Influence of age and low afterload on the stress-velocity relation of the left ventricle

Lactobacillus sake strains originally isolated from dry-fermented sausages were characterized by phenotypic and genotypic methods, including DNA-DNA hybridization, restriction fragment length polymorphism (RFLP), and 16S rDNA sequencing analysis, in order to establish their taxonomic position and relation to well defined reference species. Initially, isolates of Lact. sake showing a characteristic phenotype (melibiose-positive, maltose- and arabinose-negative) were identified by DNA-DNA hybridization. Subsequently, RFLP studies using EcoRI and HindIII as restriction enzymes, and cDNA from Escherichia coli or 16S rDNA from Lact. sake strains as probes, showed distinct polymorphism levels. Thus, EcoRI-digested DNA probed with cDNA from E. coli disclosed the presence of a unique cluster for the meat isolates tested, allowing their differentiation from the reference type strain. When HindIII-digested DNA was hybridized with the cDNA probe, strain-specific patterns were obtained, showing a higher discrimination power. Considerable strain differentiation was also observed when EcoRI and HindIII digests were hybridized with 16S rDNA probes. Finally, sequence analysis of the 16S rDNA from one isolate also revealed a certain degree of genetic variability with respect to the reference strain of Lact. sake.     

Differentiation of Helicobacter pylori strains directly from gastric biopsy specimens by PCR-based restriction fragment length polymorphism analysis without culture

Recent studies have shown the usefulness of PCR-based restriction fragment length polymorphism (RFLP) analysis for differentiating Helicobacter pylori strains isolated by culture. For this study, a PCR-based RFLP assay was developed for directly typing H. pylori strains from gastric biopsy specimens. Nineteen gastric biopsy specimens obtained from patients undergoing endoscopy for gastrointestinal complaints were cultured for isolation of H. pylori. Genomic DNA preparations from these gastric biopsy specimens and the corresponding H. pylori isolates were tested by our PCR-based RFLP assay. The 1,179-bp H. pylori DNA fragments amplified by the PCR assay were digested with the restriction enzymes HhaI, MboI, and AluI and analyzed by agarose gel electrophoresis. HhaI, MboI, and AluI digestion produced 11, 10, and 6 distinguishable digestion patterns, respectively, from the 19 H. pylori isolates tested and generated 13, 11, and 6 different patterns, respectively, from the 19 gastric biopsy specimens. The patterns from 13 of the 19 gastric biopsy specimens matched those of the H. pylori isolates from the corresponding patients. The patterns from the remaining six biopsy specimens appeared to represent infection by two strains of H. pylori; the pattern of one strain was identical to that of the isolate from the corresponding patient. By combining all the restriction enzyme digestion patterns obtained by using HhaI, MboI, and AluI, we observed 19 distinct RFLP patterns from the 19 specimens. The results suggest that the PCR-based RFLP analysis method may be useful as a primary technique to identify and distinguish H. pylori strains directly from gastric biopsy specimens without culture of the organisms.     

Typing Neisseria meningitidis by analysis of restriction fragment length polymorphisms in the gene encoding the class 1 outer membrane protein: application to assessment of epidemics throughout the last 4 decades in China

A typing method was developed for Neisseria meningitidis serogroup A by analysis of restriction fragment length polymorphisms (RFLP) of the class 1 outer membrane protein gene (porA). By using appropriate primers, an approximately 1,116-bp fragment of the porA gene was amplified by PCR and then was digested with the restriction endonuclease MspI. The digestion products were separated on 10% polyacrylamide gels and were stained with silver. One hundred three clinical isolates of group A N. meningitidis from 17 provinces of China collected over a 26-year period were analyzed. Results of MspI-generated RFLP profiles of PCR-amplified porA genes were compared with those obtained by conventional serosubtyping. There was a band of about 400 bp common to all strains examined, and the 103 strains of serogroup A resulted in 22 unique RFLP patterns. The differences in bands could be observed mainly in the range of 120 to 280 bp. The smaller fragments were useful in distinguishing meningococci with the same serosubtype. Three epidemic periods were characterized by the presence of three distinct genotypes (a1, a2, and a3), accounting for 74.5% of the strains examined (3.88, 26.21, and 44.66%, respectively). Three predominant RFLP patterns were correlated epidemiologically with cycles of epidemic meningococcal meningitis and were well-matched to the predominant serosubtypes (P1.9, P1.7, 10, and P1.9) that presented at the same prevalence cycles. The genotyping yielded information that allowed strains from one epidemic to be distinguished from those from another that would have been indistinguishable if only serotyping and serosubtyping were available. Therefore, the PCR-RFLP typing method was very useful in the epidemiologic investigation of group A meningococcal meningitis.     

Incorporation of 15N from ammonium into the N-linked oligosaccharides of an immunoadhesin glycoprotein expressed in Chinese hamster ovary cells

Thirty-six isolates, from man or swine, of Pasteurella multocida subsp. multocida producing (n = 13) or not producing (n = 23) the dermonecrotic toxin (DNT) were studied by numerical analysis, capsular typing and ribotyping. Toxigenic strains were also characterised by restriction fragment length polymorphism (RFLP) of the toxA gene and pulsed-field gel electrophoresis (PFGE). Numerical analysis differentiated the Pasteurella species and subspecies, but did not discriminate between toxigenic and nontoxigenic strains. RFLP demonstrated that toxA was located in a conserved part of the chromosome of all toxigenic strains. Ribotyping provided evidence of a close association between DNT production and one of the six EcoRI ribotypes designated as E2. In contrast, PFGE provided evidence for significant DNA polymorphism amongst the toxigenic strains. Results of phenotypic and genotypic studies suggested that toxigenic strains do not form a clone within the subspecies multocida. No difference was found between toxigenic strains of porcine or human origin by biochemical characterisation, capsular serotyping or genomic typing methods.     

Immobilized catalase in water purification systems

Plasmid screening of reference Pseudomonas pseudomallei strains isolated from patients and animals revealed cryptic plasmids with different molecular weights in 30 strains. Plasmids were investigated by restriction analysis and DNA-DNA hybridization. Cryptic plasmids were denoted as pPM1, pCM2, pCM3, and pCM4. The presence of plasmids in melioidosis agent permits their use for intraspecies typing of strains and for genetic studies.     

Widespread detection of PER-1-type extended-spectrum beta-lactamases among nosocomial Acinetobacter and Pseudomonas aeruginosa isolates in Turkey: a nationwide multicenter study

We studied the prevalence and molecular epidemiology of PER-1-type beta-lactamases among Acinetobacter, Klebsiella, and Pseudomonas aeruginosa strains isolated over a 3-month period in eight university hospitals from distinct regions of Turkey. A total of 72, 92, and 367 Acinetobacter, Klebsiella, and P. aeruginosa isolates were studied, respectively. The presence of blaPER was determined by the colony hybridization method and later confirmed by isoelectric focusing. We detected PER-1-type beta-lactamases in 46% (33/72) of Acinetobacter strains and in 11% (40/367) of P. aeruginosa strains but not in Klebsiella strains. PER-1-type enzyme producers were highly resistant to ceftazidime and gentamicin, intermediately resistant to amikacin, and susceptible or moderately susceptible to imipenem and meropenem. Among PER-1-type-beta-lactamase-positive isolates, five Acinetobacter isolates and six P. aeruginosa isolates from different hospitals were selected for ribosomal DNA fingerprinting with EcoRI and SalI. The EcoRI-digested DNAs were later hybridized with a digoxigenin-labelled PER-1 probe. The ribotypes and the lengths of blaPER-carrying fragments were identical in four Acinetobacter strains. A single isolate (Ac3) harbored a PER gene on a different fragment (approximately 4.2 kbp) than the others (approximately 3.4 kbp) and showed a clearly distinguishable ribotype. Ribotypes of P. aeruginosa strains obtained with EcoRI showed three patterns. Similarly, in Pseudomonas strains two different EcoRI fragments harbored blaPER (approximately 4.2 kbp in five isolates and 3.4 kbp in one isolate). PER-1-type beta-lactamases appear to be restricted to Turkey. However, their clonal diversity and high prevalence indicate a high spreading potential.     

Evaluation of pulsed-field gel electrophoresis as a typing system for Candida rugosa: comparison of karyotype and restriction fragment length polymorphisms

Nosocomial infections with Candida species have emerged as an increasingly important cause of morbidity and mortality in intensive care units. Ten Candida rugosa isolates from a previously documented cluster of C. rugosa infections in one hospital (nine burn unit isolates and one isolate from another hospital ward) and eight C. rugosa isolates recovered in a referral fungus testing laboratory (comparison isolates) from distinct geographic areas were investigated by molecular techniques. Isolates were from multiple anatomic sites. Pulsed-field gel electrophoresis (PFGE) of whole-cell DNA was performed with the 18 C. rugosa isolates as a marker of strain identity. The PFGE karyotypes of the C. rugosa isolates were demonstrated from four to seven chromosome bands. Karyotyping revealed the same PFGE pattern for the nine outbreak isolates from the burn unit, confirming clonal strain transmission. The isolate from the other hospital ward had a distinct karyotype. Distinct PFGE karyotype patterns were demonstrated for the eight comparison isolates. Restriction fragment length polymorphisms (RFLP) generated from whole-cell DNA digested with SfiI demonstrated the same RFLP pattern among outbreak isolates. Among comparison isolates, karyotyping distinguished some isolates that were indistinguishable by RFLP patterns. Karyotyping by PFGE appears to be the most useful molecular typing tool for discrimination among strains of C. rugosa and will be a useful marker for evaluating the epidemiology of future C. rugosa infections.     

Rapid identification of clinically significant species and taxa of aerobic actinomycetes, including Actinomadura, Gordona, Nocardia, Rhodococcus, Streptomyces, and Tsukamurella isolates, by DNA amplification and restriction endonuclease analysis

A previously described PCR-restriction fragment length polymorphism (RFLP) identification schema for Nocardia that used an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was evaluated for potential use with isolates of all clinically significant aerobic actinomycetes. The study included 28 reference (American Type Culture Collection) strains and 198 clinical isolates belonging to 20 taxonomic groups. Of these 198 isolates, 188 could be differentiated by this PCR-RFLP method. Amplicons from all aerobic actinomycete isolates lacked BstEII recognition sites, thereby distinguishing them from those of mycobacteria that contain one or more such sites. Of 29 restriction endonucleases, MspI plus HinfI produced RFLP patterns that differentiated 16 of the 20 taxa. A single RFLP pattern was observed for 15 of 20 taxa that included 65% of phenotypically clustered isolates. Multiple patterns were seen with Gordona bronchialis, Nocardia asteroides complex type VI, Nocardia otitidiscaviarum, Nocardia transvalensis, and Streptomyces spp. Streptomyces RFLP patterns were the most heterogeneous (five patterns among 19 isolates), but exhibited a unique HinfI fragment of > 320 bp. RFLP patterns that matched those from type strains of Streptomyces albus, Streptomyces griseus, or Streptomyces somaliensis were obtained from 14 of 19 Streptomyces isolates. Only 10 of 28 isolates of N. otitidiscaviarum failed to yield satisfactory amplicons, while only 6 of 188 (3.2%) clinical isolates exhibited patterns that failed to match one of the 21 defined RFLP patterns. These studies extended the feasibility of using PCR-RFLP analysis as a rapid method for the identification of all clinically significant species and taxa of aerobic actinomycetes.     

Molecular epidemiology of Vibrio cholerae O1 isolated from sporadic cholera cases in Okinawa, Japan

In July 1994, 6 cholera cases due to Vibrio cholerae O1 El Tor Ogawa sporadically appeared in Okinawa. All 6 patients had no history of traveling abroad. In the period of this cholera outbreak, a strain of V. cholerae O1 El Tor Ogawa was detected from an imported fish at the Naha port quarantine station. The isolates were characterized to clarify whether or not, they belonged to a common clone. Phenotypes were identical except that one strain revealed cured Celebes and the others were original Celebes in kappa phage typing. The restriction fragment patterns of DNA of the isolates hybridized with an enzyme-labeled oligonucleotide probe for cholera toxin gene (ctx) were identical. Randomly amplified polymorphic DNA of the isolates were identical when a primer was used, but 2 patterns were seen when another primer was used. Pulsed-field gel electrophoresis of the chromosomal DNA digested with NotI restriction enzyme showed 3 patterns. The DNA fragment pattern of the strain isolated from the imported fish was different from the clinical isolates. These results suggested that there was no epidemiological relation among the strains of V. cholerae O1 isolated during this period.     

Thyroid hormone receptor is a negative regulator in p53-mediated signaling pathways

SETTING: Molecular typing has become an important tool for examining the extent of active transmission of tuberculosis. OBJECTIVES: To examine transmission of tuberculosis in Cuba using IS6110 restriction fragment length polymorphism (RFLP) typing and to evaluate the utility of spoligotyping. DESIGN: One hundred and sixty Mycobacterium tuberculosis strains isolated over a one year period in Cuba were subjected to RFLP and spoligotyping. RESULTS: Forty-eight percent of the isolates were found in 19 clusters of strains with identical RFLP patterns. In general, cluster sizes were limited, except for two large institutional outbreaks. Age was strongly inversely correlated to clustering. Most streptomycin-resistant isolates were found in clusters. Fifteen spoligotype clusters comprised 78% of the isolates. Significantly different IS6110 RFLP types subdivided 11 spoligotype clusters, whereas none of the IS6110 clusters were subdivided by spoligotyping. CONCLUSIONS: Considering the short study period, 48% clustering is high, indicating that recent transmission plays an important role in Cuba. Although resistance is still a minor problem, transmission of streptomycin-resistant strains occurs. The high polymorphism observed with IS6110 RFLP indicates that this marker is useful for future molecular epidemiological studies in Cuba. Spoligotyping appeared less suitable for population-based studies.     

Typing of human Mycobacterium avium isolates in Italy by IS1245-based restriction fragment length polymorphism analysis

All but 2 of 63 Mycobacterium avium isolates from distinct geographic areas of Italy exhibited markedly polymorphic, multibanded IS1245 restriction fragment length polymorphism (RFLP) patterns; 2 isolates showed the low-number banding pattern typical of bird isolates. By computer analysis, 41 distinct IS1245 patterns and 10 clusters of essentially identical strains were detected; 40% of the 63 isolates showed genetic relatedness, suggesting the existence of a predominant AIDS-associated IS1245 RFLP pattern.     

Diagnosis of Mycobacterium microti infections among humans by using novel genetic markers

As a result of DNA typing of Mycobacterium microti isolates from animals in the United Kingdom and The Netherlands, we diagnosed four human M. microti infections. These are the first M. microti infections among humans to be reported. Three of the patients were immunocompromised and suffered from generalized forms of tuberculosis. The fourth patient was a 34-year-old immunocompetent male with a persistent cough and undefined X-ray abnormalities. Two of the M. microti infections were recognized by their IS6110 restriction fragment length polymorphism (RFLP) patterns, which showed a high degree of similarity with those of M. microti strains isolated from a pig and a ferret in The Netherlands. The two other human M. microti infections were recognized by using the recently developed DNA fingerprinting method, "spoligotyping," directly on clinical material. All M. microti isolates from the United Kingdom and The Netherlands were found to contain an exceptionally short genomic direct repeat region, resulting in identical two-spacer sequence reactions in spoligotyping. In contrast, the highly similar IS6110 RFLP patterns of the vole strains from the United Kingdom differed considerably from the RFLPs of all M. microti strains isolated in The Netherlands, suggesting that geographic isolation led to divergent strains in the United Kingdom and on the continent.     

Restriction fragment length polymorphism analysis and random amplified polymorphic DNA analysis of Campylobacter jejuni strains isolated from patients with Guillain-Barré syndrome

Campylobacter jejuni serotype O19 strains associated with the Guillain-Barré syndrome (GBS) and other strains were examined by restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction products of the flaA genes and by random amplified polymorphic DNA (RAPD) analysis. RFLP analysis showed that regardless of LIO serotype, geographic origins, or association with GBS, the O19 isolates shared an identical digestion pattern by each of four restriction endonucleases, DdeI, MboI, MseI, and AluI. In contrast, among C. jejuni O1 or O2 strains, RFLP patterns were different even among strains of the same LIO serotype. The results of the RAPD analysis were consistent with the flaA RFLP data. These data indicate that all of the O19 strains that were tested were closely related to one another whether they were or were not associated with GBS.     

Development of a PCR-restriction fragment length polymorphism assay using the nucleotide sequence of the Helicobacter hepaticus urease structural genes ureAB

Infection with Helicobacter hepaticus causes chronic active hepatitis in certain strains of mice and is associated with hepatocellular carcinoma in A/JCr mice. Like the gastric helicobacters, H. pylori and H. mustelae, H. hepaticus possesses a high level of urease activity. However, the H. hepaticus urease structural gene sequences have not been previously determined, and the role of the urease enzyme in colonization and in pathogenesis is not known. PCR was used to amplify a portion of the urease structural genes from H. hepaticus genomic DNA. Amplified DNA fragments were cloned, and the nucleotide sequence was determined. The deduced amino acid sequence of the partial H. hepaticus ureA gene product was found to exhibit 60% identity and 75% similarity to the predicted H. pylori UreA. The deduced amino acid sequence of a partial H. hepaticus ureB gene product exhibited 75% identity and 87% similarity to the predicted H. pylori UreB. Diversity among H. hepaticus isolates was evaluated by means of a restriction fragment length polymorphism (RFLP) assay. The 1.6-kb fragments within the ureAB open reading frames, amplified from 11 independent isolates, were digested with the restriction endonuclease HhaI. Three distinct RFLP patterns were observed. Identical RFLP profiles were noted in sequential isolates of one strain of H. hepaticus during an 18 month in vivo colonization study, suggesting that the urease genes of H. hepaticus are stable. The urease genes among H. hepaticus strains were also well conserved, showing 98.8 to 99% nucleotide sequence identity among three isolates analyzed. These findings indicate that H. hepaticus has urease structural genes which are homologous to those of the gastric Helicobacter species and that these gene sequences can be used in a PCR and RFLP assay for diagnosis of this important murine pathogen.     

AM1 theoretical study, synthesis and biological evaluation of some benzofuran analogues of anti-inflammatory arylalkanoic acids

To evaluate different methods for strain differentiation, 10 isolates of Aspergillus terreus from Germany and two epidemiologically unrelated strains were investigated. The sources of the isolates were patients with cystic fibrosis (4), immunosuppression (2), otitis externa (2), sinusitis (1) and endocarditis (1). Environmental isolates were obtained from a contaminated cell culture and from soil. The isolates did not differ in their macroscopic and microscopic morphology, in their protein patterns analysed by SDS-PAGE and in their susceptibility to amphotericin B and itraconazole. The RFLP analysis of total genomic DNA digested by EcoRI resulted in patterns that were too faint for interpretation. However, after hybridisation of the digested DNA with a short DNA probe of repetitive sequence, six different patterns were found. Based on the patterns of the randomly amplified polymorphic DNA (RAPD) with three primers, nine different genotypes were discriminate. RAPD patterns discriminated the epidemiologically unrelated reference strains (endocarditis isolate from Thailand, soil isolate from the USA) and the isolates from Germany. It is concluded that, in contrast to the phenotypic methods, the analysis of RAPD patterns is useful for strain differentiation of A. terreus.     

Species identification and virulence attributes of Saccharomyces boulardii (nom. inval.)

Saccharomyces boulardii (nom. inval.) has been used for the treatment of several types of diarrhea. Recent studies have confirmed that S. boulardii is effective in the treatment of diarrhea, in particular chronic or recurrent diarrhea, and furthermore that it is a safe and well-tolerated treatment. The aim of the present study was to identify strains of S. boulardii to the species level and assess their virulence in established murine models. Three strains of S. boulardii were obtained from commercially available products in France and Italy. The three S. boulardii strains did not form spores upon repeated testing. Therefore, classical methods used for the identification of Saccharomyces spp. could not be undertaken. Typing by using the restriction fragment length polymorphisms (RFLPs) of the PCR-amplified intergenic transcribed spacer regions (including the 5. 8S ribosomal DNA) showed that the three isolates of S. boulardii were not separable from authentic isolates of Saccharomyces cerevisiae with any of the 10 restriction endonucleases assessed, whereas 9 of the 10 recognized species of Saccharomyces could be differentiated. RFLP analysis of cellular DNA with EcoRI showed that all three strains of S. boulardii had identical patterns and were similar to other authentic S. cerevisiae isolates tested. Therefore, the commercial strains of S. boulardii available to us cannot be genotypically distinguished from S. cerevisiae. Two S. boulardii strains were tested in CD-1 and DBA/2N mouse models of systemic disease and showed intermediate virulence compared with virulent and avirulent strains of S. cerevisiae. The results of the present study show that these S. boulardii strains are asporogenous strains of the species S. cerevisiae, not representatives of a distinct and separate species, and possess moderate virulence in murine models of systemic infection. Therefore, caution should be advised in the clinical use of these strains in immunocompromised patients until further study is undertaken.     

Perception of fatigue and quality of life in patients with COPD

A flow cytometric assay has been developed for the measurement of susceptibilities to ganciclovir of laboratory strains and clinical isolates of human cytomegalovirus (HCMV). The assay uses fluorochrome-labeled monoclonal antibodies to HCMV immediate-early and late antigens to identify HCMV-infected cells and flow cytometry to detect and quantitate the number of antigen-positive cells. By this assay, the 50 and 90% inhibitory concentrations (IC50 and IC90, respectively) of ganciclovir for the AD169 strain of HCMV were 1.7 and 9.2 microM, respectively, and the IC50 for the ganciclovir-resistant D6/3/1 derivative of the AD169 strain was greater than 12 microM. The ganciclovir susceptibilities of 17 HCMV clinical isolates were also determined by flow cytometric analysis of the effect of ganciclovir on late-antigen synthesis in HCMV-infected cells. The average IC50 of ganciclovir for drug-sensitive HCMV clinical isolates was 3.79 microM (+/-2.60). The plaque-reduction assay for these clinical isolates yielded an average IC50 of 2.80 microM (+/-1.46). Comparison of the results of the flow cytometry assays with those obtained from the plaque-reduction assays demonstrated acceptable bias and precision. Flow cytometric and plaque-reduction analysis of cells infected with ganciclovir-resistant clinical isolates failed to show a reduction in the percentage of late-antigen-positive cells or PFU, even at 96 microM ganciclovir. The flow cytometric assay for determining ganciclovir susceptibility of HCMV is quantitative, and objective, and potentially automatable, and its results are reproducible among laboratories.     

Mitochondrial DNA analysis of Phialophora verrucosa

Restriction fragment length polymorphism (RFLP) of mitochondrial DNA (mtDNA) was examined in 32 isolates of Phialophora verrucosa (eight isolates from Japan, 10 from China, four from the USA, six from Venezuela and four from Colombia) and in three of Phialophora americana using five restriction enzymes. P. verrucosa isolates were divided into 10 mtDNA types based on RFLP patterns. Phylogeny constructed on sequence divergence of mtDNA indicated that P. verrucosa is a single species and isolates are clustered into three groups. Japan and the USA contained Group A and Group B isolates, China Group B isolates and South America Group B and Group C isolates. RFLP patterns of P. americana mtDNA were identical to those of Type 1 or Type 4 of P. verrucosa mtDNA, suggesting that both are identical. RFLP patterns of P. verrucosa were distinct from those of other dematiaceous fungi including Exophiala jeanselmei, E. moniliae, E. dermatitidis, E. spinifera, Cladophialophora (Cladosporium) carrionii, Fonsecaea pedrosoi, and Hortaea werneckii. These results indicate that RFLP analysis of mtDNA is a useful method for the identification, taxonomy, typing, epidemiology and phylogeny of P. verrucosa.     

Restriction fragment length polymorphism and spacer oligonucleotide typing: a comparative analysis of fingerprinting strategies for Mycobacterium bovis

The combination of conventional investigation and DNA fingerprinting is yielding important insights into the epidemiology of Mycobacterium bovis infections. Various genetic markers used in restriction fragment length polymorphism (RFLP) have recently been exploited for fingerprinting of M. bovis isolates. The newly developed spacer oligonucleotide typing aimed to investigate the polymorphism of M. tuberculosis in the DR locus, has also been applied to the molecular typing of M. bovis isolates. This work compared the performance of the insertion sequence (IS) IS6110, IS1081 and the genetic elements polymorphic G + C-rich repeat (PGRS) and direct repeat (DR) used in RFLP analysis with spoligotyping using a group of 128 Spanish M. bovis isolates. In this study, the most sensitive technique for identifying polymorphism in M. bovis was PGRS-RFLP, closely followed by IS6110-RFLP. We propose several schemes for fingerprinting of these isolates, however, the clear geographical variations found by different authors makes the study of each local situation indispensable. An international consensus in the methods used would be desirable for efficient interlaboratory comparison of strains.