Search PubMed⌕ Search

Biomedical subjects

P Boerlin

Publications and source records attributed to P Boerlin.

At least 37 records · Page 2Linked to original sources
PubMed1998

Evolution of enterohemorrhagic Escherichia coli hemolysin plasmids and the locus for enterocyte effacement in shiga toxin-producing E. coli.

This study assessed the diversity of the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene (ehxA) in a variety of Shiga toxin-producing E. coli (STEC) serotypes and the relationship between ehxA types and virulence markers on the locus for enterocyte effacement (LEE). Restriction fragment length polymorphism of the ehxA gene and flanking sequences and of the E. coli attaching and effacing (eae) gene was determined for 79 EHEC hemolysin-positive STEC isolates of 37 serotypes. Two main groups of EHEC hemolysin sequences and associated plasmids, which corresponded to the eae-positive and the eae-negative isolates, were delineated. Comparisons of the ehxA gene sequences of representative isolates of each group showed that this gene and the rest of the EHEC hemolysin operon are highly conserved. Digestion of an ehxA PCR product with the restriction endonuclease TaqI showed a unique restriction pattern for eae-negative isolates and another one for isolates of serotypes O157:H7 and O157:NM. A conserved fragment of 5.6 kb with four potential open reading frames was identified on the EHEC hemolysin plasmid of eae-positive STEC. Phylogenetic analysis of a subset of 27 STEC isolates, one enteropathogenic E. coli isolate, and a K-12 reference isolate showed that eae-positive STEC isolates all belong to a single evolutionary lineage and that the EHEC hemolysin plasmid and the ehxA gene evolved within this lineage without recent horizontal transfer. However, the eae gene and the LEE appear to have been transferred horizontally within this STEC lineage on several occasions. The reasons for the lack of transfer or maintenance of the LEE in other STEC lineages are not clear and require further study.

Adhesins, Bacterial↗
PubMed1997

Typing Listeria monocytogenes isolates from fish products and human listeriosis cases.

Seventy-two Listeria monocytogenes isolates originating from 10 different fish products of 12 producers and 47 isolates from human listeriosis cases were typed by serotyping and multilocus enzyme electrophoresis. Seventy-five of these isolates were further subtyped by restriction analysis of genomic DNA with the enzyme XhoI and by pulsed-field gel electrophoresis using the enzymes ApaI and SmaI. The results show that several L. monocytogenes clones identified by multilocus enzyme electrophoresis are frequently found in fish products of different origins. One of these clones is the same as another previously shown to be frequently associated with meat and meat products. The epidemic-associated electrophoretic type 1 was only rarely found in fish products. No association was found between any type of fish product and a particular lineage of L. monocytogenes. Both long-term persistence of a strain and simultaneous presence of several clearly distinct strains in the products of single producers were observed. The comparison of L. monocytogenes isolates from human clinical listeriosis cases in Switzerland and those from imported fish products by use of multilocus enzyme electrophoresis showed that they do not form two clearly distinct lineages but nevertheless belong to two separate populations. None of the 48 subtypes distinguished by the combination of all four typing methods could be found in both populations of human origin and those of fish origin.

Animals↗
PubMed1997

Widespread geographic distribution of oral Candida dubliniensis strains in human immunodeficiency virus-infected individuals.

Candida dubliniensis is a recently identified chlamydospore-positive yeast species associated with oral candidiasis in human immunodeficiency virus (HIV)-infected (HIV+) patients and is closely related to Candida albicans. Several recent reports have described atypical oral Candida isolates with phenotypic and genetic properties similar to those of C. dubliniensis. In this study 10 atypical chlamydospore-positive oral isolates from HIV+ patients in Switzerland, the United Kingdom, and Argentina and 1 isolate from an HIV-negative Irish subject were compared to reference strains of C. albicans and Candida stellatoidea and reference strains of C. dubliniensis recovered from Irish and Australian HIV+ individuals. All 11 isolates were phenotypically and genetically similar to and phylogenetically identical to C. dubliniensis. These findings demonstrate that the geographical distribution of C. dubliniensis is widespread, and it is likely that it is a significant constituent of the normal oral flora with the potential to cause oral candidiasis, particularly in immunocompromised patients.

AIDS-Related Opportunistic Infections↗
PubMed1996

Typing of Listeria monocytogenes by monocin and phage receptors.

One hundred strains of Listeria monocytogenes from both sporadic and epidemic cases were typed by monocin production combined with phage receptor and reverse phage receptor methods. The monocin-phage combination gave 72 types with 100% typability and 97% reproducibility. The results were compared to those of serotyping, phage typing, ribotyping, multilocus enzyme electrophoresis, restriction enzyme analysis and RAPD (random amplification of polymorphic DNA). The monocin/phage types were comparable in terms of discrimination with other methods for epidemiological investigations. The index of discrimination of using the monocin typing and phage receptor/reverse phage receptor method combination (0.99) for both the 87 epidemiologically unrelated strains and the epidemiologically important serogroup 4 strains was the highest of the seven different methods analysed. This combination of methods was simple, highly discriminatory and reproducible and can be carried out in a non-specialized laboratory. However, like most of the other Listeria typing methods, both the method and the indicator test strains need to be standardized.

Bacterial Typing Techniques↗
PubMed1996

Multilocus enzyme electrophoresis for characterization of Listeria monocytogenes isolates: results of an international comparative study.

Multilocus enzyme electrophoresis (MEE) is a standard technique that is used to elucidate the epidemiology of a variety of bacterial species. Recently, the method has been employed by several laboratories for investigations of clinical and foodborne isolates of Listeria monocytogenes. To assess the sensitivity and reproducibility of MEE in characterising L. monocytogenes isolates for epidemiological purposes and, ultimately, to agree on a standard protocol, seven laboratories participated in a blinded study of 80 strains. The strain collection included both epidemiologically related and unrelated isolates. Each laboratory used its own protocol for MEE. The number of enzymes that were assayed by the laboratories ranged from 8 to 23, and the total number of identified electrophoretic types (ETs) varied between 14 and 25. Of the II pairs of duplicate strains, the number of pairs recognised as identical by the seven laboratories ranged from 3 to 10 (median = 8). From 10 to 18 (median = 15) of the 22 groups of epidemiological related strains were recognised as homogeneous by the different laboratories. The discriminatory power of the method, calculated using Simpson's index of diversity for 69 strains (80 strains minus the 11 duplicates), ranged from 0.827 to 0.925. This relatively low discriminatory power is a consequence of a somewhat low genetic diversity of L. monocytogenes compared to other bacterial species. Efforts should be pursued to standardise the method in order to improve the intra- and inter-laboratory reproducibility.

Alleles↗
PubMed1996

High-frequency endonuclease (REA) typing: results from the WHO collaborative study group on subtyping of Listeria monocytogenes.

Eighty isolates of Listeria monocytogenes were typed by high-frequency restriction endonuclease analysis. Two laboratories participated in the study with two restriction enzymes each. The enzymes used were EcoRI, Hae1II, HhaI. and its isoschizomer Cfo1. EcoRI was less discriminatory than the other enzymes. The profiles generated by Hha1 and CfoI were not fully stable for some closely related isolates. The size and the number of restriction bands generated by Hha1 in one laboratory and its isoschizomer Cfo1 in another laboratory were directly comparable. This indicates that REA-typing may be used as a definitive typing method for Listeria monocytogenes if the typing procedure is standardized. The stability of the REA-types needs further elucidation in order to establish firm differentiation criteria for comparison of isolates.

Bacterial Typing Techniques↗
PubMed1996

The WHO multicenter study on Listeria monocytogenes subtyping: random amplification of polymorphic DNA (RAPD).

As part of a WHO multicenter study on Listeria monocytogenes subtyping methods the random amplification of polymorphic DNA (RAPD)-technique was evaluated. Six participants were asked to use a standard protocol to analyse a set of 80 L. monocytogenes strains. This set contained 22 groups of epidemiologically linked isolates and 11 pairs of duplicate strains. Using three different 10-mer primers the median reproducibility of the RAPD-results obtained by the six participants was 86.5% (range 0-100%). Failure in reproducibility was mainly due to results obtained with one particular primer. The number of epidemiological groups found to be homogeneous varied from 1-22 (median 16). However, for some groups an inhomogeneity was found by the majority of participants. The overall correlation between the results from the different participants ranged from 32 to 85%.

Bacterial Typing Techniques↗
PubMed1996

Typing Candida albicans oral isolates from human immunodeficiency virus-infected patients by multilocus enzyme electrophoresis and DNA fingerprinting.

A total of 189 Candida albicans isolates have been typed by multilocus enzyme electrophoresis. The results obtained confirm the clonal mode of reproduction of C. albicans. The C. albicans populations found in the oropharynx of human immunodeficiency virus (HIV)-infected patients, in the oropharynx of healthy carriers, or in association with invasive candidiasis could not be distinguished. No clone or group of clones could be associated with the appearance of clinical disorders or with a reduced in vitro susceptibility to the antifungal agent fluconazole. Multiple and sequential oral isolates from 24 HIV-infected patients were also typed by restriction enzyme analysis with the enzymes EcoRI and HinfI and by use of the Ca3 repetitive probe. The results obtained by the combination of all three typing methods show that all but one patient each carried a unique major C. albicans clone in their oropharynx. The 21 patients with sequential isolates had the same C. albicans clones in their throats during recurrent oropharyngeal candidiasis episodes, independently of clinical status or of changes of in vitro susceptibility to fluconazole. Finally, several isolates of the same C. albicans clone found simultaneously in the oropharynx of a patient may present different levels of susceptibility to fluconazole.

AIDS-Related Opportunistic Infections↗
PubMed1996

Subtyping Listeria monocytogenes isolates genetically related to the Swiss epidemic clone.

Macrorestriction analysis by pulsed-field gel electrophoresis was used to assess the diversity of strains within the epidemic-associated electrophoretic type 1 (ET1) clone of Listeria monocytogenes. For this purpose, a total of 144 isolates from Switzerland shown by multilocus enzyme electrophoresis to belong to the ET1 were examined. These isolates were subtyped by macrorestriction analysis using the enzymes ApaI and SmaI and field inversion gel electrophoresis. Among these 144 isolates, 45 were isolated in human listeriosis cases of the postepidemic period of 1988 to 1993 and 44 were isolated in animal listeriosis cases of the same period. Forty-seven isolates were from the epidemic period of 1983 to 1987, and eight additional isolates were from cattle from two different farms. Twenty-nine different subtypes could be identified among the 144 isolates tested. Five major subtypes were found more frequently than the others during the postepidemic period, both in humans and in animals. Two of these subtypes had been previously implicated in outbreaks of listeriosis, thus suggesting that particular pulsed-field gel electrophoresis subtypes may be frequently associated with disease in humans and animals. Two of these frequent subtypes were also suspected to be related to small clusters of listeriosis cases during the postepidemic period. The results obtained by typing epidemiologically related isolates from different animals within the same farms and from different body sites of a given patient confirmed the potential of macrorestriction analysis for epidemiological studies restricted to short periods of time and to small number of isolates. The analysis of 47 isolates related to the Swiss listeriosis epidemic period of 1983 to 1987 and the use of Southern blotting and hybridization experiments show that the interpretation of relatedness between isolates presenting slightly different macrorestriction patterns may be more complex than commonly accepted. In such cases, careful interpretation of the potential molecular mechanisms leading to the differences observed between patterns is necessary.

Animals↗
PubMed1995

Typing Listeria monocytogenes: a comparison of random amplification of polymorphic DNA with 5 other methods.

One hundred Listeria monocytogenes strains were typed by random amplification of polymorphic DNA (RAPD) with three different primers, and the results were compared with those obtained by serotyping, ribotyping, multilocus enzyme electrophoresis, restriction enzyme analysis and phage typing. The RAPD patterns of strains appear to be stable during epidemics even over periods of several years. Reproducibility of the RAPD patterns was good. The discriminatory power of RAPD typing was the best among all the methods tested. RAPD is therefore a very promising tool in the study of listeriosis epidemiology. However, the problems related to the standardization of the technique first have to be resolved before the wide use of RAPD is possible.

Bacterial Typing Techniques↗
PubMed1995

Cluster of oral atypical Candida albicans isolates in a group of human immunodeficiency virus-positive drug users.

Twenty-one chlamydospore-forming and germ tube-positive Candida albicans clinical isolates from 15 human immunodeficiency virus (HIV)-positive and 3 HIV-negative patients were examined by two different genetic methods. Multilocus enzyme electrophoresis and hybridization with the C. albicans-specific Ca3 probe showed that such isolates can be split into two genetically distinct groups that can be clearly distinguished. One group mainly contained strains with atypical sugar assimilation patterns and could be distinguished from the other group by the absence of intracellular beta-glucosidase activity. All 13 strains belonging to this group were isolated from the oral cavities of asymptomatic HIV-positive drug users and may be less pathogenic than the eight strains from the other group isolated either from HIV-positive patients with oropharyngeal candidiasis or from HIV-negative patients with invasive candidiasis.

AIDS-Related Opportunistic Infections↗
PubMed1992

Assignment of Listeria grayi and Listeria murrayi to a single species, Listeria grayi, with a revised description of Listeria grayi.

The genomic relatedness between Listeria grayi and Listeria murrayi was reevaluated by using DNA-DNA hybridization, multilocus enzyme electrophoresis, and rRNA restriction fragment length polymorphism techniques. The high levels of similarity observed between the strains of these two species confirmed the data published since 1973 and indicated that they should be considered members of a single species. On grounds of priority, the species should be named L. grayi.

DNA, Bacterial↗
PubMed1992

Delineation of Borrelia burgdorferi sensu stricto, Borrelia garinii sp. nov., and group VS461 associated with Lyme borreliosis.

We studied 48 Borrelia isolates that were associated with Lyme borreliosis or were isolated from ticks and identified three DNA relatedness groups by using the S1 nuclease method. The three DNA groups (genospecies) were associated with specific rRNA gene restriction patterns, protein electrophoresis patterns, and patterns of reactivity with murine monoclonal antibodies. Genospecies I corresponded to Borrelia burgdorferi sensu stricto since it contained the type strain of this species (strain ATCC 35210); this genospecies included 28 isolates from Europe and the United States. Genospecies II was named Borrelia garinii sp. nov. and included 13 isolates from Europe and Japan. Genospecies III (group VS461) included seven isolates from Europe and Japan.

Antibodies, Monoclonal↗
PubMed1992

Population genetic analysis of Borrelia burgdorferi isolates by multilocus enzyme electrophoresis.

Fifty Borellia burgdorferi strains isolated from humans and ticks in Europe and the United States were analyzed by multilocus enzyme electrophoresis. Eleven genetic loci were characterized on the basis of the electrophoretic mobilities of their products. Ten loci were polymorphic. The average number of alleles per locus was 5.9, with a mean genetic diversity of 0.673 among electrophoretic types (ETs). The strains were grouped into 35 ETs constituting three main divisions (I, II, and III) separated at a genetic distance greater than 0.75. Divisions I, II, and III contained 13, 6, and 16 ETs, respectively. These findings, together with previous data from DNA hybridization and restriction enzyme analysis of rRNA genes, suggest that divisions I, II, and III may represent three distinct genomic species. All three divisions contained human clinical ETs. However, in division I, which includes the ET of the type strain of B. burgdorferi, the human pathogenic ETs constituted a single clone. The ETs of division I were from west-central Europe and the United States, whereas divisions II and III contained ETs from west-central and northern Europe but not from the United States. Finally, our data show that the genetic structure of B. burgdorferi populations is clonal.

Alleles↗
PubMed1991

Taxonomy of the genus Listeria by using multilocus enzyme electrophoresis.

Seventy-three strains of the seven recognized Listeria species were studied by performing a multilocus enzyme electrophoresis analysis of 18 enzyme loci. The mean number of alleles per locus was 9.5 and all of the loci were polymorphic. A total of 56 electrophoretic types were distinguished. Cluster analysis of a matrix of the genetic distances between paired electrophoretic types revealed that there were six principal clusters at the species level (genetic distances between clusters greater than 0.8). Listeria monocytogenes, Listeria innocua, Listeria welshimeri, Listeria seeligeri, and Listeria ivanovii each corresponded to one of these clusters with no overlap. Our results are in agreement with those of previous DNA hybridization experiments (Rocourt et al., Curr. Microbiol. 7:383-388, 1982). Listeria grayi and Listeria murrayi electrophoretic types formed a unique cluster, thus reinforcing the suggestion of Wilkinson and Jones (J. Gen. Microbiol. 98:399-421, 1977) that these two species should be considered two biovars of a single species.

Alleles↗