decrease the number of illnesses or outbreaks caused by this pathogen.     

DNA amplification to enhance detection of genetically engineered bacteria in environmental samples

The polymerase chain reaction (PCR) was performed to amplify a 1.0-kilobase (kb) probe-specific region of DNA from the herbicide-degrading bacterium Pseudomonas cepacia AC1100 in order to increase the sensitivity of detecting the organism by dot-blot analysis. The 1.0-kb region was an integral portion of a larger 1.3-kb repeat sequence which is present as 15 to 20 copies on the P. cepacia AC1100 genome. PCR was performed by melting the target DNA, annealing 24-base oligonucleotide primers to unique sequences flanking the 1.0-kb region, and performing extension reactions with DNA polymerase. After extension, the DNA was again melted, and the procedure was repeated for a total of 25 to 30 cycles. After amplification the reaction mixture was transferred to nylon filters and hybridized against radiolabeled 1.0-kb fragment probe DNA. Amplified target DNA was detectable in samples initially containing as little as 0.3 pg of target. The addition of 20 micrograms of nonspecific DNA isolated from sediment samples did not hinder amplification or detection of the target DNA. The detection of 0.3 pg of target DNA was at least a 10(3)-fold increase in the sensitivity of detecting gene sequences compared with dot-blot analysis of nonamplified samples. PCR performed after bacterial DNA was isolated from sediment samples permitted the detection of as few as 100 cells of P. cepacia AC1100 per 100 g of sediment sample against a background of 10(11) diverse nontarget organisms; that is, P. cepacia AC1100 was positively detected at a concentration of 1 cell per g of sediment. This represented a 10(3)-fold increase in sensitivity compared with nonamplified samples.     

DNA amplification to enhance detection of genetically engineered bacteria in environmental samples.

The polymerase chain reaction (PCR) was performed to amplify a 1.0-kilobase (kb) probe-specific region of DNA from the herbicide-degrading bacterium Pseudomonas cepacia AC1100 in order to increase the sensitivity of detecting the organism by dot-blot analysis. The 1.0-kb region was an integral portion of a larger 1.3-kb repeat sequence which is present as 15 to 20 copies on the P. cepacia AC1100 genome. PCR was performed by melting the target DNA, annealing 24-base oligonucleotide primers to unique sequences flanking the 1.0-kb region, and performing extension reactions with DNA polymerase. After extension, the DNA was again melted, and the procedure was repeated for a total of 25 to 30 cycles. After amplification the reaction mixture was transferred to nylon filters and hybridized against radiolabeled 1.0-kb fragment probe DNA. Amplified target DNA was detectable in samples initially containing as little as 0.3 pg of target. The addition of 20 micrograms of nonspecific DNA isolated from sediment samples did not hinder amplification or detection of the target DNA. The detection of 0.3 pg of target DNA was at least a 10(3)-fold increase in the sensitivity of detecting gene sequences compared with dot-blot analysis of nonamplified samples. PCR performed after bacterial DNA was isolated from sediment samples permitted the detection of as few as 100 cells of P. cepacia AC1100 per 100 g of sediment sample against a background of 10(11) diverse nontarget organisms; that is, P. cepacia AC1100 was positively detected at a concentration of 1 cell per g of sediment. This represented a 10(3)-fold increase in sensitivity compared with nonamplified samples.     

A PCR-based assay for the detection of Escherichia coli Shiga-like toxin genes in ground beef.

A detection system based on the PCR has been developed for Escherichia coli strains which harbor the Shiga-like toxin genes. This quantitative detection system involves the 5'-->3' nuclease activity of Thermus aquaticus DNA polymerase, which cleaves an internal oligonucleotide probe that has been labeled with both a fluorescent reporter dye (6-carboxy-fluorescein [FAM]) and a quencher dye (6-carboxytetramethyl-rhodamine [TAMRA]). Parameters which affected the performance of the assay included primer probe distance, probe concentration, and probe target sequence homology. The optimized assay format includes two PCR primers that generate a 497-bp amplicon specific for the sltI gene with the fluorogenic probe located 19 bp from the upstream PCR primer. When the distance between the upstream PCR primer and the probe was reduced from 190 to 19 bp, delta RQ values increased from approximately 1.5 to 3.0. The delta RQ for Shiga-like toxin I probe 102 reached a maximum of 4.15 at concentrations between 25 and 50 nM. The assay is sensitive and can detect approximately 10 +/- 5 CFU per PCR. As few as 0.5 CFU of Shiga-like toxin I-producing E. coli per g could be detected in ground beef with only 12 h of enrichment in modified E. coli broth.     

A METHOD FOR ISOLATION OF CHROMOSOMAL AND PLASMID DNA FROM YERSINIA ENTEROCOLITICA FOR SIMULTANEOUS AMPLIFICATION BY POLYMERASE CHAIN REACTION: A POSSIBLE MODEL FOR OTHER BACTERIA

A commercial DNA isolation kit was evaluated for simultaneous isolation of chromosomal and plasmid DNA from Yersina enterocolitica for polymerase chain reaction amplification. The genomic and plasmid DNA samples obtained by use of the kit were suitable for use in polymerase chain reactions both individually and in multiplex reactions. The results obtained by the use of the kit suggest that this kit may be applied to isolate both genomic and plasmid DNA from other microorganisms for polymerase chain reaction amplification.     

Rapid and sensitive method for detection of Shiga-like toxin-producing Escherichia coli in ground beef using the polymerase chain reaction.

A rapid and sensitive method for detection of Shiga-like toxin (SLT)-producing Escherichia coli (SLT-EC) with the polymerase chain reaction (PCR) is described. Two pairs of oligonucleotide primers homologous to SLTI and SLTII genes, respectively, were used in multiplex PCR assays. The first pair generated a ca. 600-bp PCR product with DNA from all SLTI-producing E. coli tested but not from E. coli strains that produce SLTII or variants of SLTII. The second pair generated a ca. 800-bp PCR product with DNA from E. coli strains that produce SLTII or variants of SLTII but not from SLTI-producing E. coli. When used in combination, the SLTI and SLTII oligonucleotide primers amplified DNA from all of the SLT-EC tested. No PCR products were obtained with SLT primers with DNA from 28 E. coli strains that do not produce SLT or 44 strains of 28 other bacterial species. When ground beef samples were inoculated with SLT-EC strains 319 (O157:H7; SLTI and SLTII), H30 (O26:H11; SLTI), and B2F1/3 (O91:H21; SLTII variants VT2ha and VT2hb) and cultured in modified Trypticase soy broth for 6 h at 42 degrees C, an initial sample inoculum of as few as 1 CFU of these SLT-EC strains per g could be detected in PCR assays with DNA extracted from the broth cultures.