Use of multiple primers in RAPD analysis of clonal organisms provides limited improvement in discrimination.

Randomly amplified polymorphic DNA (RAPD) analysis using two or more primers has been reported to provide additional discriminatory ability over one primer used individually. This may be of particular application in epidemiological typing of clonal organisms, such as Shiga toxin-producing E. coli O157, where strain differentiation can be difficult. Using four arbitrary primers individually, and in all possible permutations, E. coli O157 isolates and other arbitrarily chosen E. coli strains were typed using RAPD analysis. For most nonclonal strains, the use of two primers resulted in increased differentiation between isolates; however, more than two primers did not increase further the discriminatory capacity. E. coli O157 isolates that produced virtually identical profiles using one primer did not show increased differentiation when using two or more primers, demonstrating that in some cases, where strains of an organism are highly related, there is limited advantage to using more than one primer in RAPD analysis.     

Evaluation of randomly amplified polymorphic DNA and pulsed field gel electrophoresis techniques for molecular typing of Dermatophilus congolensis

This study aimed to evaluate molecular typing methods useful for standardization of strains in experimental work on dermatophilosis. Fifty Dermatophilus congolensis isolates, collected from sheep, cattle, horse and a deer, were analyzed by randomly amplified polymorphic DNA (RAPD) method using twenty-one different primers, and the results were compared with those obtained by typing with a pulsed field gel electrophoresis (PFGE) method using the restriction digest enzyme Sse8387I. The typeability, reproducibility and discriminatory power of RAPD and Sse8387I-PFGE typing were calculated. Both typing methods were highly reproducible. Of the two techniques, Sse8387I-PFGE was the least discriminating (Dice Index (DI), 0.663) and could not distinguish between epidemiologically related isolates, whereas RAPD showed an excellent discriminatory power (DI, 0.7694-0.9722). Overall, the degree of correlation between RAPD and PFGE typing was significantly high (r, 0.8822). We conclude that the DNA profiles generated by either RAPD or PFGE can be used to differentiate epidemiologically unrelated isolates. The results of this study strongly suggest that at least two independent primers are used for RAPD typing in order to improve its discriminatory power, and that PFGE is used for confirmation of RAPD results.     

A comparison of three molecular typing methods for the discrimination of Salmonella enterica serovar Infantis

Seventy-six epidemiologically unrelated Salmonella enterica serovar Infantis (S. Infantis) isolates were typed by pulsed-field gel electrophoresis (PFGE), multiple amplification of phage loci typing (MAPLT) and multiple-locus variable-number tandem-repeat analysis (MLVA). PFGE, using the restriction endonuclease XbaI, generated 23 different profiles for the 76 isolates (DI=0.848). MAPLT was undertaken using a combination of 11 primer sets based on bacteriophage sequences and generated 28 different profiles (DI=0.938). By contrast, MLVA only produced nine profiles (DI=0.668) with 13 different primer sets, including the five primer sets routinely used for S. Typhimurium typing. Reducing the number of MAPLT primer sets to four still provided a diversity index of 0.838. All three typing methods revealed two distinct lineages of S. Infantis, with most isolates demonstrating genetic traits of either lineage but not both. The results demonstrate that MAPLT can potentially provide greater discrimination and separation of S. Infantis isolates than both PFGE and MLVA. Furthermore, MAPLT data can be generated much more rapidly and with reduced labour input than PFGE and without the need for expensive PFGE electrophoresis equipment, nor does it require capillary sequencing of PCR fragments to accurately determine PCR fragment lengths as is the case with MLVA.     

RAPD analysis of Aeromonas salmonicida and Aeromonas hydrophila

The randomly amplified polymorphic DNA (RAPD) technique was used to analyse the genetic differentiation of 13 strains of Aeromonas salmonicida subsp. salmonicida , and seven strains of Aer. hydrophila. Reproducible profiles of genomic DNA fingerprints were generated by polymerase chain reaction (PCR) using a single randomly designed primer. The RAPD profiles of all the non-motile aeromonads, Aer. salmonicida subsp. salmonicida were identical. However, profiles of the motile aeromonads, Aer. hydrophila differed between isolates. These findings reveal genomic homogeneity in Aer. salmonicida subsp. salmonicida and genetic variety in Aer. hydrophila strains.     

Genotypic characterization of Salmonella typhi by amplified fragment length polymorphism fingerprinting provides increased discrimination as compared to pulsed-field gel electrophoresis and ribotyping

Amplified fragment length polymorphism (AFLP) is a recently developed, PCR-based high resolution fingerprinting method that is able to generate complex banding patterns which can be used to delineate intraspecific genetic relationships among bacteria. In the present study, AFLP was evaluated for its usefulness in the molecular typing of Salmonella typhi in comparison to ribotyping and pulsed-field gel electrophoresis (PFGE). Six S. typhi isolates from diverse geographic areas (Malaysia, Indonesia, India, Chile, Papua New Guinea and Switzerland) gave unique, heterogeneous profiles when typed by AFLP, a result which was consistent with ribotyping and PFGE analysis. In a further study of selected S. typhi isolates from Papua New Guinea which caused fatal and non-fatal disease previously shown to be clonally related by PFGE, AFLP discriminated between these isolates but did not indicate a linkage between genotype with virulence. We conclude that AFLP (discriminatory index=0.88) has a higher discriminatory power for strain differentiation among S. typhi than ribotyping (DI=0.63) and PFGE (DI=0.74).     

RAPD typing for distinguishing species and strains in the genus Listeria

The randomly amplified polymorphic DNA (RAPD) technique was employed in the development of a typing protocol for Listeria isolates, particularly Listeria monocytogenes strains. A single strain of L. monocytogenes was used and 200 random decamer primers were screened for their discriminatory abilities by visualizing the amplification products electrophoretically. Three candidate primers displaying potentially useful banding patterns were selected and tested against 52 L. monocytogenes strains, encompassing 11 serotypes, and 12 other strains representing five other Listeria spp. Thirty-four banding profiles were obtained with one particular primer. RAPD analysis allowed differentiation between Listeria spp. and was found to further subdivide strains of the same serotype. Where only one primer was used strains from different serotypes were occasionally found to produce identical banding profiles. RAPD analysis, which in our hands proved to be reproducible, shows much promise as a molecular alternative to traditional L. monocytogenes typing protocols.     

Heterogeneity in expression of lipopolysaccharide by strains of Salmonella enterica serotype Typhimurium definitive phage type 104 and related phage types

AIMS: To investigate lipopolysaccharide (LPS) expression in Salmonella enterica serotype Typhimurium definitive phage type 104 (Salmonella Typhimurium DT104) and related phage types. METHODS AND RESULTS: Isolates were examined for the expression of LPS by SDS-PAGE and silver staining and subtyped by Pulsed Field Gel Electrophoresis (PFGE). The 100 isolates expressed one of two LPS profiles designated A (72%) and B (28%). LPS profiling was able to discriminate between isolates of identical PFGE type. Among 10 groups of outbreak isolates examined, each group was of a single LPS profile: A, 8/10 and B, 2/10. All 10 outbreaks were identical by PFGE analysis. CONCLUSIONS: Isolates of Salmonella Typhimurium DT104 and related phage types expressed one of two distinct LPS profiles. The two LPS profiles appear similar but shifted and in phase with one another, suggesting that the heterogeneity is due to changes in the LPS core region rather than among the repeating oligosaccharide units of the long-chain LPS. SIGNIFICANCE AND IMPACT OF THE SUTDY: LPS profiling provides a useful adjunct to PFGE and other molecular methods for the subtyping of this group of bacteria in epidemiological investigations.     

Persistence of a Salmonella enterica serotype typhimurium clone in Danish pig production units and farmhouse environment studied by pulsed field gel electrophoresis (PFGE)

The clonal relationship among Salmonella enterica serotype Typhimurium isolates from selected pig production units in Denmark was investigated by the pulsed field gel electrophoresis (PFGE) typing method to determine environmental survival and spread of Salmonella in different herds. Thirty-four Typhimurium isolated during 1996-1998 from porcine faeces and environmental samples from three pig farms designated 1, 3 and 5 were characterised by PFGE using two restriction enzymes. Farm 5 supplied piglets to farm 1 and the herds were located close to each other. Results of PFGE analysis showed both intra- and inter-relationships, i.e. identical PFGE patterns among the faecal and environmental isolates from farm 1 and farm 5. All the isolates from farm 3 irrespective of the source showed identical PFGE patterns, but were different from samples from farms 1 and 5. This study indicates spread between farms and survival of a farm-specific clone. Furthermore, identical PFGE patterns of isolates from piglet supplier and finisher herds indicate that the farrow-to-grower herd of farm 5 was sub-clinically infected prior to delivery to farm 1 and thereby caused the transmission of Salmonella.     

Isolation and characterization of monochloroacetic acid-degrading bacteria

Five Burkholderia strains (CL-1, CL-2, CL-3, CL-4, and CL-5) capable of degrading monochloroacetic acid (MCA) were isolated from activated sludge or soil samples gathered from several parts of Japan. All five isolates were able to grow on MCA as the sole source of carbon and energy, and argentometry and gas chromatography-mass spectroscopy analyses showed that these five strains consumed MCA completely and released chloride ions stoichiometrically within 25 h. The five isolates also grew on monobromoacetic acid, monoiodoacetic acid, and L-2-monochloropropionic acid as sole sources of carbon and energy. In addition, the five isolates could not grow with DCA but dehalogenate single chlorine from DCA. Because PCR analyses revealed that all five isolates have an identical group II dehalogenase gene fragment and no group I deh gene, only strain CL-1 was analyzed further. The partial amino acid sequence of the group II dehalogenase of strain CL-1, named DehCL1, showed 74.6% and 65.2% identities to corresponding regions of the two MCA dehalogenases, DehCI from Pseudomonas sp. strain CBS-3 and Hdl IVa from Burkholderia cepacia strain MBA4, respectively. The secondary-structure motifs of the haloacid dehalogenase (HAD) superfamily and the amino acid residues involved in substrate binding, catalysis, and hydrophobic pocket formation were conserved in the partial amino acid sequence of DehCL1.     

Restriction enzyme analysis of randomly amplified polymorphic DNA amplicons of Salmonella enterica ser. Enteritidis PT4 and Typhimurium DT104

Salmonella enterica serotype Enteritidis PT4 and Typhimurium DT104 isolates were characterized using a random amplification of polymorphic DNA (RAPD) protocol found previously to be highly discriminatory for isolates of Salmonella . Profiles generated with a single primer 1254, and independently 1283, successfully characterized an outbreak strain of Enteritidis PT4 but could not differentiate epidemiologically unrelated strains of Enteritidis PT4 from the outbreak strains. Primer 1254 differentiated one strain, and 1283 two strains of Typhimurium DT104 previously undifferentiated on the basis of biochemical and physical properties. Subsequent analysis using a combination of RAPD and restriction enzyme analysis could not provide additional differentiation of Enteritidis PT4 and Typhimurium DT104 isolates but did, however, exhibit the potential to be a useful combination of molecular techniques.     

Detection of Escherichia coli O157:H7 by multiplex PCR and their characterization by plasmid profiling, antimicrobial resistance, RAPD and PFGE analyses.

Twenty-five and three strains of Escherichia coli O157:H7 were identified from 25 tenderloin beef and three chicken meat burger samples, respectively. The bacteria were recovered using the immunomagnetic separation procedure followed by selective plating on sorbitol MacConkey agar and were identified as E. coli serotype O157:H7 with three primer pairs that amplified fragments of the SLT-I, SLT-II and H7 genes in PCR assays. Susceptibility testing to 14 antibiotics showed that all were resistant to two or more antibiotics tested. Although all 28 strains contained plasmid, there was very little variation in the plasmid sizes observed. The most common plasmid of 60 MDa was detected in all strains. We used DNA fingerprinting by randomly amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) to compare the 28 E. coli O157:H7 strains. At a similarity level of 90%, the results of PFGE after restriction with XbaI separated the E. coli O157:H7 strains into 28 single isolates, whereas RAPD using a single 10-mer oligonucleotides separated the E. coli O157:H7 strains into two clusters and 22 single isolates. These typing methods should aid in the epidemiological clarification of the E. coli O157:H7 in the study area.     

Molecular typing of Candida spp. by random amplification of polymorphic DNA and analysis of restriction fragment length polymorphism of ribosomal DNA repeats

Random amplification of polymorphic DNA (RAPD) using an arbitrary oligonucleotide primer (5'-CGGTGCGACG) and analysis of restriction fragment length polymorphism of ribosomal DNA (rDNA-RFLP) after digestion of genomic DNA with restriction endonuclease EcoRI were investigated as tools for genotypic delineation beyond the species level of 91 Candida clinical isolates and four reference strains including 33 Candida albicans, 19 Candida tropicalis, 22 Candida krusei and 21 Candida (Torulopsis) glabrata. Results indicated that both techniques can be useful for typing isolates of the above species, although showing a variable discriminative potential with different species. As compared to RAPD fingerprinting, the discriminative potential of rDNA-RFLP appeared to be highest for C. albicans and lowest for C. glabrata, being overall similar for C. krusei and identical for C. tropicalis. A comparative analysis of the results obtained with the two typing techniques showed that, except for C. tropicalis, they were able to provide non-redundant information, and that their use in combination could enhance the discriminative potential for delineation among C. glabrata and C. krusei isolates.     

Molecular and phenotypic characterisation of Bacillus thuringiensis isolated during epizootics in Cydia pomonella L

Twelve Bacillus thuringiensis strains were isolated from intestinal tracts of Cydia pomonella larvae during epizootics in different laboratory insect culture lines. Phenotypic and genetic similarity of these isolates, together with two cultured from Leucoma salicis larvae and 14 reference B. thuringiensis strains were determined. The epizootic bacteria did not form a single group based on numerical analysis of biochemical properties. Simple RAPD method with only one primer does not allow estimating the genetic similarity of B. thuringiensis strains. We propose a novel strategy based on combining several DNA patterns obtained by RAPD technique with different primers for B. thuringiensis typing. Majority of infections in the C. pomonella culture lines were caused by bacteria with different genotypes. However, two isolates cultured from infected insects at different time (one strain was isolated in 1990 and the other in 1992) had identical DNA fingerprint that suggested a possibility of these bacteria to survive in the laboratory and to cause infections in different years. The results of SDS-PAGE of whole-cell proteins revealed a possibility to apply protein profile analysis in epidemiological investigations of infections caused by B. thuringiensis. Strains with identical DNA patterns had very similar whole-cell protein profiles.     

Effectiveness of enterobacterial repetitive intergenic consensus PCR and random amplified polymorphic DNA fingerprinting for Helicobacter pylori strain differentiation

We compared the robustness and discriminatory power of the enterobacterial repetitive intergenic consensus (ERIC) and random amplified polymorphic DNA (RAPD) fingerprinting methods for detecting cases of mixed Helicobacter pylori infection in Peruvian shantytown residents. H. pylori isolates from 63 participants were cultured, and five single colonies and a pool of additional colonies from each participant were analyzed by ERIC-PCR and by RAPD tests with four 10-nucleotide primers (one primer per reaction). There was 94% agreement between the ERIC and RAPD profiles in classifying sets of isolates as uniform versus closely related but not identical versus probably unrelated, indicating a high kappa statistic of 0.8942. Subtle differences in related ERIC or RAPD patterns likely reflect gene transfer between strains, recombination, and/or mutation, whereas markedly different patterns reflect infection by unrelated strains. At least half of infected shantytown residents seemed to carry more than one H. pylori strain, although in 19 of 31 persons, the strains were closely related. Three RAPD tests, each with a different primer, were needed to achieve the sensitivity of one ERIC test. ERIC-PCR constitutes a resource- and time-efficient method for H. pylori strain differentiation.     

Pulsed-field gel electrophoresis of genomic restriction fragments as a tool for the epidemiological analysis of Staphylococcus aureus and coagulase-negative staphylococci

Thirteen Staphylococcus aureus and S. epidermidis strains obtained from nose and hand of two employees and one patient of a medical ward as well as two S. hemolyticus strains were analysed according to their restriction fragment length patterns (RFLP) by pulsed-field gel electrophoresis (PFGE) using the restriction enzymes SmaI and SstII. Species identification of the isolates was performed by a system which includes 20 biochemical reactions. Furthermore, the antibiotic resistance patterns of the strains were determined. While several isolates exhibited identical antibiotic susceptibilities and biochemical profiles, differences in the RFLP were obtained. In three cases, S. epidermidis strains colonizing the skin showed an identical restriction profile as isolates from the mucous membranes of the same person. We concluded that the analysis of staphylococcal strains by PFGE is an important epidemiological tool with high discrimination power.     

Characterization of halotolerant rhizobia isolated from root nodules of Canavalia rosea from seaside areas

Twelve nodule isolates from Canavalia rosea, an indigenous leguminous halophyte growing in the seaside areas of southern Taiwan, were effective symbionts for the original host and able to grow at NaCl concentrations up to 3-3.5% (w/v). The taxonomy of these isolates was investigated using a polyphasic approach, including phenotypic characteristics, banding patterns of total proteins from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), genomic fingerprint patterns from random amplified polymorphic DNA (RAPD) analysis, pulsed-field gel electrophoresis (PFGE) analysis, amplified 16S rDNA restriction analysis (ARDRA), 16S rRNA gene sequencing, and nifH gene sequencing. Based on the SDS-PAGE, RAPD, PFGE and ARDRA results, the 12 isolates are highly diverse. The 16S rRNA and nifH gene sequences were determined for isolates with distinct ARDRA patterns and compared with other members of the rhizobial species. We propose these isolates should be classified into the genus Sinorhizobium and distinguished from the current species of this genus.     

First finding of urease-positive thermophilic strains of Campylobacter in river water in the Far East, namely, in Japan and their phenotypic and genotypic characterization

Two strains of urease-positive thermophilic Campylobacter (UPTC), CF89–12 and CF89–14, which were identified as UPTC by biochemical characterization, were found for the first time in river water in the Far East, namely, in Japan. The biochemical characteristics were identical to those of strains described previously by Bolton and colleagues. Furthermore, these two strains were positive for arylsulphatase. Consequently, it was demonstrated that UPTC may possibly be differentiated phenotypically from Campylobacter lari by the arylsulphatase test, as well as urease and nalidixic acid tests. Analysis by pulsed-field gel electrophoresis (PFGE) after digestion with Apa I, Sal I and Sma I, which were found to produce distributions of DNA fragments to be suitable for analysis of the genomic DNA from the thermophilic Campylobacter , respectively, demonstrated that these three restriction enzymes produced distributions of a relatively limited number of genomic DNA fragments and also demonstrated that the PFGE profiles obtained with the three restriction enzymes were indistinguishable between the two strains, respectively. The PFGE analysis and conventional fixed-field agarose gel electrophoresis suggested that the both genomes were approximately 1862 kb in length. Even though the two isolates of UPTC were isolated from water in different rivers in Japan, the results suggested that a single strain. as opposed to two distinct strains, was isolated. PFGE profiles after digestion with Sal I and Sma I, respectively, were also demonstrated to be distinctly different among strains isolated in Japan and previously in Europe. This is the first example of the isolation of UPTC from natural sources in countries other than those in Europe.     

Trypanosoma evansi: genetic variability detected using amplified restriction fragment length polymorphism (AFLP) and random amplified polymorphic DNA (RAPD) analysis of Kenyan isolates

We compared two methods to generate polymorphic markers to investigate the population genetics of Trypanosoma evansi; random amplified polymorphic DNA (RAPD) and amplified restriction fragment length polymorphism (AFLP) analyses. AFLP accessed many more polymorphisms than RAPD. Cluster analysis of the AFLP data showed that 12 T.evansi isolates were very similar ('type A') whereas 2 isolates differed substantially ('type B'). Type A isolates have been generally regarded as genetically identical but AFLP analysis was able to identify multiple differences between them and split the type A T. evansi isolates into two distinct clades.     

Molecular divergence of the soil yeasts Williopsis sensu stricto

Fifty-three strains of saturn-spored yeasts were analyzed by means of restriction analysis of the amplified fragment of rDNA which comprised the 5.8S rRNA gene and the internal transcribed spacers ITS1 and ITS2. The use of endonucleases HaeIII and MspI enabled clear differentiation of yeast species Williopsis mucosa, W. salicorniae, Zygowilliopsis californica, Komagataea pratensis, and the Williopsis sensu stricto complex. Minisatellite primer M13 was proposed for the differentiation between twin species of Williopsis sensu stricto, which have identical restriction profiles. PCR with primer M13 enabled reidentification of a number of collection strains, species identification of saturn-spored isolates from the Far East, and detection of three strains affiliated to novel taxa. The latter have unique PCR profiles and differ in the nucleotide sequences of ITS1 and ITS2 fragments of rDNA. Possible variations in the results obtained with different molecular methods are discussed.